The Interannual variability of rainfall over homogeneous regions of Indian summer monsoon

The Indian subcontinent, due to its enormous variety of geographical features, is associated with inhomogeneity. Hence, in the present study, we have classified the whole Indian subcontinent into four homogeneous regions, such as North India, Central India, South India, and Northeast India, based on the similarity in rainfall characteristics and associations with the regional/global circulation parameters. These four major homogeneous regions have quite different climatological distribution rainfall as well as the degree of variability, depicting the need of individual exploration of them. The rainfall indices are prepared for an extended period of 120 years from 1901 to 2020 to understand the interannual variability of it over these homogeneous regions. The changes in the temporal trend with time are explored by diving the whole time period into four periods of 30 years each, i.e., 1901-1930 (Period 1), 1931-1960 (Period 2), 1961-1990 (Period 3), and 1991-2020 (Period 4). During period 4, a declining trend is seen over North India while other three regions show an increasing trend. Also, the wavelet analysis is carried out to see the periodicity of rainfall pattern and found that the interannual variability is more during the postindustrial period due to the lack of any dominant periodicity. And, finally, we investigated the teleconnection patterns during these four defined periods for all the homogeneous regions with global sea surface temperature where we get the ENSO monsoon relation is weaker during the recent period for all the regions except north India, explaining the reason behind the drying trend over there.