Multidecadal summer monsoon rainfall trend reversals in South Peninsular India: a new approach to examining long-term rainfall dataset

Abstract

A long-term (1901-2020) gridded summer monsoon rainfall dataset for South Indian Peninsula has been examined to identify prominent rainfall trend reversals during the last 120 years. The current understanding of long-term rainfall variability in India is largely based on the linear monotonic trend analysis over a large geographical area in which multidecadal signatures and their geographical variations are missed out. Therefore, multidecadal rainfall trend variations are not clearly recognized. To overcome this limitation, an innovative, multipronged, and robust methodology based on mathematical and statistical tools is developed involving: 31-years moving average of percentage departure of summer monsoon rainfall for 120 years at district level; 15-years sliding trend analysis to identify the year of inflection point based on a change in direction of the trend; K-Means cluster analysis; Z-score based normality test of clusters; and determination of prominent timeframe of reversal of multidecadal rainfall trend.