Interdecadal variation of summer rainfall in the Greater Mekong Subregion and its possible causes

This paper investigates the interdecadal variation in summer rainfall over the Greater Mekong Subregion (GMS) during 1981-2020 and its possible causes, using Climate Hazards Group Infrared Precipitation with Station rainfall datasets, European Centre for Medium-range Weather Forecasts Reanalysis fifth generation data and the atmospheric general circulation model ECHAM6. The dominant mode of summer rainfall in the GMS features a seesaw pattern with an increase in rainfall over the central-southern GMS and a decrease in rainfall in northwestern Myanmar-Yunnan. The dominant mode of the GMS summer rainfall shows a change in regime around 2001/2002. Interdecadal variability in rainfall is largely related to sea surface temperature anomalies (SSTAs) over the Western Pacific Warm Pool (WPWP). Warmer SSTAs in the WPWP lead to interdecadal variation in summer rainfall in the GMS by exciting an anomalous cyclone in the lower troposphere over the southern GMS-South China Sea. This is accompanied by anomalous ascending motions in the central-southern GMS and anomalous descending motions in northern Myanmar-Yunnan. The Matsuno-Gill mechanism, which links SSTAs with interdecadal variations in the GMS summer rainfall, is further confirmed by numerical experiments.