Future Change of Occurrence Frequency of Baiu Heavy Rainfall and Its Linked Atmospheric Patterns by Multiscale Analysis

Abstract

The future change of heavy rainfall (meso-β scale) in the Baiu season, the atmospheric patterns (over meso-α scale) of sea level pressure and surface vapor flux, and the connection between them were investigated by analyzing multiple datasets of a high-resolution non-hydrostatic regional climate model (NHRCM05) for better simulating heavy rainfall, a coarser-resolution global atmospheric climate model (AGCM20) embedding the NHRCM05, and a huge database for Policy Decision-Making for Future climate change (d4PDF) with a coarser-resolution. As a result, northern Japan and Japan-sea-side areas have a statistically significant increase of heavy rainfall that is caused by an increase in the atmospheric patterns with westward-protruding Pacific high and northward-invading vapor flux along the periphery of the high. In the Pacific side in eastern Japan, the typical atmospheric pattern prone to heavy rainfall will change in the future as it will decrease the occurrence frequency of the atmospheric pattern that presently caused heavy rainfall with cyclones located at south of Japan. Besides, the atmospheric pattern with westward-protruding pacific high, that presently caused heavy rainfall mainly in western Japan, will expand the area of heavy rainfall eastward in the future due to an eastward-invading vapor flux.