Recovery of aquifer-systems in Southwest US following 2012–2015 drought: Evidence from InSAR, GRACE and groundwater level data

During the drought period 2012–2015, some of the major metropolitans and agricultural hubs within the Southwest US, including Phoenix and Tucson in Arizona, San Joaquin Valley in California, Colorado Springs in Colorado, Las Vegas in Nevada, and Albuquerque in New Mexico, experienced significant groundwater overdraft. At the end of the drought, GRACE-based estimates of total water storage show a rising trend. Also, the precipitation anomalies, considering monthly averages over 2002–2017, are positive. But, it is unclear if a pressure equilibrium is achieved within the aquifer systems, which is a requirement for residual compaction to halt. To this end, we perform a multidisciplinary multi-resolution analysis of space-borne and ground-based observations. We find that following the drought period and during wetter years, due to reduced pumping, owing to significant precipitation and the supply of surface water, groundwater levels begin to rise at all sites while compaction of aquifer-systems continues. A multi-temporal interferometric analysis of Sentinel-1A/B SAR datasets during Nov. 2014–Nov. 2017 shows subsidence rates of ~6 mm/yr, ~3 mm/yr, ~200–300 mm/yr, ~3–4 mm/yr, ~4–6 mm/yr, ~2 mm/yr affecting parts of Phoenix, Tucson, San Joaquin Valley, Colorado Springs, Las Vegas, Albuquerque, respectively, which are attributed to delayed compaction of fine-grain aquitard layer. We conclude that the aquifer-systems did not reach pressure equilibrium at least within ~2.5 years following the drought. The data provided here can assist policymakers and urban planners to improve groundwater management plans in the southwest and elsewhere.