Comprehensive portfolio of adaptation measures to safeguard against evolving flood risks in a changing climate

Abstract

Flooding exacerbated by climate change presents growing risks to communities worldwide. Despite extensive research on flood risk, there is a lack of critical analysis of flood adaptation measures spanning traditional and emerging methods. Here, we compile a comprehensive portfolio of 39 adaptation measures classified into four groups: infrastructural/technological, institutional, behavioral/cultural, and nature-based measures. Each measure is evaluated for its advantages, disadvantages, co-benefits, and tradeoffs. Our analysis identifies four broad eras in the evolution of flood adaptation measures. While early efforts primarily focused on structural modifications, more recent projects shifted toward soft adaptation measures, with a growing interest in employing community-centered and nature-based solutions. We lay out key decision-making attributes to identify successful adaptation strategies that are socially just, practically feasible, and technically sound. Finally, we highlight gaps and provide recommendations for future research, with an emphasis on a transdisciplinary approach toward developing and implementing climate-resilient and equitable flood adaptation strategies.

Introduction

The Earth’s climate is changing, with global surface temperatures rising by ~1.1 °C over the past decade compared to pre-industrial levels¹. This warming trend is intensifying key flood drivers, including rising sea levels, increasing precipitation, and more severe storm events^2,3. Climate models project that global warming is likely to reach or exceed 1.5 °C in the near term (2021-2040) and, under current policies alone, is projected to reach ~3.1 °C by 2100, exacerbating flood risks worldwide^4,5,6,7,8,9. Sea levels are currently rising at a rate of 3–4 mm per year and are projected to increase between 0.3 and 2.0 meters by 2100, threatening coastal and low-lying areas^10,11,12. Alongside coastal inundation, other flood hazards such as fluvial flooding, land subsidence, and extreme precipitation are compounding risks and increasing the vulnerability of communities and infrastructure^{13,14,15,16,17,18}.

Flooding remains one of the most destructive climate-related hazards, contributing to profound social and economic disruption. Between 2000 and 2019, global flood-related losses totaled $651 billion (USD), affecting ~1.6 billion people¹⁹. Without proactive adaptation, these losses could increase twentyfold by the end of the century²⁰. In the U.S. alone, floods have caused 738 fatalities and nearly $200 billion in inflation-adjusted damages over the past four decades. Flood-related losses are projected to increase by 26% by 2050 due to climate change alone^21,22. These statistics highlight the urgent need for robust and comprehensive adaptation strategies to safeguard both lives and infrastructure²³.

Climate change amplifies the frequency, intensity, and complexity of flood hazards. Sea level rise, driven by thermal expansion and glacial melt, increases coastal inundation and reduces natural drainage capacity. At the same time, higher atmospheric temperatures elevate moisture-holding capacity, resulting in more intense and prolonged precipitation that overwhelms drainage infrastructure and triggers flash flooding. Storm systems, fueled by warmer ocean waters, are becoming stronger and more destructive, exacerbating both coastal and inland flood risks. These flood drivers often interact with local conditions such as land subsidence, deforestation, and aging infrastructure, creating highly localized and nonlinear flood dynamics. Consequently, effective flood adaptation requires a shift from reactive approaches to integrated, forward-looking strategies capable of addressing compound and cascading risks.

Adaptation to flood risk spans a range of strategies, including structural, nature-based, institutional, and behavioral measures. Traditional structural defenses such as levees, dams, floodwalls, and stormwater drainage systems remain critical components of many flood management plans. However, these systems face growing pressure from climatic stressors, such as sea level rise, extreme rainfall, drought, and non-climatic stressors, like land subsidence, seismic events, and inadequate maintenance (Fig. 1). Urbanization, aging infrastructure, and fragmented governance further exacerbate vulnerability. For example, the 2023 dam failures near Derna, Libya, were caused by extreme rainfall in combination with outdated infrastructure and institutional breakdown, leading to devastating losses^24,25.

Fig. 1: Stressors impacting flood protection infrastructure.

Flood protection infrastructure systems, including dams, levees, floodwalls, drainage networks, and seawalls, are increasingly stressed by a range of environmental factors that threaten their performance and longevity. These systems are exposed to both climatic stressors (e.g., extreme precipitation, prolonged drought, sea level rise, and intensified storm surges) and non-climatic stressors (e.g., seismic activity, deferred maintenance, land subsidence, and biological interference such as burrowing animals), acting alone or in combination. As these pressures intensify, the risk of infrastructure failure grows, underscoring the urgent need for both structural and non-structural adaptation strategies to build resilience and ensure long-term flood protection.

Given the rising complexity of flood risk, effective adaptation must go beyond traditional engineering solutions. Nature-based strategies such as wetland restoration, riparian buffers, and living shorelines enhance both flood resilience and ecosystem services while offering long-term cost savings. Institutional measures, including strengthened governance frameworks, emergency management systems, and integrated land use planning, are essential for managing risk in a dynamic climate. Behavioral and cultural approaches such as public education, and participatory planning further enhance community preparedness and adaptive capacity²⁶.

Despite decades of research, much of the existing flood adaptation literature has focused on individual strategies, with limited efforts to synthesize these measures into an integrated resource. To address this gap, this study compiles and critically analyzes a comprehensive portfolio of 39 flood adaptation measures, spanning 18 Infrastructural/Technological, 9 Institutional, 2 Behavioral/Cultural, and 10 Nature-Based strategies. This portfolio provides a unique and practical reference for policymakers, practitioners, and researchers to evaluate existing and emerging adaptation options. Each measure is described in terms of its advantages, disadvantages, trade-offs, and co-benefits, enabling more informed, context-sensitive decision-making. To guide effective implementation, we also identify key criteria for evaluating adaptation strategies, assuring that decisions are socially just, technically sound, and economically feasible. The paper concludes by outlining research gaps and recommendations for advancing equitable, climate-resilient flood adaptation through a transdisciplinary and systems-based approach.

Climate change adaptation

The term “climate adaptation” has seen a substantial rise in interest since it emerged as a focal point in the UN Framework Convention on Climate Change (UNFCCC) in 2001. The Paris Agreement further underscored its significance²⁷. Several definitions of climate adaptation exist throughout the literature. In this study, we adopt the definition provided by the Intergovernmental Panel on Climate Change (IPCC), which describes climate adaptation as the process of making strategic adjustments and decisions to protect communities and assets from the adverse impacts of current or future climate conditions¹. Nations around the globe have been employing adaptation measures to resist flooding for centuries, with a rapidly increasing trend over the past few decades primarily due to the escalating risk of flooding²⁸. These measures range from structural modifications, such as the heightening of flood protection infrastructure (e.g., levees), to non-structural approaches, including community outreach initiatives. Although climate adaptation measures are multifaceted and interdisciplinary in nature, these measures share the common goal of enhancing resilience to climate change. Past studies define resilience as the capacity of communities and built environments to withstand and recover from flood events^29,30. Flood resilience is particularly crucial in coastal and urban settings, where the built environment plays a central role in determining the ability of urban systems to respond to flood shocks through prevention, adaptation, or response measures³¹.

As climate change continues to amplify the frequency and intensity of extreme weather events, the demand for climate adaptation is growing, often outpacing the effectiveness of traditional mitigation measures in many situations. A business-as-usual approach may lead to a future where adaptation becomes increasingly difficult. Compounding this difficulty, adaptation efforts often require substantial investment and long implementation times, influencing decisions spanning decades and introducing uncertainties primarily as a result of climate change and future socioeconomic pathways. To navigate these complexities, adaptation measures must be grounded in robust assessments that account for climate uncertainty, enabling policymakers and stakeholders to make informed decisions and prioritize resilience-building efforts.

Evolution of flood adaptation measures

The concept of flood adaptation has evolved substantially over time, shaped by changing understandings of environmental processes, societal priorities, policy frameworks, and technological capabilities. In this section, we identify four broad eras in the evolution of flood adaptation (Fig. 2). While presented sequentially, these phases are not universally applicable and often overlap across regions depending on local conditions and governance contexts.

Fig. 2: Evolution of flood adaptation strategies in the U.S. from the pre-1950s to the present.

The figure illustrates the historical progression and growing complexity of adaptation approaches, from early reactive and infrastructure-based responses to more integrated, multi-dimensional strategies. The timeline highlights the overlapping and non-linear nature of these adaptation phases, shaped by evolving climate risks, societal priorities, and governance structures.

Historically, flood adaptation strategies were highly localized and reactive. Before the mid-20th century, societies employed a diverse array of practices such as constructing raised mounds, strategic retreats, and abandoning floodplains primarily in response to recent flood events rather than informed by formalized risk assessments. Early infrastructure, including levees and barriers, was typically built using trial-and-error approaches to mitigate known damage rather than anticipate future risk³².

A shift toward infrastructure-centric resilience emerged in the early to mid-20th century. This period emphasized engineered solutions such as levees, dams, and dikes, often designed based on cost-benefit analyses and deterministic risk frameworks aimed at maximizing economic efficiency^33,34,35. While influential, these approaches assumed environmental stationarity and failed to fully account for long-term uncertainty in hydrological or climate systems.

In the latter half of the 20th century, increasing environmental awareness catalyzed a broader view of flood management that incorporated ecological and social dimensions. There was growing recognition of the importance of maintaining natural vegetation for levee integrity and of integrating recreational and aesthetic benefits into flood infrastructure^36,37,38,39. As adaptation discourse expanded, rigid top-down regulatory frameworks gradually gave way to more adaptive governance models emphasizing local engagement, intersectoral collaboration, and context-specific solutions capable of responding to evolving climate risks⁴⁰.

By the late 20th century, as concerns about climate change grew, long-term planning and ecosystem-based management were increasingly emphasized in adaptation strategies^41,42,43,44. The dichotomy between “hard” (infrastructure-based) and “soft” (nature-based or social) measures became more prominent, and scholars and practitioners began advocating for integrated strategies that balance structural protection with environmental and social resilience^26,45,46,47.

More recently, hybrid adaptation strategies, which blend structural, nature-based, institutional, and community-centered approaches, have gained attention. These emphasize flexibility, cost-effectiveness, co-benefits, and long-term sustainability^{48,49,50,51,52}. This evolution reflects a growing acknowledgment of uncertainty in both climate projections and hydrological modeling. The limitations of traditional stationarity-based assumptions have prompted the development of adaptive planning frameworks that incorporate flexibility, robustness, and iterative learning⁵³. Notably, adaptive pathways planning and related methodologies such as decision-making under deep uncertainty provide tools to explore alternative futures, stress-test decisions, and revise strategies in light of new information, offering a more resilient foundation for flood risk management under uncertain conditions^32,54.

Although we present these four eras as a conceptual framework, they should not be interpreted as a strict linear or global progression. Regional experiences vary considerably. In some areas, large-scale structural solutions remain dominant, while others have adopted more community-based or nature-based approaches influenced by governance structures, resource availability, and local hazard characteristics. In practice, many regions operate with a blend of strategies across these phases. Finally, we recognize inherent limitations in the literature and the synthesis presented here. Engineering-focused publications often emphasize structural solutions, potentially overshadowing institutional, behavioral, or community-led strategies. Moreover, flood adaptation literature from North America and Europe tends to be more visible and accessible, while studies from the Global South, especially those in non-English languages or less-publicized outlets, are frequently underrepresented. These disparities highlight the need for more inclusive and globally representative research on flood adaptation.

Methodology

This study employed a scoping review to identify and synthesize recent literature on flood adaptation measures. Our objective was to capture the breadth and diversity of current strategies while ensuring that the selected sources provided meaningful insights into adaptation practices across global contexts. To ensure rigor, studies were included based on three primary criteria. First, eligible sources consisted of peer-reviewed journal articles, systematic reviews, case studies, or policy reports that addressed flood adaptation and, where relevant, broader climate adaptation themes. Second, the included studies needed to describe one or more flood adaptation measures in sufficient detail to enable classification. Third, the review focused on literature published between 2018 and 2024 to reflect recent advancements; however, select foundational works published before this period were also considered when deemed particularly relevant.

