Statistical and numerical assessments of groundwater resource subject to excessive pumping: Case study in Southwest Taiwan

Groundwater, a salient water resource in Taiwan, has been subject to incessant and excessive pumping, inducing serious regional land subsidence and seawater intrusion. This study aims at assessing how excessive pumping impacts groundwater variations over the Pingtung Alluvial Plain (PAP) in Southwest Taiwan using both statistical and numerical techniques. We apply nonparametric methods to analyze the changing point and annual trend in various hydro-meteorological time series (e.g., rainfall, temperature, and groundwater levels (GLs)). Afterwards, we employ an integrated surface-subsurface model referred to as WASH123D to simulate GLs under the pumping-free scenario; any discrepancies identified between simulated and observed GLs could be an indicator of unregulated/illegal pumping. We find that annual GLs exhibit a significant increasing (decreasing) trend in the western (eastern) PAP. Our numerical experiment reveals diverging trends in simulated and observed GLs, mostly at the downstream of all the major tributaries, suggesting the consequence of unregulated/illegal pumping. Furthermore, upstream pumping may reduce lateral flow towards the downstream coastal area, triggering land subsidence in remote locations.