Abstract
Throughout the western United States, seasonal snowpack is critical for water resources timing and availability and ecosystem function. Warming temperatures associated with climate change reduce snow accumulation and advance melt timing, with serious consequences for snow-dependent social and ecological systems. While many impacts of climate change on snowpack are well established, this dissertation investigates several elements of changing snowpack that have not been previously assessed. In particular, each chapter contributes to an improved understanding of the changing heterogeneity of snow under climate change. The first chapter tests the sensitivity of snow drifting to altered climate, using a physically-based hydrologic model and thirty years of hydroclimatological data at a site where aspen stands are subsidized by a wind-driven snow drift. We find a warming-induced reduction in snow drifting, increase in ecohydrologic homogeneity across the landscape, and altered interannual variability of hydrologic metrics. The second chapter assesses changes in interannual variability of snowpack magnitude and timing across the western United States, using downscaled global climate model data as forcing to the Variable Infiltration Capacity (VIC) model. We find that changes in interannual variability are spatially heterogeneous across the western U.S., but that interannual variability of annual maximum snow water equivalent (SWEmax) decreases in regions transitioning from snow- to rain-dominated precipitation regimes. Changes in the date of SWEmax are less spatially coherent, but agreement between general circulation models (GCMs) is most reliably found at relatively warm sites where the date of SWEmax variability increases. The third chapter assesses another element of snow heterogeneity by testing the effect of snowfall intensity on winter ablation. Using a statistical modeling approach with observational snow data, we find that higher snowfall intensity is associated with reduced winter ablation; projected changes in snowfall intensity will likely exacerbate warming-induced increases in winter ablation in the maritime mountains of the western U.S. and mitigate it in the cooler continental regions. Finally, a fourth interdisciplinary, collaborative chapter synthesizes research on climate change in the mountainous headwaters of the Columbia River Basin. Findings show that research in this basin is focused on climate change impacts, rather than adaptation or mitigation, that social and biophysical sciences are not well integrated, and that research priorities differ across an international boundary. Cumulatively, this set of studies advances knowledge of how the spatial and temporal heterogeneity of snowpack will respond to climate change in the western United States, with implications for snow-dependent social and ecological systems.