Projected Trends in Interannual Variation in Summer Seasonal Precipitation and Its Extremes over the Tropical Asian Monsoon Regions in CMIP5

Long-term changes in the interannual variation in summer seasonal [June-August (JJA)] precipitation over the tropical Asian summer monsoon (ASM) region were investigated using 22 simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) of the representative concentration pathway 4.5 (RCP4.5) run. Objective evaluations were performed with statistical tests to determine if there was an agreement among the multiple models. A robust increasing trend in fluctuations in the interannual variation in JJA precipitation over the ASM region was found. Expansions in both the wet and dry extremes of JJA precipitation anomalies were identified from the beginning to end of the twenty-first century, which were indicative of an intensification in interannual variation. These results indicate that the frequency and/or intensity of floods and droughts will likely increase under global warming. The spatial distribution of the projected expansion of wet and dry extremes differed over the ASM region. The signals in the wet extreme appeared throughout the whole ASM region, whereas those in the dry extreme were strong, particularly over the area from the Bay of Bengal to the equatorial western North Pacific, corresponding with the monsoon trough where the mean JJA precipitation increased.