Characteristics of intense rainfalls over southwestern Japan in the Baiu season in the CMIP3 20th Century simulation and 21st Century projection

This study examined features of intense rainfalls over southwestern japan in the baiu season (june and july) in the 20th century climate in coupled models (20c3m) and 21st century projection (special report on emission scenarios [sres] a1b) used by 18 climate models that contributed to the world climate research programme's coupled model intercomparison project phase 3 (cmip3). characteristics of daily precipitation over an area of 5° x 5° within 30°n-35°n and 130°e-135°e obtained by 20th century climate simulation were compared with observed precipitation data for a 3-year period (1997-1999). the studied area includes four meshed subareas of 2.5° x 2.5°. the four-area averaged daily precipitation and the maximum precipitation in the four areas were analyzed. the order statistics of the maximum precipitation indicated a very wide difference from model to model. to measure the temporal and spatial concentration of precipitation,concentration ratio, defined as (the average of the first-to sixth-largest maximum precipitation)/(time-area averaged precipitation) was examined. although a few models reproduced a reasonable concentration ratio comparable to observations,many other models did not reproduce a reasonable ratio. models of medium and high horizontal resolution with the arakawa-schubert cumulus scheme tended to reproduce a reasonable concentration ratio. models that simulate a realistic baiu frontal precipitation zone were able to simulate a proper concentration ratio. features of the intense rainfalls in the 21st century climate projection by the models were examined for june and july over a 3-year period (2097-2099). the characteristics of the models in regard to the intense rainfalls in the 20th century simulation were commonly found in the 21st century projections. because the difference among the models was too large with respect to the intense rainfalls,the change in intense rainfalls under the climate changes in the 21st century cannot be definitely determined by cmip3 models. © 2012,meteorological society of japan.