Researchers claim to have finally solved the riddle as to why some El Niqo events cause the Indian monsoon to fail while others do not, a finding which may lead to more accurate forecasts of drought and floods.
Drought years in India have been specifically linked to a warming of the western side of the Pacific during an El Niqo event. The warming of the Pacific causes changes in evaporation from the seas and wind patterns that generally result in reduced summer rainfall over India.
So a measure of sea surface temperatures in the Pacific has been used to issue drought warnings.
"The skill of the current monsoon forecast is low. It fails to explain more than 90 per cent of monsoon variability," Nature quoted study co-author Martin Hoerling of the US's National Oceanic and Atmospheric Administration in Boulder, Colorado, as saying.
The reason, Hoerling and his team say, is that El Niqo events come in different 'flavours': some heat the water more on the western/central side of the Pacific, others more on the eastern side.
The team's analysis of recent monsoons shows that it is the western-shifted warming that predominantly causes the Indian drought. If researchers had looked to this variable in the past, they say, it would have been possible to predict major unexpected droughts that struck in 2002 and 2004.
Scientists warn that the current trend may spell bad news for India, as droughts may become ever more frequent. There is already a trend towards lessening monsoon rains in India, says Hoerling, perhaps because of this shift in El Niqo flavours.
But the future is uncertain, as sea temperatures change, dominant El Niqo patterns, and their effects, may also alter.
However, Hoerling points out that the new way of predicting droughts certainly isn't perfect and isn't good enough to predict smaller events with accuracy.
"We're only looking for skill in predicting the devastating droughts, which may occur one year out of 10," he added.
In 1997, the twentieth century's strongest El Niqo didn't greatly affect Indian monsoon rainfall, whereas in 2002 a moderate El Niqo resulted in a severe and unexpected Indian drought.
Accurate monsoon prediction is crucial to the Indian economy as nearly one-fifth of the country's gross domestic product comes from agriculture.
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