Decreasing southwest monsoon rainfall over Myanmar in the prevailing global warming era

The characteristics of the southwest monsoon (SWM) rainfall over Myanmar were studied using APHRODITE gridded daily rainfall datasets for the period 1951-2010. Myanmar, being an agrarian economy, is predominantly dependent on the SWM rainfall. The spatial distribution of rainfall (rainy days) has shown higher rainfall of 2,000 mm (>140 rainy days) over southwest parts, rainfall of similar to 1,000 mm (100-120 days) over north and eastern parts and an arid zone with rainfall of less than approximately 500 mm (<80 days) over west central parts, all indicating earlier onset over the southwest and late onset over the northeast. Analysis of the rainfall and rainy days between the two 30 year periods 1951-1980 and 1981-2010 representative of the pre-global warming and global warming periods showed a reduction of rainfall by 100 mm and 5-10 rainy days during the later period of global warming. The Climate Research Unit and Global Precipitation Climatology Project rainfall datasets and the Geophysical Fluid Dynamics Laboratory Earth System global model simulated rainfall data for the current climate period exhibited a similar decline of SWM rainfall over major parts of Myanmar. The results indicated a 20% reduction in the mean westerly strength over south Myanmar in the global warming period, which was related to a decrease of the meridional gradient of sea surface temperatures over the Bay of Bengal. This study establishes two distinct rainfall zones in the southwest and northeast over Myanmar and a reduction of rainfall in the recent global warming period that will lead to a reduction in agriculture production.