Climatic and environmental changes in Southeast Asia

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In the present study, the past climatic changes in East and Southeast Asian monsoon region during last several decades and their relationship with recent environmental changes have been analyzed. The main results are as follows :Precipitation variations in South China during the onset phase of summer rainy season have been analyzed and the amount of precipitation is related with the onset of South China Sea summer monsoon circulation. It is highly correlated with the sea surface temperature in the South China Sea during the preceding February to April. The magnitude of 1998 flood in Chanjiang River in central China was not extraordinary big when compared with the past records. The rainfall in the catchment was not as large as that in 1954, but the flood level was higher. This is due to the change of river environment such as construction of dikes and sedimentation.Rainfall in Thailand apparently decreased in resent 40 years, especially in September. It may highly correlated with the environmental changes due to rapid deforestation. River runoff has been also decreasing due also to the social environmental changes by the increase of water usage by irrigation or other human activities.The mass flowering of tropical rain forest in Malaysia was found to correlate with La Nina events, not with E1 Nino Events as previously believed. The trigger of these events is low temperature due not to the cold surges but to the radiative cooling under the development of the subtropical high.The anomalous sea surface temperature distribution in the Indian Ocean in 1998 was triggered by the E1 Nino event.The differences of seasonal changes in Southeast Asian and western North Pacific monsoons, inter-hemispheric seasonal changes of monsoons and the important role of Asian winter monsoon on these changes have been revealed.