Impacts of long-term climate change on the groundwater flow dynamics in a regional groundwater system: Case modeling study in Alashan, China

Abstract

Groundwater flow dynamics plays a crucial role in social development and ecosystem protection. This study investigated the impacts of long-term climate change on the regional groundwater flow in Alashan, China to reveal the spatial variability of groundwater flow response to climate change and the dynamic patterns of both deep and shallow groundwater flow velocity. To this end, the hydrogeologic conditions and climate evolution history were analyzed. Based on these, four future scenarios of long-term climate change were designed, including linearly varying and cyclic changes, and numerical groundwater flow modeling was then conducted to investigate the effects of long-term climate changes on groundwater flow dynamics (including groundwater level and flow velocity). It was found that groundwater level dynamics were notably influenced by climate changes; the time scale and initial change pattern of cyclic climate influenced the amplitude and mean level of groundwater level fluctuations. In addition, our results also revealed that, for a regional groundwater system, climate change impacts on groundwater level had obvious spatial variability. Groundwater level in recharge and discharge areas were sensitive to drying and wetting climates, respectively. Thus, the spatial variability of groundwater level dynamics reflected climate change information. Moreover, groundwater flow velocity dynamics were also affected by climate changes. However, linearly varying and cyclic climates had different influences. Linearly wetting climate generally increased the groundwater flow velocity in recharge and discharge areas, but decreased that in runoff area, whereas cyclic climate induced periodical fluctuation of groundwater flow velocity. The fluctuation period of shallow groundwater flow velocity matched the full climate cycle period, whereas of the deep groundwater flow velocity was only half. This unique behavior of deep groundwater flow velocity is caused by fluctuation of the vertical velocity alternating between positive (upward flow) and negative (downward flow) values. This finding of groundwater flow velocity dynamics contributes to deeper understanding of long-term climate change effects on groundwater flow dynamics.