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Abnormal rainfall patterns forecast

N. Gopal Raj

Researchers warn of "a substantial increase in hazards related to heavy rainfall" over Central India in the coming years.

GLOBAL WARMING has been widely predicted to increase extreme weather events, including bouts of excessive rain. Now, in research just published in the journal Science, Indian atmospheric scientists say extreme rain events have grown both in number and intensity over large parts of Central India in the space of half a century.

In their paper, the researchers from the Indian Institute of Tropical Meteorology, Pune, and the Indian Institute of Science, Bangalore, warn of "a substantial increase in hazards related to heavy rainfall" over Central India in the years ahead.

The scientists analysed daily rainfall patterns during the south-west monsoon from 1951 to 2000 in an area of about 1.4 million square km in Central India extending from Uttar Pradesh in the north to Andhra Pradesh in the south and from Madhya Pradesh in the west to Bihar in the east. Episodes of "heavy" rainfall where places in Central India received 10 cm or more of rain in a single day during the monsoon had increased at the rate of 10 per cent every decade since the early 1950s.

Instances of "very heavy" rainfall where places received 15 cm or more of rain in a day had "more than doubled" between 1951 and 2000, according to the paper.

In addition, places were being deluged with more rain than before. The average intensity of the heaviest four rain events during each monsoon had grown at about 10 per cent each decade, from 18 cm in 1951 to 26 cm in 2000, the scientists noted.

The increasing trend in extreme rainfall events over Central India was "quite robust" and could continue for the next decade or two, believes B.N. Goswami, director of the Indian Institute of Tropical Meteorology and first author of the paper. As such, exceptionally heavy rain could lead to floods and mudslides, and the potential for natural disasters would also grow, he told this correspondent.

"All we have documented clearly is the increasing trend of extreme rain events," said V. Venugopal of the Indian Institute of Science who is the second author of the paper. "No analysis has been done to establish a direct connection with global warming. However, [the trend] appears to be consistent with what may be expected under global warming as demonstrated from model simulations and physical considerations."

The researchers, however, found that the increase in extreme rainfall events occurred during a period when the waters of the tropical Indian Ocean became warmer, producing more water vapour. In addition, temperatures over India too increased by 0.5 degrees C in the last 50 years, observed Dr. Goswami.

The capacity of the atmosphere to hold moisture would thereby increase and conditions could become conducive for heavy downpours.

In a separate paper published earlier this year, a group of researchers at the Indian Institute of Tropical Meteorology suggested that there could be an increase in "severe rainfall activities" across an extensive area covering the Western Ghats, Maharashtra, southern Gujarat, and parts of Central India by the end of the 21st century.

The scientists, who published their work in the journal Current Science, used a regional climate model to examine climate change scenarios that India might face.

More recently, after examining rainfall data from 100 observatories across the country, scientists at the India Meteorological Department's National Climate Centre in Pune found that extreme rainfall events during the south-west monsoon had increased significantly between 1901 and 2000 along the West Coast, Maharashtra, and southern Gujarat.

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