Assessing groundwater dynamics in data-scarce mountainous regions using a lumped parameter groundwater model

Given the pressures on water resources caused by global climate change and human activities, the assessment and management of groundwater resources in mountainous region have become increasingly important. The central mountainous region of Taiwan, as one of the significant sources of groundwater recharge, plays a critical role in overall water resource management due to its groundwater storage capacity and recharge capability. Addressing the challenges of limited survey and observational data in mountainous groundwater assessments, this study uses the lumped parameter groundwater model AquiMod to analyze long-term groundwater level changes at 23 monitoring stations in mountainous areas of central Taiwan. This study is based on long-term groundwater level monitoring data (2010-2021) analyzing the relationship between groundwater levels and precipitation, and performs model calibration and prediction. The results indicate a strong correlation between groundwater levels in mountainous areas and precipitation. While the model predictions were satisfactory for most monitoring stations, obtaining Nash Sutcliffe efficiency scores of between 0.5 and 0.9 at 14 of the 23 monitoring stations. However, poorer performance at several stations reflects limitations arising from data gaps, complex local geology, and the inability of the lumped model to represent lateral recharge or anthropogenic influences. Model sensitivity analysis further highlights the critical role of unsaturated zone parameters, such as rooting depth, soil storage and upper-layer saturated hydraulic conductivity, in shaping groundwater responses. In summary, the lumped parameter groundwater model has proven practical for evaluating groundwater in Taiwan's mountainous regions and can serve as a reference for the sustainable management of future water resources.