A holistic assessment of water resources and management in the Zarrineh river sub basin using water accounting plus

Abstract

The objective of this study is to evaluate water consumption pathways related to land use, productivity, and water productivity in the Zarrineh River sub-basin, Iran, using the Water Accounting Plus (WA+) approach. The WA+ method was chosen due to its comprehensive ability to estimate water consumption across various sectors, including land use and agricultural productivity, and its capacity to account for both inflows and losses, which makes it more suitable for analyzing the water resource situation in the Zarrineh River sub-basin compared to other water accounting approaches. This study examines water inflows and losses in the Zarrineh River sub-basin, where total water availability, including external inputs and rainfall, reaches 3610.53 Million Cubic Meters (MCM) annually. Despite substantial water resources available, 3442.70 MCM is lost through evapotranspiration, with agricultural lands accounting for 1836.13 MCM of this. These findings emphasize the critical need for efficient irrigation systems, as well as complementary techniques like shading and mulching to minimize evaporation losses. With 1747.35 MCM of exploitable water, effective management practices are essential to maximize water productivity, especially in the agriculture sector. Additionally, 185.83 MCM of recoverable outflows present an opportunity for reuse, supporting more efficient water resource management. Managed agricultural areas exhibit higher water productivity (2.54 kg/m³) compared to less efficient sectors within utilized land use (1.74 kg/m³), highlighting areas for potential improvement. Addressing non-beneficial evapotranspiration, totaling 919.4 MCM, through practices such as soil covering and reservoir management, could further enhance water conservation. These findings emphasize the importance of integrating advanced irrigation technologies, efficient water regulation systems, and improving land management to mitigate water loss, enhance productivity, and ensure sustainable water resources in the sub-basin.

Introduction

Identifying the status of water resources and implementing appropriate policies are crucial steps toward informed decision-making and good governance^1,2. Effective water management systems are essential for sustaining food security, industry, and electricity generation in river basins^3,4,5,6,7. To achieve this, a large number of datasets must be readily available in the region to establish effective management strategies. However, climate change poses significant challenges to water supply and demand, leading to new transboundary issues^8,9. In response to the increasing number of global water problems, pioneers in water management have developed scientific evidence and datasets to help decision-makers develop solutions. Reliable, accessible, and coherent datasets are fundamental to water accounting and solving water-related challenges⁹. Water Accounting Plus (WA+) is an open-access tool designed to improve water resource management by utilizing satellite observations. Karimi et al.¹⁰ applied the WA+ tool for managing complex river basins, presenting four sheets that included the resource base, evapotranspiration, productivity, and withdrawals. Recently, WA+ frameworks have been used to examine water consumption as a consumptive resource, encompassing both water consumed by natural processes (green water) and human activities (blue water)^11,12,13. For instance, in the Okavango River Basin, Africa, Droogers et al.¹⁴ demonstrated the relationship between annual precipitation and ETLook products using WA+ . Water Watch developed the ETLook algorithm to calculate large-area evapotranspiration^15,16. Godfrey and Chalmers¹⁷ and Gupta et al.¹⁸ highlighted that WA+ considers land use classifications and their relation to water consumption, environmental flow, and overall system sustainability. In the Himalayan Koshi River Basin, Khatakho and Alluaibi¹⁹ utilized WA+ for water accounting, applying key indicators such as ET Fraction, Managed Fraction, Beneficial Consumption, and Transpiration Fraction to estimate managed water. Similarly, in the Yarmouk River Basin, shared by Syria, Jordan, and OSOL, WA+ was employed to examine water resources, classify land uses, and analyze water depletion and utilization²⁰. Singh et al.²¹ assessed total water consumption, land productivity (LP), and water productivity (WP) in the Subarnarekha Basin, India, using WA+ , successfully analyzing water consumption patterns and land productivity for irrigated and rainfed crops separately. WA+ has proven to be a valuable water accounting tool, applicable from catchment to regional scales, to determine water resource depletion, storage changes, and water productivity⁹. Effective water resource management is crucial for ensuring food security, industrial needs, and energy production, particularly given the impacts of climate change on water supply and demand^22,23,24. Accurate data and reliable tools are essential for managing these resources, especially in regions facing data scarcity. While the WA+ framework offers significant advantages in water accounting, especially in data-scarce conditions, it is important to acknowledge its limitations. WA+ leverages remote sensing data, making it highly beneficial in regions where ground-based data is scarce or difficult to obtain. This approach allows for wide-scale water use estimation, which may otherwise be challenging. However, like all methods relying on remote sensing, WA+ can be affected by factors such as vegetation cover and weather conditions, which may influence data accuracy. Despite these limitations, the ability to use remotely sensed data remains a key strength of WA+ in addressing water management challenges under data-limited circumstances. Despite the widespread application of WA+ , there is limited research on its use in water-scarce sub-basins with inadequate data availability. The Zarrineh River sub-basin, a key part of the Urmia Lake basin in Iran, is facing significant water management challenges due to increasing water scarcity and inefficient use of water resources. This study aims to address the issue of water consumption and management in the sub-basin by applying the Water Accounting Plus (WA+) framework. The study covers the period from [insert time period], providing a detailed analysis of water usage and its impacts on local agricultural productivity. The problem lies in the overexploitation of water resources, especially for irrigation purposes, which has led to reduced water availability, environmental degradation, and threatens long-term water security in the region. Understanding these challenges is critical for developing sustainable water management strategies and ensuring the future of the agricultural sector in the region. The research examines the application of the WA+ tool under conditions of data scarcity and specific water challenges, presenting it as a practical model for other similar sub-basins in water-scarce regions. The research offers a comprehensive analysis of hydrological processes and water consumption patterns, helping to identify strengths and weaknesses in water resource management. By leveraging satellite data, the study enhances the accuracy and efficiency of evaluating water resources and consumption patterns, marking a novel approach in utilizing advanced technologies. Additionally, the introduction and utilization of new management indicators like ET Fraction, Managed Fraction, and Beneficial Consumption represent innovative methods for assessing and improving water management efficiency. Ultimately, this research not only identifies existing problems but also proposes practical and implementable solutions to enhance water management in the Zarrineh sub-basin, reinforcing its significance as an essential aspect of innovation.