The review process followed a structured three-step approach. First, we analyzed key sections of the IPCC 6^th Assessment Report, which informed the initial typology and categorization framework¹. Second, we conducted systematic searches using Google Scholar with a predefined set of search terms combining flood-related keywords (e.g., “flood,” “risk,” “hazard”) with adaptation-related terms (e.g., “adaptation,” “nature-based solutions,” “relocation,” “evacuation”). Here, Google Scholar was selected due to its broad interdisciplinary coverage, including peer-reviewed publications, gray literature, and policy documents that are highly relevant to the cross-sectoral nature of flood adaptation research. Third, the identified adaptation measures were classified into four main categories: (1) Infrastructural/Technological, (2) Institutional, (3) Behavioral/Cultural, and (4) Nature-Based. Measures with overlapping characteristics were consolidated into a comprehensive portfolio.

The final review yielded 173 studies. See Supplementary Data for the full list of articles reviewed and the adaptation measures extracted from each. Infrastructural measures were the most frequently represented (n = 99), followed by Nature-Based (n = 68), Institutional (n = 48), and Behavioral/Cultural measures (n = 10). The count does not sum to the total number of studies as several studies addressed two or more adaptation types simultaneously, resulting in overlaps across categories. Studies were further categorized by methodological approach: case studies, data-driven modeling, systematic reviews, historical analyses, and experimental research. Case studies and modeling-based studies dominated the dataset. Geographically, most of the reviewed studies focused on North America, Northern and Western Europe, Eastern Asia, and South Asia, with relatively fewer studies from Africa, Latin America, and the Middle East.

Figure 3 illustrates the regional distribution and classification of adaptation strategies. Notably, infrastructural approaches were dominant in North America, Europe, and Eastern Asia. These findings, however, are subject to several limitations. Structural adaptation measures are more prominently featured in engineering and technical journals, which may contribute to their overrepresentation in the literature. Similarly, studies from well-funded and widely cited regions are more likely to be included, while valuable research from underrepresented regions, especially those published in non-English languages or local outlets, may be overlooked. These limitations underscore the need for greater inclusivity and geographic diversity in future flood adaptation research, particularly to better represent institutional, behavioral, and culturally embedded practices from the Global South.

Fig. 3: Regional distribution and composition of flood adaptation measures across reviewed studies.

a Number of studies reviewed from each global region. b Stacked bar chart showing the regional distribution of adaptation measure types, Infrastructural/Technological, Institutional, Behavioral/Cultural, and Nature-Based, across the selected studies. The accompanying pie chart presents the overall composition of adaptation measures included in the portfolio, highlighting the relative prevalence of each category across the entire dataset. Shapefiles were sourced from the IPUMS International GIS Boundary Files (LSIB-based).

Flood adaptation portfolio

Various classifications for organizing adaptation measures exist in the literature, among which a widely used framework distinguishes between structural and non-structural measures. Structural measures include engineering solutions such as the construction of levees, seawalls, and berms. In contrast, non-structural measures encompass a broader array of measures, including ecosystem-based, legal, institutional, and community-based approaches. Under this umbrella, alternate terms such as hard and soft adaptation are also used²⁶. Some studies classify measures into in-situ and ex-situ adaptation, referring to locations where adaptation measures are implemented⁵⁵. Another recent approach is the Protect, Accommodate, Retreat, and Avoid (PARA) model and its variants, discussed extensively in the literature^56,57,58. However, the distinctions between these classifications are often subjective and unclear. In the current study, we organize adaptation measures based on the four categories provided in the IPCC: Infrastructural/Technological, Institutional, Behavior/Cultural, and Nature-Based adaptation measures¹. We present a portfolio of 18 Infrastructural/Technological, 9 Institutional, 2 Behavior/Cultural, and 10 Nature-Based measures, as shown in Fig. 4. Although the measures were assigned to one of four broad categories based on their primary focus, several measures from our analysis overlap multiple domains. This section presents definitions of the adaptation classifications, detailed descriptions of each measure, and their associated advantages, disadvantages, tradeoffs, and co-benefits.

Fig. 4: A comprehensive portfolio of 39 flood adaptation measures.

Synthesized from the literature and classified into four categories: Infrastructural/Technological, Institutional, Behavioral/Cultural, and Nature-Based. To aid interpretation, the dominant flood drivers (pluvial, riverine, and coastal) associated with each measure are indicated using color-coded circles. These visual cues help illustrate the typical application contexts and hazard relevance for each adaptation measure.

Infrastructural/technological measures

Infrastructural/Technological measures refer to measures that involve changes to infrastructure, such as the construction or enhancement of flood protection systems, including levees, flood walls, detention basins, and weirs^1,59. These measures have been extensively studied in Europe compared to other continents¹. While they offer a reliable form of protection, they often result in large-scale disturbances in local communities and ecosystems. These measures are generally expensive, time-consuming, and may lack the flexibility to accommodate the sudden changes in climate change projections. Additionally, infrastructural adaptation measures are characterized by their long-term nature, often lasting for several decades and potentially locking in new development and growth with the expectation of continued protection⁶⁰. This section presents a comprehensive catalog of infrastructural and technological adaptation measures detailing their advantages, disadvantages, co-benefits, and tradeoffs. A summary of these measures is provided in Table 1.

Table 1 Infrastructural/Technological measures and their advantages, disadvantages, co-benefits, and tradeoffs

Heightening of levees

Overtopping is the most common cause of levee failures⁶¹. To mitigate overtopping, increasing the height of levees along waterways is recognized as one of the oldest yet most commonly used hard adaptation methods designed to increase levees’ capacity. This method involves adding additional layers of soil, rock, or other materials to the existing levee structure to raise its elevation and provide greater protection against high water levels⁶². The heightening of levees is placed in the infrastructural/technological category because it involves substantial modifications to physical structures, employing engineering techniques and materials to enhance capacity and effectiveness. Increasing the levee height can decrease the probability of overtopping by enhancing channel capacity, but it also increases construction costs⁶³. Moreover, consideration of the levee crown width alongside height is essential to avoid compromising the integrity of the levee system⁶⁴. Heightening existing levees can also disrupt communities by changing the existing landscape and use of space⁶⁵. According to Guida et al.⁶⁶, the Tisza River in Central and Eastern Europe has experienced increased flood levels despite an extensive levee system designed to prevent catastrophic flooding. Heightening these levees was found to be more cost-effective and politically expedient than setback alternatives, offering immediate protection. However, this approach does not address the long-term issues of wetland degradation, increased flood levels, and decreased floodway carrying capacity. Consequently, while levee heightening provides short-term benefits, more sustainable solutions for long-term flood management exist. While levee heightening reduces the frequency of inundation in flood-prone areas, it also diminishes flood attenuation, leading to heightened flood discharge downstream⁶⁷. Thus, the effect of levee heightening on flood dynamics warrants careful consideration in flood risk management planning.

Notching

Notching involves deliberately lowering or removing sections of a levee to facilitate controlled flooding into adjacent floodplains. This technique aims to restore natural floodplain connectivity and enhance ecological conditions by allowing water to spill over during high flows while minimizing risks to critical infrastructure and inhabited areas⁶⁸. Notching involves the strategic modification of levee structures to manage floodwaters, justifying its placement in the infrastructural/technological category. The success of notching projects is contingent upon understanding floodplain topography, which plays a pivotal role in floodplain restoration efforts. The interaction between erosion and deposition processes continuously alters the physical landscape at notched levees. Assessing both upstream and downstream impacts is imperative, as erosion and breach widening can affect flow patterns and sediment transport dynamics⁶⁹. In the Matina River case study, Watson et al.⁷⁰ found that increasing the levee height was considered unfeasible due to substantial land loss and economic impacts on agricultural areas. Conversely, while notching can effectively manage peak flows and reduce pressure on levees, its benefits are largely localized and do not address the broader issues of floodplain management. Over time, the relief of the floodplain may evolve due to sediment redistribution and terrain reshaping during higher-magnitude floods. Notching projects hold potential ecological benefits through floodplain restoration while providing relief to levee systems, reducing the risk of catastrophic failure.

Underseepage control

Underseepage, which is exacerbated by internal erosion, is the second most common cause of levee failure after overtopping⁷¹. Underseepage control is a critical aspect of dam safety, especially for structures like the Willow Creek Dam in Oregon. Constructed between 1981 and 1983 by the US Army Corps of Engineers, this dam was the first major roller-compacted concrete dam in the U.S., primarily built for flood control⁷². During the initial reservoir filling, substantial leakage was observed through horizontal joints, reaching an alarming rate of 33 cubic meters per second. This necessitated a $2 million remediation effort involving grout injection to reduce the leakage to <11 cubic meters per second. Despite these efforts, concerns over the dam’s safety and structural integrity persist, with ongoing seepage issues contributing to dense vegetation on the dam’s face and continued debates about its long-term viability⁷². Several aspects contribute to levee underseepage, including the presence of a confining layer, geological deposition, the hydraulic conductivity of the foundation, anthropogenic activity, the influence of the root system, animal activity, natural erosion, and internal erosion⁷³. Underseepage control measures, such as cutoff walls, seepage berms, filters, relief wells, and grouting, are widely used to mitigate the risk of erosion and underseepage in levees and dams by preventing water from seeping underneath these structures^74,75. Underseepage control is classified under the infrastructural/technological category because it involves the application of specialized engineering techniques and construction methods to reinforce levee and dam structures. The successful implementation of underseepage control systems requires careful planning and execution. Prerequisites for their installation include thorough geological and hydrological studies to assess local conditions, adequate funding and resources, meaningful stakeholder engagement, regulatory approvals, and strict adherence to environmental and safety standards. Moreover, ongoing monitoring and maintenance are essential to uphold the effectiveness of these measures over time. When properly installed, underseepage control can enhance levee resilience to and better protect lives, property, and critical infrastructure from the impacts of inundation events.

River dredging

River dredging involves the removal of sediment and debris from river channels to increase their capacity and improve and regulate water flow by deepening and widening river channels. Dredging helps reduce the risk of overflow and alleviates flooding in downstream areas⁷⁶. Dredging can increase the flow capacity of a river, decreasing the risk of overtopping and preventing sediment buildup that exerts lateral pressure on flood protection infrastructure. It also has the potential to disturb riverbed stability, leading to increased erosion and causing structural damage during dredging operations⁷⁷. Despite these potential drawbacks, dredging plays a crucial role in reducing the risk of flooding in downstream communities, maintaining water quality, preserving aquatic habitats, and enhancing navigation and transportation. River dredging belongs in the infrastructural/technological category because it involves large-scale engineering operations that modify the physical characteristics of river channels. Prerequisites for dredging include environmental impact assessment, permitting and regulatory compliance, hydrology survey, design operations to minimize impacts on aquatic habitats, navigation, and water quality, as well as the development of a sediment management plan and implementation of monitoring programs⁷⁸. In the Vermilion River, south-central Louisiana, a decline in dredging activities over the past two decades has led to riverbed shoaling and diminished conveyance capacity, contributing to severe flooding⁷⁶. While dredging can effectively reduce water surface elevations during floods, it also has the potential to amplify tidal waves. The study also indicates that although spatially limited dredging can alleviate local water surface profiles, it may inadvertently increase downstream water levels during frequent events⁷⁶. Additionally, large runoff volumes from tributaries can overwhelm the increased in-channel capacity, thereby reducing the anticipated flood relief benefits from dredging efforts. Therefore, while dredging may be a helpful method for managing sedimentation and maintaining waterway access, careful planning and mitigation measures are essential to minimize its negative impacts on aquatic ecosystems and surrounding environments.

