Climate Change Impact on Snowfall, Evapotransportation and Streamflow in a Temperate, Wet Watershed

Abstract:

Climate change is expected to significantly impact hydrological processes and streamflow at a regional scale, and the motivation of this research is to gain a better understanding of these processes in temperate, wet regions. While numerous studies have recently focused on projected reductions in snowfall and the impact on streamflow in dry and mountainous regions, much less research has investigated hydrologic processes and streamflow in temperate, wet regions which are expected to receive increases in precipitation during the winter season. We use dynamically and statistically downscaled climate projections and perform hydrological simulations using the Soil Water Assessment Tool (SWAT) for central Kentucky, USA. The study region is chosen because it is located in a region that receives a mixture of rain, snow and ice in wintertime, and thus the region is expected to be particularly sensitive to future changes in precipitation and temperature. The SWAT model was first evaluated in a hindcast analyses for the South Elkhorn Watershed and then driven for future conditions by using downscaled temperature and precipitation data from three different projects including the North American Regional Climate Change Assessment Program, Coupled Model Intercomparison Project Phase 5, and Coupled Model Intercomparison Project Phase 3. The average ensemble climate change results indicates an increase in the average annual of daily temperature by 2.6^oC for the period 2046 to 2065 as compared to the period 1981 to 2000, and predicts an increase in the annual precipitation by 8%, with the majority of the increase coming in winter (14% in winter and 2% in summer). SWAT suggests a significant stream flow impact due to climate change including an increase in the average annual stream flow by as much as 26%; attributed to the fact that the climate projections predict more precipitation in winter which increases the snowfall and changes the surface albedo. Hence, the evapotranspiration predicted by SWAT is significantly decreased and causes an increase in the baseflow and average streamflow. The results are robust including 39 future projected scenarios, and current analysis includes analysis of variance to see how climate projection factors, including emission scenario, GCM choice, and downscaling method, impact the results.