The imperious monsoon rains have ruled India for centuries. Already unstable, what happens if they shift fundamentally?
The long wait for the rains suffuses many works of classical Indian literature. In these verses from The Interior Landscape: Classical Tamil Love Poems (1967), the poet and scholar A K Ramanujan evoked a sense of the monsoon’s illusions. The cassia trees are ‘gullible’, as people are prone to be. They mistake nature’s signs. They hope in portents of rain that prove illusory.
‘As if for a proper monsoon’ – but who knows what a ‘proper monsoon’ looks like any more? Over the past few decades, South Asian monsoons have swung between greater extremes of wet and dry. A monsoon’s mechanisms are so complex they resist modelling. We can send crafts to other planets but no one can predict how much rain the monsoon will bring. Accelerating climate change brings even more uncertainty. If a fundamental shift in the patterns of the monsoon comes, it will devastate the livelihoods of hundreds of millions of people.
The word ‘monsoon’ first appeared in English in the late-16th century, derived from the Portuguese monção, which comes from the Arabic mawsim (for ‘season’). Mawsim also provides the word for ‘season’ (mausam) in Urdu and Hindi. In its simplest definition, it is a weather system of regularly reversing winds, one wet and one dry season. There are many monsoon systems around the world, but the South Asian monsoon is the greatest in scale and consequence. The Indian subcontinent constitutes the core of the monsoon system because of the geological history that has left India at the edge of the Eurasian landmass, which dominates the northern hemisphere. There India sits, facing the watery expanse of the southern hemisphere.
As the Asian continent heats up each spring, the warming air above it rises. Cooler, moist ocean air moves in to take its place. The monsoon winds blow from the southwest, curved by Earth’s rotation so that they double back to grip India from both the Arabian Sea, in the southwest, and the Bay of Bengal, in the southeast. The air sweeping in from the ocean contains vast stores of solar energy in the form of evaporated water. The vapour condenses and is released as rain. It is an extraordinary and powerful system. But it is not immortal or impervious to change.
The Himalayas are a crucial part of the system. The elevation of the Tibetan plateau leads it to warm rapidly, and so drives the differences of pressure and temperature that power the monsoon system. But the mountains themselves act as a colossal barrier to the winds, concentrating the monsoon rains to the south, along the Gangetic plain.
More than 70 per cent of total rainfall in South Asia occurs during just three months each year, between June and September. Within that period, rainfall is not consistent: it is compressed into a total of just 100 hours of torrential rain, spread across the summer months. Despite advances in irrigation, 60 per cent of Indian agriculture remains rain-fed, and agriculture employs around 60 per cent of India’s population. No comparable number of human beings anywhere in the world depend on such seasonal rainfall.
Both before and after independence, the imperious power of the monsoon troubled India’s rulers. In the first decade of the 20th century, the finance minister in the imperial government declared that ‘every budget is a gamble on the rains’ – a statement that is still quoted regularly in the Indian media.
In the late 1960s, India’s prime minister Indira Gandhi said: ‘For us in India, scarcity is only a missed monsoon away.’ The foreboding remains. In a lecture at Harvard University in 2017, the environmental activist Sunita Narain declared that ‘India’s finance minister is the monsoon.’ This sense of a battle against enormous natural forces has inspired an enduring debate in India, among those who believe that science and technology could conquer nature, and those, like Narain, who advocate greater respect for nature’s limits.