Katherine M Robinson , Gwenn Elizabeth Flowers, David Robert Rounce

Runoff from glaciers accounts for half the total freshwater discharge to the Gulf of Alaska, with glacier contributions to streamflow changing as mass loss accelerates. 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. To estimate accumulation, we apply an elevation-dependent correction based on in-situ measurements. The model tuning approach incorporates observations of the geodetic mass balance and snowlines. We assess model sensitivity to the representation of supraglacial debris and the accumulation bias correction, including treatments of these processes that can be applied in the absence of in- situ data. The representation of debris produces variations <1% in the catchment-wide runoff and water budget. In contrast, accumulation inputs that omit in-situ data produce variations of 33–40% in modelled runoff relative to a catchment-specific correction. This work highlights the value of catchment-specific data and the impact that representations of debris and accumulation can have on modelled runoff.