A billion people depend on the Indian monsoon, yet predicting its success or failure has till now been a somewhat hit-or-miss affair. This could change with the discovery that conditions in the eastern Pacific hold the key.
It鈥檚 well known that the monsoon is affected by the warming of the Pacific Ocean associated with El Ni帽o events. Failed monsoons have always been accompanied by an El Ni帽o, but monsoons do not fail in every El Ni帽o year.
To better understand this link, K. Krishna Kumar of the Indian Institute of Tropical Meteorology in Pune and colleagues looked at figures for rainfall in India and sea surface temperatures from the equatorial Pacific since 1871. They found that in the years when an El Ni帽o strongly warmed the central Pacific, drought conditions ensued in India, whereas the monsoons were normal when the warming was concentrated in the eastern Pacific (Science, DOI: 10.1126/science.1131152)
Advertisement
The reason, says team member Martin Hoerling of the US National Oceanic and Atmospheric Administration in Boulder, Colorado, is that as the central Pacific warms, the atmosphere above it heats up and rises. This induces a large, dry air mass to sink over India, depriving it of nourishing rains.
Global warming and rising ocean temperatures may reinvigorate the monsoons, which have been declining over the past three decades. 鈥淭he trend could be mitigated as the eastern Pacific warms,鈥� Hoerling says.
