Threshold hydrologic change across the intermittent-persistent snow transition

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This project will develop a geographic synthesis of snow, streamflow, and soil moisture data across the western U.S. and the analyses will provide key information that can be used to identify areas most vulnerable to large hydrologic changes due to smaller snowpack accumulation. Datasets produced will be publicly available and this information can be incorporated into land and aquatic resource management, particularly in locations that lack hydrologic data. The project will train a PhD student and undergraduate research assistants, develop an interactive digital display for education outreach and student recruitment, and develop a hydrology class activity using soil moisture simulations. Loss of persistent winter snowpack impacts water resources in mountain and high latitude regions throughout the world, and the need to understand water resource vulnerability to snow loss is pressing. The central hypothesis guiding this research is that loss of a persistent snowpack triggers changes in both stream flow and soil moisture, but the magnitude of this change is greater in more arid climates. This project will document the geographic distribution of intermittent-persistent snow transitions in the western U.S. and examine how streamflow and soil moisture are affected by these transitions. Snow transitions will be mapped using both MODIS snow cover imagery and snow water equivalent data from SNOTEL sites. Indices of snow transitions will then be compared to streamflow and soil moisture data at both annual-decadal time scales and event-seasonal time scales. HYDRUS-1D simulations of soil moisture changes in response to varying scenarios of snow persistence will be developed for SNOTEL sites in two different climate regions to examine how process interactions between snow loss and hydrologic response vary with climate. The study synthesizes a top-down approach examining runoff and soil moisture changes across geographic gradients of snow persistence with a bottom-up process modeling approach examining how soil moisture responds to a transition from persistent to intermittent snow. The multi-scale approach will help in understanding how regional long-term patterns link with local conditions in individual seasons.