Ecosystem Services Mapping for Sustainable Agricultural Water Management in California's Central Valley

Accurate information on agricultural water needs and withdrawals at appropriate spatial and temporal scales remains a key limitation to joint water and land management decision-making. We use InVEST ecosystem service mapping to estimate water yield and water consumption as functions of land use in Fresno County, a key farming region in California's Central Valley. Our calculations show that in recent years (2010-2015), the total annual water yield for the county has varied dramatically from ∼0.97 to 5.37 km³ (all ±17%; 1 MAF ≈ 1.233 km³), while total annual water consumption has changed over a smaller range, from ∼3.37 to ∼3.98 km³ (±20%). Almost all of the county's water consumption (∼96% of total use) takes place in Fresno's croplands, with discrepancy between local annual surface water yields and crop needs met by surface water allocations from outside the county and, to a much greater extent, private groundwater irrigation. Our estimates thus bound the amount of groundwater needed to supplement consumption each year (∼1.76 km³ on average). These results, combined with trends away from field crops and toward orchards and vineyards, suggest that Fresno's land and water management have become increasingly disconnected in recent years, with the harvested area being less available as an adaptive margin to hydrological stress.