Material and method

Description of the study area

The Zarrine River Basin is the most important catchment area and the main inflow source for Lake Urmia, the largest saltwater lake in the Middle East and Iran, which has been shrinking in recent decades. Covering a total area of 12,025 km², the basin is located in the southern part of the lake, between longitudes 45° 46’ E to 47° 23’ W and latitudes 35°41’ S to 37° 44’ N 2 (Fig. 1). It includes parts of Kurdistan and the West and East Azerbaijan provinces, encompassing the four major cities of Miandoab, Shahindej, Takab, and Saghez. The main channel of the Zarrine River has a total length of about 300 kilometers, mostly flowing through mountainous regions. The climate in this area ranges from semi-wet cold or wet-cold in the mountains to semi-dry near the lake. Annual rainfall varies between 200 mm in the lower catchment area and 800 mm in the mountains. The average snow depth ranges from 5 to 63 mm per year, with maximum snowfall predominantly observed in the southern and western parts of the basin. The Boukan Reservoir is the most significant and largest operational dam in the basin, with a gross storage capacity of 760 million cubic meters (MCM) and a live storage capacity of 654 MCM. Its water is primarily used for agricultural irrigation and drinking water supply, estimated at 110 MCM per year. The agricultural areas within the basin cover a total area of 74,318 hectares, all irrigated by groundwater and surface water resources, including the Boukan Reservoir, as the crop-growing season mainly occurs during the dry season from mid-spring to mid-autumn^25,26.

Fig. 1

Location map of Zarrineh river sub-basin (this figure is generated in ArcGIS10.8 software, http://www.esri.com/software/arcgis).

Research methodology

The objective of this study is to evaluate water consumption pathways related to land use, productivity, and water productivity in the Zarrineh River sub-basin, Iran, using the Water Accounting Plus (WA+) approach. The collected data have been organized into worksheets, which are accessible and available for download through the WA+ platform. These worksheets contain detailed information on evapotranspiration, transpiration, evaporation, interception, and net primary production, and can be used for further analysis and modeling within the scope of this study. Figure 2 illustrates the research methodology employed in Water Accounting Plus, which incorporates remote sensing data, observed flow measurements, and information on water storage.

Fig. 2

Overview of WA+ input and output data.

Water accounting plus (WA+) framework

In WA+, a Python-based framework is utilized to generate detailed water accounts for river basins 25. This framework is designed to assess the utilization of water resources within river basins. In the WA+ system, calculations of water flow and storage are derived from land use maps that define various services, benefits, economic activities, and livelihoods. The integration of remote sensing data within WA reduces the necessity for extensive data collection and monitoring efforts 10. This approach specifically targets water consumption across various land use categories, including conservation areas, pastures, and both rainfed and irrigated agricultural practices. Put simply, water consumption data can be acquired through satellite observations 5. The most recent update to the WA+ framework, conducted in 2016, addresses the intricate hydrological processes and management challenges facing river basins by dividing them into eight components (www.wateraccounting.org). These components encompass the resource base, evapotranspiration, agricultural outputs, water withdrawal, surface water resources, groundwater, ecological services, and sustainability. The WA+ approach relies on data pertaining to rainfall, actual evapotranspiration, biomass production, land utilization, and water levels in lakes and reservoirs 10. Table 1 provide an overview of the WA+ sheets examined in this study and their respective purposes.

Table 1 Overview of the WA+ sheets and their purposes.

In their 2013 study, Karimi et al. 25 classified land use into four categories: Protected Land Use (PLU), Utilized Land Use (ULU), Modified Land Use (MLU), and Managed Water Use (MWU).

• Managed Water Use (MWU) refers to areas where water is intentionally managed through infrastructure such as dams. Examples include agricultural irrigation and domestic water usage.

• Modified Land Use (MLU) involves land that has been altered by human activities. Examples of MLU include areas used for rainfed crops and plantations.

• Utilized Land Use (ULU) includes lands with minimal human interference, often utilized for ecosystem services like grazing and timber production.

• Protected Land Use (PLU) encompasses conserved lands, such as national parks, which are preserved for environmental protection.

This study focuses on water accounting for the year 2021, specifically examining three key areas: resources, evapotranspiration, and agricultural services.

