Identification of combined influence of climatic variables on indian summer monsoon rainfall extremes

Spatio-temporal variability of Indian Summer Monsoon Rainfall (ISMR) is responsible for extreme events like floods and droughts across India. In recent decades, the incidence of extreme precipitation events during ISMR is increased significantly, which are primarily linked to climatic variables like El Niño Southern Oscillation (ENSO), Equatorial Indian Ocean Oscillation (EQUINOO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO). In this study, extreme precipitation indices (EPIs) like consecutive dry days (CDD), consecutive wet days (CWD), maximum consecutive 5-day precipitation (Rx5day), and 95th percentile (R95p) have been considered to explain the characteristics of ISMR extremes. Moreover, a regional analysis has been carried out using the multiple wavelet coherence method to determine the coupled association of climatic oscillations with EPIs. Here, two-, three-, and four- climatic variable combinations have been applied to identify the best combination which explains the fluctuations of ISMR extremes all over India. Results indicate that two or more climatic oscillations could be sufficient particularly, AMO-ENSO-EQUINOO and AMO-ENSO-PDO are the best combinations to explain the variability of ISMR extremes across India. Apart from this analysis, wavelet decomposition and reconstruction analysis have also been performed to understand the scale-specific variability of the spatial-extreme precipitation. More than half of India had a significant correlation between reconstructed modes of ISMR extremes and climatic oscillations at interdecadal and multidecadal scales (8-16 and 16-32 -years), despite their interannual periodicities. This indicates that the non-stationary behaviour of the ISMR extremes was strongly associated with climatic variables at higher scales.