Priorities for California’s Water -- Stewarding the Wet Years

Public Policy Institute of California (PPIC) | November 2nd, 2023

The 2023 water year provided a case study of California’s increasingly volatile climate, with large swings between wet and dry conditions both within and between years.

The 2023 water year provided a case study of California’s increasingly volatile climate, with large swings between wet and dry conditions both within and between years. It highlighted our need to better navigate multiple imperatives: storing more water during intense wet periods to build water supply reliability, protecting communities and infrastructure against the threat of increasingly damaging floods, and taking better advantage of wet years to improve the health of freshwater ecosystems and native fish and wildlife.

Priorities for California’s Water: Advancing Research During Uncertain Times

Public Policy Institute of California (PPIC) | November 12th, 2025

In California, research underpins all water-related activity. It is vital for coping with too much water, too little water, and rapid changes in hydrology. Whether you ar

In California, research underpins all water-related activity. It is vital for coping with too much water, too little water, and rapid changes in hydrology. Whether you are a farmer managing the precise application of water to your crops, a utility providing clean drinking water supplies to your community, or a restorationist trying to heal a damaged wetland, your actions rely upon decades of applied research that guides your actions and measures your success.  The same reliance on research applies if you are developing policies to reduce the price of water, increase its reliability, regulate its usage, and reduce hazards from floods. None of this works without a vast research enterprise that is regularly updating the science and technology we use to manage water, prepare for the future, inform the public, and address new problems as they arise. 

Probabilistic Subsidence Forecast Model for the California Aqueduct Subsidence Program, San Joaquin Valley, California: Revision 1 Design Report

California Department of Water Resources (DWR) | October 4th, 2024

This report documents the development of a probabilistic subsidence forecast model for simulating a plausible range of future land-surface altitude conditions along the C

This report documents the development of a probabilistic subsidence forecast model for simulating a plausible range of future land-surface altitude conditions along the California Aqueduct (Aqueduct) and San Luis Canal in the San Joaquin Valley (SJV), with an emphasis on areas of localized subsidence (i.e., “subsidence bowls”). The model forecasts will be used to inform long-term planning and on-going analyses of potential investments needed to provide a suitable level of performance for the Aqueduct. The forecast model is primarily based on an empirical relationship between historical subsidence rates and annual water deliveries from the Central Valley Project (CVP) and State Water Project (SWP). A key assumption of the model is that the rate of groundwater overdraft, which contributes to loss of aquifer storage and permanent land subsidence, is correlated with CVP and SWP deliveries, and specifically with higher groundwater storage loss during severe drought years. Another key assumption is that the same rates of subsidence will continue even after groundwater levels decline and extraction may be coming from deeper parts of the aquifer system. If the geology and/or aquifer properties change dramatically in response, then these new conditions may have an unmodeled impact on future rates. 

Procedures to evaluate sea-level change: impacts, responses, and adaptation

U.S. Army Corps of Engineers (USACE) | June 30th, 2014

Productive wetlands restored for carbon sequestration quickly become net CO2 sinks with site-level factors driving uptake variability

PLOS | March 25th, 2021

Inundated wetlands can potentially sequester substantial amounts of soil carbon (C) over the long-term because of slow decomposition and high primary productivity, partic

Inundated wetlands can potentially sequester substantial amounts of soil carbon (C) over the long-term because of slow decomposition and high primary productivity, particularly in climates with long growing seasons. Restoring such wetlands may provide one of several effective negative emission technologies to remove atmospheric CO2 and mitigate climate change. However, there remains considerable uncertainty whether these heterogeneous ecotones are consistent net C sinks and to what degree restoration and management methods affect C sequestration. Since wetland C dynamics are largely driven by climate, it is difficult to draw comparisons across regions. With many restored wetlands having different functional outcomes, we need to better understand the importance of site-specific conditions and how they change over time. We report on 21 site-years of C fluxes using eddy covariance measurements from five restored fresh to brackish wetlands in a Mediterranean climate. The wetlands ranged from 3 to 23 years after restoration and showed that several factors related to restoration methods and site conditions altered the magnitude of C sequestration by affecting vegetation cover and structure. Vegetation established within two years of re-flooding but followed different trajectories depending on design aspects, such as bathymetry-determined water levels, planting methods, and soil nutrients. A minimum of 55% vegetation cover was needed to become a net C sink, which most wetlands achieved once vegetation was established. Established wetlands had a high C sequestration efficiency (i.e. the ratio of net to gross ecosystem productivity) comparable to upland ecosystems but varied between years undergoing boom-bust growth cycles and C uptake strength was susceptible to disturbance events. We highlight the large C sequestration potential of productive inundated marshes, aided by restoration design and management targeted to maximise vegetation extent and minimise disturbance. These findings have important implications for wetland restoration, policy, and management practitioners.

Progress on Incorporating Climate Change into Planning and Management of California’s Water Resources

California Department of Water Resources (DWR) | July 9th, 2006

On June 1, 2005, Governor Arnold Schwarzenegger issued Executive Order S-3-05 establishing greenhouse gas emissions targets for California and requiring biennial reports

On June 1, 2005, Governor Arnold Schwarzenegger issued Executive Order S-3-05 establishing greenhouse gas emissions targets for California and requiring biennial reports on potential climate change effects on several areas, including water resources. The Governor established a Climate Action Team (CAT) to guide the reporting efforts. The CAT selected four climate change scenarios that reflect two greenhouse gas emissions scenarios represented by two Global Climate Models (GCMs). The CAT requested that those four climate change scenarios be used whenever possible in the climate change reporting efforts. This report is the Department of Water Resources response to the Executive Order. This report describes progress made incorporating climate change into existing water resources planning and management tools and methodologies.

