Impact of groundwater extraction on subsurface thermal regimes

Groundwater is widely exploited, leading to groundwater depletion, and a reduction of river flows. While the impact of climate change and hydrologic forcings on the hydrogeological cycle has long been demonstrated, a lack of observations of subsurface thermal changes on the scale of decades is hampering the accurate understanding of how human activities change subsurface thermal regimes (i.e. the spatiotemporal evolution of the subsurface temperature). In this paper, we analyze new temperature data illustrating the complex interplay of climate warming and anthropogenically enhanced groundwater flow on subsurface thermal regimes from two sites in different hydrogeological settings. A heuristic numerical model is used for the interpretation of the observed temperature anomalies. We demonstrate that pumping may have a significant impact on the thermal regime of an aquifer, and that depending on hydrogeological conditions and the natural geothermal gradient, this impact might be even more important than that of climate warming.