Projection of future climate change over Japan in ensemble simulations with a high-resolution regional climate model

Abstract

Future changes in surface air temperature and precipitation over Japan by the end of the 21st century are projected by a well-developed non-hydrostatic regional climate model with a grid spacing of 5 km under the RCP8.5 scenario. Uncertainties in the projected temperature and precipitation are also evaluated with the results obtained from ensemble simulations using this high-resolution model. The projected future climate indicates robust increases in the annual-mean surface air temperature for all regions in Japan. In contrast, many regions do not exhibit statistically significant changes in annual precipitation. In some regions and months, however, monthly precipitation in a couple of members of the ensemble simulations has a statistically significant decrease or increase. Monthly precipitation over the eastern Japan Sea side (EJ) region in December has relatively robust decreases. These decreases are attributed to decreases or weakening of convection over the Japan Sea polar air-mass convergence zone, which is accounted for by the weakening of large-scale low-level northwesterly winds associated with the winter monsoon. The relationship between precipitation and convergence in the EJ region is consistent with the results above: Convective clouds are shallower in the future climate compared with those in the present climate.