Resource base sheet

The water resources sheet provides information about water volume. The variables and indicators of the water resources sheet for Zarrineh river sub-basin include rainfall (Padvection), sweetened flow (Qdesal), surface inflow (Qswin), underground inflow (Qgwin), outflow the basin (External), recycled precipitation (Precycled), storage changes (± ΔS), gross inflow, net inflow, natural evapotranspiration (Landscape ET), rainfall evapotranspiration (Rainfall ET), exploitable water, Reserved outflow, Non-Utilizable outflow, Available water, Utilizable outflow, Utilized flow, Incremental evapotranspiration (Incremental ET), natural, man-made, other, non-recoverable flow, consumed water, non-consumed water, depleted water, outflow, recycled evapotranspiration (ETrecycled), evapotranspiration (ET), surface outflow to the sea (Qswoutlet), surface outflow (Qswout), underground outflow, outflows (External).

Evapotranspiration sheet

The amount of evapotranspiration for the four types of land use in the region was determined separately using satellite images and local cultivation patterns. Through the WaPOR portal, three distinct values were obtained for evapotranspiration: the contributions from interception, soil, and transpiration. Each of these parameters was classified into two categories based on their exploitation: beneficial and non-beneficial. This classification was made using water consumption data and values derived from evapotranspiration algorithms. In this sheet, it is shown how land use is categorized into beneficial and non-beneficial types for management purposes in the study area.

Agricultural services sheet

This sheet consists of two sections: water usage and the productivity of land and water. It provides figures for biomass production, water efficiency, crop yields, and overall crop productivity. Specifically, it showcases agricultural output relative to water consumed, highlighting the productivity of land and water resources. Biomass production is assessed by analyzing the distinct contributions of evaporation and transpiration in line with the region’s cultivation practices, utilizing evapotranspiration algorithms. Thus, productivity levels are derived from biomass measurements. The output of biomass per unit of water used reflects the efficiency of water utilization by plants, indicating opportunities for improved management practices²⁷.

WA+ performance indicators

A essential aspect of the WA+ framework is the development of specific indicators that reflect the performance of various sheets. These indicators have been derived based on the characteristics of the variables present in the WA+ framework sheets, which are utilized to assess the status of the basin^10,27. The indicators and their descriptions are detailed in Table 2.

Table 2 Extracted indicators from the reports of the WA+ framework for Zarrineh river sub-basin.

Data processing

The WA+ framework utilizes the analysis of satellite imagery, incorporating data on water resources and focusing on the basin level. It relies on satellite observations sourced from the FAO’s WaPOR products, which provide insights into evaporation, transpiration, interception, and land use.

Meteorological data

Annual precipitation data were obtained from the synoptic and climatology stations located within the study area. These data for the year 2021 were used to analyze inter-annual variability in precipitation and for the management of water resources in the region. Data on surface and groundwater flows were obtained from the Iran Water Resources Management Company (https://www.wrm.ir).

Satellite data

Patterns of variation in evapotranspiration (ETa), transpiration (T), evaporation (E), interception (I), and net primary production (NPP) were examined using data derived from the WaPOR V2.0 product (https://wapor.apps.fao.org/home/WAPOR_2/2). The initial land use map for the WA+ application in the Urmia Basin was provided by the FAO. This dataset was chosen based on its validation against international, national, and regional studies, which confirmed its reliability. The validation results highlighted WaPOR’s high spatial resolution, capability to assess water demand over different timeframes, consistency without data gaps, and suitability for long-term assessments. To illustrate spatial variations, classification maps were generated, providing insights into differences in water consumption, agricultural output, and biomass production across the study area. Finally, the outputs of the figures were processed using ArcGIS (ArcMap) version 10.8.2, QGIS version 3.34.1, and Excel 2013.

The FAO’s WaPOR product (FWP)

To enhance water use efficiency in agriculture, the United Nations Food and Agriculture Organization (FAO) is developing a remote sensing tool called WaPOR (Water Productivity Open Access Portal), designed to generate a publicly accessible database from remote sensing data²⁸. Evapotranspiration is calculated in WaPOR using the ETLook algorithm²⁹. However, the Penman–Monteith (PM) equation is also employed to estimate evapotranspiration based on meteorological conditions such as air temperature, solar radiation, vapor pressure, and wind speed. This method is recommended by the FAO for estimating both actual and reference evapotranspiration³⁰. The ETLook algorithm in WaPOR slightly modifies the Penman–Monteith equation to estimate evapotranspiration by incorporating remote sensing data (e.g., soil moisture, surface albedo, solar radiation, NDVI, land cover, and DEM) alongside meteorological data. Since April 2009, this product has provided data on daily, 10-day, monthly, and annual time scales, with coverage at three levels: local (30 m), national (100 m), and continental (250 m), encompassing much of Africa and parts of Asia (see FAO, 2017 for more information). The dataset used for this analysis is the ETIa-WaPOR V2.0 product, available on the WaPOR website (https://wapor.apps.fao.org/home/WAPOR_2/1). According to Bastiaanssen et al.²⁹, ETIa-WaPOR is based on a modified version of ETLook (ETLook-WaPOR). In FAO-56 Drainage Paper (Allen, Pereira, Raes, & Smith, 1998), the Penman–Monteith approach combines the energy balance equation with the aerodynamic equation. In ETLook-WaPOR, actual evapotranspiration (ETa) is estimated using remote sensing data based on the Penman–Monteith equation²⁸. ETIa-WaPOR calculates evapotranspiration by separately defining soil evaporation and transpiration using Eqs. (1) and (2). The interception is determined by factors such as vegetative cover, leaf area index (LAI), and physical canopy percentage (PCP). The total evapotranspiration (ETI-WaPOR) is obtained by summing evaporation, transpiration, and interception.