Intentional breaches

Intentional breaches are planned openings in flood protection infrastructure designed to redirect floodwaters away from critical infrastructure or populated areas. By strategically breaching levees, authorities can manage floodwater more effectively and minimize damage to surrounding communities⁷⁹. This strategy is categorized under infrastructural/technological measures because it involves the deliberate engineering and modification of flood protection infrastructure to control floodwaters. Intentional breaches of levees, such as the 2011 breach of the Birds Point Levee south of Cairo, Missouri, exemplify the concept of “graceful failure” where systems are designed to fail in a controlled manner to mitigate flood risks⁸⁰. This strategy involves diverting floodwaters to designated floodways, protecting communities and infrastructure. Recent analysis identified 17 potential sites on the Birds Point Levee for floodwater detention through graceful failure, evaluated based on their capacity to store floodwaters at various elevations⁸⁰. In the context of restoring lowland rivers, the topography of floodplains holds critical importance⁸¹. The development of floodplain topography at intentional levee breaches hinges on various factors related to breach hydraulics and sediment deposition. These factors include the transport capacity of sediment from the main river through the breach onto the floodplain, the sediment supply available to form a splay complex, and the characteristics of the flood pulse that inundates the floodplain⁸². The interplay of erosion and deposition processes at intentional levee breaches continually reshapes the physical structure of the landscape. It is crucial to assess both upstream and downstream impacts of a levee breach, as erosion and widening of the breach may alter flow dynamics and sediment transport. Over time, the relief of the floodplain may evolve as higher-magnitude floods redistribute sediment and reshape the terrain. Intentional breaches have the potential to have ecological benefits through floodplain restoration^83,84,85, as well as provide more control over where the flooding will occur first⁸⁶.

Relocation

Relocation or managed retreat involves the strategic relocation of flood-prone homes and buildings to higher ground without altering the levee infrastructure itself. This approach falls under infrastructural/technological adaptation because it aims to mitigate flood risks by modifying the physical landscape and infrastructure, physically moving vulnerable structures away from areas prone to inundation, reducing exposure to flood hazards, and safeguarding lives and property^87,88. In the U.S., a number of towns have completed or are planning partial or complete relocations as part of managed flood retreat efforts⁸⁹. Recent relocation projects in the U.S. typically include federally funded property acquisitions and have been substantially funded by the Federal Emergency Management Agency (FEMA), mostly through its Hazard Mitigation Grant Program⁸⁹. A managed retreat can offer a more environmentally friendly, long-term, and sometimes more cost-effective approach to hazard mitigation than structural flood protection. While relocation can effectively remove the risk of flooding a community, it is limited by the social implications of displacing communities, along with the unequal distribution of federal property acquisition funds⁹⁰. A study also evaluates the effectiveness of managed flood retreats and community relocations in 11 small rural towns in the Midwest USA, which relocated to mitigate flood risks from major riverine floods⁸⁹. Their analysis highlights varied outcomes: while towns like Niobrara, NE, and Soldiers Grove, WI, saw successful flood risk mitigation and community stability post-relocation, others like Leavenworth, IN, experienced reintroduced flood risks due to new developments on former floodplains. Additionally, relocations often led to short-term population declines but frequently resulted in population rebounds or growth over time. The study underscores that while relocations are generally effective in reducing flood risks, they are complex and costly, and future projects should learn from these cases to improve long-term outcomes⁸⁹. As flood frequency and intensity continue to rise, community relocation is increasingly considered an alternative to current strategies focused on engineering protection and rebuilding after disasters.

Multifunctional design of seawalls

The multifunctional design of seawalls integrates ecological considerations with structural requirements to protect shorelines from erosion, flooding, and wave impacts while enhancing biodiversity and ecosystem services. This strategy involves advanced engineering and modification of coastal defenses to enhance their protective capabilities while integrating ecological features, justifying its placement in the infrastructural/technological category. Traditional seawall designs (e.g., vertical, curved, and riprap) each offer distinct benefits and challenges. Vertical seawalls provide stability but can exacerbate wave reflection and toe scouring, whereas curved seawalls, which reduce wave overtopping and energy, offer better stability but are more complex to construct. Riprap retaining walls are cost-effective, absorb wave energy, and are easily repairable, often used in combination with other types⁹¹. A study evaluates the effectiveness of seawalls in mitigating storm surge damage along the Eastern U.S. coastline, highlighting the substantial costs associated with coastal flooding and the necessity for effective defenses⁹². Their model indicates that low seawalls (0.9–1.2 m high) can critically reduce damage from frequent surges. In contrast, higher seawalls are deemed maladaptive due to the lock-in effect limiting flexibility in adaptation and necessitating continuous height increases to keep pace with rising sea levels. Incorporating eco-engineering approaches, such as increasing topographic complexity, can mitigate wave impacts and enhance biodiversity, addressing the deficits of traditional structures⁹³. Seawalls with added microhabitats can mimic the complex topography of natural rocky shores, providing refuge from predation and environmental stressors, which increases niche space and surface area⁹⁴. By adding habitat structures, multifunctional seawalls can improve species diversity and filtration rates, which are crucial for water quality and ecosystem health⁹⁵. These interventions not only strengthen the resilience of coastal defenses but also support a variety of ecological functions, making them a valuable strategy for sustainable coastal management.

Dam rehabilitation

Dams play a crucial role in flood control, mitigating the impact of flooding events on downstream communities and ecosystems. Dam rehabilitation is placed in the infrastructural/technological category because it involves technical interventions and upgrades to existing dam structures to address flood risks and changing environmental conditions. Continuous monitoring, maintenance, and rehabilitation of dams, particularly in the U.S., where the average age of dams is 63 years⁹⁶. A study also assesses flood risks in the Bago River Basin, Myanmar, with a focus on dam operations for flood control⁹⁷. They find that dam operations substantially reduce downstream flood hazards and damage. Accurate flood damage estimation is crucial for evaluating flood prevention measures and crafting effective policies. The study highlights that while future extreme floods could cause severe damage, effective dam management, along with additional measures such as land-use planning and crop adaptation, can help mitigate these impacts⁹⁷. Traditional dams serve several purposes such as reducing flood frequency and the extent of flooded areas, while detention dams, specifically designed for flood control and mitigation, detain excess water during high-flow periods and release it gradually downstream. Detention dams help manage peak flows by restricting water flow during high-flow periods, thus reducing the risk of downstream flooding^98,99. However, ensuring dam safety is paramount, with aging dams facing increased risk due to changing climatic conditions and potential failures^72,100. Renovation efforts, including structural retrofits, fishway installations, reservoir reoperation, and sustainable sediment management, are essential to prolong reservoir life and mitigate dam impacts, especially in the face of evolving societal expectations and climate change¹⁰¹.

Construction of weirs

Weirs serve as hydraulic structures deployed across rivers and streams to regulate water flow, playing multifaceted roles in various water management aspects. The construction of weirs involves engineering and building hydraulic infrastructure. Therefore, it is categorized as an infrastructural/technological adaptation measure. Flood control is a primary purpose of weirs, aiming to control the volume and rate of water flow to prevent downstream flooding¹⁰². Additionally, weirs facilitate water measurement, water diversion for irrigation or industrial purposes, and navigation by maintaining specific water levels^102,103. Weirs, including varieties like labyrinth, piano key, and submerged weirs, interrupt river hydrodynamics while preserving water and accumulating sediment, thereby impacting water quality¹⁰⁴. Adapting existing weirs is crucial for managing floods and regulating seasonal inundation, as demonstrated along rivers like the Rhine and Dambovita, where weirs are utilized for flood protection while considering environmental concerns¹⁰³. Gate operation management is essential for weir efficacy in improving water quality, especially concerning high algal biomass concentrations, emphasizing the significance of monitoring and operational planning¹⁰⁵. A study investigates the ecological impact of large weir constructions on river habitats in South Korea, focusing on the Nakdong and Geum Rivers, which underwent modifications during the Four Large Rivers Project, and comparing them to the unaltered Seomjin River¹⁰⁶. The findings revealed that the Nakdong and Geum Rivers experienced a substantial increase in permanent water area by 36% and 11%, respectively, while seasonal and non-flooded habitats decreased substantially, highlighting the long-term habitat alterations caused by weir construction. In contrast, the Seomjin River, without weirs, exhibited minimal habitat changes, underscoring the direct impact of weir installations on the other rivers¹⁰⁶. In summary, weirs serve as pivotal components in water resource management, offering versatile solutions for flood control, water diversion, and water quality enhancement while necessitating careful consideration of environmental impacts and operational strategies.

Construction of flood walls

Flood walls are robust barriers, often constructed from concrete and sometimes steel sheet piles driven deep into the ground to fortify flood defense systems and safeguard communities against flooding. By reinforcing or adding to the flood defense system, flood walls instill confidence in protection measures, enabling communities to remain in place even during severe flood events¹⁰⁷. Flood walls are considered an Infrastructural/Technological measure because they represent a direct, structural approach to flood management. There are several types of flood walls, but the majority of these are I-walls and T-walls. For instance, after Hurricane Katrina, the United States Army Corps of Engineers (USACE) extensively used concrete T-walls with batter piles in the Hurricane Storm Damage and Risk Reduction System¹⁰⁸. In several sections, these I-walls or T-walls were installed within the existing levee embankments. The design and selection of flood walls, such as I-walls and T-walls, depend on factors like availability of real estate, availability of earthen material since levees can be cheaper, exposed wall height, and required flood protection height^109,110. In a detailed case study of the 17th Street Canal flood wall failure in New Orleans during Hurricane Katrina, the stability of the flood wall was shown to be highly dependent on both the design and the materials used¹¹¹. The study highlights the substantial influence of underlying soil conditions on the functionality of flood walls, with non-homogeneous soil profiles necessitating careful consideration during the design phase. Moreover, robust design considerations were emphasized to account for varying soil strengths and the impact of water surcharges on the ground surface¹¹¹. Additionally, various considerations, including the risk of overtopping, vegetation, encroachments, and foundation pipes, must be accounted for in flood wall construction to ensure their effectiveness and stability over time.

Construction of flood protection for individual buildings

Flood protection for individual buildings involves implementing building-level flood protection measures such as flood barriers, raised foundations, waterproofing, amphibious buildings, and retrofitting to minimize flood damage to homes, businesses, and infrastructure. It is an infrastructural/technological measure because it involves the use of engineering and construction techniques to modify or enhance building structures. These measures help to reduce property loss and ensure the safety of occupants during flood events¹¹². These building-level measures contribute to reducing property loss and ensuring occupant safety during flood events. Flood resilience of buildings necessitates considering building occupation and material use under different flood conditions. This approach entails diversifying flood-proofing measures and defense levels based on vulnerability, considering the cost-effectiveness of different solutions¹¹³. Flood-proofing strategies can be achieved by elevated configuration, dry proofing by sealing or shielding, wet proofing, floating or amphibious solutions, temporary barriers, and pump systems at the building level¹¹⁴. The same study examined flood protection measures along the Mela River in northeastern Sicily; the effectiveness of flood doors and windows for individual structures was highlighted¹¹⁴. While traditional levees can reduce flood damage, their high costs often make them impractical for small-scale areas like the Mela catchment. In contrast, flood-proofing offers a more cost-efficient solution for protecting single houses, although they do not mitigate broader flood impacts. These measures can be implemented based on flood patterns, building elevation requirements, legal regulations, compliance of homeowners and businesses, and available funding and support¹¹⁵. Recent studies further distinguish traditional property-level protection (PLP), which focuses on keeping water out from the broader concept of Property Flood Resilience (PFR), which assumes that some water ingress is inevitable and therefore couples resistance devices with recoverability features such as waterproof plasters, raised utilities, and sacrificial finishes¹¹⁶.

Construction of channels and floodways

Channels and floodways are engineered pathways designed to direct excess water away from developed areas during flooding events. The construction of channels and floodways is an infrastructural/technological measure because it involves the deliberate modification of the landscape to create controlled pathways that manage and redirect floodwaters. Directing floodwaters along predetermined routes, channels, and floodways helps prevent the inundation of homes, businesses, and vital infrastructure¹¹⁷. Sampang City, East Java, frequently faces flooding from the Kali Kemuning River. A study highlights the importance of incorporating floodways as a solution to manage these floods¹¹⁸. They emphasize that the design of floodways is influenced by runoff discharge and runoff coefficients, which are affected by changes in land use/land cover. They demonstrate that integrating floodways with normalized river dimensions can effectively prevent flooding, provided that the floodway dimensions are appropriately adjusted according to varying runoff coefficients¹¹⁸. Floodways established along rivers can be intentionally inundated during severe floods to attenuate water levels and reduce downstream flood damage and losses¹¹⁸. For instance, the Dutch flood management strategy involves setting aside land along rivers to widen floodplains and create retention basins for occasional inundation while still allowing for multifunctional uses such as agriculture or recreation¹¹⁹. The decision regarding when and how much water to divert into floodways is influenced by various factors, including upstream hydrological conditions, the size and location of the floodways, the effectiveness of the levee protection, potential flood losses in the event of levee failures, and the impact of such failures on downstream flood levels¹¹⁹. Additionally, flood diversions can redirect floodwaters into off-channel storage areas, relieving pressure on the main channel and levee system and allowing the river to accommodate higher flow volumes¹²⁰. By strategically managing floodwaters by implementing channels and floodways, communities can enhance their resilience to flooding while safeguarding vital assets and infrastructure.

