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Grad student talk: Snow fractions and runoff ratios

Thursday, October 18, 2018, 12:30PM - 1:30PM


Kate Hale

As the climate warms, the fraction of precipitation falling as snow is expected to decrease. In snow-dominated mountainous regions, where reliance on snowpack and snowmelt is great, a reduction in snowfall fraction prompts us to examine downstream changes in streamflow and water resources.  Shifts in precipitation phase are expected to alter the magnitude of ecosystem productivity, the timing of water resource availability, and, ultimately, the amount of annual streamflow. We focus on the rain-snow transition zone in mid-latitude mountain ranges like the Rocky Mountains. The objective of our study is to understand how climate warming, and associated shifts in evaporative demand and precipitation phase, will alter streamflow generation in the rain-snow transition zone of the mid-latitude Rocky Mountains. The Distributed Hydrology Soil Vegetation Model is used to simulate streamflow within Gordon Gulch of the Boulder Creek CZO, a watershed within the rain-snow transition of the Colorado Front Range. We discover, over three water years, that streamflow declines under the influence of warming.  But, on monthly and seasonal timeframes, streamflow fluctuates in change, increasing in winter and spring months and decreasing in summer and fall months. The presence of snow reveals a buffer effect, decreasing the magnitude of streamflow loss compared to a snow-free environment. Unique to the rain-snow transition zone, as snow shifts to rain, water enters the system immediately as direct precipitation instead of remaining within the snow pack until melt season.