Global warming linked to bigger monsoons

updated 10:43 p.m. ET Nov. 30, 2006

WASHINGTON - India’s monsoon rains have intensified over the last half-century as average temperatures have risen, and more severe weather could be in store if global warming continues, scientists reported Thursday.

Heavy rains come more frequently and are more severe now than they were in 1951, the researchers wrote in the journal Science.

At the same time, moderate rains — the kind that are more easily absorbed — decreased, leaving the mean rainfall record about the same as it was five decades ago.

“The extreme events are so damaging because they pour in a large amount of rainfall over a small area in a very short time, leading to flash floods and landslides,” B.N. Goswami of the Indian Institute of Tropical Meteorology wrote in answer to e-mailed questions.

“On the other hand, weak and moderate events do not cause such damage and help recharge the ground water,” Goswami wrote.

If this trend continues, the number of extreme rain events could reach 100 per year, more than double the 45 or so such events common in the 1950s in central India, he wrote.

The researchers defined an extreme rain event as one where at least 3.9 inches (100 mm) of rain fell.

The average temperature increase in India between 1950 and 2000 is about 0.9 degree Fahrenheit (0.5 degree Celsius), Goswami said. That corresponds with the global rise in temperature.

Most scientists believe global warming is caused by the release of greenhouse gases, including carbon dioxide emitted by motor vehicles and some factories. These gases trap heat near Earth’s surface like the glass walls of a greenhouse.

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