Trends in Precipitation Extremes over India

One of the most significant consequences of global warming due to increase in greenhouse gases would be an increase in magnitude and frequency of extreme precipitation events. In the present study the trends in extreme rainfall indices for the period 1901-2000 were examined for 100 stations over India. The trends for the southwest monsoon season and annual period were calculated separately. The results show that most of the extreme rainfall indices have shown significant positive trends over the west coast and northwestern parts of Peninsula. However, two hilly stations considered (Shimla and Mahabaleshwar) have shown decreasing trend in some of the extreme rainfall indices. About 60-90% of the annual rainfall over India is received during the southwest monsoon season (June to September), which is vital for the economy of the country. Inter-annual variation of seasonal and annual rainfall is a subject for more serious research work in India. However, information about the long term trends of rainfall is also important. Previous studies have addressed the issue of changes in the mean rainfall. For example, Guhathakurta and Rajeevan (2006) have shown that there is no long term trend in the southwest monsoon seasonal rainfall over the country as a whole, but there are significant regional variations. However, changes in extreme precipitation are also equally important to investigate. Impact of climate changes are felt most strongly through changes in climate extremes. Any positive or increasing trend in the extreme rainfall events is also a serious concern. The recent extreme heavy rainfall event occurred over Mumbai on 26 th July 2005 prompts us to think whether there is any significant trend in extreme rainfall events over different parts of India. One of the most significant consequences of global warming due to increase in greenhouse gases would be an increase in magnitude and frequency of extreme precipitation events. These increased extreme precipitation events can be attributed to increase in moisture levels, thunderstorm activities and large scale storm activity. In the global warming scenario, climate models generally predict an increase in large precipitation events (Houghton et al 2001). The numerical modelling community and data analysts have shown interest on the issue of extreme events occurring around the world.