Comparison of Near Future (2015-2039) Changes in the East Asian Rain Band with Future (2075-2099) Changes Projected by Global Atmospheric Models with 20-km and 60-km Grid Size

Abstract

Global warming projection experiments were conducted using a 20-km mesh global atmospheric model, focusing on the near future (2015-2039, 25 years) change in the rain band of East Asian summer monsoon. In the present-day climate simulations (1979-2003, 25 years), observed historical sea surface temperature (SST)s are given to the models. For the near future and the future (2075-2099, 25 years) climate, A1B emission scenario is assumed. To assess the uncertainty of climate change projections, we performed ensemble simulations with the 60-km resolution model combining four different SSTs and three atmospheric initial conditions. Projections by the 20-km and 60-km models consistently show the increase of July precipitation over Japan, but magnitude of change and level of statistical significance in the near future are smaller than those in the future. The near future projections suggest the delay in the termination of rainy season over Japan, although this delay is less evident and less robust compared with that in the future. We confirmed that the near future climate is located approximately midway between the present-day climate and the future climate, mainly because forcing by greenhouse gases in the near future is also located midway between the present-day climate and the future climate.