Precipitation extremes during Indian summer monsoon: role of cyclonic disturbances

The Indian summer (JJAS) shows high variability in both space and timescales. Changes in precipitation extremes play an important role on the regional scale due to their serious socio-economic consequences. This study, therefore, is mainly focused on understanding the variation of precipitation extremes during summer monsoon season in the presence of cyclonic disturbances forming over the Bay of Bengal (BOB), Arabian Sea, Land Area (LA) and Total. For this, several indices of observed precipitation extremes, in terms of frequencies, intensities and spell duration have been computed for the period 1951-2007 using daily APHRODITE data of 0.5A degrees latitude x 0.5A degrees longitude resolution. Correlation analysis reveals that a large part of the country exhibits positive relationship between the indices of precipitation extremes and frequency of cyclonic disturbances. Correlations with the indices of frequencies defined as seasonal count of days when rainfall exceeds 30, 20 and 10 mm show that spatial extent and strength of the positive relationship decreases with increase in threshold values. Disturbances forming over BOB play dominant role in precipitation during Indian summer monsoon.