The Sacramento Valley grows rice, tree nuts and fruits, tomatoes, alfalfa, and dozens of other crops. This region applies around 10,100 hm3 of water for irrigation of over 839,000 ha. The southern and larger part of the CV, the San Joaquin Valley , includes the San Joaquin River Basin with low average precipitation , and the Tulare Lake Basin with slightly more precipitation. The SJV has even more crop diversity than the north. It has experienced steady declines in field crops such as cotton, grains, and alfalfa that have been replaced by tree nuts. The SJV applies around 22,860 hm3 of water for irrigation of over 2 million ha. The west side of the southern SJV is affected by soil salinization due to the rising water table above the Corcoran clay layer and poor drainage . Water supplies for irrigation come from the Sierra Nevada and northern basins runoff delivered through local, state, and federal water projects as surface water and from local groundwater. The Sacramento River and the San Joaquin River basins drain to the Sacramento San Joaquin Delta , which also serves as the water supply hub agricultural and urban use in the SJV and some coastal areas. Coastal California. The south and central parts of the long coastal region, about 1,200 km from San Diego to Oregon, contain a series of relatively cool and agriculturally intensive valleys producing high revenue-per-ha crops such as citrus, avocados, berries, fresh vegetables, large square planting pots greenhouse and nursery crops, and high-priced wine grapes.
Coastal irrigation is mostly supplied by pumping from coastal aquifers and small surface water diversion projects. Annual precipitation in the Coastal hydrologic regions varies widely between 250 and 2,500 mm/y in the north coast, but with much lower average annual precipitation in the south coast . Similar to precipitation, mean annual temperatures are much more varied along the coast relative to the CV. The coastal counties account for about 25% of total farm revenue in California and apply roughly 3,500 hm3 of irrigation water over 543,000 ha. Southern California. The Southern California region consists of a significant and broad array of cropping systems and water sources and includes the counties of Los Angeles, Riverside, San Bernardino, San Diego, Orange, and Imperial. It overlaps with the southern portions of Coastal California. Nowhere in this region are the conflicts and possible consequences of climate change on irrigated agriculture more challenging than in the Imperial Valley, which borders Mexico to the south, Arizona to the east, and San Diego County to the west. While the region receives less than 75 mm/y of precipitation on average, senior water rights to the Colorado River coupled with an extended growing season and warm climate enable a diverse range of crops . Within Imperial County sit two of the most senior water rights holders for Colorado River water—the Imperial Irrigation District and the Palo Verde Irrigation District . Of the 5,400 hm3 California annual allocation Colorado River Compact, IID’s claim is 3,800 hm3 while PVID’s allocation is roughly 420 hm3 annually in applied water. The region also hosts the Salton Sea, the largest lake in California, a terminal hypersaline lake receding due to lower inflows.
First, warming influences the form of precipitation , and the rate and seasonality of mountain snow melt both of which affect the timing and intensity of runoff. Warming also constrains water supplies, increases water demands, and affects other biophysical components of crops. Third, climate change is also aggravating some of the entrenched conflicts between California’s agriculture and other sectors. And fourth, the climate vulnerability of California’s agriculture is also partly determined by evolving global market demand which is also affected by climate change. Effects of Climate-Related Stressors. Increase in temperatures and alteration of precipitation patterns, including the reduction of precipitation falling as snow, are having direct impacts on California agriculture. Sea-level rise and atmospheric carbon concentration may also affect water supplies and growing conditions and yields for some crops and regions . Increased evaporative demands. Higher temperatures and atmospheric moisture deficit may increase soil evaporation and crop irrigation requirements. This furthers the gap between water availability and demand contributing to increased scarcity. In California, reference evapotranspiration increased between 50 and 100 mm/y during the 1980 to 2020 period, with higher temperatures contributing more than 70% of the rise . During the 2022 drought, similar increases in annual ETo were estimated across the state due to antecedent dry soil conditions and a thirsty atmosphere . Higher crop water demands are expected to continue while warming persists, increasing the likelihood of evapotranspiration-induced droughts . Change in water availability. While California climate projections do not show a clear trend in average annual precipitation , the alteration of precipitation patterns—including precipitation volatility and rain/snow patterns—are affecting water supplies, particularly the seasonal availability. Precipitation volatility is causing more intense swings between dry and wet periods. Anthropogenic forcing is found to yield large twenty-first century increases in the frequency of wet extremes, and smaller but statistically robust increases in dry extremes . Given California’s reliance on large reservoir storage, this could result in less water available during the irrigation season as reservoirs would likely release more water during winter for flood protection. Recent studies highlight that the seasonal snow pack is receding considerably and will likely continue receding with warming .
