Comprehensive Trend Analysis of Past Century Indian Summer Monsoon Rainfall and its Variability

Abstract

The importance of rainfall for an agrarian economy like India is quite well known, especially during the Indian summer monsoon months viz. June through September. Analysis of rainfall characteristics over the past century can present an idea of the variability of rainfall. Variability of rainfall has been observed in intraseasonal as well as intra-annual time scales. This study is aimed at comprehensively analyzing the annual as well as seasonal rainfall trends over India and different homogenous rainfall regions of India over a period of 119 years (1901-2019). Results from the study infer that there has been an increasing trend in rainfall over low rainfall regions such as northeast India there is a decreasing trend over central and northeastern India. The annual rainfall and monsoon rainfall over India as a whole present an increasing trend but the number of extreme rainfall years have increased in recent times. A major concern of decreasing rainfall has been observed over central India where there is a decreasing rainfall trend with an increase in the number of break days over the past 30-40 years. Major findings of this study are that the number of excess/deficit monsoon seasons has rapidly increased post-1960 with more deficit rainfall years.