Water shortage risks from perennial crop expansion in California’s Central Valley

Abstract

California's Central Valley is one of the world's most productive agricultural regions. Its high-value fruit, vegetable, and nut crops rely on surface water imports from a vast network of reservoirs and canals as well as groundwater, which has been substantially overdrafted to support irrigation. The region has undergone a shift to perennial (tree and vine) crops in recent decades, which has increased water demand amid a series of severe droughts and emerging regulations on groundwater pumping. This study quantifies the expansion of perennial crops in the Tulare Lake Basin, the southern region of the Central Valley with limited natural water availability. A gridded crop type dataset is compiled on a 1 mi 2 spatial resolution from a historical database of pesticide permits over the period 1974-2016 and validated against aggregated county-level data. This spatial dataset is then analyzed by irrigation district, the primary spatial scale at which surface water supplies are determined, to identify trends in planting decisions and agricultural water demand over time. Perennial crop acreage has nearly tripled over this period, and currently accounts for roughly 60% of planted area and 80% of annual revenue. These trends show little relationship with water availability and have been driven primarily by market demand. From this data, we focus on the increasing minimum irrigation needs each year to sustain perennial crops. Results indicate that under a range of plausible future regulations on groundwater pumping ranging from 10% to 50%, water supplies may fail to consistently meet demands, increasing losses by up to 30% of annual revenues. More broadly, the datasets developed in this work will support the development of dynamic models of the integrated water-agriculture system under uncertain climate and regulatory changes to understand the combined impacts of water supply shortages and intensifying irrigation demand.

Wetland Conservation: Challenges Related to Water Law and Farm Policy

“…Corn, hay (including but not limited to alfalfa), soybeans, cotton, rice and wheat dominate water use of crops in the U.S. (Marston et al 2018), but locally pecans, almonds, alfalfa, or other crops can dominate local and regional water consumption, which emphasizes the need to develop local solutions to water shortages. For example, annual water requirements of perennial nut crops can put more stress on water resources than annual crops (Mall and Herman 2019) and limit drought management options (Johnson and Cody 2015;Mall and Herman 2019). As noted by Richter et al (2020a), alfalfa accounts for a disproportionate amount of water use in the west and a reduction in this crop can be a key component of water savings strategies.…”

Toward Data‐Driven Generation and Evaluation of Model Structure for Integrated Representations of Human Behavior in Water Resources Systems

“… Historical change in crop type in the Tulare Basin, California from 1974 to 2016. Each spatial location is 1 mi 2 , and tree crops are defined as in Mall and Herman (2019). The gray lines indicate county boundaries within which crop prices are reported annually.…”

California's food-energy-water system: An open source simulation model of adaptive surface and groundwater management in the Central Valley

“…where X2 = delta 'X2' salinity line (km) (CADWR, 2018;ID4, 2018). Land cover data is determined based on crop types described in historic pesticide permitting data (Mall and Herman, 2019) or listed in agricultural water management plans, aggregated by irrigation district. Daily consumptive demands are calculated by applying expected seasonal ET requirements (ITRC, 2003) to the total crop acreage, by district, such that:…”