Quantifying Changes in Groundwater Storage and Response to Hydroclimatic Extremes in a Coastal Aquifer Using Remote Sensing and Ground-Based Measurements: The Texas Gulf Coast Aquifer

Abstract

With the increasing vulnerability of groundwater resources, especially in coastal regions, there is a growing need to monitor changes in groundwater storage (GWS). Estimations of GWS have been conducted extensively at regional to global scales using GRACE and GRACE-FO obser-vations. The major goal of this study was to evaluate the applicability of uninterrupted monthly GRACE-derived terrestrial water storage (TWSGRACE ) records in facilitating detection of long-and short-term hydroclimatic events affecting the GWS in a coastal area. The TWSGRACE data gap was filled with reconstructed values from multi-linear regression (MLR) and artificial neural network (ANN) models and used to estimate changes in GWS in the Texas coastal region (Gulf Coast and Carrizo–Wilcox Aquifers) between 2002 and 2019. The reconstructed TWSGRACE, along with soil moisture storage (SMS) from land surface models (LSMs), and surface water storage (SWS) were used to estimate the GRACE-derived GWS (GWSGRACE ), validated against the GWS estimated from groundwater level observations (GWSwell ) and extreme hydroclimatic event records. The results of this study show: (1) Good agreement between the predicted TWSGRACE data gaps from the MLR and ANN models with high accuracy of predictions; (2) good agreement between the GWSGRACE and GWSwell records (CC = 0.56, p-value < 0.01) for the 2011–2019 period for which continuous GWLwell data exists, thus validating the approach and increasing confidence in using the reconstructed TWSGRACE data to monitor coastal GWS; (3) a significant decline in the coastal GWSGRACE, at a rate of 0.35 ± 0.078 km3·yr−1 (p-value < 0.01), for the 2002–2019 period; and (4) the reliable applicability of GWSGRACE records in detecting multi-year drought and wet periods with good accuracy: Two drought periods were identified between 2005–2006 and 2010–2015, with significant respective depletion rates of −8.9 ± 0.95 km3·yr−1 and −2.67 ± 0.44 km3·yr−1 and one wet period between 2007 and 2010 with a significant increasing rate of 2.6 ± 0.63 km3·yr−1 . Thus, this study provides a reliable approach to examine the long-and short-term trends in GWS in response to chang-ing climate conditions with significant implications for water management practices and improved decision-making capabilities.