The Sierra Nevada mountains function as a natural reservoir: They store water during winter and spring when reservoirs need to be partly empty for flood protection, and supply irrigation during the spring and summer, especially for the CV crops. By 2050, snow pack in the Sierra Nevada’s– which historically provides approximately 30% of California’s annual supply, is expected to decline by as much as 45% . With less snow and earlier melting, the function of the snow pack must change , and adaptation measures in the form of reservoir reoperation may reduce supply losses . Sea level rise. Rising sea levels are constraining water supplies in at least two ways. First, sea level rise may increase salinity in some areas of the SSJD, a hub from which California’s two major water projects pull supplies, compromising water deliveries to the south and creating water quality–driven deficits in supply for agriculture and cities . Second, in coastal areas that rely on groundwater for irrigation, sea level rise increases the risk of saline intrusion. This has already affected aquifers in the central and south coasts of California . Other climate effects on California’s crops. A complex crop pattern in California presents a challenge to predict future climate impacts on crop yields. Research suggests a potentially broad decline in the productivity of some specialty crops, including vines, nuts, and citrus . With the exception of alfalfa, declines in the yields of field crops will likely occur as well, particularly toward the end of the twenty-first century. Impacts of warmer climate, including fewer winter chill hours, may affect yields in tree crops . Conversely, some studies argue that higher atmospheric carbon concentrations may lead to increased yields in some crop varieties . Projected declines in crop yields have also been linked to new or more abundant pests, diseases, and invasive species in response to climate-related shifts in the resources, habitat, and ecological interactions that regulate their distribution, abundance, and behaviors . Increase in pest pressure, altered disease dynamics, and greater vulnerability of drought-stressed plants to pest and disease infections will further stress cropping systems, especially since over reliance on common biocides may result in ineffective pest control. Periodic crop failures or generally lower yields of specialty crops may also occur as rising temperatures and water limitations inhibit pollinator activity and synchrony of plant and pollinator life cycles . These impacts place additional importance on research and development to help California, and agricultural globally, plastic square planter pots adapt effectively to climate change through innovation. California Agriculture Conflicts with Other Sectors. Conflicts over water use are a global phenomenon, with recorded incidences dating back to 5000 BC . With climate change resulting in an increase in water scarcity such conflicts are likely to be exacerbated . Limiting conflict requires significant changes in governance and cooperation, which has been difficult to achieve. California’s water conflicts were immortalized in the 1974 movie, “Chinatown,” which provided a fictionalized account of the conflict involving the Los Angeles Department of Water and Power and Owens Valley ranchers in the early 20th century . Agriculture, municipal users and environmental demands have been in constant competition for increasingly scarce water. This is no surprise given that 40% of all water in California— and 80% of consumed water—is used by irrigated agriculture , percentages broadly consistent with irrigation use in other arid and semiarid regions globally . Conflict in two California regions stands out given the size of the agricultural industry and its historic water rights, and how water use and rights are at odds with environmental flows, municipal growth, and a better understanding of sustainable water availability. Central Valley. Agriculture and environment. Reduced water in streams due to increased diversions and degraded water quality from non-point source pollution have compromised water supplies for ecosystems and communities in California.
In the late 1960s, operation of the CVP and SWP made evident a sharp decline in native fish populations attributed to lower and quality-degraded stream flow . In response, regulations were developed requiring state and federal agencies to modify operations and set water quality standards to protect fish and wildlife, which decades later resulted in the CVP Improvement Act of 1992 . The tension between water quality protection and water allocation for users statewide, including in-Delta farming, persisted as higher SSJD outflows were accomplished by reducing SSJD upstream diversions and/or reducing SSJD exports south. These environmental conflicts with agricultural production, particularly over water use, will likely increase under climate change as drought intensity and frequency increase. Conflicts among agricultural-related sectors. As in other regions, periodic cuts in surface water access have been partially offset by increased groundwater pumping. In California, such drought-related increases in pumping added to the existing CV overdraft of roughly 2,000 hm3 per year. An increasing number of domestic wells have gone dry given rural communities well depths typically are not as deep as agricultural operators , disproportionately affecting disadvantaged rural communities, particularly in the SJV. In addition, degraded groundwater water quality due to nitrate contamination from fertilizer over application has further compromised safe drinking water supplies in many rural locations lacking economies of scale for adequate water treatment . The Sustainable Groundwater Management Act of 2014 mandated long-term reductions in consumptive groundwater use through locally developed groundwater sustainability plans. When coupled with the effects of environmental regulations and climate change, meeting these long-term reductions will necessarily mean less irrigated land with estimates ranging between 180 and 350 thousand fewer hectares . While SGMA does not require groundwater users meet sustainability plans until early 2040s, water restrictions over the last decade since SGMA passage highlight the challenges that will confront irrigated agricultural operators in the SJV. Continued irrigation of crops such as fruits, tree nuts, and vegetables during recent droughts has come at the expense of increased fallowing of field crops. Higher short-term net revenues per unit of water and the threat of significant loss in capital from not irrigating trees and vines underlie the economics of such decisions when water cuts are expected to be temporary. Despite these pressures, water-intensive forage crops, such as alfalfa hay and corn silage, continue in the SJV to feed the 90% of California’s dairy cows that reside there. Because of high transport cost per unit of value, much of the alfalfa hay and all the corn silage is grown near dairy farms even in areas with little to no access to surface water. These economic pressures from increased area of tree nut orchards and dairy forage demand have made meeting local groundwater sustainability in parts of the SJV especially challenging. Southern California. Agricultural and urban interactions. Colorado River water users are negotiating new water-sharing agreements that are intended to govern Colorado River operations and management beginning in 2026 and will likely result in reductions of lower Basin state allocations, including California’s, to bring the Basin back into long-term balance under climate change .