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The Western United States is dominated by snow water hydrology systems in forest catchments. Climate change is causing forest disturbances to increase in severity and occur more frequently. The consequences of these disturbances impact the ecology of these systems as well as the timing and quantity of streamflow from snowmelt and runoff. I examined the headwaters of the Rio Grande (RGHW), a snow water dominated system, which has suffered tree mortality as a result of multiple that occurred in 2013, as well as beetle kill dating back to the late 1990s. Using geospatial data collected on beetle kill severity and fire data, I quantified the percentage mortality by area. I then compared this to available streamflow and SNOTEL data to determine the effect of disturbance history on streamflow. Using annual streamflow and SNOTEL data as an input/output ratio, I concluded that years 2015 & 2016 had a higher than historical ratio of streamflow (output) for precipitation (input) received by the RGHW. The most likely mechanism causing the increased runoff ratio can be attributed to the increased hydrophobicity of the soil, as well as a decrease in transpiration rates due to tree mortality. Despite these changes in hydrology, the watershed returns to the historic range within just a few years as the soil recovers and revegetation leads to an increased demand for water. The results of my study have larger implications for water forecasting in the west, which continues to suffer from larger, more frequent disturbances, as well as a growing population and an increasing daily average temperatures resulting from climate change.

theydman@colostate.edu

College of Natural Resources Undergraduate Student, Colorado State University