Moving Toward a Multi-Benefit Approach for Water Management

Pacific Institute | April 11th, 2019

There is broad recognition that adapting to climate change, coupled with the need to address aging infrastructure, population growth, and degraded ecosystems, will re

There is broad recognition that adapting to climate change, coupled with the need to address aging infrastructure, population growth, and degraded ecosystems, will require rethinking programs and policies and investing in our natural and built water systems. There are a variety of strategies for addressing water challenges, from watershed restoration and efficiency improvements to vegetated swales and green roofs. Because water is deeply linked with economic, environmental, and community wellbeing, many of these strategies can also provide other benefits, such as reducing energy use and greenhouse gas emissions, providing wildlife habitat, and enhancing community livability.

Multi-century reconstructions of temperature, precipitation, and runoff efficiency for the Upper Colorado River Basin

U.S. Geological Survey (USGS) | January 27th, 2017

With increasing concerns about the impact of warming temperatures on water resources, more attention is being paid the relationship between runoff and preci

With increasing concerns about the impact of warming temperatures on water resources, more attention is being paid the relationship between runoff and precipitation, or runoff efficiency. Temperature is a key influence on Colorado River runoff efficiency, and warming temperatures are projected to reduce runoff efficiency. Here, we investigate the nature of runoff efficiency in the upper Colorado River (UCRB) basin over the past 400 years, with a specific focus on major droughts and pluvials, and to contextualize the instrumental period. We first verify the feasibility of reconstructing runoff efficiency from tree-ring data. The reconstruction is then used to evaluate variability in runoff efficiency over periods of high and low flow, and its correspondence to a reconstruction of late runoff season UCRB temperature variability. Results indicate that runoff efficiency has played a consistent role in modulating the relationship between precipitation and streamflow over past centuries, and that temperature has likely been the key control. While negative runoff efficiency is most common during dry periods, and positive runoff efficiency during wet years, there are some instances of positive runoff efficiency moderating the impact of precipitation deficits on streamflow. Compared to past centuries, the 20th century has experienced twice as many high flow years with negative runoff efficiency, likely due to warm temperatures. These results suggest warming temperatures will continue to impact runoff efficiency in wet or dry years, and that future flows will be less than anticipated from precipitation due to warming temperatures.

Municipal Recycled Water (Resource Management Strategy)

California Department of Water Resources (DWR) | July 29th, 2016

California is increasing its integration of municipal recycled water into its water supply portfolio. In some regions of the state, recycled water meets approximately 7 p

California is increasing its integration of municipal recycled water into its water supply portfolio. In some regions of the state, recycled water meets approximately 7 percent of water supply demands. Although the statewide total is an increase since California Water Plan Update 2009 (Update 2009) was released, it is still far short of previously established goals. Municipal recycled water benefits the state and individual water users by reducing long-distance water conveyance needs, providing local water supplies, and being a drought-resistant resource. This resource management strategy report will describe the current status of recycled water in California, what some of the challenges are to its increasing use, and the resources needed to continue to increase municipal recycled water use.

Municipal Service Review and Sphere of Influence Update for the Orange County Water District Including a Feasibility Analysis of the Potential Consolidation of Orange County Water District and Municipal Water District of Orange County

Local Agency Formation Commission of Orange County | November 15th, 2024

Navigating Transformations in 2023: The Metropolitan Water District of Southern California Year in Review

Metropolitan Water District of Southern California (MWD) | April 13th, 2024

New Sources for California’s Water Supply

State of California | March 1st, 2016

The Assembly Select Committee on Water Consumption and Alternative Sources was established in February 2015 to examine the strategies California could take to improve wat

The Assembly Select Committee on Water Consumption and Alternative Sources was established in February 2015 to examine the strategies California could take to improve water conservation and expand the portfolio of water sources. Given that California rose to the challenge of conservation, the committee turned its attention to alternative water source strategies such as stormwater capture, ocean desalination and water recycling, holding specific hearings to discuss the latter two in greater detail. This report is the culmination of several hearings held across the state on issues of water use and opportunities for expanding water sources. It includes summaries of expert testimony at those hearings, including illustrative slides from their presentations, as well as a list of key findings and recommendations compiled by committee staff and approved by the Chair. These findings and recommendations were not voted on by members of the Select Committee and may not reflect the view of each Select Committee member. This report is meant to provide knowledge regarding California’s drought, climate change future, and viability of water sourcing strategies including stormwater capture, water recycling and desalination. This knowledge will be essential in adapting California’s water infrastructure to climate changes and devising the most effective and environmentally friendly approach to endure the next California drought.

