Insights from modelling the climate-glacier-groundwater response cascade in a glacierised headwater catchment

Abstract:

Proglacial aquifer storage response to climate change and glacier retreat is uncertain: driven in part by perturbations in diffuse recharge inputs from rainfall and snow melt and in part by shifts in meltwater runoff dynamics and focused recharge from glacier-fed river channels. When forecasting climate change impact on proglacial groundwater storage dynamics, one must consider linkages along the climate-glacier-groundwater response cascade. This cascade remains poorly understood because: i) it necessitates a sophisticated numerical modelling approach that can account for climate-cryosphere-hydrosphere feedbacks; and ii) such an approach can only be validated with observation data that are rarely available in mountain catchments. This study addresses both of these issues by using a novel numerical modelling framework to simulate proglacial groundwater storage dynamics under climate change and glacier retreat scenarios in a well-characterised and monitored headwater catchment in south-east Iceland. The study provides three principal insights into the drivers and impacts of twenty-first century climate change on proglacial groundwater storage dynamics which include:

1. Meltwater-fed river channels are a significant source of proglacial groundwater recharge. In the study catchment, the meltwater channel provides up to 20% total recharge.
2. Glacier retreat and the reduction in meltwater runoff result in the flattening of diurnal river flow oscillations, which could inhibit river recharge in the future by up to 29%.
3. Twenty-first century groundwater storage and seasonal dynamics in this temperate study catchment are remarkably resilient to glacier retreat and are driven mainly by shifts in diffuse recharge.