The last week of May saw weathermen and economists rejoice as “pre-monsoon” and “monsoon-like” rainfall finally hit the shores of Kerala and Karnataka. After two consecutive drought years, the India Meteorological Department, as well as private forecasters, are predicting a better-than-normal monsoon with close to 106 per cent of the long period average of 89 cm during June-September.
The monsoon, which accounts for about 80 per cent of India’s total showers, is the lifeblood of the nation. Half our population depends directly on agriculture, with about two-thirds of our farm land irrigated by rainfall. Droughts wreak havoc on the economy as a whole, with industry lobby group Assocham estimating that the last two consecutive drought years may have cost the country ₹65,000 crore, and put as many as 33 crore people at risk.
The monsoon has been largely seen as a predictable affair by the Indian subcontinent for millennia, with generations having danced to its rhythmic arrival and departure. But will this rhythm remain the same forever?
One of the phenomena affecting this rhythm is ‘El Niño’, meaning ‘The Little Boy,’ or ‘Christ Child’. First spotted by South American fishermen in the 1600s, El Niño is the warm phase of the El Niño Southern Oscillation (ENSO), a climate event that happens due to the unusual warming of sea surfaces in the Pacific Ocean interacting with the atmosphere. On average, an El Niño arrives every three to seven years, and affects the weather in large parts of the world. A related, and somewhat contrasting phenomenon is the ‘La Nina’, which is marked by a cooling of ocean surface waters.
While the monsoon’s arrival and intensity are governed by a number of variables with varying levels of consistency, a key ingredient is the difference between land and sea temperatures. Under normal circumstances, land warms faster than the sea, and attracts moisture-laden winds from the Indian Ocean, which then precipitate over the parched peninsula. Deviations from normal surface temperatures due to El Niño reduce this gradient, impacting the monsoon heavily. This effect is even more pronounced in South Asia due to the land-locked nature of the Indian Ocean, with no access to the poles.
The most recent spell of El Niño was one of the longest and strongest ever, and besides leading to unusually warm winters, was seen as a prime driver of the poor monsoon in the last two years. It is thanks to the dissipation of the El Niño event — and emergence of La Nina conditions — that this year promises to be better for agricultural markets.
ENSO isn’t the only factor affecting the monsoon. There’s the Indian Ocean Dipole (a local phenomenon, somewhat similar to El Niño), Inter-Tropical Convergence Zones (which can hasten the arrival of monsoon), cloud configuration, atmospheric conditions and oceanic parameters, to name but a few.
However, the silent juggernaut behind South Asia’s changing monsoon is anthropogenic climate change — the emission of greenhouse gases in the atmosphere due to human activity .
While it is not possible to pin down climate change as the reason behind a particularly extreme event such as a cyclone or a flood, we know that 90 per cent of the heat from global warming during the last four decades has been accumulated in the oceans, effectively making them heat sinks and intensifying El Niño events. This idea is supported by the fact that in the past 140 years, the three strongest El Niño years were 1982, 1997 and 2015. Similarly, a 2015Nature study of monsoon data across South Asia over the last century found a downward trend overall, with a 10-20 per cent decrease in rainfall over central and east India.
A warming planet means that the atmosphere can hold more moisture, which can delay monsoons, and then lead to heavier rainfall when it does occur. Climate change is also thought to increase the inter-annual variability of the monsoon in the future, outside of an El Niño state. Both flood and drought phenomena could be more severe, as was seen in July 2005, when Mumbai received over one metre of rainfall in a single day.
Unfortunately, we are still waiting for the day when we’ll be able to accurately predict the day-to-day and intra-seasonal variability of the monsoon. We remain far from confident in our climate models. As of now, our understanding of the various processes affecting the state of precipitation in this challenging region, where vast water bodies interact with the atmosphere over plains, deserts, and mountains, is severely limited.
However, what we do know is that for millions of Indians (and, effectively, for every resident of South Asia), the variability of rainfall, even on narrow time scales, can have disproportionately large impacts, with short, intense showers leading to floods and weeklong delays leading to droughts.
The only way to prepare for the future is to face climate change head-on, by enacting large-scale mitigation measures as well as adapting our economy and society to the changing climate.
