El Nino has been causing a lot of anxiety since the beginning of the year. This “little boy” has raised a big scare about deficit Monsoon rains. And since we have been saying since March that Monsoon will be normal, I personally find myself explaining why we think so. In this article, I am going to put down my thoughts on why I think it is going to be a normal Monsoon.
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. Yes, it is true that El Nino is linked to poor Monsoon rains in the Indian sub-continent, (60% of all evolving El Nino years are droughts). Since 2000, all drought years (02,04, 09, 14) 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 the El Nino episode is a continuing El Nino from last year, the Monsoon in the second year does not fail as often as it fails in the first year of evolution. 2014 was a year that had an evolving El Nino and had a drought (88% of the LPA). The El Nino of 2015 is continuing from last year. It is less likely to fail.
Back to back droughts are rare
Climatologically, the probability of back to back droughts are very rare. In the last 140 years, it has been witnessed only four times - in 1904-05, 1965-66, and 1985-86-87. The previous year experienced drought due to an evolving El Nino and this year is most likely to receive normal Monsoon rains.
Skymet’s dynamic models
Skymet has been working on dynamic models for a decade and it has been put to test since 2012. In each year since 2012, Skymet’s monsoon forecast has been right. Skymet has been able to catch one deficit and one drought well in advance in the past. We have also back tested our models for the Monsoon for the past 30 years and the success rate is 74%. It is these models that since January are consistently showing a normal Monsoon. They are considering the strong El Nino.
Devolving El Nino vs a strengthening one
I need to make a confession. We [Skymet] since March have been saying that this El Nino is a continuing El Nino from last year, and something that will devolve over the season. We are correct on the first part but incorrect on the second. The El Nino in the Eastern Pacific has actually strengthened. But I must say that we are cognizant of the fact and our models are taking the strengthening into consideration.
Our models and statistics are converging, we do not have space for doubt yet. I suspect, the reason for this convergence is the India Ocean Dipole (IOD).
The IOD refers to a phenomena in the equatorial waters of the Indian Ocean. It is defined by the difference in the sea surface temperature between the 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 the Indian 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 Monsoon rains.
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 the LPA. In other words a postive IOD might insulate us from the El Nino. I think that is what 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.
So as one of my reporter friends said “Dabang Skymet sticks to 102.”
Impact of Typhoons in the West Pacific
Weather forecasters worldwide are also putting forward arguments about enhanced typhoons causing deficit rains. The effect of El Nino is also manifested in increase in the frequency of Typhoon in the western Pacific. Western Pacific is active throughout the year and normally also sees 20 storm/typhoons. We cannot deny the fact that typhoons affect the Indian Monsoons, but not to the extent of bringing a drought.