Impacts of Beetle Kill on Modeled Streamflow Response in the North Platte River Basin

A beetle epidemic has been sweeping its way across the western United States and into portions of southern Canada that has caused millions of acres of forests to ultimately die. This beetle outbreak, that many have come to know simply as “beetle kill”, has caused many scientists to feel that such dramatic changes in land cover could potentially alter the hydrology throughout much of the West. One of the most important hydrological processes that beetle kill has the potential to impact is streamflow. This paper attempts to evaluate the hydrological impacts on streamflow from land cover change due to beetle kill in the North Platte River Basin (NPRB), by utilizing a hydrological model, Variable Infiltration Capacity (VIC). VIC is a land surface hydrological model that, for this analysis, has been calibrated and validated for the periods of 1950-1980 and 1981-2000, respectively, by using daily meteorological forcings and monthly streamflow data. In order to quantify the impacts on streamflow, land cover was changed by decreasing forest canopy coverage in order to mimic beetle kill for five different simulations, based on results obtained from basin level estimates of canopy loss, with error, using remote sensed data. Based on these five simulations, an increase of approximately 1% to 10% in decadal streamflow was observed for a decrease of 16% to 40% in forested land cover. Additionally, the average change in forest cover of 28% produced an increase in decadal streamflow of roughly 5%. However, based on model limitations and general assumptions, this estimate of increased streamflow was likely a high estimate. Given beetle kill did not fully manifest itself in the NPRB until roughly 2007/2008, modeling the proposed changes in land cover for the period 1950-2000 was performed in order to see the possible implications beetle kill would have had in the past. By doing so, the results could then be applied to the present day to try and predict what effects beetle kill could have in the future.