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Including the temperature changes of the Indian Ocean in forecasting models could greatly increase the predictability of El Niño and La Niña events, helping farmers and planners prepare for droughts, say researchers.

Together, El Niño and La Niña — the periodic warming and cooling, respectively, of the Pacific Ocean  — account for around a third of the variability in Indian monsoon rainfall and affect rainfall in parts of Africa, Latin America and South-East Asia as part of the climate phenomenon known as the El Niño Southern Oscillation (ENSO).

ENSO occurs every three to seven years. El Niño and La Niña events cannot be predicted with any certainty before the Northern Hemisphere Spring, nine months before the height of their effects — too late for farmers needing to prepare for heavier or lighter rainfall.

Research published in Nature Geoscience this week (21 February) has shown that analysing temperature changes in the Indian Ocean allows forecasts to be made 14 months in advance, several months earlier than at present.

Scientists already know that the Indian Ocean Dipole — a swap in sea surface temperature between the western and eastern Indian Ocean that occurs approximately every two years — is associated with El Niño and La Niña events.

But now researchers analysing sea surface temperatures between 1981 and 2009 have found that a negative phase of the dipole — a warm western and cool eastern Indian Ocean — is usually followed by an El Niño event just over a year later. Similarly, La Niña follows the opposite temperature pattern.

Jérôme Vialard, a researcher at the French Laboratory of Oceanography and Climate, and co-author of the research, told SciDev.Net that increasing the predictability of drought by months could enable warnings to be given, water restrictions imposed and farming practices changed.

"Gaining extra time is important because these are decisions which are made at the timescale of a season," he said.

Co-author Takeshi Izumo, at the Research Institute for Global Change in Yokohama, Japan, pointed to other possible benefits such as better forecasting of malaria outbreaks and forest fires — both of which can be influenced by El Niño.

Peter Webster and Carlos Hoyos, of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology in the United States, wrote in an accompanying article that predicting the onset of El Niño and La Niña events has long been a goal of global science.

But they said the link with the Indian Ocean dipole must be confirmed over the 100 years that sea surface temperatures have been available.

The study calls for better understanding of the links between the Indian and Pacific oceans, for which improved Indian Ocean monitoring systems are needed. Some improvements, such as the Indian Ocean Observing System (IndOOS) "are hopefully underway" already, said Izumo.

Link to the full paper in Nature Geoscience

Link to news and views article in Nature Geoscience

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