Groundwater provides temporary resilience to alpine catchments in glacial retreat

Abstract

Abstract Surface runoff from melting alpine glaciers increases until the glaciers reach a condition called “peak water” beyond which surface runoff decreases as ice volume diminishes. Recent research indicates that a fraction of this meltwater recharges mountain-block aquifers thereby providing vital support to baseflow in alpine streams and perennial flow from alpine springs. However, the response of baseflow to deglaciation has not been thoroughly quantified. Combining statistical timeseries analysis of discharge data with the delayed flow index (DFI), we show that the proportion of baseflow in post-peak water discharge has increased compared to pre-peak discharge in three glacial catchments in the Swiss Alps. The timing of peak water is not concurrent with the baseflow response. The increase in baseflow is sustained for 20 to 40 years after the occurrence of peak water; however, this is a transient response. In fact, one catchment has lost baseflow support and is now responsive to seasonal precipitation events. Given the slower response times of groundwater, baseflow will eventually decrease in these catchments making them more responsive to precipitation events and less resilient to fluctuations in precipitation once the ice is gone. These conditions will have severe impacts to alpine streams and springs and their ecosystems.