Characteristic features of hourly rainfall in India

Hourly rainfall data recorded at 72 Self Recording Raingauge Stations (SRRG) for the period 1969-2006 are utilized to study the characteristic features of hourly rainfall and diurnal variations of rainfall in India. Temporal changes in the short duration (less than 12 h) rainfall extremes are examined. Time distribution of a heavy rain spell of 24 h duration, which is an important component in water resources management and flood control studies, is analysed. Different aspects of hourly rainfall such as, average number of rain hours in a year, empirical probability distribution functions have also been examined. Analysis indicates, many stations in India have recorded more than 10 cm of rainfall in an hour's duration. Such stations are located along the west coast, foothills of Himalayas and along the tracks of monsoon disturbances. Extreme rainfall events of various duration (3-12 h) show increasing trends, significant at 5 level, at many stations located in central India and peninsular India except for southern part of west coast. Time distribution of hourly rainfall shows that, on average, 25 of the daily rainfall can be received in just 3 h, while 80 can occur in 12 h during the heavy rain spells of 24-h duration.