An analysis of trends in the rainfall and droughts occurring in the southwest monsoon and northeast monsoon systems in the southern Peninsular India

Abstract

A detailed climatic classification of Karnataka and Tamil Nadu States of southern Peninsular India which receive rainfall from both southwest and northeast monsoon has been made by using the data of all provincial raingauge stations in these States for the period 1901-75 and a comparison of the same is made with earlier classifications.

A comparison of the rainfall normals (1901-1950) with the rainfall amounts recorded at different stations in these States during 1951-1975 indicates that decreases in annual rainfall have occurred in the latter period for many regions in Tamil Nadu which receive rainfall predominently during northeast monsoon, whereas increases have occurred in Malnad area, coastal Karnataka and north Interior Karnataka which receive rainfall mostly during southwest monsoon. Maps showing differences between rainfall during these periods have been presented. Trends of annual rainfall as well as rainfall during principal seasons, viz., southwest monsoon, northeast monsoon and pre-monsoon thunderstorm season of typical stations in these regions have been studied and results discussed. Use of auto-regressive models for study of trends is discussed.