Abstract
Human impacts from dams reduce river sediment fluxes and are primary causes of coastal erosion worldwide. Here we provide new satellite-derived shoreline observation techniques to examine beach area trends across the diverse coastal settings of California. Contrary to global trends, these data reveal that the most heavily urbanized and dammed region of southern California experienced net beach growth of over 2 million m2 during 1984-2024. While several beaches experienced severe erosion, overall widening is explained by sufficient sediment supply and concentrated widening from longshore transport captured at coastal structures and in littoral convergence zones. These results indicate that adequate sediment sources exist in this human-modified landscape to mitigate coastal erosion, but that this sediment is not effectively distributed to vulnerable beaches. This highlights the critical role that longshore sediment transport plays in long-term beach trends and illuminates management opportunities for coastal sustainability at the regional scale.
Data availability
Beach segment locations, source CoastSat transects, and mean annual shoreline positions and annual values of uncertainty for all 329 beach segments of California are tabulated and published in Warrick (2025)74. The raw shoreline position measurements that were used to derive the mean annual shoreline positions are published and available from the CoastSat data publication by Vos42, version 1.5. Beach width measurements for each CoastSat transect are published in Warrick and Buscombe76. Hindcast wave data were obtained from the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis Version 5 (ERA5) hindcasts of as detailed by Soci et al.61 and made available at https://www.ecmwf.int/en/forecasts/dataset/ecmwf-reanalysis-v5 (accessed May 14, 2025). Beach nourishment rates were obtained from the ASBPA National Beach Nourishment Database as detailed by Elko et al.64 and made available at: https://asbpa.org/national-beach-nourishment-database/ (accessed May 14, 2025). Mean river discharge of littoral-grade sand for the Santa Barbara Littoral Cell was obtained from Barnard and Warrick54.
Code availability
Codes used to generate shoreline positions from satellite imagery are provided in the gitbub site: https://github.com/kvos/CoastSat. Codes used to compute deseasonalized annual shoreline positions from the raw CoastSat data are provided in the USGS Software Release by Warrick44: https://doi.org/10.5066/P1UYMOK7.
References
Mehvar, S. et al. Quantifying economic value of coastal ecosystem services: a review. JMSE 6, 5 (2018).
Zhang, F., Wang, X. H., Nunes, P. A. L. D. & Ma, C. The recreational value of Gold Coast beaches, Australia: an application of the travel cost method. Ecosyst. Serv. 11, 106–114 (2015).
Defeo, O. et al. Threats to sandy beach ecosystems: a review. Estuar. Coast. Shelf Sci. 81, 1–12 (2009).
Castelle, B. & Masselink, G. Morphodynamics of wave-dominated beaches. Camb. Prism. Coast. Futures 1, e1 (2023).
FitzGerald, D. M., Fenster, M. S., Argow, B. A. & Buynevich, I. V. Coastal Impacts Due to Sea-Level Rise. Annu. Rev. Earth Planet. Sci. 36, 601–647 (2008).
Warrick, J. A., East, A. E. & Dow, H. Fires, floods and other extreme events–How watershed processes under climate change will shape our coastlines. Camb. Prisms Coast. Futures 1, e2 (2023).
Armstrong, S. B. & Lazarus, E. D. Masked shoreline erosion at large spatial scales as a collective effect of beach nourishment. Earth’s. Future 7, 74–84 (2019).
King, E. V. et al. Wave, tide and topographical controls on headland sand bypassing. J. Geophys. Res. Oceans 126, (2021).
Komar, P. D. Beach Processes and Sedimentation. (Prentice Hall, 1998).
Short, A. D. Australian beach systems: Are they at risk to climate change? Ocean Coast. Manag. 224, 106180 (2022).
Syvitski, J. et al. Earth’s sediment cycle during the Anthropocene. Nat. Rev. Earth Environ. https://doi.org/10.1038/s43017-021-00253-w (2022).
Castelle, B. et al. Impact of the winter 2013–2014 series of severe Western Europe storms on a double-barred sandy coast: Beach and dune erosion and megacusp embayments. Geomorphology 238, 135–148 (2015).
Wang, H. et al. Recent changes of sediment flux to the western Pacific Ocean from major rivers in East and Southeast Asia. Earth-Sci. Rev. 108, 80–100 (2011).
Alves, B., Angnuureng, D. B., Morand, P. & Almar, R. A review on coastal erosion and flooding risks and best management practices in West Africa: What has been done and should be done. J. Coast Conserv 24, 38 (2020).
