BackWhy Skymet is still sticking to its ‘normal’ monsoon forecast
If El Nino is a continuation from 2014, then the monsoon in 2015 isn't likely to fail
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El Nino has been causing a lot of anxiety since the start of the year.
This “little boy" (meaning of Spanish words El Nino) has raised a big scare about a deficit monsoon in India. We have been saying since March that the monsoon will be normal, and let me explain why.
First, let’s look at this problem statistically. El Nino, which leads to abnormal warming of the equatorial Pacific Ocean, triggers both floods and droughts in different parts of the world.
It is linked to poor monsoon in the Indian subcontinent (60% of all evolving El Nino years are droughts).
Since 2000, all drought years (2002, 2004, 2009 and 2014) have been in evolving El Nino years.
But there are exceptions.
We’ve had four El Nino years from 1953 to 1963 and all the four years witnessed normal or above-normal rainfall.
Second, if this El Nino episode is a continuing one from last year, the monsoon in the second year does not fail. 2014 was a year that had an evolving El Nino and had a drought (88% of the long-period average rainfall, or LPA). The El Nino of 2015 is a continuation from last year.
Climatologically, the chance of a back-to-back drought is very rare. In the last 140 years, it has been happened only four times—1904-05, 1965-66, and 1985-86, 1986-87.
Dynamic models
Skymet has been working on dynamic models for a decade and they have been put to the test since 2012. In each year since then, Skymet’s monsoon forecast has been right. It has been able to predict one monsoon deficit and one drought. We have also back-tested our models for past 30 years and the success rate is 74%. It is these models that since January are forecasting a normal monsoon.
Devolving El Nino vs a strenghtening one
I need to make a confession. We (Skymet) have since March been saying that this El Nino is a continuation from last year, and that it will devolve over the season. We are correct on the first part but incorrect on the second.
The El Nino in eastern Pacific Ocean has actually strengthened. But I must say that we are aware of the fact and our models are taking this into consideration. Our models and statistics are converging. I suspect the reason for this convergence is the Indian Ocean Dipole (IOD).
The dipole effect
The IOD refers to a phenomenon in the equatorial waters of the Indian Ocean. It is defined by the difference in sea surface temperatures between two areas—a western pole near the Arabian Sea and an eastern pole closer to the Bay of Bengal. If the sea surface temperature of the western end rises above normal and becomes warmer than the eastern end, it leads to a positive IOD. This condition is favourable for monsoon and carries the potential to somewhat neutralize the adverse effect of El Nino.
I believe in looking closer home and would like to give more weightage to the systems in the Indian Ocean. There are indications that the Arabian Sea will be warm throughout the monsoon months, leading to sufficient convection and, thereby, enhancing the rainfall.
The year 1997 was a strong El Nino year, but due to a positive IOD, we received normal rains to the tune of 102% of LPA. In other words, a postive IOD might insulate us from El Nino. I think that is happening here. The year 1987 was also a strong El Nino year, which brought drought in India.
Most of the weather agencies across the world are possibly relating this year to 1987, but I think 2015 is more like 1997.
Impact of typhoons in the West Pacific
Weather forecasters worldwide are also putting forward arguments about enhanced typhoons causing a rain deficit.
The effect of El Nino is also manifested in the increased frequency of typhoons in the western Pacific.
The region is active throughout the year and normally sees 20 storms/typhoons. We cannot deny the fact that typhoons affect rainfall in India, but not to the extent of bringing a drought.
Jatin Singh is founder and CEO of Skymet, India’s first private-sector weather forecast company.
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