MA: University of Colorado Boulder, 2018.
As the climate warms, the fraction of precipitation falling as snow is expected to decrease. In snow-dominatedmountainous 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. Here, I focus on the rain-snow transition zone, which, in mid-latitude mountain ranges like the Rocky Mountains, is large and most vulnerable to changes in climate and warming. The objective of my 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 Critical Zone Observatory, a watershed within the rain-snow transition of the Colorado Front Range. I discover that streamflow decreases an average annual 37% under the influence of warming. But, on a seasonal time frame, streamflow increases in winter and spring months and decreases 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, warming induces a shift in the timing of terrestrial water inputs from snowmelt and rainfall. In this context, terrestrial water inputs increase during the time of year when atmospheric water demand is relatively low, increasing the partitioning of terrestrial water inputs to streamflow. As a result, streamflow increases by 13% during winter and spring months, off-setting the net decrease in streamflow associated with warming. This off-setting effect has large implications for hydrological and ecological processes, and for water resource management across Earth’s mountainous regions.