Besset, M., Anthony, E. J. & Bouchette, F. Multi-decadal variations in delta shorelines and their relationship to river sediment supply: an assessment and review. Earth Sci. Rev. 193, 199–219 (2019).
Li, X., Liu, J. P., Saito, Y. & Nguyen, V. L. Recent evolution of the Mekong Delta and the impacts of dams. Earth Sci. Rev. 175, 1–17 (2017).
Trimble, S. W. Contribution of stream channel erosion to sediment yield from an urbanizing watershed. Science 278, 1442–1444 (1997).
Russell, K. L., Vietz, G. J. & Fletcher, T. D. Global sediment yields from urban and urbanizing watersheds. Earth Sci. Rev. 168, 73–80 (2017).
Anthony, E. et al. A 7000-year record of human influence on Global River Deltas: Geomorphology, stratigraphy, the Anthropocene overprint and future. Earth Sci. Rev. 271, 105302 (2025).
MacKenzie, K. M., Singh, K., Binns, A. D., Whiteley, H. R. & Gharabaghi, B. Effects of urbanization on stream flow, sediment, and phosphorous regime. J. Hydrol. 612, 128283 (2022).
Vitousek, S., Barnard, P. L. & Limber, P. Can beaches survive climate change? J. Geophys. Res. Earth Surf. 122, 1060–1067 (2017).
Cooper, J. A. G. et al. Sandy beaches can survive sea-level rise. Nat. Clim. Chang. 10, 993–995 (2020).
Cosby, A. G. et al. Accelerating growth of human coastal populations at the global and continent levels: 2000–2018. Sci. Rep. 14, 22489 (2024).
Willis, C. M. & Griggs, G. B. Reductions in fluvial sediment discharge by coastal dams in California and implications for beach sustainability. J. Geol. 111, 167–182 (2003).
Inman, D. L. & Chamberlain, T. K. Littoral Sand Budget along the Southern California Coast. 245–246 (1960).
Patsch, K. B. & Griggs, G. B. Littoral Cells, Sand Budgets, and Beaches: Understanding California’s Shoreline. 40 (2006).
Hapke, C. J., Reid, D. & Richmond, B. Rates and trends of coastal change in california and the regional behavior of the Beach and Cliff System. J. Coast. Res. 253, 603–615 (2009).
Slagel, M. J. & Griggs, G. B. Cumulative Losses of Sand to the California Coast by Dam Impoundment. J. Coast. Res. 243, 571–584 (2008).
Shepard, F. P. Beach Cycles in Southern California. 33 p. (1950).
Inman, D. L. & Brush, B. M. The coastal challenge. Sci., N. Ser. 181, 20–32 (1973).
Yates, M. L., Guza, R. T. & O’Reilly, W. C. Equilibrium shoreline response: Observations and modeling. J. Geophys. Res. 114, (2009).
Flick, R. E. The myth and reality of Southern California beaches. Shore Beach 61, 3–13 (1993).
Thorne, K. M., MacDonald, G. M., Chavez, F. P., Ambrose, R. F. & Barnard, P. L. Significant challenges to the sustainability of the California coast considering climate change. Proc. Natl. Acad. Sci. Usa. 121, e2310077121 (2024).
Griggs, G. & Patsch, K. California’s coastal development: Sea-level rise and extreme events—Where do we go from here? Shore & Beach 15–28 https://doi.org/10.34237/1008722 (2019).
King, P. G. et al. Valuing beach ecosystems in an age of retreat. Shore beach 86, 45–59 (2018).
Vitousek, S., Vos, K., Splinter, K. D., Erikson, L. & Barnard, P. L. A model integrating satellite-derived shoreline observations for predicting fine-scale shoreline response to waves and sea-level rise across large coastal regions. JGR Earth Surf. 128, e2022JF006936 (2023).
Amrouni, O., Heggy, E. & Hzami, A. Shoreline retreat and beach nourishment are projected to increase in Southern California. Commun. Earth Environ. 5, 274 (2024).
Warrick, J. A. & Rubin, D. M. Suspended-sediment rating curve response to urbanization and wildfire, Santa Ana River, California. J. Geophys. Res. 112, (2007).
King, P. G., McGregor, A. R. & Whittet, J. D. Can California coastal managers plan for sea-level rise in a cost-effective way? J. Environ. Plan. Manag. 59, 98–119 (2016).
