SATELLITE OBSERVATIONS OF GROUNDWATER DEPLETION IN THE WESTERN U. S. HIGHLIGHT THREATS TO WATER AND FOOD SECURITY

As the California drought enters its fourth year, and the western United States its fifteenth, groundwater resources are coming under increasing stress. As the traditional water supply strategic reserve in times of drought, groundwater is a critical element of resiliency and the ability to withstand prolonged, extremely dry conditions. In California for example, at the time of writing, groundwater is supplying 70% of statewide water supply.

In this presentation I review recent work using data from the NASA Gravity Recovery and Climate Experiment (GRACE) mission that characterizes drought and groundwater depletion throughout the region. Results from California's Central Valley and from the Colorado River Basin will be presented. We find that groundwater depletion is proceeding at unsustainable rates in both regions, in particular, during drought. Given uncertainties regarding the continuation of current drought conditions, coupled with expectations for more frequent drought conditions and population growth in the coming decades, implications for risks to the water security of the western United States are discussed.