The India Climate Observatory

Commentary, action and research on climate and development in India

How El Niño plans to hijack monsoon 2015

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ICP_El_Nino_monsoon_20150526_smWhether the monsoon starts off on time, whether the June, July, August and September rainfall averages are met, and whether the seasonal pattern of the monsoon is maintained are expectations that must now be set aside.

According to the Climate Prediction Center’s ENSO probability forecast, there is a 90% chance that El Niño conditions will prevail through June to August of the northern hemisphere and a more than 80% percent chance El Niño will last throughout all of 2015.

The Ministry of Earth Sciences El Niño/La Nina, Indian Ocean Dipole Update (10 May 2015)

The Ministry of Earth Sciences El Niño/La Nina, Indian Ocean Dipole Update (10 May 2015)

What this means, especially when record warm global atmospheric temperatures (because we in South Asia and our neighbours in East Asia have continued burned coal as if the resulting CO2 and soot simply doesn’t exist) are being set, is the remaining months of 2015 – the monsoon period included – will bring strange, dangerous and extreme weather. We have already seen that over the last week, with the death toll from the heat wave having crossed 550.

For the first time since 1998 – ­the year of the strongest El Niño on record, which played havoc with the
world’s weather patterns and was blamed for 23,000 deaths worldwide – ­ocean temperatures in all five El Niño zones have risen above 1 degree Celsius warmer than normal at the same time. That is read by climatologists and ocean scientists as presaging an El Niño that is moderately strong to strong. The forecast models updated in May are now unanimous that El Niño is going to keep strengthening through the rest of 2015. (See also the official forecast from the USA’s government climate science agency.)

El Niño’s home is in the tropical eastern Pacific, but we in India need to watch the waters to our south very closely. New research published in the journal Nature Geoscience has examined records going back to 1950 and noticed that Indian Ocean absorbed heat at a low level until 2003. Thereafter, the excess oceanic heat in the Pacific Ocean found its way through the Indonesian archipelago and into the Indian Ocean. This is the gigantic reservoir of watery heat that is going to dictate terms to our summer monsoon, or what our school textbooks call the south-west monsoon.

It is a worry for the entire South Asian region – India, Pakistan, Sri Lanka, Bangladesh, Nepal, the Maldives, Burma, Afghanistan and Bhutan. That is why when the Forum on Regional Climate Monitoring-Assessment-Prediction for Asia (FOCRA) issued its seasonal outlook for June to August 2015 it predicted weaker than normal Indian summer and East Asian monsoons. Precipitation over land is influenced by external factors such as the El Niño Southern Oscillation (the ENSO), the ‘Indian Ocean Dipole’, the ‘Arctic Oscillation’, and so on.

There may be a “timely onset” of the monsoon, as the venerable IMD is used to saying, but that doesn’t mean our troubles are over. Far from it.

ENSO, ISMR, EQUINOO and rain

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RG_ICP_20140605An editorial in the journal Current Science (25 May 2014) has helpfully linked three phenomena that will affect the monsoon of 2014. The first is the El Niño (and the El Niño Southern Oscillation or ENSO) over the Pacific Ocean, considered unfavourable for us and the monsoon. The editorial has pointed out that El Niño has featured in the news already, with likely impacts being considered such as “a decrease of about 1.75% of GDP”. The question the editorial asks is: how reliable is the forecast of an impending El Niño? When it does occur, will it bring a deficit monsoon or a drought inevitably?

The second phenomenon is the Indian summer monsoon rainfall (abbreviated to ISMR by those who study climate for the sub-continent). The Current Science editorial makes an important point which is, studying the relationship between the sufficiency of the monsoon, the GDP and food-grain production during 1950–2004 reveals that the magnitude of the adverse impact of deficit rainfall is much larger than the magnitude of the positive impact of above average rainfall. This means that India being able to predict the possibility of drought (and therefore factors that influence it such as the ENSO) is more important than being able to predict a good monsoon.

The editorial has said that the ISMR “is significantly correlated with this ENSO index, with the relationship explaining 29% of the variance of monsoon rainfall”. Thus the warm phase of ENSO, which is characterised by more rainfall over the equatorial central Pacific, is associated with a decrease in rainfall over India. Now that we know this, what are the implications for monsoon 2014? By April, the warm phase of ENSO has already commenced with enhanced convection/rainfall over the central Pacific and all the models predict that it will amplify and persist until the end of the summer monsoon (the models vary in how they look at linked phenomena and the specific conclusions but agree broadly that El Niño conditions are here.

While the editorial has said that by “mid-June we should get a better idea of whether an El Niño is imminent”, the already unfavourable ENSO conditions mean that the probability of drought has gone up to just over 30%. If an El Niño does fully develop by end-June, the chance of a drought increases to 70%.

The explanation becomes more complete with the assessment of the third phenomenon. This is the Equatorial Indian Ocean Oscillation (EQUINOO). In 2003, it was discovered that in addition to ENSO, EQUINOO plays an important role in the variations, from one year to the next, of the ISMR. There is what is called “a see-saw between a state with enhanced rainfall over western equatorial Indian Ocean and suppressed rainfall over eastern equatorial Indian Ocean” (and its opposite). How this becomes manifest from one year to the next is considered by climatologists to account for about 19% of the variance of the monsoon rainfall.

The equation that we will have to finish writing and balance in the next few weeks is this. During the Indian summer monsoon season, ENSO and EQUINOO are poorly correlated – an ENSO unfavourable to us can be counter-balanced to some degree by a favourable EQUINDO. When both are unfavourable to us, drought has occurred. But the records also show that twice recently, in 1963 and in 1997, a favourable EQUINDO has protected us from the harmful impact of an El Niño. We need, in short, to be watching closely multiple large climatic phenomena every day until at least end-June. Is the IMD up to the job?