Snow Sublimation from Two Arid Basins

Snow cover sublimation directly impacts water input to the soil. In mountainous forested terrain, available energy, the exposed surface area of a snow cover, and exposure time with the atmosphere vary greatly by elevation, aspect and forest cover density. It is therefore difficult to scale up results from previous site specific short term studies. Sublimation from intercepted snow and the snowpack are simulated at 30-m resolution over the Salt River and Verde River basins in the southwest USA for years 2008 (wet year) and 2007 (dry year). Independent observations at AmeriFlux sites agree well with downscaled meteorological input and model agreement with vapor flux observations from above canopy towers is comparable to more localized modelling efforts. Increased forest cover density increases total simulated sublimation primarily due to increased interception but also due to extended duration of the ground snowpack. Increased forest cover only decreases ground sublimation for isolated environments favoring long duration in the spring (e.g., south aspect high elevations and heavily forested mid-elevations). The two basins differ in distributions of elevation and forest cover density, with the Salt having the greater portion of forested land and high elevation land. Therefore, simulated sublimation was much greater on the Salt, particularly during the wet year, 2008. Overall, the fraction of total snowfall sublimated is similar between the basins because of the lesser snowfall received by the Verde basin. However, this contribution of sublimation to total ablation appears to be more variable on the Verde basin, with a much greater difference in the sublimated snowfall fraction between the 2007 and 2008 simulations than the Salt. Forest density can change rapidly due to natural and anthropogenic factors and these results can benefit water resource management and improve understanding of ecosystem function.