Asian Summer Monsoon and its Associated Rainfall Variability in Thailand

Abstract

"The Asian monsoon is an important component of the Earth’s climate. Its associated rainfall variability is a crucial factor for Thailand’s socio-economic development, water resources and agricultural management. An analysis shows that the Thailand rainfall annual cycle is in phase with the Indian summer monsoon (ISM) and the western North Pacific summer monsoon (WNPSM). On the basis of the Empirical Orthogonal Function (EOF) analysis, the dominant spatial-temporal interannual variability in summer monsoon rainfall (Jun.–Sep.) during 1975-2006 could be explained by the first two EOF modes, accounting for 34% of the total variance. The EOF1 was spatially dominated by strong positive signals in the central and east, whereas the EOF2 exhibited dipole variability. The coefficient time series of EOF1 significantly correlated positively with ISM index, but negatively with WNPSM index. The results suggest that summer monsoon rainfall in Thailand is higher (lower) than normal during the strengthening (weakening) of ISM. In contrast, rainfall in the north-east (central) is surplus (deficit) during the strengthening (weakening) of WNPSM. These findings imply that, on an interannual time scale, ISM and WNPSM exert their influence to a different extent on summer monsoon rainfall in Thailand. A clear picture of linking mechanisms and interactions with another climate mode in the Indo-Pacific sector needs to be understood. This knowledge is essential for effectively adapting to climate-related hazards and rainfall extremes and for better management of water resource and agriculture in Thailand, especially under current/future warming conditions."