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India Monsoons Intensifying, Hazard Risks Increasing, Study Says

Sean Markey
for National Geographic News
December 1, 2006
 
India's monsoon rains are getting heavier, with more severe weather likely in the future, according to scientists who examined daily rainfall records since 1951.

"The magnitude of the strongest events has increased substantially over the past 50 years" in central India, lead study author B. N. Goswami, of the Indian Institute of Tropical Meteorology in Pashan, said in an email.

"Such events are associated with flash floods and mudslides. [And] our results indicate increasingly higher potential for such hazards in coming years."

(Related photo: "Mouse Rides Frog in India Monsoon: [July 5, 2006].)

At the same time, days with light to moderate rains during the June to September monsoon period are decreasing, the team reports today in the journal Science.

Moderate rains are desirable because they more readily soak into the ground, watering crops and filling aquifers and wells.

Overall, the seasonal average rainfall has changed little since 1951, with today's more frequent downpours offset by more dry days.

Intensifying Rains

India's weather is governed by its prevailing winds, which blow out to sea during the long dry season.

During the summer monsoon season the wind direction shifts, bringing cooler, moist air from the Indian Ocean and Arabian Sea over the Indian subcontinent (India map).

In their study, researchers analyzed daily rainfall data collected from 1,803 sites across central India between 1951 and 2000.

The team found that the total number of days with heavy rainfall—defined as four inches (ten centimeters) or more—increased 10 percent a decade since the early 1950s.

At the same time, days that saw downpours of 6 inches (15 centimeters) or more increased at least two-fold during the same period, "indicating a large increase in disaster potential," the study authors wrote.

Floods and Drought

Julia Slingo, director of climate research at the National Centre for Atmospheric Science at the University of Reading in England, says the study's overall findings are quite convincing.

She said the study is significant, because it shows that while mean rainfall may be stable, "there are changes in [how] the rain arrives—and that in itself has [important] implications."

Indian society has become highly attuned to long-standing monsoon patterns, Slingo said, noting that around 80 percent of the nation's 1.1 billion people depend on agriculture-related activities.

Too much or too little rain can spell disaster.

During the 2005 monsoon season, for example, a record 37 inches (94 centimeters) of rain fell on the financial capital of Mumbai (Bombay) in a single day in July.

The record rainfall flooded the city, wiped out surrounding shantytowns, and shut down the Mumbai stock exchange. More than a thousand people died in the deluge.

By contrast, monsoon rains were light in July 2002, causing widespread crop failures and water shortfalls, Slingo said. The drought cut 3 percent from India's gross domestic product that year.

"These extreme events emphasize the vulnerability of India to changes in monsoon behavior," she said, adding that predicting the global warming impact on India is a critical research priority.

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