California droughts

California droughts
Name	California droughts

Contents

California droughts are recurring prolonged periods of below-average precipitation affecting California and adjacent regions. They influence urban water supplies, agricultural production, and natural ecosystems across the Central Valley, Sierra Nevada, and Southern California. These events intersect with federal and state institutions, shaping responses by bodies such as the California Department of Water Resources, United States Bureau of Reclamation, and the Federal Emergency Management Agency.

Overview and Definition

Drought in California is typically defined through hydrological, agricultural, and socio-economic indicators measured by agencies like the National Oceanic and Atmospheric Administration, United States Geological Survey, and the California Natural Resources Agency. Standard metrics include snowpack in the Sierra Nevada, reservoir storage at Shasta Lake and Lake Oroville, streamflow in the Sacramento River and San Joaquin River, and indices developed by the United States Drought Monitor and the North American Drought Monitor. Legal and policy definitions appear in statutes administered by the California State Water Resources Control Board and the California Energy Commission.

Notable drought episodes include the early 20th‑century droughts documented during the era of the Los Angeles Aqueduct expansion and the 1928–34 events that preceded the construction of projects like the Central Valley Project and the California State Water Project. The 1976–77 drought prompted emergency declarations involving the National Guard (United States) and influenced legislation such as state water allocations overseen by the California Legislature. The 1987–92 drought and the 2007–09 drought stressed institutions including the Metropolitan Water District of Southern California and prompted water transfers among districts like the Santa Clara Valley Water District and the Contra Costa Water District. The severe 2012–2016 drought led to statewide emergency proclamations from the Governor of California and regulatory actions by the State Water Resources Control Board; it also affected infrastructure projects such as the Delta–Mendota Canal and spurred litigation in courts including the California Supreme Court. The multi-year 2020s drought coincided with wildfire seasons involving agencies like the United States Forest Service and influenced federal legislation debated in the United States Congress.

Droughts arise from interactions among atmospheric patterns such as the El Niño–Southern Oscillation, the Pacific Decadal Oscillation, and persistent high‑pressure ridging linked to the North Pacific High. Anthropogenic warming associated with international efforts tracked by bodies like the Intergovernmental Panel on Climate Change amplifies evaporative demand and reduces Sierra Nevada snowpack relative to historical baselines used in studies by the Lawrence Berkeley National Laboratory and the Scripps Institution of Oceanography. Land‑use changes across the Central Valley—including expansion of irrigated acreage by entities such as the Imperial Irrigation District—and transbasin diversions like the Los Angeles Aqueduct alter hydrologic response and water availability. Teleconnections involving the Arctic Oscillation and atmospheric rivers originating near the North Pacific Ocean also modulate seasonal precipitation.

Drought reduces storage in reservoirs such as Folsom Lake and Millerton Lake, constrains allocations from the State Water Project and the Central Valley Project, and forces operational changes at facilities like the Oroville Dam. Agricultural impacts are concentrated in counties such as Fresno County, Kern County, and Imperial County where growers organized through associations like the California Farm Bureau Federation and the Western Growers Association adjust cropping and groundwater pumping. Ecosystems affected include the Sacramento–San Joaquin Delta, riparian corridors supporting species like the Delta smelt and Chinook salmon, and forests managed by the California Department of Forestry and Fire Protection. Economic sectors dependent on water—wine regions in Napa Valley and California's Central Coast, municipal utilities such as the San Francisco Public Utilities Commission, and hydropower generation at facilities operated by the California Independent System Operator—face revenue and reliability challenges.

Responses have combined supply projects, demand management, and regulatory reform. Infrastructure initiatives include reservoirs, groundwater banking programs in basins overseen by the California Department of Water Resources, and interties operated by agencies like the Metropolitan Water District of Southern California. Groundwater regulation under the Sustainable Groundwater Management Act and conservation mandates enforced by the State Water Resources Control Board aim to reduce overdraft in basins such as the San Joaquin Valley. Market mechanisms including water markets and transfers among entities like the Semitropic Water Storage District and the Turlock Irrigation District provide reallocation tools. Emergency measures have included voluntary and mandatory urban conservation directed by municipal bodies like the Los Angeles Department of Water and Power and federal assistance coordinated with the United States Department of Agriculture.

Monitoring relies on networks operated by the National Weather Service, the California Data Exchange Center, and satellite missions such as those run by NASA and the European Space Agency. Hydrologic and climate modeling is advanced by universities and laboratories including the University of California, Berkeley, California Institute of Technology, Stanford University, and the Pacific Institute. Scenario projections in reports by the Intergovernmental Panel on Climate Change and the California Energy Commission indicate increased frequency of extreme drought combined with shifts from snow to rain that affect reservoir operations. Adaptive planning tools used by agencies like the California Natural Resources Agency incorporate ensemble modeling, paleoclimate reconstructions from the U.S. Geological Survey, and stakeholder processes involving municipal water suppliers and agricultural districts.

Category:Climate of California Category:Water resource management in California