Anderson, R. B. The taboo of retreat: The politics of sea level rise, managed retreat, and coastal property values in California. Econ. Anthropol. 9, 284–296 (2022).
Vos, K., Harley, M. D., Splinter, K. D., Simmons, J. A. & Turner, I. L. Sub-annual to multi-decadal shoreline variability from publicly available satellite imagery. Coast. Eng. 150, 160–174 (2019).
Vos, K. Time-series of shoreline change along the Pacific Rim. Zenodo https://doi.org/10.5281/zenodo.7758183 (2025).
Warrick, J. A. et al. Shoreline seasonality of California’s Beaches. JGR Earth Surf. 130, e2024JF007836 (2025).
Warrick, J. A. Shoreline STL Decomposition Software. https://doi.org/10.5066/P1UYMOK7 (2025).
Young, A. P. et al. Southern California coastal response to the 2015–2016 El Niño. JGR Earth Surf. 123, 3069–3083 (2018).
Barnard, P. L. et al. Extreme oceanographic forcing and coastal response due to the 2015–2016 El Niño. Nat. Commun. 8, 1–8 (2017).
Barnard, P. L. et al. The impact of the 2009-10 El Niño Modoki on U.S. West Coast beaches: EL NIÑO impact on USA west coast beaches. Geophys. Res. Lett. 38, n/a-n/a (2011).
Storlazzi, C. D. & Griggs, G. B. Influence of El Nino-Southern Oscillation (ENSO) events on the evolution of central California’s shoreline. Geol. Soc. Am. Bull. 112, 236–249 (2000).
Warrick, J. A., Vos, K., Buscombe, D., Ritchie, A. C. & Curtis, J. A. A Large Sediment Accretion Wave Along a Northern California Littoral Cell. JGR Earth Surf. 128, e2023JF007135 (2023).
Vos, K., Harley, M. D., Turner, I. L. & Splinter, K. D. Pacific shoreline erosion and accretion patterns controlled by El Niño/Southern Oscillation. Nat. Geosci. 16, 140–146 (2023).
Griggs, G. B. & Patsch, K. B. Natural Changes and Human Impacts on the Sand Budgets and Beach widths of the Zuma and Santa Monica littoral cells, Southern California. Shore Beach 86, 3–16 (2017).
Kahl, D. T., Vulis, L. M., Schubert, J. E. & Sanders, B. F. Characterizing longshore transport potential and divergence of drift to inform beach loss trends. Coast. Eng. 189, 104473 (2024).
Warrick, J. A. Littoral sediment from rivers: patterns, rates and processes of river mouth morphodynamics. Front. Earth Sci. 8, 355 (2020).
Barnard, P. L. & Warrick, J. A. Dramatic beach and nearshore morphological changes due to extreme flooding at a wave-dominated river mouth. Mar. Geol. 271, 131–148 (2010).
Ludka, B. C., Guza, R. T. & O’Reilly, W. C. Nourishment evolution and impacts at four southern California beaches: a sand volume analysis. Coast. Eng. 136, 96–105 (2018).
Valiente, N. G., McCarroll, R. J., Masselink, G., Scott, T. & Wiggins, M. Multi-annual embayment sediment dynamics involving headland bypassing and sediment exchange across the depth of closure. Geomorphology 343, 48–64 (2019).
Warrick, J. A. et al. Large-scale dam removal on the Elwha River, Washington, USA: Source-to-sink sediment budget and synthesis. Geomorphology 246, 729–750 (2015).
Limber, P. W., Patsch, K. B. & Griggs, G. B. Coastal sediment budgets and the littoral cutoff diameter: a grain size threshold for quantifying active sediment inputs. J. Coast. Res. 2, 122–133 (2008).
O’Reilly, W. C., Olfe, C. B., Thomas, J., Seymour, R. J. & Guza, R. T. The California coastal wave monitoring and prediction system. Coast. Eng. 116, 118–132 (2016).
O’Reilly, W. C. et al. Interannual wave-driven shoreline change on the California coast. Nat. Commun. 16, 9967 (2025).
Soci, C. et al. The ERA5 global reanalysis from 1940 to 2022. Quart. J. R. Meteor. Soc. 150, 4014–4048 (2024).
Vos, K. et al. Benchmarking satellite-derived shoreline mapping algorithms. Commun. Earth Environ. 4, 345 (2023).
Syvitski, J. P. M. & Milliman, J. D. Geology, geography, and humans battle for dominance over the delivery of fluvial sediment to the coastal ocean. J. Geol. 115, 1–19 (2007).