$$\lambda E=\frac{\delta \left({R}_{n,soil}-G\right)+\frac{{\rho }_{air}{C}_{P}({e}_{sat}-{e}_{a})}{{r}_{s,soil}}}{\delta +\gamma (1+\frac{{r}_{s.soil}}{{r}_{s.soil}})}$$

(1)

$$\lambda T=\frac{\delta \left({R}_{n,canopy}\right)+\frac{{\rho }_{air}{C}_{P}({e}_{sat}-{e}_{a})}{{r}_{a,canopy}}}{\delta +\gamma (1+\frac{{r}_{s.soil}}{{r}_{a,canopy}})}$$

(2)

where E and T (mm/day) are the evaporation and transpiration, respectively and λ is the latent heat of vaporization. Rn (MJ m⁻² day⁻¹) of the soil (R_n,soil) and canopy (R_n,canopy) is the net radiation and G (MJ m⁻² day⁻¹) is the ground heat flux. Ρair (kg/m³) is the density of air, CP (MJ kg⁻¹ C) is the specific heat of air, (e_sat–e_a) (kPa) is the vapour pressure deficit (VPD), ra (s/m) is the aerodynamic resistance, rs (s/m) is the soil resistance, or canopy resistance when using the Penman–Monteith-model to estimate evaporation or transpiration, respectively. Δ = d(e_sat)/dT (kPa/C) is the slope of the curve relating saturated water vapour pressure to the air temperature, and γ is the psychometric constant (kPa/C).

Result and discussion

Analyzing WA+ input data

Table 3 shows the rainfall, contributions from each evapotranspiration parameter (transpiration, evaporation), net biomass productivity, and primary net production amount from the Zarrineh River sub-basin. It can be observed that out of the total 224.38 mm of evapotranspiration, 65 percent is attributed to transpiration by plants (147.93 mm), 33 percent to evaporation from plants (74.87 mm), and 7 percent to other forms of evaporation (74.87 mm). Among the total transpiration, the largest share is transpiration, while the smallest share is interception.

Table 3 Rainfall and the contribution from each parameter of transpiration, evaporation and interception from Zarrineh river sub-basin.

Figure 3 presents the WaPOR output products for the Zarrineh River sub-basin, including evapotranspiration, evaporation, transpiration, interception, and net biomass water productivity.

Fig. 3

Spatial maps required in the framework of WA+ for Zarrineh river sub-basin (this figure is generated in ArcGIS10.8 software, http://www.esri.com/software/arcgis).

WA+ land use

The initial land use map for the application of WA+ in the Zarrineh River sub-basin was prepared by WaPOR. According to this map, 12 types of land use are identified within the 12,025 km² basin. Grassland is the largest land use class, covering 8801 km². After pastures, cropland rainfed currently occupies 13.7% of the land area with 1627.43 km². Wheat and barley, summer fields, and orchards make up the three land use classes with 925.93 km² of cropland, irrigated or under water management, representing 7.7% of the total land area. The other classes of land include cropland, fallow (453.34 km²), built-up (78.16 km²), Bare/sparse vegetation (54.11 km²), Water bodies (24.08 km²), and tree cover: closed, unknown type occupy 2.41 and 3.61 km² respectively) (Table 4 and Fig. 4).

Table 4 Classification of land use in Zarrineh river sub-basin.

Fig. 4

(a) Land use and (b) the percentage of each land use based on the latest classification of the region in the WaPOR database (this figure (a) is generated in ArcGIS10.8 software, http://www.esri.com/software/arcgis and figure (b) is generated in Excel 2013).

Based on the potential for managing water and land resources, WA+ classifies land use into four main categories. Using this classification, the land use map of the Zarrineh River sub-basin was converted into a WA+ land use classification map. The principal land use category according to WA+ is Utilized Land Use (ULU), which occupies 74% of the sub-basin’s total land area. This is followed by Modified Land Use (MLU), which covers approximately 14% of the area, and Managed Water Use (MWU), which accounts for about 12% (see Fig. 5).

Fig. 5

WA+ Land use categories for Zarrineh river sub-basin (this figure is generated in ArcGIS10.8 software, http://www.esri.com/software/arcgis).

Table 5 illustrate the shares of evaporation-transpiration and its components for each category of land use in Zarrineh river sub-basin.

Table 5 The shares of evaporation-transpiration and its components for each category of land use in Zarrineh river sub-basin.

Resource base sheet

Figure 6 illustrates the WA+ resource base sheet for the Zarrineh River sub-basin for the accounting year 2021. The total water inflow to the sub-basin is recorded as 3600.53 MCM. This inflow includes all external sources such as runoff and surface water. After considering exchanges and storage, the net inflow to the sub-basin stands at 3610.53 MCM, indicating a positive difference primarily due to precipitation.

Fig. 6

WA+ Resources base sheet for Zarrineh river sub-basin.

