Integration of GRACE, ground observation, and land-surface models for groundwater storage variations in South Korea

Terrestrial water storage (TWS) comprises all forms of water stored in the Earth's surface. The gravity recovery and climate experiment (GRACE) twin satellite provides an efficient method of assessing TWS changes (TWSCs) by measuring variations in the Earth's gravity. GRACE-derived TWS is equivalent to the sum of all forms of water such as surface water, soil moisture, snow water equivalent, and groundwater. Therefore, groundwater storage and its variations can be estimated when other variables are determined. We used Level-3 data (RL 05) to estimate monthly TWSC in South Korea. Data were obtained from land-surface models (LSMs) of global land data assimilation system (GLDAS), ground observations from water management information system (WAMIS) and rural agricultural water resources information system (RAWRIS). GRACE-derived groundwater storage changes (GWSCs) were -0.18 +/- 6.5 cm month(-1) on average, indicating the decrease of groundwater. We validated the GRACE-derived GWSC by comparing the changes with well-derived GWSC obtained from in situ groundwater observation wells of Korean national groundwater monitoring networks (NGMNs). This satellite-based remote-sensing methodology can provide an efficient tool for the nationwide planning and management of groundwater.