Some aspects of daily rainfall distribution over India during the South-West monsoon season

Abstract

This paper presents the results of an analysis of the daily rainfall at 365 Indian stations for the 80-year period, 1901-1980. The rainfall data relate to the south-west monsoon season June to September (122 days), which accounts for the major part of the annual rainfall over most parts of the country. For each of the stations the rain-days are arranged in ascending order of rain amount, and the association between the cumulated percentage rain amount (x) and the cumulated percentage number of rain-days (y), designated as the normalized rainfall curve (NRC), is calculated. It has been shown in an earlier study that x and y are related by the equation x = y exp [-b(100-y)^c], where b and c are empirical constants that depend on the coefficient of variation (CV) of the rainfall series. This equation has been utilized to study various parameters of the daily rainfall distribution. The coefficient of variation of the daily rainfall series varies between 100 per cent and 230 per cent at individual stations, with nearly half the number of stations having CV values in the range 130-150 per cent. The number of days of significant rainfall (days with rainfall greater than the mean intensity per rain-day) constitute about 30 per cent of the total number of rain-days and account for about 75 per cent of the seasonal rainfall at almost all the stations.