Priorities for California's Water: Responding to the Changing Climate

Public Policy Institute of California (PPIC) | November 18th, 2021

Water is central to how California adapts to a changing climate. To those of us steeped in the complexities of managing the state’s water resources, the current fast-mo

Water is central to how California adapts to a changing climate. To those of us steeped in the complexities of managing the state’s water resources, the current fast-moving drought—coming on the heels of the record-breaking 2012–16 drought—is a stark reminder that we must accelerate preparation for the disruptive changes underway. Californians have taken steps to address major threats to our water resources. But a recent IPCC report underscored that the climate is changing faster than anticipated, and that many of these changes are already locked in. Rising temperatures are making our winters shorter and our droughts more intense, outpacing our ability to manage water supplies and the natural environment. We need to act with urgency to adapt to these changes. And we need to rethink how we store water. This brief examines how the current drought and a changing climate are affecting California’s ability to manage water and lays out priority actions to address major challenges—including some urgent short-term actions should the drought continue into next year.

Priorities for California’s Water: Are We Ready for Climate Change?

Public Policy Institute of California (PPIC) | November 12th, 2024

California faces many immediate challenges around water management, but as the record-breaking heat of 2024 makes clear, temperatures are rising—and Californians are co

California faces many immediate challenges around water management, but as the record-breaking heat of 2024 makes clear, temperatures are rising—and Californians are contending with the consequences. In a PPIC poll earlier this year, residents named climate change, forest fires and wildfires, and water supply and drought as the most important environmental issues facing the state. 

Progressive forest canopy water loss during the 2012–2015 California drought

National Academy of Sciences (NAS) | December 28th, 2015

The 2012–2015 drought has left California with severely reduced snowpack, soil moisture, ground water, and reservoir stocks, but the impact of this estimated mi

The 2012–2015 drought has left California with severely reduced snowpack, soil moisture, ground water, and reservoir stocks, but the impact of this estimated millennial-scale event on forest health is unknown. We used airborne laser-guided spectroscopy and satel- lite-based models to assess losses in canopy water content of California’s forests between 2011 and 2015. Approximately 10.6 million ha of forest containing up to 888 million large trees experienced measurable loss in canopy water content during this drought period. Severe canopy water losses of greater than 30% occurred over 1 million ha, affecting up to 58 million large trees. Our measurements exclude forests affected by fire between 2011 and 2015. If drought conditions continue or reoccur, even with temporary reprieves such as El Niño, we predict substantial future forest change.

Projected U.S. drought extremes through the twenty-first century with vapor pressure deficit

Nature Portfolio (Springer Nature) | May 21st, 2022

Global warming is expected to enhance drought extremes in the United States throughout the twenty-first century. Projecting these changes can be complex in regions with

Global warming is expected to enhance drought extremes in the United States throughout the twenty-first century. Projecting these changes can be complex in regions with large variability in atmospheric and soil moisture on small spatial scales. Vapor Pressure Deficit (VPD) is a valuable measure of evaporative demand as moisture moves from the surface into the atmosphere and a dynamic measure of drought. Here, VPD is used to identify short-term drought with the Standardized VPD Drought Index (SVDI); and used to characterize future extreme droughts using grid-dependent stationary and non-stationary generalized extreme value (GEV) models, and a random sampling technique is developed to quantify multimodel uncertainties. The GEV analysis was performed with projections using the Weather Research and Forecasting model, downscaled from three Global Climate Models based on the Representative Concentration Pathway 8.5 for present, mid-century and late century. Results show the VPD based index (SVDI) accurately identifies the timing and magnitude short-term droughts, and extreme VPD is increasing across the United States and by the end of the twenty first century. The number of days VPD is above 9 kPa increases by 10 days along California’s coastline, 30–40 days in the northwest and Midwest, and 100 days in California’s Central Valley.

Prolonged California aridity linked to climate warming and Pacific sea surface temperature

Nature Portfolio (Springer Nature) | September 15th, 2016

California has experienced a dry 21st century capped by severe drought from 2012 through 2015 prompting questions about hydroclimatic sensitivity to anthropogen

California has experienced a dry 21st century capped by severe drought from 2012 through 2015 prompting questions about hydroclimatic sensitivity to anthropogenic climate change and implications for the future. We address these questions using a Holocene lake sediment record of hydrologic change from the Sierra Nevada Mountains coupled with marine sediment records from the Pacific. These data provide evidence of a persistent relationship between past climate warming, Pacific sea surface temperature (SST) shifts and centennial to millennial episodes of California aridity. The link is most evident during the thermal-maximum of the mid-Holocene (~8 to 3 ka; ka = 1,000 calendar years before present) and during the Medieval Climate Anomaly (MCA) (~1 ka to 0.7 ka). In both cases, climate warming corresponded with cooling of the eastern tropical Pacific despite differences in the factors producing increased radiative forcing. The magnitude of prolonged eastern Pacific cooling was modest, similar to observed La Niña excursions of 1o to 2 °C. Given differences with current radiative forcing it remains uncertain if the Pacific will react in a similar manner in the 21st century, but should it follow apparent past behavior more intense and prolonged aridity in California would result.