Construction of drainage and pump systems

Increasing the capacity of drainage and pump systems involves upgrading or expanding existing infrastructure to enhance its ability to manage flood risks in vulnerable areas. These systems can expedite the removal of excess water during intense storm events, reducing the likelihood of flooding¹²¹. Drainage and pump systems are considered an Infrastructural/Technological measure because they involve the engineering and upgrading of infrastructure systems. A study investigated the effectiveness of enhanced pump operations and capacity expansions in improving urban drainage system resilience in Seoul, a highly urbanized city with waterways such as the Han River and Dorim stream¹²². The research focused on a drainage system covering 2.5 km², incorporating 10 pump stations and two detention reservoirs. By evaluating various operational scenarios, including adjustments to pump stop levels and capacities, the study found that the operational strategies, such as implementing expanded pump capacities and additional monitoring, improved system resilience¹²². An emerging strategy involves adding smart drainage systems that utilize artificial intelligence and machine learning algorithms to steer water to the least sensitive parts of storage basins, minimizing damage by continuously learning and adapting to environmental conditions¹²³. In urbanized areas, anthropogenic factors such as land use and storm drainage systems influence surface overland flow processes. The presence of impervious surfaces like rooftops, roads, and squares increases the surface runoff rate and volume, altering the natural flow direction¹²⁴. Storm drainage systems, including storm sewers and pumping stations, play a vital role in mitigating surface inundations by draining excess runoff into underground sewers. If the surface runoff exceeds the capacity of the drainage system, water overflows onto land surfaces, leading to inundation. Flood damage can be reduced by redesigning and enlarging the capacities of storm sewer systems or pumping stations in the inundation-prone areas. Improving and expanding these drainage systems requires an approved point of discharge, proper permitting, retention/detention, an understanding of water dynamics, and identifying the best location¹²⁵.

Construction of detention basins

Detention basins, also known as detention areas, serve as crucial components of river flood risk management by temporarily retaining floodwater volumes^23,126. Detention basins fit into the Infrastructural/Technological category because they are engineered structures designed to mitigate peak flows and reduce water levels during extreme events. They are widely implemented in flood-prone regions across several major river basins^127,128. These basins offer several advantages, such as reducing downstream flood hazards and risks, improving ecosystem quality, and providing additional services like pollution reduction and recreational opportunities¹²⁸. However, their implementation poses challenges, including the need for land occupation, potential impacts on land use practices, and the requirement for careful planning and optimization to address issues such as population growth and land development pressures, especially in densely populated areas^129,130. Nonetheless, recent research emphasizes evaluating the efficacy of detention basins not only in terms of reducing peak flows but also in mitigating flood damage, highlighting their importance as adaptive measures in flood risk management strategies²³. A study of the Poisar River catchment in Mumbai, India, examined the hydrological impacts of land use changes and the implementation of detention basins on urban flood hazards¹³¹. The researchers found that rapid urbanization led to substantial increases in peak discharge during flood events. However, the introduction of detention basins markedly reduced peak discharge, flood extent, and flood hazard areas, demonstrating the effectiveness of these basins as a flood control measure, particularly during severe flood events¹³¹. Detention basins, with their multifaceted benefits and challenges, stand as essential adaptation measures in the face of rising river flood risk, necessitating a balanced approach that considers both their effectiveness and potential limitations in flood risk management strategies.

Construction of landside stability berms

Berms are defined as shelves interrupting the continuity of a levee or earthen dam slope. Berms fall into the infrastructural/technological category because they are specifically engineered structures designed to enhance the stability and functionality of levees and earthen dams. They serve various purposes, including increasing slope stability, controlling erosion, extending seepage paths, and providing areas for construction and maintenance work. Berms can also act as effective seepage control measures when equipped with filters and drains. Different types of berms, such as upstream and downstream berms, toe berms, and waste berms, offer diverse functionalities, including augmenting seepage capacity, reducing liquefaction potential, and contributing to slope stability¹³². Seepage berms are particularly effective in preventing underseepage-related failures of levees and are often used alongside relief wells to manage seepage exits at the levee toe¹³². In a case study on climate change adaptation, the authors evaluate the costs and benefits of constructing an 8.2 mile berm along the Hackensack River in Bergen County, New Jersey, following the devastation of Hurricane Sandy¹³³. The study examines a 50 year period and demonstrates that investment in the berm is cost-effective, with substantial long-term financial benefits, including the prevention of residential and commercial damages. Additionally, the berm would greatly enhance the region’s resilience to future flooding events and provide substantial environmental and social benefits, such as the restoration of wetlands and the development of recreational areas to improve community well-being¹³³. While berms may not drastically decrease total eroded volume, they typically delay bank retreat, providing valuable time for mitigation efforts¹³⁴. Overall, berms represent a versatile and valuable adaptation option for reinforcing levees against flood hazards.

Construction of closure structures

Closure structures are engineered barriers or gates designed to close off openings in flood defense systems during flood events to prevent the ingress of floodwaters into protected areas¹³⁵. This infrastructure requires specific technology to enhance flood defense systems on an as-needed basis, justifying their classification as an infrastructural/technological measure. Closure structures are essential if relocating or raising roads and pathways through levees is not possible. They can help maintain the integrity of levee systems and prevent inundation of flood-prone areas by improving emergency response, flood control, risk reduction, maintenance, and controlled releases. They mitigate flood risks for communities on an as-needed basis by safeguarding communities, preventing inundation, minimizing property damage, protecting infrastructure, and ensuring the safety of residents during high-water events¹³⁶. Closure structures can also control the release of water from storage reservoirs and manage its flow through, around, or over dams¹³⁷. The city of Padova, situated amidst the Brenta and Bacchiglione rivers and their interconnected channels, has experienced severe flooding historically and in recent years. Proper operation of floodgates at the Voltabarozzo Control Structure is crucial for balancing the discharge load across the Brenta-Bacchiglione river network. These floodgates are operated based on predefined, static operation rules that depend on real-time flow variables at different locations within the river network. This approach minimizes flood risk by optimally operating existing floodgate structures without substantial additional costs, demonstrating a cost-effective flood management solution¹³⁸. Effective implementation of levee closure structures requires hydrological and hydraulic analysis, geotechnical investigation, hydraulic modeling, regulatory compliance, environmental impact assessment, and community engagement.

Construction of revetments

Revetments encompass various techniques such as placed-rock, gabion, and concrete block structures strategically placed along riverbanks to manage water flow dynamics. They fit into the infrastructural/technological category as they consist of constructed features that are specifically designed to stabilize riverbanks and levee systems. By mitigating the risk of inundation and minimizing the destructive potential of floodwaters, revetments contribute to enhancing the resilience of communities situated in flood-prone areas¹³⁹. However, while revetments can be helpful in managing erosion due to water flow and increasing the stability of levees, if they fail, it could have devastating results on river dynamics and levee strength, potentially resulting in the failure of the levee¹⁴⁰. Therefore, special attention should be paid to the stability of levee revetments and foundations, considering factors such as riverbed scouring and the dissipation of river water energy^140,141. Additionally, revetments are introduced to a levee system to protect the crest and river-side slope of the levees against surge overflow and wave overtopping, which are crucial for ensuring a viable and safe levee system. Various strengthening systems, including cellular confinement systems, reinforced grass, concrete block systems, and soil cement/roller-compacted concrete, have been introduced to protect levees from erosion by surge overflow, wave overtopping, transverse and parallel flow¹⁴². In Ovar, a municipality in Portugal, substantial coastal erosion and sediment deficits have been exacerbated by dam constructions and sand dredging. A case study evaluating different intervention scenarios for longitudinal revetments revealed that raising the crest level is the most viable option due to its cost-effectiveness and efficiency in reducing overtopping. In contrast, artificial nourishment was deemed the least favorable due to high costs and the instability it introduces. Building an intermediate berm presented a viable middle-ground solution with moderate costs and benefits¹⁴³. The implementation of revetment strategies has the potential to safeguard communities against flood-related hazards. However, the long-term resilience and stability of revetments must be considered in the face of changing water flow dynamics and potential inundation risks.

Construction of gabion walls

Gabion walls serve multiple purposes, such as erosion control, soil reclamation, retaining structures, and stream canal linings^144,145. These walls consist of rectangular baskets made of zinc-coated steel wires filled with stones or cobbles, providing a flexible and monolithic structure. Gabion walls belong to the infrastructural/technological category because they are engineered structures that support flood control. Their construction is facilitated by the utilization of local materials, making them adaptable to various sites, and their high drainage properties make them suitable for soils prone to settlement¹⁴⁴. Over time, gabion walls naturally enhance their strength and effectiveness as voids fill with silt and vegetation. Despite their advantages, failures in gabion walls are often attributed to factors such as improper stones, poor workmanship, and inadequate construction procedures rather than design flaws. Therefore, it is crucial to address construction-related issues, explore alternative materials and techniques, and conduct comprehensive site investigations to effectively prevent and mitigate gabion wall failures¹⁴⁶. In a study examining the long-term effectiveness of gabion structures along the Zealand River, New Hampshire, gabion walls and sills were initially successful in mitigating flood flows, limiting bank erosion, and trapping bedload sediment. However, over time, these structures frequently became undercut, toppled, or overtopped due to ongoing channel incision and undermining, leading to substantial geomorphological changes and ecological challenges. The findings underscore the importance of thorough evaluation and robust maintenance planning for the continued effectiveness of gabions in river stabilization efforts¹⁴⁷. Gabion walls offer numerous benefits, such as flexibility, permeability, low maintenance, simple construction, minimal foundation depth, and environmental sustainability due to their ability to allow small plants to take root, reinforcing the soil and improving the structure’s lifespan¹⁴⁵.

Institutional adaptation measures

Institutional adaptation measures involve modifications to governance structures, policies, and organizational frameworks to better manage climate risks¹. These measures include the development of regulations, such as zoning laws and building codes, the implementation of insurance schemes, and the creation of coordination mechanisms to improve institutional responses to climate impacts. However, there may be a reporting bias, as many institutional responses are documented in grey literature. Institutional adaptation emphasizes enhancing multi-level governance and building institutional capabilities to integrate climate adaptation into existing policy frameworks effectively. This section offers an extensive catalog of institutional adaptation measures, outlining their benefits, drawbacks, associated co-benefits, and potential tradeoffs. A summary of these measures can be found in Table 2.

Table 2 Institutional adaptation measures and their advantages, disadvantages, co-benefits, and tradeoffs

Flood monitoring and warning systems

The implementation of flood monitoring and warning systems involves the installation of sensors, gauges, and monitoring stations to track water levels, rainfall intensity, and weather forecasts. These systems provide real-time data and early warnings to communities, enabling timely evacuation and preparedness actions¹⁴⁸. These systems play a crucial role in providing advance notice of impending floods, facilitating the implementation of emergency plans, and minimizing the adverse impacts of floods¹⁴⁹. The development and implementation of flood monitoring and warning systems fall under the infrastructural/technological category because they involve creating and deploying advanced technological infrastructure for real-time flood detection and response. A case study highlights Bangladesh’s heightened vulnerability to floods due to its socio-economic conditions and geographic location within the Ganges-Brahmaputra-Meghna basins¹⁵⁰. Focusing on the Sirajganj district, which has experienced severe flood damage in multiple years, the study found that traditional embankments are ineffective in mitigating flood risks. The research demonstrated that impact-based forecasting and warnings could be more effective than traditional flood warnings, as they translate hydro-meteorological forecasts into actionable information for end users such as farmers and disaster management personnel¹⁵⁰. Several countries have operational flood warning systems, such as the Flood Forecasting system of DELFT-FEWS and the Central America Flash Flood Guidance^151,152. Flood warning systems typically consist of four key elements: detecting flood potential, forecasting flood hazards, issuing warnings to authorities and the public, and coordinating flood response¹⁵³. These systems utilize various methods, including monitoring weather patterns, estimating rainfall from satellite imagery, and analyzing hydrologic and hydraulic models¹⁵⁴. Monitoring and warning systems are vital; effective flood management also requires evacuation plans, community trust, and evacuation capability. While many large-scale flood warning systems exist, many communities still lack their own monitoring and alert systems, highlighting the need for enhanced preparedness¹⁵⁵.

