Quantifying Change in Groundwater Storage in the Coastal Region of Texas

Groundwater is the sole source of freshwater in most coastal regions and is highly vulnerable due to natural (e.g., seawater intrusion) and anthropogenic (e.g., excessive pumping) influences. Direct and continuous monitoring of groundwater storage (GWS) change at regional scales using in-situ measurements remains challenging due to an insufficient amount of ground-based measurements and large subsurface heterogeneity. The Gravity Recovery and Climate Experiment (GRACE) measures spatial and temporal variations in the Earth's gravity field and is widely used to quantify the continuous spatial and temporal variations in terrestrial water storage (TWS) and GWS. We examined the temporal variations in TWS and GWS in the coastal region of Texas using data from five different GRACE products, soil moisture storage (SMS) from the six land surface models (LSMs), and surface water storage (SWS) from Texas Water Development Board database. Preliminary results show a decrease in TWS and GWS in this region at the rate of -4.6 ±0.5 mm/yr and -2.1±0.5 mm/yr, respectively during the period from April 2002 through June 2017. The largest depletion rates were observed during the 2010-2012 severe drought period. Both the TWS and GWS show an increase following the 2015 Texas record floods. GRACE-derived GWS trend estimates are being validated against ground-based measurement (i.e., groundwater level data) over the entire coastal region of Texas. Results from this study will help further our understanding of groundwater availability and variability under the increased stress on groundwater resources due to climate variability and increasing demand of groundwater resources. The adapted approach could be used to investigate the response of hydrogeologic systems to climatic and anthropogenic forces in the coastal areas around the world.