The India Meteorological Department’s climate forecast system was ill-equipped to gauge crucial oceanic phenomena, as a result of which it had to revise its prediction for rainfall from the Southwest Monsoon from “above normal” to “normal”, a top official said.
The IMD will now make necessary amendments to its existing climate models for better prediction in the future, M Rajeevan, Secretary, the Ministry of Earth Sciences, said.
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It, at present, uses the National Centers for Environmental Prediction (NCEP) Climate Forecast System Version 2 (CFSv2), procured from the US, to understand oceanic patterns. The system was modified to suit IMD’S requirements.
As per IMD’s initial forecast, rainfall from the Southwest Monsoon was expected to be “above normal”. September was expected to receive “excess” rainfall, but that did not happen.
This was primarily due to La Nina, an oceanic phenomenon linked to cooling of Pacific waters resulting in better monsoon in the Indian sub-continent. The IMD had expected a “full-blown” La Nina, which did not occur.
Another phenomenon that occurred was a negative Indian Ocean Dipole, also known as Indian El-Nino and associated with warming of Indian Ocean waters. A negative IOD also has an bad impact on the monsoon.
“In La Nina, we would have got more rain. But, in between, Indian Ocean warmed up. The Indian Ocean Dipole was negative. So that was not well anticipated by the model. The model has problem and it is not good in predicting changes in the Indian Ocean.
“We don’t understand the Indian Ocean processes well and have very less observations. The dynamics are different from Atlantic and Pacific Oceans. We need to have a lot of observations and start doing it,” Rajeevan said.
He said changes will be made to the CFSv2 model to better understand such patterns as even minor changes in the sea surface temperature makes a significant impact on the monsoon.
“Changes in the Indian Ocean are very small, but these can make a big difference,” he said.