Characteristics of southwest summer monsoon rainfall events over East India

Abstract

The variability in Indian summer monsoon rainfall (ISMR) has an immense socioeconomic impact on India, especially over the monsoon core region. In this study, a thorough analysis of the ISMR (June to September—JJAS) has been performed for East India (EI), a part of the monsoon core zone, and for its four subdivisions (Odisha, Chhattisgarh, Jharkhand, and Bihar). The long-term climatology, variability, and trends of various categorical rainfall events as defined by India Meteorological Department (IMD) have been analyzed by using IMD high-resolution (0.25° × 0.25°) gridded dataset for 116 years (1901–2016). Also, the percentage contribution of various rainfall events to the total seasonal rainfall and wet days is estimated. To get the changes in the frequency of various dry spells, rainfall events, and associated seasonal rainfall, study period is divided into two halves, earlier period (P1: 1901–1958) and recent period (P2: 1959–2016). The results suggest that the percentage contribution of medium-intensity rainfall events (7.6–64.4 mm/day) to the total ISMR is higher (~ 72%) followed by high-intensity rainfall events (~ 15%) and low-intensity rainfall events (12%), while most percentage contribution to the total number of wet days is from low-intensity rainfall events (~ 54%) followed by medium-intensity rainfall events (~ 43%) and high-intensity rainfall events (~ 3%). In the recent period (P2), the ISMR significantly decreased over the central part of EI because of the significant decrease in the frequency of low and medium-intensity rainfall events and wet days. The remarkable decrease of wet days leads to an increase in the short (1 week) and long-duration (> 2 week) dry spells in P2. And at the same time, high-intensity rainfall events significantly increased over EI in the recent period (P2) and led to an increase in the flood situation over this region. The profound relation of deficit rainfall of EI with ENSO is getting weak in the P2. This study is certainly useful in determining the effects on various sectors because of the variability and changes in various categorical extreme rainfall events, short and long-duration dry spells during summer monsoon time over EI. Also, this study may assist the risk management sectors in acclimating advanced technologies for a sustainable future in the changing climate of the present global warming era.