Inspections and maintenance

Regular inspections and maintenance of flood protection infrastructure, drainage systems, and flood-prone areas are essential for identifying vulnerabilities, addressing potential hazards, and ensuring the effectiveness of flood mitigation measures. These activities involve the systematic evaluation and upkeep of physical infrastructure and ensuring that technological systems remain effective and resilient against potential flood risks, justifying its placement in this category. Proper maintenance helps to prevent system failures and reduce the risk of flooding¹⁵⁶. Flood defenses require regular interventions to cope with long-term degradation processes, changes in performance requirements, and hydraulic loads¹⁵⁷. The degradation of flood defenses can occur through continuous-progressive degradation, which is typically a slow process, or shock-based degradation caused by randomly occurring shocks of varying sizes¹⁵⁸. The case study of the Eilandspolder in North Holland, underscores the importance of rigorous inspections and maintenance for levee safety¹⁵⁹. It advocates integrating real-world observations and degradation effects into levee safety assessments, allowing for a more accurate and performance-based evaluation. This approach emphasizes the need for continuous monitoring and timely repairs to ensure that levees maintain their protective functions against flooding¹⁵⁹. Optimal inspection frequency and intervention levels for shock-based degradation depend on the inter-arrival time and size of shocks. Additionally, more frequent monitoring and maintenance not only enhances safety and risk reduction but also contributes to community confidence, economic stability, and growth¹⁶⁰. Planning the frequency of levee inspections and maintenance requires understanding structural components, historical data, hydraulic patterns, and weather and climate events.

Effective groundwater management

Adaptation through groundwater management is a tool for providing protection against flooding, ensuring freshwater supplies, and supporting climate-resilient spatial planning. Effective groundwater management is categorized as an institutional adaptation measure as it involves coordinated policies, regulations, and practices that govern the sustainable use and protection of groundwater resources, integrating them into broader flood risk reduction and climate resilience strategies. In the case of New Orleans, a city with over 50% of its area below sea level, complex hydrogeology substantially influences groundwater dynamics and the associated risks of flooding and levee underseepage. Particularly, areas with permeable sediments and shallow confined aquifers face elevated risks of groundwater flooding. A study underscores the importance of understanding these hydrogeologic factors, as they help identify geo-hazard areas and inform more resilient engineering designs for coastal cities facing similar challenges¹⁶¹. Groundwater, although a vital resource, is being overexploited globally at unsustainable rates, leading to critical environmental concerns¹⁶². Effective management practices, such as improved land management in upper basins, rainwater harvesting, and the use of previous pavements in urban areas, can enhance groundwater recharge and sustainability¹⁶³. Groundwater acts as a natural buffer against both floods and droughts, recharging during floods and providing water during droughts, thus mitigating the impacts of both extremes¹⁶⁴. Additionally, targeted recharging of excess wet season flows into aquifers can protect downstream areas and boost agricultural productivity. However, frequent flooding poses risks of groundwater contamination, as surface flows can carry pollutants into aquifers, necessitating careful management to maintain groundwater quality¹⁶⁴. Despite its importance, groundwater management is often neglected, highlighting the need for integrated disaster risk reduction strategies that consider both floods and droughts.

Policy and institutional strengthening

Policy and institutional strengthening are critical for effective flood risk management. This method involves enhancing the capacity and coordination of institutions and policies to effectively manage and govern flood risk through improved frameworks, leadership, and stakeholder engagement, justifying their placement into the institutional adaptation measures category. Institutions shape human interactions and flood risk governance through various actor networks, resources, and multi-level coordination mechanisms¹⁶⁵. However, fragmented responsibilities among government organizations and insufficient collaborative public engagement create substantial institutional hurdles, compounding technical challenges in flood risk management. Programs like ACCCRN, 100 Resilient Cities, and Water as Leverage in Southeast Asia have made strides in building local institutional capacities by funding pilot projects and establishing knowledge networks to support local governments in mainstreaming resilience policies¹⁶⁶. Adaptive capacity, a key attribute of resilience, can be enhanced through robust institutional frameworks that incorporate proactive leadership and public participation. Effective utilization of adaptive capacity criteria is crucial for assessing and designing resilience strategies. This approach helps in identifying strengths, weaknesses, and potential synergies within institutional systems, thereby bolstering urban flood resilience¹⁶⁷.

Funding for flood mitigation and recovery

Funding and financial support for flood mitigation projects, infrastructure improvements, and disaster recovery efforts may include aid from federal, state, and local government grants, loans, and assistance programs¹⁶⁸. This institutional adaptation measure involves financial mechanisms and government programs that are essential for supporting infrastructure improvements, disaster recovery, and equitable flood risk management. In October 2015, South Carolina experienced severe flooding from Hurricane Joaquin, causing widespread damage to infrastructure, homes, and businesses. Only 28% of over 101,000 applicants for Individual Assistance received support, with disparities evident: higher-income areas received more aid, while Black populations and renters were underserved in both Small Business Administration (SBA) loans and National Flood Insurance Program (NFIP) payouts. This case study highlights the inequities in disaster recovery funding, underscoring the need for more equitable distribution in future disaster responses¹⁶⁹. To adequately address flood risk, public funding should focus on both flood mitigation and recovery^170,171,172. In the U.S., the Federal Emergency Management Agency (FEMA) offers the Flood Mitigation Assistance (FMA) program, which provides nearly $175 million in competitive grants to state, local, tribal, and territorial governments to reduce flood risks. Grants are awarded based on eligibility, project ranking, and cost-effectiveness to reduce National Flood Insurance Program (NFIP) claims. However, socially vulnerable counties are shown to be less likely to receive FMA funding¹⁷³. Additionally, FEMA’s Public Assistance (PA) program supports the repair and rebuilding of public and some private non-profit infrastructure and reimburses state and local governments for emergency management¹⁷⁴. The PA program’s importance is expected to grow with the increasing frequency and intensity of natural hazards. However, there are potential equity issues, as more resource-rich areas tend to benefit more from PA funds, demonstrating the importance of targeting vulnerable groups while ensuring equity in access to recovery funds¹⁷³.

Proactive planning for emergency action

Emergency action plans enable communities to respond effectively to flood emergencies and coordinate emergency services, evacuation procedures, and relief efforts. These plans outline roles, responsibilities, and protocols for local authorities, first responders, and community members during flood events¹⁷⁵. Proactive planning for emergency action fits into the institutional adaptation measures category because it involves developing and coordinating structured plans and protocols by local governments and authorities. They establish clear procedures for emergency response actions, such as evacuation routes, shelter locations, and communication protocols, ensuring a coordinated and efficient response. Additionally, emergency action plans facilitate the identification and coordination of resources needed for response and recovery efforts, including personnel, equipment, and supplies^176,177. Benefits of emergency action plans include better preparedness, reduced casualties and damage, and improved coordination, while drawbacks involve the risk of outdated information, lack of stakeholder engagement, and difficulties adapting to unforeseen events. Local governments play a critical role in managing disasters at the community level, leveraging their familiarity with local communities to effectively implement emergency management strategies¹⁷⁸. In Kebomlati Village, Indonesia, effective planning for emergency action has proven essential in mitigating the impacts of frequent natural disasters such as river flooding, drought, and forest fires. The establishment of a Flood Disaster Management Committee, encompassing multiple stakeholders, highlights the critical role of coordinated emergency action. Furthermore, the strategic use of social capital and technology for communication and volunteer training exemplifies how preparedness and community collaboration can critically enhance disaster response efforts¹⁷⁹. Current emergency action plans typically lack a comprehensive integration of climate change projections, which are crucial for anticipating and preparing for more severe and frequent flood events in the future. To avoid conflicts and duplication of efforts, there is also a need for improved mechanisms for cross-jurisdictional coordination, particularly in regions where floodwaters may affect multiple communities simultaneously. Challenges and failures in emergency management processes serve as opportunities for leaders and organizations to enhance their capabilities and confidence through continuous improvement efforts.

Establishment of multi-layer safety

Multi-layer safety refers to the concept of implementing redundant or overlapping layers of flood protection measures to enhance the overall resilience of flood defense systems. This approach emphasizes comprehensive measures for protection, prevention, preparedness, and recovery to ensure a robust response to potential hazards¹⁸⁰. The establishment of multi-layer safety fits into the institutional adaptation measures category because it requires coordinated efforts across various policy domains and stakeholders to implement successful overlapping and redundant flood protection strategies. Multi-layer safety incorporates tactics such as compartmentalization, the subdivision of the at-risk area into smaller sections. This approach involves enhancing and, in some cases, removing certain flood defenses and community-level safety plans to manage water flow and protect urban areas during flood events¹⁸¹. Incorporating both public protection measures and individual protection measures into a multi-layer safety approach offers a comprehensive strategy to mitigate flood risk at both community and property levels. By combining structural defenses with targeted interventions for individual buildings, this approach not only enhances flood resilience but also fosters a synergistic effect that provides greater resistance to flood hazards than either measure alone¹⁸². However, the successful implementation of multi-layer safety necessitates collaborative efforts among stakeholders, integration of objectives from various policy domains, and careful consideration of a range of measures across spatial scales and time horizons¹⁸³. This approach can also have high associated costs. Shanghai faces severe risks from coastal flooding due to its low-lying geography and historical reliance on outdated hard defenses like sea dikes and floodwalls. Projections indicate that Shanghai could experience the highest increase in flood risk worldwide due to climate change and socioeconomic development⁴⁸. Hard strategies, such as storm-surge barriers, substantially reduce expected annual damages but come with high costs, whereas soft strategies like wet-proofing and coastal wetlands offer better benefit/cost ratios but are less effective against future risks. The hybrid strategy, which combines both approaches, provides the optimal balance of cost, effectiveness, and risk reduction, outperforming single-strategy approaches in managing future flood risks⁴⁸.

Real-time control of reservoirs and detention basins

Real-time control (RTC) of reservoirs and detention basins represents an advanced and adaptive flood mitigation strategy that leverages real-time data streams, including rainfall forecasts, river stage levels, and sensor network outputs, to dynamically adjust gate operations and optimize stormwater storage and discharge^184,185. Unlike traditional static infrastructure, which is typically designed based on historical hydrologic patterns, RTC enables predictive and responsive system management. This functionality is especially critical in the context of climate change, which is increasing the intensity and frequency of extreme precipitation events, and in rapidly urbanizing areas with high levels of impervious surfaces that amplify runoff volumes¹⁸⁶.

RTC offers numerous benefits, including the ability to reduce downstream flood peaks, extend detention and retention times, and support multi-objective system performance ranging from flood mitigation to water supply management and ecological preservation¹⁸⁷. Importantly, while RTC relies on engineered infrastructure, it is also inherently institutional in nature. Effective deployment requires coordinated governance reforms, revised operational policies, inter-agency collaboration, and financial incentives for municipalities to invest in sensor networks, telemetry systems, and data-driven modeling platforms¹⁸⁶.

A case study from Southwest Granby, Quebec, highlights the practical benefits of RTC. The system demonstrated the capacity to delay peak flows by up to 36 h, prevent overflows during extreme rainfall events, and improve pollutant sedimentation by extending storage times¹⁸⁶. Additional studies also show that RTC can enhance water quality by reducing pollutant loads, managing sedimentation, and limiting combined sewer overflows¹⁸⁸.

