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Hale, Katherine E. ¹ ; Wlostowski, Adam N. ² ; Badger, Andrew M. ³ ; Lestak, Leanne R. ⁴ ; Anderson, Suzanne P. ⁵ ; Molotch, Noah P. ⁶

¹ Institute of Arctic and Alpine Research, University of Colorado
² Institute of Arctic and Alpine Research, University of Colorado
³ Cooperative Institute for Research and Environmental Science, University of Colorado
⁴ Institute of Arctic and Alpine Research, University of Colorado
⁵ Institute of Arctic and Alpine Research, University of Colorado
⁶ Institute of Arctic and Alpine Research, University of Colorado

Annual snowpack within mountainous regions in the Western United States serves as an essential hydrologic resource for downstream communities. Acting as a reservoir throughout the year, the local snowpack of an area dictates water availability and strongly influences ecological processes. Across seasons, these areas experience shifts from rain to snow and vice versa throughout the shoulder seasons of fall and spring. Yet with changing atmospheric temperatures and increased net radiation, we expect these shoulder seasons will shift to incorporate more rain later in the fall and earlier in the spring. We know that downstream annual water availability changes as a result of precipitation amount, but the water availability changes due to precipitation form, rain to snow, is less understood.

The effects of rain and snow transitions have been analyzed at a larger scale using the Budyko Curve framework and mechanistic modeling: suggesting that there is greater streamflow efficiency, the quantity of precipitation seen downstream, with greater annual snowfall. The effects of rain and snow transitions on small scale, mountainous catchments remain to be discovered. Utilizing Boulder Creek (CO) and Reynolds Creek (ID) Critical Zone Observatory catchment data to drive the Distributed Hydrology Soil and Vegetation Model (DHSVM), we assess streamflow efficiency across a range of annual snow fractions. Using observed streamflow data, local meteorological data and national soil and vegetation data at a 20-meter resolution, we manipulate the amount of annual rain and snow via model-based scenarios within a given catchment.

By changing snow fraction we explore the catchment response to precipitation type and the streamflow efficiency downstream. Any response in streamflow efficiency to precipitation type provides large implications for water resources and management on both a small and large scale across these mountainous regions.

Berghuijs, W. R., Woods, R. A., & Hrachowitz, M., 2014, A precipitation shift from snow towards rain leads to adecrease in streamflow. Nature Climate Change, v. 4(7), p. 583-586.

Milly, P. C. D., 1994, Climate, soil water storage, and the average annual water balance, Water Resources Research, v. 30(7), p. 2143-2156.

Wigmosta, M.S., L. Vail, and D. P. Lettenmaier, 1994, A distributed hydrology-vegetation model for complex terrain, Water Resources Research, v. 30, p. 1665-1679.