Public Update for Drought Response Groundwater Basins with Potential Water Shortages and Gaps in Groundwater Monitoring

California Department of Water Resources (DWR) | June 30th, 2014

Year 2013 closed as the driest in recorded history for many areas of California. On January 17, 2014, Governor Brown signed a Proclamation of a State of Emergency in resp

Year 2013 closed as the driest in recorded history for many areas of California. On January 17, 2014, Governor Brown signed a Proclamation of a State of Emergency in response to the drought. This Public Update addresses Order #11 of the Governor’s Proclamation and provides information regarding groundwater basins with potential water shortages and gaps in groundwater monitoring. Groundwater is a vital resource in California providing close to 60 percent of the state’s water supply in a dry year. Drought conditions typically result in an increase of groundwater well activity and pumping to compensate for water supply shortages. Increased groundwater pumping can lead to adverse conditions including dry wells, subsidence, decreased water quality, saline intrusion, and stream depletion. Evaluation of available data produced the following: Groundwater levels have decreased in nearly all areas of the state since spring 2013, and more notably since spring 2010. Since spring 2008, groundwater levels have experienced all-time historical lows (for period of record) in most areas of the state and especially in the northern portion of the San Francisco Bay Hydrologic Region, the southern San Joaquin Valley, and also for the South Lahontan and South Coast hydrologic regions. In many areas of the San Joaquin Valley, recent groundwater levels are more than 100 feet below previous historical lows. The greatest concentration of recently deepened wells is in the fractured bedrock foothill areas of Nevada, Placer, and El Dorado counties. The Kaweah and Kings subbasins have the greatest numbers of deepened wells in an alluvial groundwater basin. Thirty-six alluvial groundwater basins that have a high degree of groundwater use and reliance may possess greater potential to incur water shortages as a result of drought. The basins exist in the North Coast, Central Coast, Sacramento River, Tulare Lake, and South Coast hydrologic regions. Of California’s 515 alluvial groundwater basins, 169 are fully or partially monitored under the California Statewide Groundwater Elevation Monitoring (CASGEM) Program. Forty of the 126 High and Medium priority basins are not monitored under CASGEM. There are significant CASGEM groundwater monitoring data gaps in the Sacramento, San Joaquin River, Tulare Lake, Central Coast, and South Lahontan hydrologic regions. Although there are 4,122 CASGEM wells and 39,429 Voluntary wells in the Water Data Library groundwater level database, gaps in groundwater monitoring persist. Several areas of the state lack a current groundwater management plan that addresses all related requirements of the California Water Code. DWR is contracting with National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory for use of satellite-based radar data to measure subsidence in the Sacramento and San Joaquin valleys. NASA, the U.S. Geological Survey, and U.S. Department of Agriculture are developing an automated system for estimating fallowed agricultural acreage.

Public Update for Drought Response: Groundwater Basins with Potential Water Shortages, Gaps in Groundwater Monitoring, Monitoring of Land Subsidence, and Agricultural Land Fallowing

California Department of Water Resources (DWR) | November 25th, 2014

California’s Water Year 2014 (October 1, 2013 through September 30, 2014) was one of the driest in decades and followed two consecutive dry years throughout the state.

California’s Water Year 2014 (October 1, 2013 through September 30, 2014) was one of the driest in decades and followed two consecutive dry years throughout the state. Water year 2014 was the fourth driest year on record after 1924, 1931, and 1977, based on the Sacramento Valley water year index, and the second driest year on record after 1977, based on the San Joaquin Valley water year index. On January 17, 2014, Governor Brown signed a Proclamation of a State of Emergency in response to the drought. In accordance with the proclamation, the Department of Water Resources (DWR) prepared Public Update for Drought Response, Groundwater Basins with Potential Water Shortages and Gaps in Groundwater Monitoring, dated April 30, 2014. On April 25, 2014, the governor issued a second emergency proclamation to strengthen the state’s ability to manage water and habitat effectively in drought conditions and called on all Californians to redouble their efforts to conserve water. In accordance with Order #11 of the April proclamation, this report provides additional and expanded information on groundwater basins with potential water shortages, gaps in groundwater monitoring, monitoring of land subsidence, and agricultural land fallowing.

Quantification Settlement Agreement and Related Agreements and Documents to which Southern California Agencies are Signatories

California Natural Resources Agency (CNRA) | October 10th, 2003

Rapid vegetation redistribution in Southern California during the early 2000s drought

American Geophysical Union (AGU) | August 31st, 2012

Climate change in semi-arid, midlatitude mountain environments is expected to shift the spatial patterns of temperature, water availability, and vegetation upslope. Veg

Climate change in semi-arid, midlatitude mountain environments is expected to shift the spatial patterns of temperature, water availability, and vegetation upslope. Vegetation growing near its low-elevation range limit may prove especially vulnerable to mortality and decline. We investigated the altitudinal pattern of conifer mortality that occurred from 2002 to 2004 in Southern California’s San Jacinto Mountains. We found that conifer mortality was focused in the lower portion of the midmontane conifer range, which drove the midmontane conifer distribution upslope. We investigated past reports of conifer mortality in Southern California by searching historical newspaper accounts. We found evidence of previous episodes of conifer mortality that coincided with past droughts, and which may have caused vegetation redistribution in the past. We interpret the early2000s mortality and associated vegetation redistribution as a response to natural decadal tocentennial climate variability. Moreover, we hypothesize this response mode will dominatethe early impact of global climate change on semi-arid forest, which, in turn, may complicate efforts to distinguish between ecological changes attributable to natural climate variability and those attributable to global climate change.

Recent California Water Transfers: Implications for Water Management

Natural Resources Journal (University of New Mexico) | December 1st, 1995

The 1991 and 1992 California Drought Emergency Water Banks were the first large water transfer programs in the nation in which the State served as the predominant

The 1991 and 1992 California Drought Emergency Water Banks were the first large water transfer programs in the nation in which the State served as the predominant broker for water trades. Although the State-sponsored Water Banks have drawn widespread attention, there have been a great number of water transfers and exchanges taking place in California independently of the State. These non-State transfers illustrate well the widespread applicability of transfers in managing water resource systems, as well as the multiple mechanisms available for effecting water transfers. This paper focuses on California's recent experiences with water transfers, and offers a series of potential lessons for federal, state, and local managers for integrating water transfers in regional water resource systems.