Despite its advantages, RTC presents certain challenges. These include high initial capital and installation costs, the need for ongoing data collection and system calibration, and potential vulnerabilities associated with sensor malfunctions or communication failures. Nonetheless, the overall benefits of enhanced flood resilience, deferred infrastructure expansion, and improved water quality make RTC a highly promising and scalable solution, particularly in urban areas facing increasing climate variability and uncertainty.

Managing residual flood risk behind levees

One critical yet often underemphasized dimension of flood risk management is addressing residual risk behind levees, i.e., the risk that persists due to levee overtopping or failure during events that exceed their design standards. Despite providing a sense of security, levees can create false perceptions of safety, increasing development in protected areas, a phenomenon known as the “levee effect”¹⁸⁹. A study provides a comparative analysis of how the U.S., France, and Quebec address this issue through regulatory flood maps¹⁹⁰. While France and Quebec incorporate residual risk zones into flood regulation and land-use planning, the U.S. only includes these areas in regulatory flood maps if levees are not FEMA-accredited. This variation has substantial implications for risk communication, emergency planning, and insurance uptake.

Effective management of residual risk requires integrating multiple non-structural measures such as land use regulations, flood insurance, and emergency preparedness protocols alongside engineered infrastructure. It also demands regulatory transparency, public engagement, and consistent communication strategies. This topic highlights a key area where institutional adaptation intersects with infrastructural reliability, reinforcing the need for layered, cross-sectoral adaptation planning¹⁹⁰.

Behavioral/cultural adaptation measures

Behavioral/Cultural Adaptation Measures involve changes in individual and community behaviors, practices, and cultural norms to reduce vulnerability to climate impacts¹. These measures are the most commonly observed form of adaptation, with extensive evidence showing individuals and households adopting strategies such as flood protection for homes, drought-resistant agricultural practices, relocation from hazard zones, and shifting livelihoods. In agriculture, for example, households are increasingly switching to crops and livestock that are more resilient to drought, heat, moisture, pests, and salinity. While behavioral changes are often the first line of defense, they are followed by technological innovation, infrastructural development, nature-based solutions, and institutional adaptation in broader climate resilience strategies. This section provides an extensive overview of behavioral and cultural adaptation measures, outlining their benefits, drawbacks, additional advantages, and associated tradeoffs. Table 3 offers a concise summary of these measures.

Table 3 Behavioral/Cultural adaptation measures and their advantages, disadvantages, co-benefits, and tradeoffs

Community education and awareness programs

Community education and awareness programs are essential components of adaptive flood risk management. These initiatives support the broader shift away from overreliance on large-scale structural interventions by emphasizing the importance of behavioral change, local engagement, and non-structural strategies. Classical studies have long cautioned against excessive dependence on engineering solutions, noting that such approaches can sometimes exacerbate flood risks¹⁹¹. For example, the practice of “straitjacketing” continuously elevating and reinforcing levees may simply displace floodwaters to downstream or adjacent areas, amplifying risks elsewhere. Another well-documented phenomenon is the “levee effect,” in which the presence of flood defenses fosters a false sense of security, encouraging development in flood-prone areas and ultimately increasing vulnerability when defenses are overtopped or fail^{191,192,193,194}.

Recognizing these unintended consequences has prompted calls for more holistic, integrated flood adaptation strategies. These approaches increasingly emphasize the role of community agency, social networks, and local knowledge in fostering resilience¹⁹⁵. Empowering communities to actively participate in flood risk planning and response builds ownership, promotes more context-specific solutions, and enhances long-term adaptation outcomes. Community-led initiatives are particularly valuable in identifying localized vulnerabilities, developing appropriate interventions, and ensuring that measures are socially acceptable and sustainable.

Education and awareness programs fall within the behavioral/cultural category of adaptation measures because they aim to enhance individual and collective understanding, attitudes, and practices related to flood preparedness and response. A study outlines that effective community education spans multiple domains: disaster risk education, prevention education, preparedness training, and emergency response planning¹⁹⁶. Another study further stresses the need for a comprehensive and sustained approach to education that builds both technical knowledge and civic responsibility¹⁹⁷.

In practice, the effectiveness of education programs depends on how well they are tailored to local contexts. In Accra, Ghana, for example, recurring seasonal floods are compounded by rapid urbanization, poor drainage, and limited maintenance of infrastructure. Structural measures have often proven ineffective, and relocation or eviction programs have met with strong community resistance, demonstrating the need for meaningful engagement through education and awareness initiatives¹⁹⁸. Flood education can be disseminated through various media, including public campaigns, community events, school curricula, and visual materials. These programs should go beyond basic instruction to promote hands-on learning, enhance self-awareness, and foster long-term behavioral change¹⁹⁹.

Previous flood experience also plays a substantial role in shaping risk perception and adaptive behavior. Households that have experienced flooding tend to show higher levels of preparedness, partly because these events elevate awareness and highlight the importance of mitigation²⁰⁰. However, large-scale flood awareness campaigns have shown limited effectiveness, suggesting a need for more focused, community-based education initiatives to better engage households and businesses in integrated flood risk management²⁰¹.

Diversification of crops and livestock

Climate change poses a threat to food security in several regions of the world. In response, farmers worldwide are adopting innovative strategies. Diversification of crops and livestock involves changes in community behaviors to enhance resilience and adaptability, justifying its placement in the behavioral/cultural adaptation category. An interesting and creative example can be observed among farmers in Bangladesh, who have started rearing ducks instead of chickens for their ability to fly and swim, resulting in higher survival rates during floods²⁰². Additionally, a study highlights the importance of community education and awareness programs in the context of managing catastrophic risks, particularly in the flood-prone regions of Khyber Pakhtunkhwa, Pakistan²⁰³. Given the region’s high susceptibility to climate change and frequent flooding, local households have adopted both on-farm and off-farm livelihood diversification strategies to cope with these challenges. By educating communities about the benefits of diversifying livelihoods, especially through livestock investments, farmers can reduce their reliance on vulnerable crop yields and better adapt to flood risks²⁰³. Furthermore, several studies focus on investigating crop response to climate stressors such as extreme precipitation, storms, snow, hailstorms, and floods in a combined effort to develop climate-resilient crops^204,205. The task of “adapting” crops has become a major challenge for breeders, extending beyond economic interests to address national and global food security concerns.

Nature-based adaptation measures

Nature-based adaptation measures refer to strategies that leverage natural systems and processes to mitigate climate risks and bolster resilience¹. These approaches include actions such as wetland restoration, which can serve as natural flood buffers, and the implementation of green infrastructure to manage flood risks. Nature-based solutions encompass a range of ecosystem management practices, including species regeneration projects, wind breaks, erosion control, reforestation, and riparian zone management. While these measures enhance and protect ecosystem services, they also play a critical role in reducing the vulnerability of communities to the impacts of climate change. This section provides an inventory of nature-based adaptation measures, outlining their strengths, limitations, co-benefits, and tradeoffs. A summarized overview of these measures is available in Table 4.

Table 4 Nature-based adaptation measures and their advantages, disadvantages, co-benefits, and tradeoffs

Set-back

A set-back involves strategically altering levees to create additional space for water storage during high-flow events. Setback fits within the nature-based adaptation measures category as it utilizes natural floodplain restoration to enhance water storage, improve river ecosystem health, and reduce flood risks. By allowing controlled overflow into a designated floodplain, this approach reduces pressure on the main flood protection infrastructure and helps prevent catastrophic breaches. Inspired by floodplain restoration efforts, this approach aims to improve hyporheic flow between rivers and their floodplain regions, thus potentially enhancing river ecosystem health²⁰⁶. For instance, levee L536 on the Missouri River, built in 1951 and repeatedly damaged by floods, underwent a setback after a devastating flood in 2019. This project reconnected 5.2 km² of floodplain and was successful due to collaboration among local districts, USACE, non-profits, and federal and state agencies. The setback also integrates conservation lands into a habitat complex, enhancing ecological benefits^207,208. By moving levees further away from the river channel, setback projects can increase floodplain area and facilitate better biogeochemical processing, water quality improvement, and habitat restoration²⁰⁶. While setbacks offer promising flood protection benefits by reducing water surface elevation and lessening the intensity of flood hazards acting on levees, they also pose challenges such as erosion and sediment management risks^207,208. A major limitation of set-back adaptation is that it requires real estate landward. Therefore, the costs to set-back levees could be high. However, with careful planning and consideration of site-specific factors such as geomorphic characteristics and sediment distribution, setbacks may present an innovative and environmentally sustainable solution for flood risk management improvement²⁰⁹.

Permeable pavements

Permeable pavements offer a sustainable solution to the challenges posed by urban stormwater management and flood control. Their design incorporates a permeable upper surface, sand, a bedding gravel layer, a base course layer, and natural soil, which collectively decrease the volume and rate of stormwater, contributing to reduced drainage system needs and potentially lowering the carbon footprint of drainage construction²¹⁰. Unlike traditional drainage systems, which can be expensive and impractical in densely populated areas, permeable pavements are categorized as nature-based adaptation measures as they mimic natural hydrological processes by facilitating the infiltration, storage, evaporation, and detainment of runoff. These pavements are categorized based on their structure into drainage pavements, semi-permeable pavements, and fully permeable pavements²¹¹. In a case study conducted on a two-way, six-lane road in Nanjing, the authors investigated the effectiveness of permeable pavement in mitigating urban runoff and reducing flood risks²¹². The findings revealed that permeable pavements, particularly those with increased gravel thickness, substantially reduced surface runoff and delayed flood peaks. These results underscore the importance of carefully considering soil type and pavement design in urban planning for flood risk management²¹². As urbanization increases impermeable surfaces, the risk of flooding rises, making permeable pavements an attractive solution due to their ability to allow infiltration of rainfall and surface runoff, thereby reducing stormwater volume and aiding groundwater recharge^210,213. However, conventional permeable pavements are prone to clogging, which diminishes their performance and requires costly maintenance²¹⁴. High-strength clogging-resistant permeable pavements, developed to address these issues, boast improved performance and can be utilized on heavily trafficked roads, enhancing urban flood resilience. Consequently, new design guidance is essential to fully leverage the unique properties of these advanced materials.

Green roofs and walls

Green roofs and walls offer multifaceted benefits in urban areas, particularly in the context of climate change and rapid urbanization. Green roofs and walls fit within the category of nature-based adaptation measures as they naturally manage stormwater through the absorption and retention of rainwater. In addition to their environmental benefits, green roofs and walls play a crucial role in flood control by reducing surface runoff and enhancing infiltration. By storing rainfall in their soil substrate and delaying runoff peak generation, green roofs mitigate the impacts of extreme rainfall events, thereby reducing the risk of urban flooding²¹⁵. Similarly, green walls help absorb and retain rainwater, reducing the volume of runoff and alleviating pressure on drainage systems during heavy precipitation events. Additionally, they enhance biodiversity, reduce energy consumption, prevent pollution, and contribute to urban aesthetics^216,217,218. Native vegetation is often preferred for its adaptability and ecosystem restoration capabilities. However, structural limitations in older buildings and the need for ongoing maintenance and irrigation can present challenges to widespread adoption²¹⁹. In Chile, rapid population growth and urban development have led to frequent flooding in central cities during the winter due to outdated rainwater drainage systems. A study proposes green roofs as a potential solution to mitigate these floods. Their simulations suggest that covering at least 60% of available roof surfaces could reduce flooding during heavy rain events²²⁰. However, the high costs and limited incentives for green roof implementation in Chile present challenges, highlighting the need for tailored green technology promotion in developing countries²²⁰. Overall, the utilization of green roofs and walls represents a sustainable strategy for enhancing urban resilience and addressing diverse environmental concerns. These nature-based solutions contribute to sustainable stormwater management strategies in urban areas, making them valuable components of flood control infrastructure.

