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Miscellaneous Nov 13, 2023

What a year it has been. Hot, sultry, dry. Commonplace features across the length of the country for the most part, potentially the hottest year on record and June-August 2023 was also the Northern Hemisphere's hottest meteorological summer on record. We have been happy to sit in rooms with arctic-grade air-conditioners, sipping chilled, purified water.

Tomatoes were making headlines, and export bans on varieties of rice seemed to send Indians halfway across the world in North America into a tizzy along with the unwanted temperature records. Monsoons that ran in surplus in the subcontinent for a few short years are suddenly running large deficits in certain areas. There is plenty at play though and we would do well to, if I may say so, recall. After nearly a 7-year absence, El Niño is back.

With that, I welcome you to Climatology 101, where we try to decipher some of the most esoteric concepts as if I have truly mastered them all. (P.S. I obviously haven’t) First principles first. Simply put, the Sun heats the Earth’s surface unevenly. A low-pressure system is formed due to localized heating caused by greater sunshine over landmasses or water. Since the warm air in localized areas is less dense than the surroundings, it rises, lowering the atmospheric pressure. The opposite gives rise to high-pressure systems. Air generally moves from a region of higher pressure to that of lower pressure, thus creating what we know as wind. Naturally, winds also blow from high-pressure areas to low-pressure areas.

Now, what really is the monsoon?
The term refers to the big seasonal winds that bring bountiful rain to the subcontinent from the oceans down south - nothing that we did not learn as we traversed high school. Perhaps, too much of an effort to remember though. Let us walk down memory lane. All tropical zones on both sides of the equator receive some consequential rainfall owing to the seasonal march of the doldrums, which are together called the intertropical convergence zone or ITCZ. Doldrums are low-pressure regions formed by the heating of the sun, causing a convection of hot air that moves upwards and draws colder air from surrounding land and water. What do we know of the Earth’s axis? It causes seasons through uneven heating and so when the northern hemisphere is hotter, the ITCZ moves up into the northern hemisphere closer to the Tropic of Cancer in India and closer to the Tropic of Capricorn during the southern summer.

Why is the ITCZ important?
Because it is almost always accompanied by thunderstorms and rainfall. The hot, moist air is forced into the colder upper atmosphere. So, what’s this got to do with our monsoon? The Indian monsoon, more commonly known as the Southwest monsoon – as is probably evident at this point - is a result of the ITCZ moving up towards the Tropic of Cancer, inevitably bringing rain into the subcontinent in two branches: the Arabian Sea branch which hits the Western Ghats first (bringing rain into Coimbatore from sometime in May); and the Bay of Bengal branch, which brings rain to the eastern half of the subcontinent. What makes the monsoon stronger is the presence of the Tibetan plateau, which upon being persistently heated, draws the ITCZ even closer to the subcontinent, thus bringing more rainfall. Funnily enough, this “tropical” phenomenon extends beyond the Tropic of Cancer itself. Even further north in Central Asia, the heating is so strong that it draws winds and rain into the continent from the Pacific coastline of Asia, causing what one may call an “East-Asian monsoon.” When winds from the southwest blow across the subcontinent into the Himalayas, they are thrust upward, a phenomenon known as orographic lift. There, they dump almost all their moisture on the windward slopes giving rise to some of the wettest places in the world such as Mawsynram and Cherrapunji.

The opposite occurs in the winter as the ITCZ moves further south, creating an area of extensive high pressure in continental Asia - known to be amongst the strongest of such high-pressure zones on Earth – and colder winds move towards the ITCZ in the south. However, the monsoon winds over Peninsular India do not change direction. Rather, they retreat as they came earlier in the year. Over the warmer water, say in the Bay of Bengal, these winds meet, creating cyclonic formations which revolve in an anti-clockwise direction as they do all over the northern hemisphere and often bring rains to Tamilnadu. The state receives a large chunk of its annual rainfall this way. The overall dynamics can stretch as far as Australia, which is cooled during the northern summer and acts as a high-pressure zone, contributing to wind movement and vice-versa during the southern summer.

