Extreme Precipitation in 150-year Continuous Simulations by 20-km and 60-km Atmospheric General Circulation Models with Dynamical Downscaling over Japan by a 20-km Regional Climate Model.

Continuous simulations from the middle of the 20th century to the end of the 21st century were performed using a 20-km atmospheric general circulation model (AGCM), and a 60-km AGCM with dynamical downscaling via a 20-km regional climate model (RCM), to explore the transitional changes in regional extreme events. The representative scenario simulations by the AGCMs followed the protocol of the High Resolution Model Intercomparison Project experiments. In addition, ensemble simulations using four emission scenarios were conducted using the 60-km AGCM with 20-km RCM downscaling. Regardless of the emission scenario used, the global-mean relative increase in annual maximum daily precipitation (Rx1d) was roughly proportional to the increase in the global-mean surface air temperature (SAT), consistent with previous results from coarser-resolution climate models. It means that the relationship is also valid for a higher-resolution model. A similar correlation between Rx1d and SAT was seen also in the values averaged over the Japanese land area in the 20-km AGCM and the 20-km RCM simulations after applying a 10-year running mean. However, it was not so clear in the 60-km AGCM, mainly because of insufficient grid points over land in Japan in the 60-km AGCM owing to too large noise. This suggests that transitional changes in Rx1d at regional scales such as the Japanese land area can only be represented by using a model resolution as high as 20 km, unless using ensemble simulations. [ABSTRACT FROM AUTHOR]