Uncertainty in the Future of Seasonal Snowpack Over North America

Snow cover extent and snow water equivalent (SWE) are rapidly changing over North America. This study investigates the uncertainty in the projected changes in North American snow cover for the middle of the 21st century using the North American Regional Climate Change Assessment Program (NARCCAP) ensemble of dynamically downscaled regional climate models (RCMs). Across the NARCCAP models, temperature is projected to increase everywhere while precipitation is shown to increase everywhere except the western U.S. In this region, the NARCCAP models disagree on the sign of the change in precipitation during the Fall and Winter. Corresponding with these changes in temperature and precipitation, the NARCCAP models robustly show that SWE is projected to decrease over most of North America. The only exception to this is in the high-latitudes, where SWE is projected to increase during the coldest months corresponding with increases in precipitation. There is considerable uncertainty in the magnitude of changes in SWE over north America, especially in the west. Variations in magnitude correspond with baseline SWE amounts from the current climate simulations as well as variations in the drivers of the change, namely temperature and precipitation. Changes in temperature and precipitation also lead to changes in the timing of the snow cover season. The first snow covered date is projected to occur later in the fall while the last snow-covered date is shown to occur earlier in the spring. These shifts result in a reduction in the total number of snow-covered days. There are notable differences across the ensemble in the change in the number of snow-covered days in the western US. Also, changes in the first and last dates with snow cover are uncertain in the central plains of North America, primarily due to interannual variability in this region. (KEYWORDS: North American snow cover, snow water equivalent, climate change, climate models, NARCCAP)