Nonstationarity in the global terrestrial water cycle and its interlinkages in the Anthropocene

National Academy of Sciences (NAS) | October 28th, 2024

Climate change and human activities alter the global freshwater cycle, causing nonstationary processes as its distribution shifting over time, yet a comprehensive underst

Climate change and human activities alter the global freshwater cycle, causing nonstationary processes as its distribution shifting over time, yet a comprehensive understanding of these changes remains elusive. Here, we develop a remote sensing–informed terrestrial reanalysis and assess the nonstationarity of and interconnections among global water cycle components from 2003 to 2020. We highlight 20 hotspot regions where terrestrial water storage exhibits strong nonstationarity, impacting 35% of the global population and 45% of the area covered by irrigated agriculture. Emerging long-term trends dominate the most often (48.2%), followed by seasonal shifts (32.8%) and changes in extremes (19%). Notably, in mid-latitudes, this encompasses 34% of Asia and 27% of North America. The patterns of nonstationarity and their dominant types differ across other water cycle components, including precipitation, evapotranspiration, runoff, and gross primary production. These differences also manifest uniquely across hotspot regions, illustrating the intricate ways in which each component responds to climate change and human water management. Our findings emphasize the importance of considering nonstationarity when assessing water cycle information toward the development of strategies for sustainable water resource usage, enhancing resilience to extreme events, and effectively addressing other challenges associated with climate change. Click here for a plain language summary from NASA.

Observational evidence of increased afternoon rainfall downwind of irrigated areas

Nature Portfolio (Springer Nature) | April 10th, 2025

Irrigation plays a vital role in addressing the growing food demand of an increasing global population. It represents one of the most critical and direct human interventi

Irrigation plays a vital role in addressing the growing food demand of an increasing global population. It represents one of the most critical and direct human interventions on the coupled water and energy cycles. As irrigated farmland continues to expand, understanding the climate impact of extensive irrigation becomes increasingly important. Yet, the effect on rainfall patterns near irrigated areas remains unclear. Here, using two global, high-resolution, sub-daily precipitation datasets, we show that afternoon rain events occur more often 10 km to 50 km downwind and less often upwind of extensively irrigated land. However, we also find that the total amount of heavy afternoon rain downwind of irrigated areas is lower than upwind. Our results establish large-scale observational evidence of the local precipitation dynamics surrounding irrigated areas; these insights will help constrain the representation of these processes in next-generation climate and weather forecasting models and provide valuable insights for regional water management.

Observed and projected changes in snow accumulation and snowline in California’s snowy mountains

Climate Dynamics (Springer) | May 25th, 2023

The Sierra Nevada and Southern Cascades—California’s snowy mountains—are primary freshwater sources and natural reservoirs for the states of California and Nevada.

The Sierra Nevada and Southern Cascades—California’s snowy mountains—are primary freshwater sources and natural reservoirs for the states of California and Nevada. These mountains receive precipitation overwhelmingly from wintertime storms including atmospheric rivers (ARs), much of it falling as snow at the higher elevations. Using a seven-decade record of daily observed temperature and precipitation as well as a snow reanalysis and downscaled climate projections, we documented historical and future changes in snow accumulation and snowlines. In four key subregions of California’s snowy mountains, we quantified the progressing contribution of ARs and non-AR storms to the evolving and projected snow accumulation and snowlines (elevation of the snow-to-rain transition), exploring their climatology, variability and trends. Historically, snow makes up roughly a third of the precipitation affecting California’s mountains. While ARs make up only a quarter of all precipitating days and, due to their relative warmth, produce snowlines higher than do other storms, they contribute over 40% of the total seasonal snow. Under projected unabated warming, snow accumulation would decline to less than half of historical by the late twenty-first century, with the greatest snow loss at mid elevations (from 1500 to 3300 m by the mountain sub-regions) during fall and spring. Central and Southern Sierra Nevada peaks above 3400 m might see occasionally extreme snow accumulations in January–February resulting entirely from wetter ARs. AR-related snowlines are projected to increase by more than 700 m, compared to about 500 m for other storms. We discuss likely impacts of the changing climate for water resources as well as for winter recreation.

Observed increasing water constraint on vegetation growth over the last three decades

Nature Portfolio (Springer Nature) | June 18th, 2021

Despite the growing interest in predicting global and regional trends in vegetation productivity in response to a changing climate, changes in water constraint on vegetat

Despite the growing interest in predicting global and regional trends in vegetation productivity in response to a changing climate, changes in water constraint on vegetation productivity (i.e., water limitations on vegetation growth) remain poorly understood. Here we conduct a comprehensive evaluation of changes in water constraint on vegetation growth in the extratropical Northern Hemisphere between 1982 and 2015. We document a significant increase in vegetation water constraint over this period. Remarkably divergent trends were found with vegetation water deficit areas significantly expanding, and water surplus areas significantly shrinking. The increase in water constraints associated with water deficit was also consistent with a decreasing response time to water scarcity, suggesting a stronger susceptibility of vegetation to drought. We also observed shortened water surplus period for water surplus areas, suggesting a shortened exposure to water surplus associated with humid conditions. These observed changes were found to be attributable to trends in temperature, solar radiation, precipitation, and atmospheric CO2. Our findings highlight the need for a more explicit consideration of the influence of water constraints on regional and global vegetation under a warming climate.