Analysis of spatial patterns of daily precipitation and wet spell extremes in Southeast Asia

Abstract

ABSTRACTThe study investigates the spatial distribution of extreme daily rainfall and wet spells in Southeast Asia (SEA) at annual, seasonal, and intraseasonal scales using 16 years of data from the Tropical Rainfall Measurement Mission. A detailed analysis is conducted using various indices that characterize exceedance probabilities and relative contribution of extremes to the total rainfall. The selected indices include the Gini index, which is a measure of overall inequality, and is employed for the first time to examine SEA rainfall characteristics. The favoured regions (hotspots) of rainfall extremes during each season are identified, and their linkages with terrain and seasonal winds discussed. The intraseasonal variability in rainfall extremes is investigated by focusing on different phases of the Madden–Julian Oscillation (MJO). At the annual scale, four main hotspots are observed, which are located off the coast of Myanmar, over eastern Indian Ocean, northwestern Borneo and over Philippines. A majority of indices shows considerable land–sea contrast, with lower values over land. Lower Gini index as obtained for land regions indicate that the rainfall distribution, and the relative contribution of each class to the total rainfall are more uniform over land compared to sea. The land–sea contrast in indices is stronger during boreal summer and winter, and weaker during boreal fall. During boreal spring, the Myanmar coast has high probability of extremes, which further increases during boreal summer. The most evident hotspot regions during boreal fall and winter are along the coast of Vietnam, and the eastern coast of Malay Peninsula, respectively. The wind‐terrain interactions play a crucial role in determining the location of most hotspots. In general, the impact of active (suppressed) MJO phases is to increase (decrease) the probability of extremes in the study domain. However, local scale departures from this general pattern are observed, which are discussed in this work.