by José M. Rodríguez-Flores, Spencer A. Cole, Alexander Guzman, Josué Medellín-Azuara, Jay R. Lund, Daniel A. Sumner

California’s Central Valley is the source of more than $30 billion of farm value. It produces more milk than any state outside California, and dominates national production of dozens of fruits, vegetables, tree nuts and rice. The valley has two main parts: the Sacramento Valley (north) and the San Joaquin Valley (south); each has particular distinguishing agricultural features (such as soil, hydrology, climate, and economy) that have driven how agriculture and water infrastructure have developed. This post reviews the evolution of the major crops and crop categories produced in the Central Valley of California from 1990 to 2019.

Figure 1 shows cropland use in the Sacramento Valley across three decades. Rice acreage has covered about half of the land used for crops in the valley for many decades. The price and yield of rice have been relatively stable in this period, and acreage has temporarily declined mainly during severe drought periods.  Figure 1 shows sharp drought declines in rice harvested area, such as in the early 1990s and the 2013-2015 period, which recovers with water availability in wetter years. Three decades ago, other grains were second to rice in land use, but now nut crops mainly walnuts, have more acreage than the grain crops. There has been an upward trend in more profitable tree nut crops such as almonds, pistachios and walnuts since the early 2010s, even during the 2012-2016 drought. These perennial crops have shown technology-driven increases in yields and higher prices in the last ten years, but are somewhat more water intensive (requiring 3 to 4 acre-feet per acre) and allow much less flexibility in water use from year to year.

In the San Joaquin Valley (SJV) almonds, pistachios, and walnuts are currently among the dominant commodities by acreage (Figure 2) and production value. These crops now cover over 50% of total irrigated area in the SJV, where Fresno and Kern counties are the main almond producers. Cotton was the most planted single commodity for during the middle of the 20th century in the southern SJV until its production began a sharp decline in the 1990’s as subsidies were reduced and nut acreage began its rapid expansion. Miscellaneous vegetables, melons, tomatoes, fruit and hay and other field crops make up most remaining crops, with their acreages also declining in the last decade.

The crop mix in the SJV has changed with expected future crop demands, relative prices, production costs, and water conditions. For example, alfalfa acreage declined steadily since 2009 because of lack of growth in the California dairy industry, and low returns relative to tree nuts and some annual crops such as tomatoes. The San Joaquin Valley is now dominated by tree nut crops, that climate-limited ranges which align with California’s Central Valley climate.

Central Valley agriculture is supported by California’s array of intertied water supply infrastructure, including surface and groundwater storage, and conveyance, which provides a delivery system for perennial crops with inflexible water demands over the growing season and from year to year. These factors, along with significant long-term improvements in crop yields for several crops and higher expected prices, have encouraged expansive growth in almonds, pistachios, and walnuts.

In dry periods, cropping decisions are limited by water availability and sometimes increased water costs from transfers or groundwater pumping. Apart from old tree removals, acreages of perennial crops (tree nuts, grapes, and citrus trees) remain roughly constant during droughts due to high upfront costs involved in cultivation and higher revenue per harvested acre or acre-foot of water. Most land use reductions occur in crops with more flexibility and for which net return per unit of water is relatively low such as grain, hay and other field crops.

Almonds, pistachios and walnuts grew substantially even in the 2012-2016 drought due in part to high prices and continued expectations of high future prices which outweighed costs of water limitations and concerns about future water access. With the Groundwater Sustainability Plans (GSPs) required by the 2014 Sustainable Groundwater Management Act, some orchard retirement to cope with water scarcity may become a more frequent drought adaptation tool as GSP mandated cutbacks represent a longterm reality in many sub-regions.. For example, corn grown for silage might be expected fall severely in dry periods, but actually maintained substantial acreage in recent droughts because of its key role in local dairy rations and because it is too expensive per unit of value of haul more than 50 miles or so. Corn acreage provides a useful area to spread cow manure, which is unsuitable to distribute through drip fertigation systems. In contrast, alfalfa, which is also water intensive and typically used as a dry roughage feed crop, saw a downward trend in acreage during droughts (Figure 2) as has been regularly shipped into the San Joaquin Valley from Northern California and other states. Alfalfa hay can also use reduced water in drought years at the expense of fewer cuttings and therefore lower yields per acre.

Historically, cropping decisions differ between the Sacramento Valley, where rice production in the north declines somewhat and in the San Joaquin Calley, where hay, corn silage, grain and cotton decline when water is scarce. While many Groundwater Sustainability Agencies have not yet fully implemented groundwater use limitations, such reductions will be a major part of a portfolio of water management actions to achieve local and regional balances in abstraction and recharge by 2040.

Readers interested in visualizing and downloading DWR data on historical water and cropland use and County Agricultural Commissioners’ Report data on crop prices, land use, crop yield and production value, visit the UC Merced – Water Systems Management Lab website in the agricultural data section: https://wsm.ucmerced.edu/agricultural-data/.

Further reading

Hanak, E., Jezdimirovic, J., Green, S. & Escriva-Bou, A. “Replenishing Groundwater in the San Joaquin Valley”. (2018).

Hanak, E. et al. “Water and the Future of the San Joaquin Valley” (2019).

Lund, J., Medellin-Azuara, J., Durand, J. & Stone, K. “Lessons from California’s 2012–2016 Drought”. J. Water Resour. Plan. Manag. 144, 04018067 (2018).

Mall, N. K. & Herman, J. D. “Water shortage risks from perennial crop expansion in California’s Central Valley”. Environ. Res. Lett. 14, 104014 (2019).

Lund J. “Why California’s agriculture needs groundwater management” California WaterBlog. (May 26, 2014).           

Josué Medellín-Azuara and Jay Lund,“Jobs and Irrigation during Drought in California”.  California WaterBlog. (June 6, 2021)

José M. Rodríguez-Flores and Spencer A. Cole  are respectively Ph.D. candidate and M.S. student at the Environmental Systems graduate program at UC Merced, Alexander Guzman is a former Junior Research Specialist and Lab Manager of the Water Systems Management Lab at UC Merced, Josué Medellín-Azuara is an associate professor at the Department of Civil and Environmental Engineering at UC Merced, and an associate director at the UC Davis Center for Watershed Sciences, Jay R. Lund is a Professor of Civil and Environmental Engineering at UC Davis, where he is also Co-Director for UC Davis Center for Watershed Sciences, Daniel A. Sumner is the Frank H. Buck Jr. Distinguished Professor in the Department of Agricultural and Resource Economics at UC Davis.