Modeling Interannual Variability in Snow-Cover Development and Melt for a Semiarid Mountain Catchment

Observed changes in midelevation snow cover and duration have raised concerns over future impacts of global warming on snowmelt-dependent water resources and ecosystems. However, predictions of future changes in snow hydrology and water supply from mountain basins are complicated by natural variability in climate and interactions among topography, vegetation structure, wind and radiation energy, and snow deposition. In this study, interannual variability in snow-cover development, snow melt, and runoff is assessed for a range of precipitation and temperature conditions typical of a mountain catchment, the Reynolds Mountain East (RME) basin, in Idaho. A spatially distributed energy and mass balance snow model, Isnobal, coupled with a windfield and snow redistribution model, is used to continuously simulate snow accumulation and melt for five individual snow seasons (1984, 1986, 1987, 2001, and 2006), representing the historic range of climatic variance. The modeling results compare well with the field measurements of snow water equivalent for all simulation snow seasons (Nash-Sutcliffe model efficiency coefficient of 0.81 to 0.97). The modeling scheme used in this study demonstrates spatial and temporal differences in snow-cover development and melt processes in complex mountain terrain. During all simulation snow seasons, the forested site was shown to hold more snow, generate more snowmelt, and melt later than the exposed site of the basin. Comparison of simulation results for wet and dry snow seasons showed that the snow melts earlier and a greater fraction of surface water input (SWI) is utilized to fill soil water storage during dry seasons than in wet snow seasons. This study demonstrates differences in snowmelt volume and timing during wet and dry seasons within a mountain basin. It will improve understanding of how interannual variability affects the delivery of water from the seasonal snowcover to the soil and streams of mountain basins, and can provide useful inputs to the decision-making process for reservoir and water management strategies for utilizing surplus or supplementing deficit water supplies during wet and dry years, respectively.