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This study presents the reversal nature in rainfall over heavy rainfall zone (HRZ; more than 80% of the long period average (LPA) of the Indian summer monsoon rainfall (ISMR)) and low rainfall zone (LRZ; less than 40% of ISMR-LPA) in India. The India Meteorological Department (IMD) high-resolution (0.25° × 0.25°) dataset is used from 1901 to 2016. The single and multiple change-point detection techniques are used to find the change in rainfall patterns over both regions. Further, the study period is divided into two halves P1 (1901–1958) and P2 (1959–2016) to examine the change in rainfall patterns in the recent and past periods. In P2, the rainfall pattern gets reversed, and ISMR has shown a significant increasing (decreasing) trend over the LRZ (HRZ). The increasing/decreasing number of moderate- and high-intensity rainfall events is one of the causes for this reversal pattern. Additionally, the number of dry days is increased over the HRZ and decreased over the LRZ. This study further confirms that the “dry becomes drier and wet becomes wetter” paradigm is not solely acceptable for India. The present study provides information about changes in dry days and ISMR variability in the context of climate change, which will be useful to agricultural risk management, water resources, drought monitoring, model developers, and policy planner on the adaptation strategies for climate change.

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.

This study presents the reversal nature in rainfall over heavy rainfall zone (HRZ; more than 80% of the long-period average (LPA) of the Indian summer monsoon rainfall (ISMR)) and low rainfall zone (LRZ; less than 40% of ISMR-LPA) in India. The India Meteorological Department (IMD) high-resolution (0.25˚×0.25˚) dataset is used from 1901 to 2016. The single and multiple change point detection techniques are used to find the change in rainfall pattern over both the regions. Further, the study period is divided into two halves P1 (1901-1958) and P2 (1959-2016) in order to study change in rainfall pattern in the recent and past periods. In P2, rainfall pattern gets reversed and interestingly ISMR has shown an increasing trend over LRZ and a decreasing trend is noticed over HRZ and the results are statistically significant. The increasing/decreasing number of moderate and high intensity rainfall events are the main cause for this reversal pattern. Additionally, the number of dry days is increased over the HRZ and deceased over the LRZ. This study further confirms that ‘dry becomes drier and wet becomes wetter’ paradigm is not solely acceptable for India. The present study provides information about changes in dry days and ISMR variability in the context of climate change, which will be useful to agricultural risk management, water resources, drought monitoring, model developers, and policy planer on the adaptation strategies for climate change.

The Indian southwest monsoon season is considered the lifeline of the region's socioeconomic wellbeing. It is recognized that even small variations often lead to notable impacts on the regional economy and agricultural productivity. As a precursor to droughts, this study identifies from century-long data, Monsoon Sparse Zone (MSZ) as a locale with less seasonal rainfall compared to the long-term average climatology. Identifying the MSZ is crucial to understand the spread and propagation of drought-prone areas. The present study investigates the nature of the major MSZ shift in India during the past 116 years (1901–2016) and probable meteorological factors responsible for that transitions. For this purpose, the high-resolution daily rainfall analysis from India Meteorological Department (IMD) and other surface and upper air meteorological parameters from, the NOAA, CRU, and NCEP-NCAR are used. Two drought indices are used to study the MSZ and its epochal shifts during the past century over India. The MSZ locales follow the counter-clockwise shift from west to north-central India through the peninsular region from one to another epoch (each of 29 years) that is statistically significant. The MSZ shifting is insensitive to epochal duration selection. Large-scale and regional processes that may impact the shift of MSZ are analyzed. The El Nino-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) have strong influences on the MSZ shift. Additional synergistic effect of large-scale – factors such as westward shifting of subsidence branch of the Walker circulation, the orientation of IOD and local-scale phenomena like the increased surface temperature, moisture flux inflow from the Bay of Bengal, also have shifts aligning to cause this detectable and significant change in the MSZ locales. The presence of MSZ conforms to the drought-prone area over India and has a direct influence on water resources, agriculture, and allied sectors.