Simulating the Impact of Drought on California’s Central Valley Hydrology, Groundwater and Cropping

This paper describes an efficient methodology to link a comprehensive, distributed hydrologic model for California’s Central Valley to a crop production model. The resulting hydro-economic model allows for the dynamic calculation of crop acreages in response to water availability without simplifying groundwater or stream flow dynamics by the assumption of linearity or by resorting to a lumped-parameter approach.
The linked hydro-economic model is used to simulate the effects of several drought scenarios on Central Valley’s agriculture and the groundwater resources. The drought scenarios are constructed as surface flow reductions that range from 30% to 70% for periods spanning from 10 to 60 years, with a 10-year spin-up and a 30-year recovery. The main finding is that Central Valley agriculture as a whole is resilient to severe drought. Despite an almost 40% cut in surface water deliveries for irrigation, the region suffers only a 10% cut in irrigated crop acres. However, after 60 critically dry years in a row, the linked model suggests that there will be regional impacts, including moderate impacts in the north Central Valley (Sacramento River Basin), locally severe in the middle of the Valley (San Joaquin River Basin), and severe in the south (Tulare Basin). The model runs indicate that extensive pumping during such a drought can cause permanent subsidence and may lead to new equilibrium groundwater levels.