Katherine M Robinson , Gwenn Elizabeth Flowers, David Robert Rounce

Runoff contributions from glacierized catchments are changing in response to accelerating mass loss. We reconstruct the 1980-2022 mass balance, runoff and water budget of the ~70% glacierized Kaskawulsh River headwaters in Yukon, Canada, using an enhanced temperature-index model driven by downscaled and bias-corrected reanalysis data. Debris is treated using melt-scaling factors based on site-specific measurements of the critical debris thickness. Accumulation is estimated from downscaled precipitation bias corrected based on in-situ measurements. Model tuning incorporates observations of the 2007-2018 geodetic mass balance and seasonal snowline positions on the Kaskawulsh Glacier. We assess model sensitivity to the representation of supraglacial debris and accumulation, including treatments of these processes that can be applied in the absence of in-situ data. Different representations of debris produce <1% variation  in the catchment-wide runoff and water budget. In contrast, accumulation estimates that omit in-situ data produce 33-40% variations in modelled runoff relative to those that use these data. This work identifies site-specific measurements of accumulation as critical to accurate estimates of mass balance and runoff for the Kaskawulsh Glacier, in contrast to site-specific characterization of the effects of debris which influence estimated thinning rates at the glacier terminus but have little impact on the glacier-wide runoff.