Projection of Future Climate Change over Japan in Ensemble Simulations Using a Convection-Permitting Regional Climate Model with Urban Canopy

This study investigates future changes in temperature and precipitation extremes over Japan by the end of the 21st century using ensemble simulations under the Representative Concentration Pathway 8.5 scenario projected by a convection-permitting regional climate model with a grid spacing of 2 km. For all ensemble members, the projected future climate indicates robust increases in the 99th percentile of hourly temperature over all regions of Japan. In contrast, the 99th percentile of hourly precipitation increases over the northern and part of the eastern regions of Japan, particularly on the Sea of Japan side of northern Japan in July. A couple of local-scale areas in Hokkaido are identified as a cause of significant increases in rainfall over this region. Increases in horizontal convergence near the surface and in the middle troposphere are responsible for increased heavy precipitation over a local-scale area of Hokkaido in July. The enhanced convergence near the surface can be attributed to strengthened westerly wind, whereas that in the middle layer can be explained by vertically unstable layers.