Projected 21st Century Coastal Flooding in the Southern California Bight. Part 1: Development of the Third Generation CoSMoSModel

Journal of Marine Science and Engineering (MDPI) | May 24th, 2018

Due to the effects of climate change over the course of the next century, the combination of rising sea levels, severe storms, and coastal change will threaten the susta

Due to the effects of climate change over the course of the next century, the combination of rising sea levels, severe storms, and coastal change will threaten the sustainability of coastal communities, development, and ecosystems as we know them today. To clearly identify coastal vulnerabilities and develop appropriate adaptation strategies due to projected increased levels of coastal flooding and erosion, coastal managers need local-scale hazards projections using the best available climate and coastal science. In collaboration with leading scientists world-wide, the USGS designed the Coastal Storm Modeling System (CoSMoS) to assess the coastal impacts of climate change for the California coast, including the combination of sea-level rise, storms, and coastal change. In this project, we directly address the needs of coastal resource managers in Southern California by integrating a vast range of global climate change projections in a thorough and comprehensive numerical modeling framework. In Part 1 of a two-part submission on CoSMoS, methods and the latest improvements are discussed, and an example of hazard projections is presented. Click here for Part 2.

Projected 21st Century Coastal Flooding in the Southern California Bight. Part 2: Tools for Assessing Climate Change-Driven Coastal Hazards and Socio-Economic Impacts

Journal of Marine Science and Engineering (MDPI) | July 2nd, 2018

This paper is the second of two that describes the Coastal Storm Modeling System (CoSMoS) approach for quantifying physical hazards and socio-economic hazard exposure in

This paper is the second of two that describes the Coastal Storm Modeling System (CoSMoS) approach for quantifying physical hazards and socio-economic hazard exposure in coastal zones affected by sea-level rise and changing coastal storms. The modelling approach, presented in Part 1, downscales atmospheric global-scale projections to local scale coastal flood impacts by deterministically computing the combined hazards of sea-level rise, waves, storm surges, astronomic tides, fluvial discharges, and changes in shoreline positions. The method is demonstrated through an application to Southern California, United States, where the shoreline is a mix of bluffs, beaches, highly managed coastal communities, and infrastructure of high economic value. Results show that inclusion of 100-year projected coastal storms will increase flooding by 9–350% (an additional average 53.0 16.0 km2) in addition to a 25–500 cm sea-level rise. The greater flooding extents translate to a 55–110% increase in residential impact and a 40–90% increase in building replacement costs. To communicate hazards and ranges in socio-economic exposures to these hazards, a set of tools were collaboratively designed and tested with stakeholders and policy-makers; these tools consist of two web-based mapping and analytic applications as well as virtual reality visualizations. To reach a larger audience and enhance usability of the data, outreach and engagement included workshop-style trainings for targeted end-users and innovative applications of the virtual reality visualizations.

Projected Brackish Water Desalination Projects in California

California Department of Water Resources (DWR) | February 20th, 2024

California’s Water Supply Strategy: Adapting to a Hotter, Drier Future (Water Supply Strategy), adopted by the Newsom Administration in 2022, identifies multiple action

California’s Water Supply Strategy: Adapting to a Hotter, Drier Future (Water Supply Strategy), adopted by the Newsom Administration in 2022, identifies multiple actions necessary to bolster water supply reliability in the face of climate change. The first set of actions drive the development of new water supplies and set explicit goals for expanding the production of both recycled and desalinated water. Action 1.2 includes specific targets for expanded brackish water desalination: 28,000 acre-feet by 2030, and 84,000 acre-feet by 2040. The Water Supply Strategy identifies five steps toward achieving this goal.

Projected Changes in California’s Precipitation Intensity-Duration-Frequency Curves

California Public Utilities Commission (CPUC) | August 15th, 2018

Traditionally, infrastructure design and rainfall-triggered landslide models rely on the notion of stationarity, which assumes that the statistics of hydroclimati

Traditionally, infrastructure design and rainfall-triggered landslide models rely on the notion of stationarity, which assumes that the statistics of hydroclimatic extremes (e.g., rainfall, streamflow, etc.) do not change significantly over time. However, during the last century, we have observed a warming climate with more intense precipitation extremes in some regions, likely due to increases in the water holding capacity of the atmosphere. Consequently, infrastructure and natural slopes will likely face more severe climatic conditions, with potential human and socioeconomic consequences. Here, we outline a framework for quantifying climate change impacts on natural and man-made infrastructure using bias-corrected multi-model simulations of historical and projected precipitation extremes. The approach evaluates changes in rainfall intensity-duration- frequency (IDF) curves and their uncertainty bounds using a non-stationary model based on Bayesian inference. We show that highly populated areas across California may experience extreme precipitation that is more intense and twice as frequent, relative to historical records, despite the expectation of unchanged annual mean precipitation. Since IDF curves are widely used for infrastructure design and risk assessment, the proposed framework offers an avenue for assessing infrastructure resilience and landslide hazard in a warming climate.