Analysis of groundwater flow in mountainous, headwater catchments with permafrost

Abstract Headwater catchments have a direct impact on the water resources of downstream lowland regions as they supply freshwater in the form of surface runoff and discharging groundwater. Often, these mountainous catchments contain expansive permafrost that may alter the natural topographically controlled groundwater flow system. As permafrost could degrade with climate change, it is imperative to understand the effect of permafrost on groundwater flow in headwater catchments. This study characterizes groundwater flow in mountainous headwater catchments and evaluates the effect of permafrost in the context of climate change on groundwater movement using a three‐dimensional, finite element, hydrogeologic model. The model is applied to a representative headwater catchment on the Qinghai‐Tibet Plateau, China. Results from the model simulations indicate that groundwater contributes significantly to streams in the form of baseflow and the majority of groundwater flow is from the shallow aquifer above the permafrost, disrupting the typical topographically controlled flow pattern observed in most permafrost‐free headwater catchments. Under a warming scenario where mean annual surface temperature is increased by 2°C, reducing the areal extent of permafrost in the catchment, groundwater contribution to streamflow may increase three‐fold. These findings suggest that, in headwater catchments, permafrost has a large influence on groundwater flow and stream discharge. Increased annual air temperatures may increase groundwater discharge to streams, which has implications for ecosystem health and the long‐term availability of water resources to downstream regions.