RAINFALL VARIABILITY OVER SOUTH-EAST ASIA - CONNECTIONS WITH INDIAN MONSOON AND ENSO EXTREMES - NEW PERSPECTIVES

Seasonal and annual rainfall data for 135 stations for periods varying from 25 to 125 years are utilized to investigate and understand the i nterannual and short-term (decadal) climate variability over the South -east Asian domain. Contemporaneous relations during the summer monsoo n period (June to September) reveal that the rainfall variations over central India, north China, northern parts of Thailand, central parts of Brunei and Borneo and the Indonesian region east of 120 degrees E v ary in phase. However, the rainfall variations over the regions surrou nding the South China Sea, in particular the north-west Philippines, v ary in the opposite phase. Possible dynamic causes for the spatial cor relation structure obtained are discussed. Based on the instrumental d ata available and on an objective criteria, regional rainfall anomaly time series for contiguous regions over Thailand, Malaysia, Singapore, Brunei, Indonesia and Philippines are prepared. Results reveal that a lthough there are year-to-year random fluctuations, there are certain epochs of the above-and below-normal rainfall over each region. These epochs are not forced by the El Nino/La Nina frequencies. Near the equ atorial regions the epochs tend to last for about a decade, whereas ov er the tropical regions, away from the Equator, epochs last for about three decades. There is no systematic climate change or trend in any o f the series. Further, the impact of El Nino (La Nina) on the rainfall regimes is more severe during the below (above) normal epochs than du ring the above (below) normal epochs. Extreme drought/flood situations tend to occur when the epochal behaviour and the El Nino/La Nina even ts are phase-locked. (C) 1997 by the Royal Meteorological Society.