What’s El Niño even got to do with this?
Let us get this straight. This year’s monsoon, and perhaps the average climate of the world, has been clouded by the predicted rise of a phenomenon known as El Niño. It is normally known to suppress monsoon rainfall here in India and elsewhere in Africa, bringing drought-like conditions. At the same time, it brings flooding to parts of the Americas. If the El Niño episode is strong enough, the annual average near-surface global temperature between 2023 and 2027 is expected to be more than 1.5°C above pre-industrial levels for at least one year, which is the limit set in the Paris Climate Accords. According to the World Meteorological Organization, there is a 98% likelihood that at least one of the next five years, and the five-year period as a whole, will be the warmest on record.

So, what is El Niño and how does it affect the Indian monsoon?
El Niño refers to an abnormal warming of surface waters in the equatorial Pacific Ocean. This nifty phenomenon was first observed in the 1600s by Peruvian fishermen, who noted that the waters felt warmer near the coast in the month of December. Naturally driven by the tradition associated with the month, they called it "El Niño de Navidad", Spanish for the newborn Christ. An El Niño event is typically declared when sea surface temperatures in the tropical eastern Pacific rise to at least 0.5C above the long-term average. The opposite phase, La Niña, which is the abnormal cooling of sea surface waters in the same region, is known to aid rainfall over India. There is a third neutral phase as well, in which the sea surface temperatures remain roughly within the long-term average. Together, these three phases in the Pacific Ocean are referred to as the El Niño Southern Oscillation or ENSO. Typically, this anomaly happens at irregular intervals of two to seven years and lasts nine months to two years.
In a normal year, the relatively warmer Indian Ocean has a translated region of lower pressure, thus strengthening the winds that come in from the Pacific through Southeast Asia. This is further aided during the monsoon given that the pressure is lower over the landmass of India, thanks to the ITCZ’s northerly shift. However, courtesy El Niño, the hotter coastline near the Americas, particularly around the Peruvian coast, creates a larger region of low pressure there which drives the moisture-laden winds away from the western Pacific (the region near northern Australia and Southeast East Asia) towards South America, effectively weakening the trade winds or even entirely reversing them. This robs the Indian subcontinent of its normal monsoon rains. The larger the temperature and pressure difference, the larger the rainfall shortage in India. Since 1950, out of the 13 droughts that India has faced, 10 have been during El Niño years and one in La Niña year.

What implications does it have now, months after the monsoon?
The monsoon arrived late this year but surprisingly retreated after the expected date. After bountiful rains in July, the prevalence of El Niño conditions forced a longer-than-usual break in the monsoon across the country except in regions closer to the Himalayas. Together, these are expected to affect cropping cycles significantly, impacting agriculture adversely and possibly keeping food inflation high throughout the rest of the year. The expectation is that this El Niño will last into April 2024, which could potentially imply a delayed or perhaps even weakened monsoon as far as the subcontinent is concerned. We may be witnessing storms in patches, but the outlook has remained below average. On an overall note, we did get off lucky this year in terms of the impact El Niño had, thanks to a nifty little Indian Ocean equivalent which we will see about shortly.

So costly tomatoes all the way to Pongal?
Maybe, maybe not. The Pacific Ocean isn’t the only water body experiencing this heating effect. There is a similar phenomenon associated with the Indian Ocean, commonly dubbed as the Indian Ocean Dipole or IOD. The IOD refers to a swing in sea surface temperatures from warm to cool in the waters to the south of Sri Lanka. A positive IOD is a phase where these waters are warmer than near the Indonesian coast, driving winds towards the western half of the Indian Ocean and subsequently into the subcontinent aiding rainfall, while a negative does the opposite. However, the IOD is considerably less powerful compared to El Niño, resulting in relatively minimal impact. Note that a strong, positive IOD was the reason that the monsoon of 2019 went into a surplus. This year, a positive IOD (though not as strong as the 2019 event) has already shaved off some of the impact that the current El Niño event was supposed to have. However, this has not wiped off the deficits of the monsoon. It is expected that the impact will be felt strongly as the harvest season approaches in January. Combined with a strong El Niño event, we may even break the records set in the previous instance in 2016; certainly not the good ones.
A bit long drawn, but the next time you’re at the market frowning at the shopkeeper or hollering at the water management authorities for irregular pumping of water, look to the sky. It is imperative to know better than that - to optimize our usage and storage capabilities rather than lose one’s bearings for the underlying cause is a part of the very nature of this planet.


N Krishna

You may know me as the guy who talks and writes like a sergeant, is an av-geek and works out obsessively, but not as one who laughs with a full heart and cooks like it’s an experiment.