Trends in Extreme Wet Events during Summer Monsoon Season over India

Abstract

India is a predominantly agrarian country with most of the agriculture in India being rainfed. Summer monsoon means life-giving rains for the entire Indian subcontinent. In India, the success or failure of the harvest and water scarcity in any year is always considered with the greatest concern. Extreme wet and dry events play a vital role in the intra-seasonal variability of monsoon rainfall. Particularly, in recent times, the occurrences of wet spells over India have led to widespread floods in the country. With changing climatic conditions, the occurrence and prediction of these extreme events have become a major stabilizing factor for the millions inhabiting the country. In this study, using 117 years (1901-2017) of high resolution daily gridded rainfall data, trends in extreme high rainfall events over six regions of India have been examined. The temporal change in extreme rainfall events during the time period 1901-1950 and 1951-2017 in summer monsoon months (June, July, August and September) has also been examined, in order to understand the increasing effect of anthropogenic factors after 1950. Using standardized scores (z-scores), each grid cell is analyzed to identify the number of extreme wet spells experienced during the study period. The analysis reveals that the number of extreme wet events showed an increasing trend in the month of June, as against a decreasing trend in July, after 1950, in most of the regions. In the recent period, the number of wet extreme events also show a decreasing trend in the northeastern region, which is considered as one of the rainiest zones of the world. As the present study tries to evaluate the changing trend of extreme wet events, it will help in formulation of hazard management strategies and policies by government planners.