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Abstract

Rain-gauge, satellite-derived, and re-analysis datasets were evaluated for trends in mean and extreme rainfall in and around S-SE Asia over 1979-2022. Results indicate rainfall increases in most of maritime and coastal regions and over adjacent seas during the wet season. Rain-gauge data show strong increases exceeding 50% in annual mean precipitation and various extreme precipitation indices over Vietnam and the northwestern part of Mainland Southeast Asia (MSEA) where precipitation is largely fed by moisture originated from the adjacent seas and the NW part of the Indian Ocean. Increasing precipitation trends are associated with strong warming-driven evaporation increases over the Indian Ocean. A moisture budget trend analysis using ERA5 re-analysis data shows that increasing evaporation results in increasing atmospheric vapour transport over the NW Indian Ocean along the pathway which typically supplies moisture to S-SE Asia during the summer monsoon season. The major part of increased moisture supply from the Indian Ocean ends up as precipitation over the Indian Peninsula and the adjacent oceanic regions, the Bay of Bengal, in particular. ERA5 also reveals pronounced increases in winter precipitation over the MSEA, in accordance with rain-gauge data, associated with strongly increasing transport of moisture originated from the South China Sea and the western tropical Pacific.