Wetland restoration and creation

Wetland restoration and creation are essential strategies for enhancing ecosystem services and mitigating the adverse effects of urbanization and climate change. Wetlands are categorized as nature-based adaptation measures as they provide crucial benefits such as carbon storage, sediment trapping, nutrient retention, and flood reduction, which are vital for maintaining ecological balance and supporting human communities²²¹. The loss and degradation of wetlands, primarily due to urban expansion, diminish their capacity to regulate floods and other natural hazards²²². A study explores the role of wetlands in flood resilience within the Nenjiang River Basin in Northeast China. Their research highlights that wetlands are highly effective at reducing stream flows, particularly during extreme flow conditions. Wetlands in the Nenjiang River Basin play a key role in flood risk reduction, with their efficiency in mitigation closely tied to their location and size within the watershed²²³. Constructed wetlands, engineered for purposes like wastewater treatment, and restored wetlands, aimed at rejuvenating ecological functions, both play vital roles in flood management by controlling water flow rates and trapping nutrients during flooding^224,225. Integrated Constructed Wetlands (ICW), which combine elements of both constructed and restored wetlands, offer a holistic approach to wetland service replacement, though they require further research to optimize design and management practices²²⁵. Additionally, geographical variations influence the effectiveness of wetlands in flood mitigation, with upstream wetlands notably reducing downstream peak flow and volume, though they may also exacerbate flooding under certain conditions²²³. Therefore, strategic wetland restoration and creation are crucial for bolstering flood resilience, particularly in urban and developing regions where the impacts of extreme hydroclimatic events are most pronounced²²².

Establish riparian buffers

Riparian buffers, which serve as transitional areas between terrestrial and aquatic ecosystems, are vital for maintaining ecological balance and providing numerous ecosystem services. These zones facilitate the exchange of energy and matter through processes such as surface runoff, subsurface flow, and flooding, thus playing a critical role in river dynamics, bank stability, and aquatic habitat suitability²²⁶. Riparian buffers are classified as nature-based adaptation measures because they enhance flood resilience and support ecological health while also mitigating the impacts of human-induced changes. These buffers support watershed functions and ecosystem services, especially where maintaining forest land cover is challenging²²⁷. These buffers can increase forest cover, enhance baseflow, and reduce peak flows in developing watersheds, although their effectiveness varies across different subbasins. Riparian vegetation can also provide social and cultural benefits by creating usable green space²²⁸. However, riparian zones are highly susceptible to human-induced changes such as urbanization, deforestation, and floodplain exploitation, which can increase flood vulnerability and degrade their ecological functions²²⁹. In the Meramec River Basin, a vital area for freshwater biodiversity in the U.S., riparian buffers are explored as climate adaptation tools to manage riverine flow and thermal regimes. A study finds that expanding riparian buffers can reduce the number of days exceeding high water temperatures, thus alleviating thermal stress and benefiting aquatic ecosystems. However, while these buffers are effective in mitigating temperature increases, their impact on streamflow regimes is more limited²³⁰. Given their ecological importance, there is a need for proactive management strategies and policy reforms to protect and restore riparian zones, ensuring their continued provision of critical services such as water purification, biodiversity conservation, and recreational opportunities²³¹.

Implement beach and shoreface nourishment

Beach and shoreface nourishment are strategies employed globally to counteract coastal erosion and maintain socio-economic value, as well as to protect people and property²³². These practices involve the addition of large quantities of sand to beaches or shoreface, often sourced from inland sand pits, lagoons, estuaries, navigation channels, nearshore zones, offshore seafloors, or nearby jetties²³³. Coastal zones are vital for activities such as marine resource utilization, tourism, and infrastructure. Beach and shoreface nourishment strategies help to sustain ecosystems while also supporting socio-economic activities and addressing the impacts of sea-level rise and storm events, justifying their placement in the nature-based adaptation category. In a study conducted along the Dutch coast, characterized by its sandy shores and micro-tidal environment, the behavior of beach and shoreface nourishment was observed and modeled. The research found that while beach nourishment offers immediate flood protection by raising the beach elevation and preventing wave overtopping, shoreface nourishment provides a more sustained defense. Although slower to impact the inner surf zone, shoreface nourishments proved to be more persistent, with 40-80% of the added volume remaining after 3 years, offering a long-term sub-tidal buffer against storm erosion²³⁴. Beach nourishment has the potential to prevent coastal flooding and mitigate erosion, influenced by long-term sea-level rise and sediment availability. Effective management of beach nourishment requires monitoring coastal erosion and deposition over appropriate temporal and spatial scales, which depend on local conditions, stresses, and financial resources²³⁵. Despite their benefits, including enhanced recreational opportunities and rapid recovery post-storms, beach nourishment projects are finite and can have maintenance costs that are higher than hard structures due to shorter maintenance intervals^233,236. Additionally, beach and shoreface nourishments can have complex environmental implications, necessitating regular maintenance and comprehensive environmental impact evaluations to ensure sustainable coastal development^237,238.

Implement living shorelines

Living shorelines represent a multifaceted approach to coastal resilience, integrating habitat restoration, coastal engineering, and conservation strategies to mitigate erosion, wave damage, and flood risks. Living shorelines are categorized as nature-based adaptation measures because they employ natural and restored coastal features to enhance coastal resilience while also providing additional ecological and socio-economic benefits that support sustainable coastal management. These approaches encompass a diverse range of natural and constructed or restored features such as salt marshes, wetlands, mangroves, coral reefs, oysters, dunes, and maritime forests. In a study conducted along the southern coast of Rhode Island, numerical simulations were used to assess the effectiveness of living shoreline methods in mitigating coastal erosion. Rhode Island’s sandy coastline is particularly vulnerable to storm-induced breaching and overtopping. Additionally, state regulations discourage the use of hard coastal protection structures. The study found that living shorelines could be more effective at reducing erosion than traditional methods like offshore breakwaters²³⁹. Through the strategic use of vegetation, wave energy is dissipated, sand dunes are stabilized, and wave height and erosion are reduced more effectively than in non-vegetated areas²⁴⁰. Furthermore, living shorelines offer co-benefits beyond hazard mitigation, including habitat creation, improved ecosystem services, recreation opportunities, and increased economic value. These nature-based solutions are particularly appealing in contrast to traditional hard armoring methods like sea walls, which often disrupt natural processes and increase vulnerability²⁴¹. Living shorelines also exhibit greater resilience to sea-level rise as they accommodate marsh migration and adapt to changing coastal conditions²⁴¹. However, successful implementation relies on key factors such as wave energy, land use, sediment volumes, and community willingness to adopt innovative methods²⁴⁰. Municipalities play a crucial role in facilitating the adoption of living shorelines through land use planning zoning regulations and by setting examples for shoreline management practices. Despite regulatory challenges and jurisdictional complexities, continued community involvement and communication are essential for the success and expansion of living shoreline projects²⁴².

Vegetation on levee slopes

Intentional vegetation on levee slopes involves strategically planting grasses, shrubs, or trees along levees to stabilize soil, reduce erosion, and enhance the resilience of flood defenses²⁴³. Vegetation helps absorb rainfall, slow runoff, and improve soil permeability, reducing the risk of levee failure and enhancing flood protection²⁴⁴. Vegetation on levee slopes is classified under nature-based adaptation measures because it leverages natural processes such as soil stabilization and erosion control provided by grasses, shrubs, and trees to enhance the structural integrity of levees and improve their flood protection capabilities. Encouraging vegetation growth is a simple and cost-effective approach to bolstering levee stability. However, the impact of vegetation on levee slopes can vary depending on factors such as slope stability, levee dimensions, soil type, accessibility for maintenance, and the specifics of maintenance plans²⁴⁵. In a study on the Green-Duwamish River in King County, Washington, authors investigate the complex relationship between woody vegetation and the structural integrity of levees. The study finds that while the presence of deep-rooted trees and plants on levees can enhance stability by reinforcing soil and reducing erosion, the effects of vegetation are context-dependent²⁴⁶. Improperly maintained vegetation can pose risks, such as weakening the levee structure or creating pathways for water seepage, highlighting the need for careful management of levee vegetation²⁴⁶. While vegetation can offer hydrological benefits by reducing sediment mobility and increasing sediment retention, it may also exacerbate instability during flooding events by forming piping channels and affecting hydraulic conductivity. Therefore, the implementation and effects of vegetation on levee slopes require careful consideration on a case-by-case basis.

Forest fire prevention

Forest fire prevention strategies aim to mitigate the risk of wildfires, which can exacerbate flooding by increasing soil erosion and runoff in fire-affected areas²⁴⁷. Forest fire prevention strategies are categorized as nature-based adaptation measures because they focus on maintaining natural vegetation and soil stability, which helps to mitigate the increased flood risk associated with wildfire-affected areas. Wildfires not only threaten lives and cause environmental pollution but may also degrade river morphology and increase flood risk downstream for several years. From a hydrological perspective, post-fire degraded vegetation cover, reduced hydraulic resistance, and decreased soil infiltration capacity tend to generate higher surface runoff in basins^248,249. This heightened surface runoff has the potential to increase flood risk downstream of burned areas for several years²⁵⁰. Additionally, wildfires alter hydrological processes by reducing forest water use due to vegetation loss, leading to increased runoff during intense rainfall events²⁵¹. Several studies report an increase in landslides after wildfires, mainly attributed to loss of root reinforcement^252,253,254. A study examines post-fire management strategies in Haifa, a city on the northern hillslope of Mt. Carmel, which is characterized by hot, dry summers and short, rainy winters, heightening the risk of fires and subsequent flooding. The research highlights how forest fires can lead to substantial changes in soil properties, including increased erosion and reduced vegetation cover, which contribute to more frequent and severe flooding²⁵⁵. To address these challenges, the study evaluates various post-fire management practices such as natural revegetation, afforestation, erosion barriers, and geotextiles to mitigate the impacts of fires by improving soil stability and reducing runoff²⁵⁵. Due to the complex relationship between burned landscapes and variability in precipitation events, post-fire hydrologic responses can vary widely, from minimal impact to devastating floods and hazardous debris flows. Therefore, employing effective forest fire prevention strategies can be a crucial tool for reducing flood risk by maintaining soil infiltration capacity, preserving vegetative cover to slow runoff, and enhancing hydraulic resistance²⁵¹.

Bio-inspired improvements of soils in flood protection infrastructure

Recent developments in bio-inspired engineering have yielded promising techniques for strengthening and enhancing the resilience of soils employed in flood-protection infrastructure^256,257. Foremost among these innovations are Microbially Induced Calcite Precipitation (MICP) and biopolymer soil treatments, which have garnered substantial research interest²⁵⁷. By emulating natural processes, both approaches improve key geotechnical properties such as strength, stiffness, and erosion resistance while providing environmentally sustainable alternatives to conventional chemical stabilization methods. MICP involves stimulating microbial activity in the soil to precipitate calcium carbonate, which binds soil particles together²⁵⁸. This process increases soil strength and stiffness, reduces permeability, and improves resistance to erosion. Similarly, the use of biopolymers naturally derived long-chain molecules has shown substantial benefits in enhancing soil cohesion and compressibility²⁵⁹. Biopolymers can create a protective matrix that binds particles and reduces susceptibility to disintegration under hydraulic or mechanical stress.

These enhancements are particularly valuable for earthen flood protection systems such as levees, where soil strength and erosion resistance are critical to maintaining structural stability²⁶⁰. Improved soil strength contributes directly to increased slope stability, reducing the likelihood of slope failure during high-water events. Moreover, erosion is a primary mechanism driving levee overtopping and breach initiation, particularly under repeated cycles of wetting and drying. Bio-inspired soil improvements have demonstrated the potential to mitigate these vulnerabilities by increasing the soil’s resistance to erosive forces and enhancing durability across fluctuating environmental conditions. Several previous studies have validated the effectiveness of MICP and biopolymer treatments in laboratory and field settings²⁵⁷. These approaches not only improve performance under normal operating conditions but also offer increased resilience during extreme events, making them highly suitable for application in the context of climate-adaptive infrastructure systems.

