The potential of GRACE gravimetry for the detection of the groundwater storage in an island watershed by applying the downscaling method

Since the successful launch of the Gravity Recovery and Climate Experiment (GRACE) on March 17^th, 2002, that is related to the observations of ocean, climate and geology, several scientists adopted the satellite gravimetry for the detection of Terrestrial Water Storage (TWS) variations. In the field of hydrogeology, GRACE can present numerous advantages, such as the accurate estimations in currents and gravity fields. Many studies proved that the high-precision GRACE gravimetry can observe the groundwater storage (GWS) variations. Most of them investigate large-scale GWS variations (over 50,000 km²). However, there are few relative researches that focus on scales smaller than 5,000 km².

The purpose of this study is to investigate the potential of GRACE gravimetry for observing the GWS variations in small-scale regions by applying down-scaling method. Specifically, this study presents the Zhuoshui River alluvial fan ( 1,800 km²) that is located in central Taiwan as a case example. The in situ hydrological data of 222 observation wells, 18 hydrological stations, and 76 rainfall stations (2000-2017) that were used to analyze the water storage variations by applying the water budget method were compared with the GWS data (2002-2017) evaluated by GRACE gravimetry in order to detect the similarities and differences in both methods, as well as to prove the feasibility of the GRACE gravimetry in small-scale regions. Under the study results, the small watershed water resource management can be monitored by the GRACE gravimetry.

Keyword: GRACE, groundwater