The occurrence of exceptionally heavy rainfall events and associated flash floods in many areas during recent years prompted the researchers to study long-term changes in extreme rainfall over India.
Understanding the changes in extremes weather events is more important than the changes in mean pattern for better disaster management and mitigation. The analysis of the frequency of rainy days, rain days and heavy rainfall days as well as one-day extreme rainfall and return period has been carried out in this study to observe the impact of climate change on extreme rainfall events and flood risk in India.
The study tries to bring out some of the interesting findings that are very useful for hydrological planning and disaster management. Extreme rainfall and flood risk are increasing significantly in the country except some parts of central India. The study broadly indicates that the frequency of heavy rainfall events are decreasing in major parts of central and north India while they are increasing in peninsular, east and north east India.
This study reveals the noticeable changes in the extreme rainfall events that occurred over India in the past century. They are -
- The country experienced large spatial variations in annual normal rainy days. Annual normal rainy days varied from 10 days over extreme western parts of Rajasthan to the high frequency of 130 days over northeastern parts of the country.
- The non-parametric test as well as the linear trend analysis identified decreasing trends in the frequency of wet days in most parts of the country. Trend analysis of frequency of rain days, rainy days and heavy rainfall days showed significant decreasing trends over central and many parts of north India; and increasing trends over peninsular India. Also, the great desert areas of the country have experienced increased number of wet days.
- Analysis of one-day extreme rainfall series has shown that the intensity of extreme rainfall has increased over coastal Andhra Pradesh and its adjoining areas, Saurashtra and Kutch, Orissa, West Bengal, parts of northeast India, and east Rajasthan. Significant decrease in intensity as well as frequency of extreme rainfall has been observed over Chhattisgarh, Jharkhand and some parts of north India.
- The flood risk also increased significantly over India. The flood risk was more in the decades 1981–1990, 1971–1980 and 1991–2000. The increase of flood risk has increased during the last two decades mostly over the eastern coast, West Bengal, east Uttar Pradesh, Gujarat and Konkan region.
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