Future Changes in Rainy Season over East Asia Projected by Massive Ensemble Simulations with a High-resolution Global Atmospheric Model

抄録

 In this study, future changes in the rainy season in East Asia are projected based on massive ensemble simulations of about 100 members with a 60-km mesh global atmospheric model (the 60-km model hereinafter) called the “Database for Policy Decision-Making for Future Climate Change (d4PDF)”. For the present-climate, historical observed sea surface temperatures (SSTs) are prescribed to the 60-km model. In the future, 4°C warmer climate relative to the preindustrial climate, six different SST distributions projected by Atmosphere–Ocean General Circulation Models of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) are given to the 60-km model. In the future, summer precipitation will generally increase in most regions of East Asia, but will decrease over western Japan. Precipitation decreases in June around 30-35°N over China, Korea and Japan. The Probability Density Function directly was derived from the massive ensemble simulations at each grid point in June and revealed that the most intense precipitation increase will occur in some regions where moderate precipitation decreases will take place in terms of the simple ensemble average. In western Japan, the onset of rainy season will delay and the retreat will occur earlier, resulting in a shorter rainy season. The decrease of precipitation in June over western Japan may be attributed to the counter-effect of the convergence of moisture to the south of Japan, originating in the southward shift of the western North Pacific subtropical high. The projected decrease in June precipitation over western Japan is confirmed to be robust, regardless of model differences in horizontal resolution, convection schemes, and with/without air-sea interactions.