India's Mahanadi River (as seen from orbit) on 7 August 2006. As the monsoon struck, the river began running high and wide, changing from from dark blue to pale blue, a sign that mud-laden run-off is present.
Credit: NASA/Earth Observatory
Global warming is intensifying the monsoon in Central India, according to a study that warns of increasing risk from heavier rains during the season.
The research, published in the latest issue of the U.S. journal Science, reinforces claims that global warming is boosting the power and number of storms and other extreme weather events across the world.
Heavy monsoon rains in central India between 1981 and 2000 were more intense and frequent than in the 1950s and 1960s, and increased by 10 per cent since the early 1950s. Severe rains doubled over the same period.
At the same time, there were fewer moderate rains, say the team led by B.N. Goswami from the Indian Institute of Tropical Meteorology in Pune, India. The trends are likely linked to rising global temperatures, Goswami said.
Scientists had already observed that the Asian monsoon gained in strength over the past few centuries. In 1994, the United Nation's Intergovernmental Panel on Climate Change warned that global warming could intensify and increase the variability of the monsoon.
But the data on average rainfall in India did not show any substantial change. The study by Goswami and colleagues suggests that this can be explained by the decrease in moderate rainfall and does not point to a stability of the monsoon.
The researchers, who used data from 1,803 stations over Central India between 1951 and 2000, explain that previous studies on extreme rainfall trends in India had been inconclusive.
Suruchi Bhatwal, a senior scientist at the Tata Energy Research Institute in New Delhi, said Indian climate change research has been constrained by limited resources and models that have made predictions unreliable.
She warned that a future increase in heavy rains would cause floods and crop damage, with drastic effects on agriculture and food security.
More than half the world's population depends on the annual Asian monsoon to bring much-needed water for agriculture and basic human needs.
But the rains can be perilous, causing landslides, flash floods and crop damage as well as social, economic and environmental damage. Surging floodwaters in the 2002 monsoon killed more than 800 people in Bangladesh, India and Nepal, displacing millions of others.
In 2003, a study by the World Meteorological Organisation blamed global warming for the record number of extreme weather events such as floods and tornadoes.
