ANALYSIS OF GROUNDWATER FLOW IN MOUNTAINOUS, HEADWATER CATCHMENTS WITH PERMAFROST

Headwater catchments have a direct impact on the water resources of downstream lowland regions as they supply freshwater in the form of 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 critical 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 on groundwater movement using a three-dimensional, finite element, hydrogeologic model. The model is applied to a representative headwater catchment on the northern 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 temperature is increased by 2 °C, the areal extent of permafrost in the catchment decreases by 28%. With this reduction in permafrost extent, 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 temperatures will increase groundwater discharge to streams, which has implications for ecosystem health and the long-term availability of water resources to downstream regions.