The total depleted water is 2698.52 MCM. Out of 1561.52 MCM of water that was actively managed, a significant portion was allocated to manage land use areas. The exploitable water in the basin is 1747.35 MCM, signifying the amount of water available for agricultural, industrial, and environmental use. 185.83 MCM of water was recorded as utilizable outflow, meaning this amount of water leaves the system but can be used elsewhere in the future. There is 0 MCM recorded for non-utilizable outflows, indicating that all outflows are somehow available for use or consumption. 0 MCM was allocated to protected land use, indicating no specially designated conservation areas within the sub-basin. Similarly, no water was allocated to modified land use (0 MCM). 1836.13 MCM of water was consumed on managed land use areas, showing that these lands are the primary consumers of water resources, making water management on these lands crucial. Out of the total water inflow to the basin, 3424.70 MCM was consumed, with the majority being used in managed lands. This suggests that evapotranspiration from agricultural and managed areas significantly contributes to water loss.1561.52 MCM of water was actively managed and utilized, including for irrigation, industrial, and environmental purposes. This indicates that the active management of water resources plays a vital role in water distribution. 185.83 MCM of water left the basin as utilizable outflow, indicating the potential for future water recovery and reuse. The absence of non-utilizable outflow reflects an efficient use of water in the basin. The results showed that a major portion of water consumption in the Zarrineh River sub-basin stems from evapotranspiration on managed lands, emphasizing the need for advanced irrigation techniques and measures to reduce evaporation in agricultural areas. The high amount of actively managed and exploitable water indicates efficient water resource management in the basin, highlighting the importance of maintaining such practices. Although managed agricultural areas exhibit higher productivity compared to other sectors, the factors contributing to this productivity deserve further exploration. The higher productivity in these areas can be attributed to several key factors, including:

• Optimal water management: The use of efficient irrigation systems, such as drip irrigation and sprinkler systems, minimizes water loss and optimizes water usage, which is crucial for maintaining crop yield in water-scarce regions.

• Improved soil fertility: The application of both organic and chemical fertilizers enhances soil quality, providing crops with the necessary nutrients for higher yields.

• Adoption of modern agricultural practices: Techniques such as crop rotation, pest management, and the use of drought-resistant seed varieties allow for more sustainable farming practices and better productivity.

• Access to infrastructure: Managed agricultural areas generally have better access to infrastructure, including transportation networks, market access, and technical services, all of which facilitate higher productivity.

• Government support and training programs: Local and national policies, along with farmer education programs, play a significant role in promoting the adoption of efficient farming practices and boosting productivity.

By considering these factors, it becomes clear that the higher productivity in managed areas is not only a result of technological advancements but also a combination of infrastructural, economic, and policy-related supports. This breakdown provides a more comprehensive understanding of the dynamics at play in these areas. 185.83 MCM of utilizable outflow demonstrates the basin’s potential for water recovery and future use, providing opportunities for better water management strategies. Given this significant amount of recoverable water, it is essential to explore specific water reuse strategies to maximize the efficient utilization of available resources. Several regions facing similar water scarcity challenges, such as those highlighted by Ahangari Hassas & Taghizadegan Kalantari³¹, Hosseinishad et al.³², ElSayed et al.³³, Egbuikwem et al.³⁴, and Jeong et al.³⁵, have successfully implemented strategies like wastewater recycling, agricultural water reuse, and surface water management to supplement irrigation needs. These approaches can be adapted to the Zarrineh River Sub-Basin to enhance water recovery, reduce dependency on fresh water sources, and improve the overall sustainability of water usage in the region. In this study, the effectiveness of the WA+ framework in enhancing water management has been demonstrated across various regions, a concept already explored in numerous studies. For instance, Delavar et al.³⁶ showcased the application of WA+ in evaluating water conservation strategies for the Lake Urmia basin, where it was integrated with agro-hydrological models to provide a more comprehensive understanding of water usage. Similarly, Patle and Sharma³⁷ underscored the significance of WA+ in analyzing water consumption trends and agricultural outputs in the Mahi River basin, revealing its importance for both policymakers and researchers in optimizing water use and agricultural productivity. Moreover, Kivi et al.²⁷ highlighted the utility of WA+ in assessing groundwater balance in the Plasjan basin, where its integration significantly reduced uncertainty in water resource management. In parallel, Ghorbanpour et al.¹¹ applied WA+ for sustainable water resource management in northwestern Iran, demonstrating its role in improving productivity in water-scarce regions, a crucial aspect for areas experiencing water shortages. The findings of these studies align with the objectives of our research. This comparison underscores the growing potential of the WA+ framework in improving water efficiency across diverse applications and geographical settings.

Evapotranspiration sheet

The provided sheet (Fig. 7) offers an in-depth breakdown of the evapotranspiration (ET) for the Zarrineh River Basin, categorized into non-manageable, manageable, and managed sectors, based on the Water Accounting Plus (WA+) framework. The ET values are expressed in MCM, providing a clear picture of water loss through evaporation and transpiration across different land uses.

Fig. 7

WA+ Resources base sheet for Zarrineh river sub-basin.

Non-manageable sector

This sector includes protected land use, such as forests, shrublands, natural grasslands, water bodies, wetlands, glaciers, and other similar landscapes. ET in this sector is zero (0.0 MCM), this means that evapotranspiration is so minimal in these areas that it is not measurable or significant. In other words, these areas are considered non-manageable in terms of water management, as evapotranspiration is not significant enough to be incorporated into water management strategies.

Manageable sector

The manageable sector comprises two subcategories: utilized land use and modified land use. Utilized land use has an ET of 1703.2 MCM, with forests (8.8 MCM), shrublands (6.1 MCM), and natural grasslands (1683.5 MCM) being the major contributors. Most of the transpiration here is from forests and natural ecosystems. Modified land use (e.g., rainfed crops, forest plantations) accounts for 327.8 MCM of ET, with rainfed crops being the largest source (327.8 MCM). This category presents substantial room for improving water management. Since these areas are human-modified and under active use, implementing more efficient water management strategies can potentially reduce water loss through evapotranspiration.

