Did the Southwest US aquifer-systems recover from the 2012-2015 drought? Insight from InSAR, GRACE and groundwater level data

The Southwest US is home to several significant metropolitans and agricultural hubs, including Phoenix and Tucson in Arizona, San Joaquin Valley in California, Colorado Springs in Colorado, Las Vegas in Nevada, and Albuquerque in New Mexico, and the region has a history of massive groundwater overdraft. At the end of the unprecedented drought of 2012-2015, estimates of total water storage based on data from GRACE gravity satellites show a rising trend, and precipitation anomalies become positive compared with the monthly averages over the period 2002-2017. In this study, we investigate how an abundance of surface water helped with the aquifer's recovery during the post-drought period. We analyze the post-drought aquifer status by performing a multidisciplinary multi-resolution analysis of space-borne and ground-based observations. Subsidence rates are derived from a multi-temporal interferometric analysis of Sentinel-1A/B SAR datasets from Nov. 2014 - Nov. 2017, and they reach at least several mm/yr in parts of almost all metropoles. While we uncover rising groundwater levels at all sites during the post-drought period in response to reduced pumping and increasing supply of surface water, we also find that compaction of the aquifer-system continues. We attribute the continued subsidence to delayed compaction of the fine-grain aquitard layer and conclude that the aquifer-systems did not reach the pressure equilibrium at least within ~2.5 years following the drought. Our findings have important implications for the effectiveness of groundwater management plans in the Southwest US.