Recovery of Hydrological Conditions in California: A GIS Case Study

California had been in a state of drought since 2011 until the spring of 2017, with a state of emergency causing water restrictions across the state since 2014. Per the U.S. Drought Monitor, 100% of the state was at least abnormally dry and 21% of the state was in exceptional drought conditions. That all changed during the winter of 2016-17, when the summer upper-level ridge broke down and precipitation returned to the state, effectively ending the drought as the state of emergency was lifted in April 2017. In order to determine how this alleviation occurred, NASA GES DISC data was used in GIS platforms to study the synoptic weather patterns, precipitation, soil moisture variables, and vegetation recovery from the fall of 2016 through January 2017. Namely, this study makes significant use of the MERRA-2 model and the GPM IMERG data to study how anomalous the rainfall was during this past winter, building a 30-year precipitation climatology from MERRA-2 in order to do so. Over the past 10 years, California and Nevada have cumulatively run a precipitation deficit of 781 mm/m2, which is more than a year’s worth of rain. During this last winter, precipitation was 21-28% above normal, allowing for the deficit to decrease by more than 100 mm/m2. GRACE satellite and model assimilation data show a robust recharge of soil moisture and groundwater throughout much of California through January 2017, allowing for a return of vegetation and normal irrigation practices during this growing season.