Managed sector

The managed sector encompasses irrigated crops, managed water bodies, and residential/industrial areas. The total ET here is 995.7 MCM, with irrigated crops accounting for 579.4 MCM. This highlights the significant role of agriculture in water consumption. Managed water bodies (72.9 MCM) and settlements (31.3 MCM) also contribute to the overall ET. Non-conventional water use, such as water for livestock, greenhouses, and energy production, adds another 667.9 MCM to the total ET, mostly related to indoor and industrial water use.

The sheet distinguishes between beneficial and non-beneficial evapotranspiration. Non-beneficial ET (i.e., water loss through evaporation that does not contribute to crop production or other human uses) is 919.4 MCM. Beneficial ET (i.e., evapotranspiration that supports agriculture or other productive activities) is 1603.1 MCM, which is mostly driven by agricultural activities. This distinction is crucial because it highlights areas where interventions could reduce non-beneficial ET, thus improving overall water efficiency. Since managed areas, particularly irrigated crops, account for a large portion of ET, improving irrigation practices can significantly reduce water loss. Adopting efficient irrigation systems like drip irrigation and sprinkler systems is essential to minimize non-beneficial water loss and optimize water usage in agriculture. However, their successful implementation in the Zarrineh River Sub-basin presents several challenges that must be addressed to ensure effective adoption and long-term sustainability. Firstly, technical challenges may arise due to the region’s limited infrastructure and access to advanced technology. In some areas, the installation and maintenance of these systems could be hindered by a lack of local resources or insufficient technical expertise. Additionally, economic barriers such as high initial costs and ongoing maintenance expenses may limit the adoption of these systems, particularly among small-scale farmers with limited financial capacity. Furthermore, social and cultural factors could influence the acceptance of new irrigation methods. Resistance to change due to traditional farming practices and a lack of awareness about the benefits of modern systems might pose a challenge in ensuring widespread adoption. Lastly, environmental and geographical conditions, including high temperatures and low rainfall in certain areas, may reduce the efficiency of these systems, making them less effective in some parts of the sub-basin. Addressing these challenges through targeted interventions, such as government support programs, training for local farmers, and region-specific adaptation strategies, will be critical to the successful implementation of advanced irrigation technologies in the study area. Over-extraction of groundwater for irrigation purposes can lead to a decline in groundwater levels, salinization of both soil and groundwater, and ultimately, environmental crises. Therefore, the adoption of efficient irrigation methods such as drip irrigation and sprinkler systems, along with the implementation of smart water management systems, can contribute to improving water use efficiency and preserving groundwater resources. This is consistent with the results of Wael et al.³⁸ and Bouimouass et al.³⁹, who emphasized the impact of irrigation methods on groundwater behavior. Furthermore, Nazari et al.⁷ contribute important insights into assessing actual water savings (RWS) gained from innovations in irrigation technologies, offering guidance on improving water efficiency and long-term sustainability. Future research will be necessary to model the long-term effects of these irrigation methods on groundwater resources and explore more sustainable solutions. The high level of non-beneficial ET (919.4 MCM) indicates considerable water loss through evaporation, particularly from bare soil and unmanaged water bodies. Implement measures such as mulching, crop cover, and shade structures in agricultural areas to reduce soil evaporation. Additionally, covering reservoirs and water storage facilities with floating covers can help reduce evaporation. Specifically, the feasibility of these methods depends on climatic conditions, available resources, and the characteristics of each region.

Soil covering

The use of soil coverings can effectively reduce non-beneficial evapotranspiration. However, there are challenges such as high costs, the need for specific materials, and the impact on soil properties. In areas with limited water resources, this method could be particularly practical in regions requiring irrigation. For example, in countries like the United States and Australia, soil covering has been used as an effective solution to reduce evaporation from soil surfaces in agriculture.

Reservoir management

Regarding reservoir management, controlling evaporation from reservoir surfaces using methods like installing specialized covers or utilizing natural coverings can be effective. These methods are especially important in hot and dry regions with high evaporation rates. However, the costs of installation and maintenance of these systems, as well as the need for technical assessments to ensure their optimal performance, should be considered.

The non-conventional water use sector presents an opportunity to relieve pressure on conventional water resources by utilizing recycled and treated wastewater. Expand the use of greywater recycling and wastewater treatment for irrigation and industrial purposes. This is especially important in urban and industrial sectors where water demand is high. Since agriculture accounts for most of the beneficial ET (1603.1 MCM), improving crop selection and cultivation practices could enhance water productivity. Encourage the cultivation of drought-resistant crops and promote water-efficient farming techniques to maximize beneficial water use and reduce overall ET. Based on the climatic and soil conditions of the Zarrineh River sub-basin, drought-resistant crops such as barley, wheat, maize, sesame, pistachio, fig, and sunflower can be cultivated in the study area. Comparable methods have been emphasized in the studies of Ramos et al.⁴⁰ and Wang et al.⁴¹, underscoring their efficacy in reducing water loss and enhancing agricultural water management. As ET is a critical component of the water balance, integrating water management practices across all sectors is essential for sustainable development. Adopt an Integrated Water Resources Management (IWRM) approach to ensure coordination among agriculture, urban development, and environmental management sectors. This can help balance water needs while minimizing water loss. By adopting IWRM, it will be possible to improve coordination among the agriculture, urban development, and environmental management sectors. This approach will not only help balance water needs across sectors but also minimize water loss through better planning, efficient water use, and integrated water management strategies. In particular, in the Zarrineh River sub-basin, applying IWRM can facilitate sustainable water use in agriculture, enhance urban water supply systems, and ensure environmental conservation by optimizing water distribution and fostering collaboration among stakeholders.

