Irrigation system for Delta field. Photo: Amber Manfree
Rain or shine, farmers in California use about the same amount of water every year, while residential water use varies considerably with precipitation.
A research team led by UC San Diego’s John Helly processed 15 years’ worth of water-use data from the state’s Department of Water Resources, reporting in the March 2022
issue of San Francisco Estuary and Watershed Science
that while “the annually precipitated water supply in the Bay-Delta” varied by 30%, agricultural water use scarcely changed year to year. “The water management system maintained nearly constant agricultural water use even in periods of intense drought, with year-to-year variation of about 7%,” the authors wrote. Residential water use showed more variability, swinging by 20% from one year to the next--mainly, the authors theorize, as the result of voluntary and mandated water conservation during droughts. Though Helly says he had no expectations of what his data analysis would find, he says “it makes sense” that agricultural swings in water use are less extreme than residential ebbs and flows. Long-term financial investments in water-intensive crops, he suggests, could motivate farmers to do everything in their power--like drilling deeper wells when necessary--to minimize annual variation in water flow. “Farms seem to use as much water as they can get, probably because they have a lot invested in their industry, whereas urban areas have more flexibility to conserve during droughts,” Helly says. He is now planning a follow-up study of how the water balance in California is affected by human behavior and land use.