Aquifer Response Lag to Meteorological Droughts from GRACE Satellites

Climate change increases the probability of drought occurrence in many parts of the United States and worldwide. Aquifer response to these drought events vary in space and time. This project seeks to understand the response of aquifers to drought events by quantifying the lag time between meteorological droughts and groundwater droughts using the Standardized Precipitation and Evapotranspiration Index (SPEI) and Gravity Recovery and Climate Experiment (GRACE) derived groundwater storage anomalies. Ten major aquifer systems in the continental United States were selected for analysis: Columbia Plateau, Arizona Alluvial, Snake River Basin, Upper Colorado, Pennsylvanian, Mississippi Embayment, Texas Gulf Coast, Edwards-Trinity Plateau, Floridian, Central California, and the High Plains Aquifer Systems. Groundwater storage anomaly data was derived from GRACE total water storage anomaly data by removing all other hydrologic components using the Global Land Data Assimilation System’s (GLDAS) Community Land Surface Model (CLM) of 1.0-degree spatial resolution monthly datasets. Timeseries on monthly intervals for both the derived groundwater storage and SPEI were created for the period of April 2002 to June 2021. Each selected aquifer system had a meteorological drought occur at least three times during the study period, with a maximum occurrence of fifteen in central California. There is a temporal gap in between the original GRACE mission and the launch of GRACE-Follow on (GRACE-FO) from June 2017 to June 2018, five of the ten selected aquifers had meteorological droughts occur in this gap, which have been excluded. Preliminary results indicate that the lag time between the start of the two types of droughts for these aquifer systems is between zero and one month, while the lag time between the end of these types of droughts is more widely varied, between zero and eight months. As these results are varied, contextualizing them with more in-depth looks at the aquifer system characteristics is important and is the next step in furthering our understanding of aquifer responses to the increasing number of probable drought events.