More Indian Monsoons?

Extreme rainfall events like monsoons can have devastating consequences including landslides, flash floods, and crop destruction. Even more alarming, most climate models have predicted that extreme rainfall events will become more common as global surface temperature increases, though observational evidence of this trend has been scarce. In a Report in the 1 Dec 2006 Science, Goswami et al. analyzed a daily rainfall data set for central India and showed that there has been an increase in the frequency and intensity of heavy rain events (greater than or equal to100 mm/day of rain), and a decrease in the frequency of light to moderate rain events (greater than or equal to 5 mm/day, but less than100 mm/day) during the monsoon seasons from 1951 to 2000. Interestingly, the seasonal mean monsoon rainfall in India has been relatively stable for the past half century. But the researchers point out that this is because the increasing contribution of heavy rain events is offset by the decreasing contribution of lighter rain events. The findings suggest that severe rain events over central India may become more common if global warming continues as expected.

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Science 1 December 2006:
Vol. 314. no. 5804, pp. 1442 - 1445
DOI: 10.1126/science.1132027

Reports
Increasing Trend of Extreme Rain Events Over India in a Warming Environment

B. N. Goswami,1* V. Venugopal,2 D. Sengupta,2 M. S. Madhusoodanan,2 Prince K. Xavier2
Against a backdrop of rising global surface temperature, the stability of the Indian monsoon rainfall over the past century has been a puzzle. By using a daily rainfall data set, we show (i) significant rising trends in the frequency and the magnitude of extreme rain events and (ii) a significant decreasing trend in the frequency of moderate events over central India during the monsoon seasons from 1951 to 2000. The seasonal mean rainfall does not show a significant trend, because the contribution from increasing heavy events is offset by decreasing moderate events. A substantial increase in hazards related to heavy rain is expected over central India in the future.

1 Indian Institute of Tropical Meteorology, Doctor Homi Bhabha Road, Pashan, Pune 411 008, India.
2 Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, Karnataka 560 012, India.

* To whom correspondence should be addressed. E-mail: goswami@tropmet.res.in