Cryosphere-groundwater connectivity in the mountain water cycle - where does meltwater go?

Both the mountain cryosphere -- comprising glaciers, snow, and permafrost -- and groundwater play crucial roles in shaping the hydrological cycle. However, their connectivity is not well understood. Understanding the importance of sub-surface meltwater flowpaths and the role of groundwater in mountain regions is critical to untangle 1) the fate of meltwater in the hydrological cycle and 2) the sensitivity of groundwater to a changing meltwater supply due to climate change.

Here, we synthesize studies which investigated the dynamics of meltwater flow through mountain aquifers. In general, snow-groundwater connectivity is better described than glacier-groundwater connectivity. However, estimations of meltwater recharge fluxes vary considerably across studies, which is not only a function of inherent catchment characteristics but also of the different methods used for the assessments. Estimates of the source contributions of mountain groundwater range between 2-60% for glacier melt and between 40-80% for snowmelt. These large numbers suggest that cryosphere-groundwater connectivity and the consequent delay in meltwater flow needs to be part of our conceptual understanding of the mountain water cycle. Still, there is a clear lack of understanding at which spatio-temporal scales this connection operates.

As glaciers retreat and snowpack diminishes, the relative importance of groundwater as catchment storage is expected to increase. This increase may however be partly compromised by declining recharge from the mountain cryosphere and changed recharge dynamics, with yet unknown effects on catchment-scale hydrological processes. We suggest a roadmap for future work to better quantify mountain cryosphere-groundwater connectivity and to predict climate change impacts on mountain water supplies.