7-On Variability of Wet Season over Major River Basins of India.

Abstract

Longest possible instrumental area-averaged monthly, seasonal (winter JF, summer MAM, monsoon JJAS and post-monsoon OND) and annual rainfall series have been developed for each of the 11 major river basins and the West Coast Drainage System (WCDS) of India using highly quality-controlled data from well spread network of 316 raingauges. For the period 1901-2005 with complete data of all stations the area-averaged series has been prepared from simple arithmetic mean of the gauges in the particular basin, and for period prior to 1901 (sometimes going back to 1813) with lesser observations the series is constructed by applying established objective method. For different basins the starting year of rainfall data is as (ending year is always 2005): The Indus 1844; The Ganga 1829; The Brahmaputra 1848; The Sabarmati 1861; The Mahi 1857; The Narmada 1844; The Tapi 1859; The Godavari 1826; The Krishna 1826; The Mahanadi 1848; The Cauvery 1829 and The WCDS 1838. Fluctuation characteristics of the annual rainfall over different basins are briefly described. In tropical monsoonal climate understanding regional variability of the wet (or rainy) season is as important as the variability of rainfall, very little attempt is made to study the later compared to former. The present study intends to document climatology, as well as fluctuation characteristics of the parameters of wet season (starting date, ending date and duration) over major basins of the country using longest available rainfall sequences.