Elko, N. et al. A century of U.S. beach nourishment. Ocean Coast. Manag. 199, 105406 (2021).
Yates, M. L., Guza, R. T., O’Reilly, W. C. & Seymour, R. J. Overview of seasonal sand level changes on southern California beaches. Shore Beach 77, 39–46 (2009).
Rangel-Buitrago, N. & Neal, W. The unsustainable harvest of coastal sands. Science 382, 1116–1118 (2023).
Greimann, B., Sheydayi, P., Vargas, S., Lai, Y. & Mefford, B. Developing Mitigation Plans for Matilija Dam Removal. in World Environmental and Water Resources Congress 2008 1–9 (American Society of Civil Engineers, 2008). https://doi.org/10.1061/40976(316)349.
Cui, Y. et al. Analyses of the erosion of fine sediment deposit for a large dam-removal project: an empirical approach. Int. J. River Basin Manag. 15, 103–114 (2017).
Ulibarri, N. et al. Barriers and opportunities for beneficial reuse of sediment to support coastal resilience. Ocean Coast. Manag. 195, 105287 (2020).
Goodrich, K. A. et al. Toward improved sediment management and coastal resilience through efficient permitting in California. Environ. Manag. 72, 558–567 (2023).
Ludka, B. C. & and 15 others. Sixteen years of bathymetry and waves and San Diego beaches. Sci. Data 6, (2019).
Vitousek, S. et al. The future of coastal monitoring through satellite remote sensing. Camb. prisms Coast. futures 1, e10 (2023).
Vos, K., Harley, M. D., Splinter, K. D., Walker, A. & Turner, I. L. Beach slopes from satellite-derived shorelines. Geophys. Res. Lett. 47, (2020).
Warrick, J. A. Data to Support Analyses of Widening and Narrowing of Beach Segments in California. https://doi.org/10.5066/P139YRVP (2025).
Cleveland, R. B., Cleveland, W. S., McRae, J. E. & Terpenning, I. STL: A seasonal-trend decomposition procedure based on loess. J. Off. Stat. 6, 3–73 (1990).
Warrick, J. A. & Buscombe, D. Data to Support Analyses of Shoreline Seasonal Cycles for Beaches of California. U.S. Geological Survey Data Release https://doi.org/10.5066/P14WWHOJ (2024).
Adams, P. N., Inman, D. L. & Graham, N. E. Southern California deep-water wave climate: characterization and application to Coastal Processes. J. Coast. Res. 244, 1022–1035 (2008).
Warrick, J. A. & Farnsworth, K. L. Sources of sediment to the coastal waters of the Southern California Bight. in Earth Science in the Urban Ocean: The Southern California Continental Borderland (Geological Society of America, 2009). https://doi.org/10.1130/2009.2454(2.2).
San Diego Association of Governments (SANDAG). Coastal Regional Sediment Management Plan for the San Diego Region. 220 https://dbw.parks.ca.gov/?page_id=29337 (2009).
Gadd, P. E., Leidersdorf, C. B., Hearon, G., Shak, A. T. & Ryan, J. Use Of “Statistical” Depth Of Closure To Resolve Historical Changes In Shorezone Volume, Huntington Beach Littoral Cell, Ca, Usa. in Coastal Engineering 2006 5302–5311 (World Scientific Publishing Company, 2007). https://doi.org/10.1142/9789812709554_0444.
Acknowledgements
This work was supported by the U.S. Geological Survey’s Coastal and Marine Hazards and Resources Program through the Remote Sensing Coastal Change project. Additional funding provided by NASA grant NNH21ZDA001 (BS, TH). Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Author information
Authors and Affiliations
Contributions
J.A.W.—Primary author, data analyses, synthesis. K.V.—Data generation (shoreline change), data analyses. D.B.—Study design, data analysis, secondary author. A.R.—Study design, data analysis. S.V.—Data synthesis, secondary author. T.H.—Data generation and synthesis (longshore transport, sediment budgets). B.S.—Study design, primary author.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Peer review
Peer review information
Nature Communications thanks Aikaterini Konstantinou and the other anonymous reviewer(s) for their contribution to the peer review of this work. A peer review file is available.
Additional information
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary information
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Warrick, J.A., Vos, K., Buscombe, D.D. et al. Net widening of Southern California beaches. Nat Commun (2026). https://doi.org/10.1038/s41467-026-68880-9
Received:
Accepted:
Published:
DOI: https://doi.org/10.1038/s41467-026-68880-9
