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Abstract

Streamflow timing and magnitude from snowmelt runoff often exhibits large interannual variability in semi-arid regions; variability that is exacerbated by more frequent droughts and intense wildfires. Headwater catchments located within the rain-snow transition tend to be more susceptible to climate change since warming temperatures reduce late spring and early summer snow drift water storage. The Johnston Draw (JD) sub-catchment (1.8 km²) of the Reynolds Creek Experimental Watershed (RCEW) in southwestern Idaho has been intensively monitored since 1960 and is an ideal setting for investigating climate change effects on snow accumulation, ablation and subsequent streamflow responses. Using a physically based energy balance snow model (iSnobal) driven by eleven automated weather stations and a priori information on snow depth variability from multiple airborne lidar surveys, we are able to explicitly account for snow drift accumulation and melt throughout the season and compare the resulting runoff with streamflow measurements from the catchment outlet weir. Recent research using this modeling approach in JD has shown that snow drifts are responsible for up to 6 times more surface water input (SWI), or the sum of annual rainfall and snowfall, than the catchment average. Additionally, the importance of snow drifts to streamflow generation is only expected to increase due to their resiliency to rain-on-snow events that tend to cause melt elsewhere in the catchment. Here we will present details of these recent findings and look forward to new research questions that will be addressed after an upcoming Johnston Draw prescribed fire in September 2023.