Reconstructing a multi-decadal runoff record for a highly-glacierized catchment in Yukon, Canada

Runoff from glaciers accounts for nearly half of the total freshwater discharge to the Gulf of Alaska, with glacier contributions to streamflow expected to change as glacier mass loss accelerates. We reconstruct the 1980-2022 runoff and water budget of the Kaskawulsh River Headwaters, a 70% glacierized catchment in Yukon, Canada, primarily occupied by the Kaskawulsh Glacier. We use a glacier mass-balance model driven by downscaled and bias-corrected reanalysis data, and assess model sensitivity to treatments of debris cover and snow accumulation developed with and without site-specific observations. The choice of debris treatment produces variations of <1% in the catchment-wide discharge and water budget. The estimated annual discharge differs by 31-44% when using treatments of accumulation that omit site-specific measurements compared to a site-specific correction. The water budget averaged over 1980-2022 is primarily dominated by glacier-ice melt (61%), followed by snowmelt (31%), rainfall (6%), and superimposed ice melt (2%). We estimate substantial increases in runoff from glacier ice melt in all summer months over time, suggesting that this catchment has not yet reached peak water.