Scale-Related Effects of Interactions Between Topography, Climate, and Seasonality on Snow Accumulation and Melt

The heterogeneity of mountain snow distribution and melt has vital implications across all spatial scales. Computationally efficient means of capturing this is required by fine-scale models applied to small mountain watersheds where heterogeneity affects runoff, erosion, water quality, and ecology; by moderate-scale models applied to larger river basins where its effect on runoff peaks and timing are seen; and in global-scale models where snow affects earth-atmosphere fluxes and circulation patterns. Further understanding of how the heterogeneity of snow distribution and melt scale will serve to guide determinations of appropriate model structures. Snow distribution is determined by meteorological forcings at the earth's surface with scaling largely dependent on the interactions between weather and topography. Meteorological forcings and associated scaling characteristics relative to snow distribution are constantly changing in response to local, synoptic, seasonal, and decadal cycles. Determining appropriate length scales for representing spatial variability across all conditions is essential for capturing both short-term impacts and those associated with long-term climate change. This research examines the interactions between weather, seasonality, and terrain and their effects on the scaling properties of the forcing processes controlling snow distribution and melt. The research is conducted using a physically-based, spatially distributed snow model with a process- based model scale to simulate snow distribution and melt over a 14 km2 mountainous catchment in southwestern Idaho, USA. Length scales of all forcing parameters are analyzed for different climatic scenarios and at different times of year. The sensitivity of modeled snow distribution and melt to the scaling of the forcing parameters is also characterized. This research will serve as a guide in determining which and under what conditions, snow-distribution processes can be appropriately up-scaled, and likewise which processes and under what conditions require an accounting of sub-grid variability.