Water and land productivity sheet

This sheet provides a detailed overview of land use categories, biomass production, and biomass water productivity in the Zarrineh River Basin. The values are broken down into three major sectors: conserved land use, utilized land use, modified land use, and managed water use. The table reveals the efficiency of water and land usage in terms of biomass production across different land use categories, providing insights into the sustainability and productivity of agricultural and natural systems.

Conserved land use

In the case of conserved land use, there is no registered biomass production or water productivity. This is expected as conserved land generally refers to protected areas where human intervention and active management are limited or absent, with a focus on conservation rather than resource extraction (Fig. 8).

Fig. 8

Water and land productivity sheet for Zarrineh river sub-basin.

Utilized land use

Evapotranspiration (ET) for utilized land use is 1703.22 MCM. The biomass production in this sector is 0.10 million tons of crop (Mtc) with a corresponding land productivity of 5492.99 kg/ha. The biomass water productivity (the ratio of biomass production to the volume of water used) is calculated as 1.74 kg/m³. This relatively low water productivity suggests that, while the land productivity is high, there may be inefficiencies in water use. Optimizing irrigation techniques and increasing water efficiency could result in better water productivity.

Modified land use

ET in modified land use is 327.76 MCM, and biomass production is considerably higher, with 5.60 Mtc produced. The corresponding land productivity is 3397.31 kg/ha. Biomass water productivity is 2.46 kg/m³, which shows improved water use efficiency compared to the utilized land use sector. The modified land use sector, which likely includes rainfed crops and plantations, demonstrates a better balance between water consumption and biomass production. This could be a result of more deliberate management practices that maximize productivity while limiting water loss.

Managed water use

In the managed water use sector, ET is 667.90 MCM, and the biomass production is 3.49 Mtc. The land productivity is 4722.21 kg/ha, while the biomass water productivity stands at 2.54 kg/m³.Managed water use, which includes irrigated agriculture, shows the highest biomass water productivity in the table, indicating efficient use of water for biomass generation. This could be attributed to more controlled and regulated water usage in this sector, where water management strategies such as irrigation scheduling and efficient irrigation systems like drip irrigation are more prevalent.

Despite the high land productivity observed in this area, the biomass water productivity in the utilized land use sector is the lowest, measured at 1.74 kg/m. To enhance water use efficiency, it is recommended to implement water-saving irrigation techniques such as drip irrigation or deficit irrigation. These methods can reduce water waste while maintaining or even enhancing crop yields. Modified land use shows a better balance between water usage and biomass production, with water productivity at 2.46 kg/m³. Continue to promote conservation tillage and rainwater harvesting techniques to further improve the sustainability of this land use type. Expanding the use of drought-resistant crop varieties could also boost land productivity while conserving water. The managed water use sector has the highest biomass water productivity at 2.54 kg/m³, indicating efficient water use. However, the land productivity in this sector, at 4722.21 kg/ha, is lower compared to utilized land use. There is room to optimize crop selection and improve irrigation scheduling to balance water use with land productivity. Introducing crop rotation and IWRM techniques can further enhance the efficiency of both water and land use. The variation in biomass water productivity across different land use sectors shows the need for a more coordinated approach to managing water and land resources. Adopt an Integrated Water and Land Management approach, where water allocation is optimized based on the land’s productivity potential. This could involve creating a zoning system where high-productivity areas receive more water resources, while low-productivity or conserved lands are managed with minimal intervention. To ensure continuous improvement in water and land productivity, regular monitoring of biomass production, evapotranspiration rates, and water productivity across all land use sectors is essential. Establish real-time monitoring systems using remote sensing and GIS tools to track water use efficiency and biomass production. These systems can provide data-driven insights for policymakers and farmers to make informed decisions on water and land management. Also, to enhance both land and water productivity, it is essential to implement integrated approaches focused on increasing yield per unit of land, as demonstrated by the research of Abejo et al.⁴², Giménez et al.⁴³, and Trunov et al.⁴⁴. Moreover, improving water use efficiency is vital for the sustainable management of irrigation systems, as highlighted by Randev⁴⁵, Tang et al.⁴⁶, and Villa et al.⁴⁷. The adoption of these strategies will play a significant role in boosting overall productivity and ensuring the long-term, efficient utilization of both land and water resources.

WA+ performance indicators

Table 6 presents a series of performance indicators based on Water Accounting Plus (WA+) data, focusing on the efficiency and sustainability of water resources and land use. These indicators help assess water productivity, evapotranspiration efficiency, and the balance between different sources of water (blue and green water) in the region. The interpretation of each indicator is as follows:

Table 6 WA+ Performance indicators.

Exploitable water fraction

At 48%, less than half of the available water resources are considered manageable, suggesting that a significant proportion of water is either inaccessible or lost to non-beneficial uses like evaporation. Enhancing water management strategies can help improve this ratio, leading to better water allocation for productive purposes.