Decision-making for successful adaptation

In the face of evolving flood risks due to climate change, it is imperative to adopt a comprehensive approach to identify the most successful or series of successful adaptation measures. Currently, approaches like the Dynamic Adaptive Policy Pathways (DAPP) and Dynamic Adaptive Policy Pathways for multi-risk (DAPP-MR) are employed to plan both short- and long-term adaptation measures^261,262. A study emphasizes that flood-adaptation decisions must address deep uncertainty situations in which the probability distributions of key drivers (e.g., flood frequency, exposure growth, behavioral response) are themselves unknown or contested⁵⁴. They advocate moving from single-scenario, deterministic analyses toward exploratory modeling with large ensembles of plausible futures, coupled with multi-objective robust decision-making techniques, to identify adaptation pathways that perform acceptably across a broad spectrum of uncertain conditions. These methods investigate sequences of adaptation measures or pathways, considering a range of future scenarios. However, at the foundational level, we argue that a successful flood adaptation strategy must be tailored for each project, ensuring it is socially just, practically feasible, and technically sound (Fig. 5). This requires a multi-attribute decision-making process that carefully considers each project’s unique technical and socioeconomic characteristics.

Fig. 5: The three foundational attributes of a successful flood adaptation measure.

Practical Feasibility, Technical Soundness, and Social Justice. These pillars collectively ensure that adaptation strategies are not only implementable and effective under evolving climate conditions but also equitable and aligned with community needs and institutional capacities.

Past studies indicate that socially vulnerable groups are often overrepresented in 100 year flood zones and levee-protected areas in the U.S.^263,264,265. Thus, adaptation measures must be socially just to minimize these flood risk disparities. Social justice in adaptation addresses systemic inequities by promoting inclusivity, transparency, and equitable resource allocation through community engagement and participatory decision-making processes^266,267. A successful measure should also account for the varying adaptive capacities and risk thresholds of communities. We emphasize that social justice should be incorporated into every stage of the adaptation process to ensure that community perspectives and stakeholder feedback are integral to decision-making, with the goal of minimizing risk disparities among communities²⁶⁷.

Practical feasibility is the extent to which adaptation measures are considered possible, either in binary terms or under specific conditional criteria¹. Assessing practical feasibility ensures that adaptation measures can be successfully implemented while ensuring compliance with environmental and regulatory constraints. Practically feasible measures should also consider the technical expertise and experience of available human resources. Moreover, assessments include evaluating trade-offs and prioritizing based on short- and long-term costs, including labor, land purchase, and materials, which vary with local geographic and socio-economic conditions²⁶⁸. Importantly, practical feasibility also incorporates institutional, cultural constraints, and societal acceptance, recognizing that successful implementation requires acceptance and alignment within these broader contexts.

For adaptation measures to be effective, they must be technically sound, grounded in proven methodologies, and supported by reliable engineering design. These measures should be resilient under multi-hazard conditions. Furthermore, these measures should be designed with flexibility in mind, allowing for incremental improvements over time. This adaptive capacity is essential for providing both immediate and long-term performance as climatic conditions evolve. By incorporating regular assessment and updating mechanisms, these strategies can remain effective even as environmental and socioeconomic conditions change, ensuring sustained protection and resilience for communities.

Research gaps and opportunities

Flood adaptation is a critical component of managing the growing risks posed by climate change, yet substantial gaps remain in both our understanding and implementation of effective measures. Advancing flood adaptation requires collaborative, cross-disciplinary progress^269,270. Our review of flood adaptation research has identified key research gaps and opportunities, including: Integrating qualitative and quantitative approaches to improve decision-making, Bridging policy fragmentation to create cohesive and adaptive frameworks, Clarifying evolving risk thresholds for more effective risk management, Enhancing site-specific decision-making by balancing feasibility, technical soundness, and social justice, Leveraging emerging technologies and Big Data to strengthen flood resilience, and Incorporating vulnerability attributes to promote equitable adaptation strategies. Given the multidisciplinary nature of flood adaptation research, we acknowledge that these gaps may not fully encompass all existing research opportunities.

The first key gap is the limited integration of qualitative insights into quantitative risk assessment frameworks. While quantitative metrics such as expected annual damage or flood levels are commonly used, they fail to capture the nuanced perceptions of risk and the social realities on the ground^264,271. A 2017 study demonstrates that reliance solely on qualitative flood risk mapping can lead to a coarse hazard classification that does not adequately represent actual flood scenarios²⁷². Conversely, participatory integrated assessment tools combine scientific models with stakeholder insights, enabling decision-makers to evaluate adaptation choices within real-world constraints²⁷³. Moreover, incorporating indigenous knowledge and community-specific insights into quantitative models is essential. Studies argue that relying exclusively on quantitative methods overlooks social and cultural components of flood risk. Local knowledge, stakeholder experiences, and community-specific challenges remain underrepresented in current risk assessment frameworks^274,275. Future research should, therefore, focus on developing methodologies that systematically incorporate qualitative data such as local expertise, participatory inputs, and self-assessment insights into quantitative risk modeling frameworks. This integrated approach would provide a more holistic view of flood risk, effectively addressing both the technical and social dimensions of adaptation.

The second critical research gap lies in the coordination of policy for flood adaptation. Even with substantial advances in modeling and decision-support tools, their potential is undermined by fragmented policy frameworks. Flood adaptation is inherently multifaceted and spans multiple levels of governance, local, national, and even international, resulting in different agencies and stakeholders often operating in silos. This fragmentation not only limits the effective implementation of adaptation measures but also creates challenges in aligning objectives across various policy sectors, where actions in one area may spill over and conflict with those in another. For instance, a policy decision to release water from a dam to fight wildfires may seem beneficial for emergency response; however, the rapid opening and closing of water levels can adversely impact levee integrity, thereby compromising flood protection measures downstream²⁷⁶. Future research should focus on developing comprehensive policy frameworks that foster inter-agency collaboration, ensure horizontal and vertical policy integration, and address potential spillover effects²⁷⁷.

A third gap is the lack of clarity and consistency in defining risk thresholds and tipping points. There is an inherent ambiguity in determining what constitutes “acceptable,” “tolerable,” and “intolerable” flood risk. These thresholds vary not only across regions but also over time due to urbanization and changes in land use, land cover, and even adaptive actions. For example, the Dynamic Adaptive Policy Pathways (DAPP) framework, Adaptation-Tipping-Point (ATP) or Adaptive Delta Management employs tipping points defined by performance or risk thresholds, yet these thresholds differ by location and time^{261,262,278,279}. Research opportunities exist to empirically investigate how these variable risk thresholds influence adaptive behaviors²⁸⁰.

Fourth, there is a persistent challenge in supporting site-specific decision-making that balances technical feasibility, social justice, and practical implementation, particularly in the context of deep uncertainty. The proposed multi-attribute decision-making process, which balances practical feasibility, technical soundness, and social justice, highlights an interesting area for further investigation. Research should explore how these attributes interact and how trade-offs are managed in real-world settings. For instance, while technically sound measures may offer robust protection, they might not be socially just if they fail to address the needs of vulnerable communities. Future studies could focus on developing decision-support tools that explicitly incorporate these attributes, helping policymakers design strategies that are both effective and equitable.

Fifth, emerging technologies, including artificial intelligence (AI) and Earth observations, offer promising opportunities to improve flood risk management and adaptation planning^281,282. However, a persistent challenge remains in capturing the full complexity of flood risk, which involves interactions among natural, built, and social systems over varying spatial and temporal scales. For example, performing a regional-scale assessment of levees requires real-time hydrological data and remote sensing imagery, which are critical for accurately characterizing real-time risk²⁸³. Further research is needed to investigate how emerging technologies can enhance forecasting, optimize adaptation pathways, and facilitate real-time decision-making in flood management.

Another important research gap lies in managing residual flood risk behind levees. While hydraulic infrastructure remains central to flood protection, events in the U.S., France, and Quebec demonstrate that areas behind levees can still face substantial risks during levee breaches or overtopping events. Despite recognition of this issue, current policies and regulatory frameworks vary widely, leading to inconsistencies in how these residual risks are managed, communicated, and mapped¹⁹⁰. More research is needed to develop integrated approaches that explicitly address residual risk, including improvements in risk mapping, governance mechanisms, and community-level communication strategies.

Finally, integrating socio-economic factors into adaptation decision-making requires further exploration. Past studies have shown that socially vulnerable groups are disproportionately located in areas of heightened flood risks^{263,265,284,285}. Future research should investigate the mechanisms by which socioeconomic or demographic vulnerabilities influence adaptive capacity, examining how investments in flood protection can be reallocated to mitigate these disparities. Studies demonstrate that integrating distributive justice measures into flood adaptation models not only enhances the assessment of impacts on different groups over time but also helps address existing inequalities in flood risk management²⁸⁶. By integrating equity considerations into adaptation decision-making, researchers can identify opportunities to improve resource allocation and reduce risk disparities.

Although this study employed the four broad categories of Infrastructural/Technological, Institutional, Behavioral/Cultural, and Nature-Based measures, several examples from our findings reveal overlapping domains that warrant further investigation. For instance, relocation of at-risk communities cannot succeed solely through infrastructural planning; it requires policy frameworks for land acquisition, funding mechanisms, and cultural acceptance to minimize social disruption. Similarly, living shorelines and wetland restoration require institutional coordination for zoning, technical planning, and community participation. Even conventional measures such as flood monitoring and warning systems represent a fusion of domains: they involve advanced sensor technologies (infrastructural/technological), data governance strategies (institutional), and timely public communication (behavioral/cultural). These examples highlight the importance of developing future frameworks that better capture these intersections to improve the effectiveness and equity of flood adaptation strategies.

Concluding remarks

The initial step towards enhancing the resilience of flood protection systems involves identifying and compiling traditional and emerging flood adaptation measures in a portfolio. Our scoping review of past literature identified 39 adaptation measures and their unique advantages, disadvantages, co-benefits, and tradeoffs. These measures were categorized into four classifications: (i) Institutional/technological (18 measures), which provide immediate and reliable protection, enhancing flood resilience and defense capabilities. However, they come with high costs and potential environmental disruptions, necessitating integration with other approaches for sustainable flood resilience. (ii) Institutional (9 measures) that are aimed at enhancing governance structures and policies for long-term flood resilience. They offer a systematic approach to managing climate risks but face challenges such as fragmented responsibilities and resource inequities. Success depends on robust frameworks, proactive leadership, and inclusive stakeholder participation. (iii) Behavioral/cultural (2 measures) that aim to empower communities to reduce climate vulnerability through low-cost, adaptable practices. These measures foster resilience but may face resistance to change and require sustained community engagement. Integration with broader strategies is essential to address severe climate risks. (iv) nature-based (10 measures) that leverage natural systems to enhance resilience, offering co-benefits like biodiversity enhancement and water management. However, they are site-specific and require careful planning, ongoing management, and community engagement to be effective within a broader climate adaptation strategy.

Effective flood adaptation necessitates an integrated approach to address the evolving risks associated with climate change. The challenge for decision-makers lies in identifying the most optimal adaptation measures. We propose that measures must be tailored to the unique requirements of each project. Here, we propose that adaptation strategies must be tailored to each specific project to ensure they are socially just, practically feasible, and technically sound. This involves addressing systemic inequities, incorporating community input, and evaluating the practicality of measures in relation to environmental, regulatory, and resource constraints while also ensuring technical robustness and the ability to adapt over time. The absence of one essential attribute may adversely affect the overall effectiveness and sustainability of adaptation efforts. For instance, neglecting social justice could lead to inequitable outcomes, while neglecting technical soundness may lead to failure under an evolving climate; fulfilling both social justice and technical soundness, however, neglecting practical feasibility results in issues in adaptation implementation. Therefore, a balanced approach is necessary for the long-term effectiveness of flood adaptation efforts.

Despite substantial advancements in flood adaptation research, there is a global need to advance these efforts through multidisciplinary collaboration. Here, we identify eight key research themes and highlight associated gaps that require attention. These gaps present opportunities for further exploration and development, highlighting the complexity and the need for a transdisciplinary approach in flood adaptation research. A notable gap includes the development of a risk-based adaptation framework for flood protection infrastructure that addresses social disparities, integrates community feedback, accounts for evolving hazard patterns and their impacts on defense systems, and quantitatively assesses the performance of adaptation. Such a framework has the potential to provide decision-makers with a robust tool to enhance the resilience and equity of flood adaptation measures.