Abstract
Proglacial aquifers are an important water store in glacierised mountain
catchments that supplement meltwater-fed river flows and support
freshwater ecosystems. Climate change and glacier retreat will perturb
water storage in these aquifers, yet the climate-glacier-groundwater
response cascade has rarely been studied and remains poorly understood.
This study implements an integrated modelling approach that combines
distributed glacio-hydrological and groundwater models with climate
change projections to evaluate the evolution of groundwater storage
dynamics and surface-groundwater exchanges in a temperate, glacierised
catchment in Iceland. Focussed infiltration along the meltwater-fed
Virkisà River channel is found to be an important source of groundwater
recharge and is projected to provide 14-20% of total groundwater
recharge by the 2080s. The simulations highlight a mechanism by which
glacier retreat could inhibit river recharge in the future due to the
loss of diurnal melt cycling in the runoff hydrograph. However, the
evolution of proglacial groundwater level dynamics show considerable
resilience to changes in river recharge and, instead, are driven by
changes in the magnitude and seasonal timing of diffuse recharge from
year-round rainfall. The majority of scenarios simulate an overall
reduction in groundwater levels with a maximum 30-day average
groundwater level reduction of 1 m. The simulations replicate
observational studies of baseflow to the river, where up to 15% of the
30-day average river flow comes from groundwater outside of the melt
season. This is forecast to reduce to 3-8% by the 2080s due to
increased contributions from rainfall and meltwater runoff. During the
melt season, groundwater will continue to contribute 1-3% of river flow
despite significant reductions in meltwater runoff inputs. Therefore it
is concluded that, in the proglacial region, groundwater will continue
to provide only limited buffering of river flows as the glacier
retreats.