Storage change fraction

The minimal change (0.01%) suggests that groundwater resources are relatively stable. However, this could also imply low recharge rates or limited exploitation. Given the importance of groundwater for sustaining agriculture and ecosystems, the stability of this resource is a positive sign but should be monitored for potential overuse.

Blue evapotranspiration fraction

With 69% of blue water being lost to evapotranspiration, a substantial portion of available freshwater is not directly benefiting crops or human activities. This high ratio points to the need for better water management, such as improved irrigation techniques or drought-resistant crops that minimize water loss through evapotranspiration.

Green evapotranspiration fraction

31% of green water is consumed by evapotranspiration, which is comparatively lower than blue water. Since green water is critical for rainfed agriculture, this ratio suggests that there is room for optimizing the efficiency of rainfed systems, perhaps through soil moisture retention techniques like mulching or conservation tillage.

Evaporation fraction

A significant 34% of water is lost to evaporation. Reducing this through measures such as mulching, planting shade trees, or using greenhouses could help retain more water for productive uses⁴⁸.

Transpiration fraction

66% of the water lost to evapotranspiration is beneficially used by plants for growth. This is a positive indication, as it means most of the water is contributing to biomass production. Improving transpiration efficiency through precision irrigation or crop selection can further increase the ratio of beneficial water use.

Beneficial evapotranspiration fraction

At 59%, more than half of the water lost to evapotranspiration is considered beneficial, but this still leaves a significant portion that could be optimized. Reducing non-beneficial evaporation and enhancing transpiration rates can improve overall water productivity.

Managed evapotranspiration fraction

37% of evapotranspiration is actively managed, suggesting that there is considerable room for improvement in managing water resources. Increasing this ratio through better irrigation techniques and water conservation methods can lead to higher water productivity and more efficient use of available water.

Water productivity for rainfed crops

With a water productivity of 1.9 kg/m³, rainfed agriculture shows moderate efficiency. To increase this, implementing techniques such as soil moisture conservation, mulching, and improving crop varieties could help enhance yields without increasing water use.

Water productivity for irrigated crops

The water productivity for irrigated crops is higher at 2.5 kg/m³ compared to rainfed crops, which reflects the benefits of controlled water use through irrigation. However, this Fig can still be improved through the adoption of efficient irrigation systems like drip irrigation, precision farming, and water recycling techniques.

Although Table 6 presents a comprehensive set of performance indicators based on Water Accounting Plus (WA+), including traditional metrics such as water productivity and evapotranspiration ratios, new indicators such as ET Fraction, Managed Fraction, and Beneficial Consumption were also introduced to provide more insights into the efficiency and sustainability of water use in the region. These indicators help assess the proportion of water that is efficiently utilized for productive purposes, as well as the potential for optimizing water management strategies. Specifically, ET Fraction indicates the share of evapotranspiration that is beneficial for crops and ecosystems, while Managed Fraction reflects the proportion of water that is actively managed through techniques like irrigation, contributing to improved water productivity. Lastly, Beneficial Consumption quantifies the amount of water consumed in a way that directly supports agricultural growth and ecosystem health. These indicators, when used together with traditional measures, offer a more nuanced view of water efficiency, guiding efforts to improve both rainfed and irrigated systems. The performance indicators outlined in Table 6 provide critical insights into the efficiency of water and land use in the basin. While certain areas, such as irrigated agriculture, show promising water productivity, there are significant opportunities to enhance both rainfed and irrigated systems. By focusing on improved water management practices, reducing non-beneficial water losses, and optimizing evapotranspiration, the overall sustainability and productivity of water resources in the region can be substantially improved.

Conclusion

This study analyzes water consumption and resource management in the Zarrineh River sub-basin using the Water Accounting Plus (WA+) framework. The main objective of the research was to assess the water resource status and identify the challenges and opportunities in water management, particularly in the agricultural sector. The total water inflow to the sub-basin is recorded as 3600.53 MCM. This inflow includes all external sources such as runoff and surface water. After considering exchanges and storage, the net inflow to the sub-basin stands at 3610.53 MCM, indicating a positive difference primarily due to precipitation. The exploitable water in the basin is 1747.35 MCM, signifying the amount of water available for agricultural, industrial, and environmental use. 185.83 MCM of water was recorded as utilizable outflow, meaning this amount of water leaves the system but can be used elsewhere in the future. The majority of this loss occurs from agricultural lands, highlighting the need for efficient irrigation systems such as drip and sprinkler systems, as well as methods like shading and mulching to reduce evaporation. One of the key findings of this study is the significant disparity in water productivity between managed and unmanaged lands. In managed areas, the average biomass production is 2.54 kg/m³.of water consumed, indicating the potential for improving productivity in other areas. Additionally, non-beneficial evapotranspiration, totaling 919.4 MCM, is primarily due to uncovered soils and unmanaged water resources. This emphasizes the need for measures such as mulching and covering reservoirs to reduce these losses and improve overall water efficiency. While the use of satellite technology and remote sensing data offers significant advantages, it requires adequate infrastructure and additional costs for implementation. Future recommendations include advancing smart irrigation systems, promoting the use of new technologies to improve water efficiency, developing training programs for farmers to familiarize them with these technologies, and encouraging the implementation of Integrated Water Resources Management (IWRM) systems. Additionally, expanding the use of recycled water and establishing monitoring and evaluation systems for better water resource management in this region and other similar sub-basins is recommended.