County-Scale Climate Projections Over Minnesota and the Effects of Lakes

Climate projections for three future shared socioeconomic pathway scenarios from six CMIP6 global climate models (GCMs) were dynamically downscaled over Minnesota with the regional Weather Research and Forecasting model coupled to a lake model at 4-km horizontal resolution representing energy and moisture fluxes over more than 60 lakes inside the state borders. Warming over Minnesota is projected to increase in all seasons, especially in winter. Snow depth and lake ice cover is expected to decrease. However, compared to GCM projections, our results show stronger increases in spring and early summer precipitation, potentially from the extra evaporation over lakes. This trend especially manifests in heavier precipitation events. Precipitation is expected to decrease during the peak growing season in middle and late summer. We anticipate that temperature and precipitation values will be significantly different by the middle and end of the 21st century, respectively, from what has been observed at the beginning of the 21st century. Winters and summers are expected to be up to 7 and 4°C warmer, respectively, especially over northern and central Minnesota. Average spring precipitation may increase by more than 1 mm d⁻¹ over central Minnesota. Despite generally stronger precipitation, winter snow depth is projected to decrease by more than 12 cm, especially around the Lake Superior shores and in northern Minnesota. Lake ice cover is projected to decrease by more than half over deeper lakes. The number of lake ice days per year and days per year with snow depth of more than 2.54 cm may decrease by up to 70 and 55, respectively.