40 Essay |The South Asian monsoon The EconomistJune 29th 2019
21colleagues, the odds of each year’s gamble are now better known.
But obvious steps that might lower the stakes being played for are
still not taken. Storage systems in cities have fallen into disuse;
aquifers under farmland are depleted year by year faster than the
monsoons can refill them. In a country where more people will
face the risks of climate change in the decades to come than any
other, the problems of the current climate are being ducked.
The metamorphosis brought by the burst of the monsoon is
profound. Brown landscapes turn green, dusts become muds,
cracks turn into mouths through which the earth slakes its thirst.
The Ganges and the other great rivers fill then overflow, spreading
silt-rich fertility across their floodplains. In the countryside the air
takes up the petrichor aroma of fresh earth. In gardens, the scent of
frangipani carries on the damp breeze; in cities, that unmistakably
Indian blend of ordure, asphalt and spice.It’s a sea breeze
The people respond. The rains bring a sense of relief and a new
sensuality. In “The Cloud Messenger” by Kalidasa, one of the great-
est Sanskrit poets of north India, the meeting of earth and clouds is
nothing less than a kind of lovemaking. In the Sangam literature of
the deep south, the heroine waits for her lover, who is away seek-
ing war, wealth and adventure, to return with the rains. People still
tell stories of inhibitions cast aside and new lovers taken. The
heart takes on the driving, unpredictable rhythms of the rain.
For all its complexity and importance, on every scale from that
of smallholders to empires, at its heart the monsoon is something
fairly simple: a season-long version of the sea breezes familiar to
all those who live by coasts. Because land absorbs heat faster than
water does, on a sunny day the land, and the air above it, warm fast-
er than adjoining seas. The hot air rises; the cooler air from above
the sea blows in to take its place.
A monsoon is the same sort of phenomenon on a continental
scale. As winter turns to summer, the Indian subcontinent warms
faster than the waters around it. Rising hot air means low pressure;
moist maritime water is drawn in to fill the partial void. This moist
water, too, rises, and as it does, its water vapour condenses, releas-
ing both water, to fall as rain, and energy to drive further convec-
tion, pulling up yet more moist air from below.
There are other monsoonal circulations around the world—in
Mexico and the American south-west and in west Africa, as well as
in East Asia, to the circulation of which the South Asian monsoon
is conjoined. But geography makes the South Asian monsoon par-
ticular in a number of ways. The Indian Ocean, unlike the Pacificand the Atlantic, does not stretch up into the Arctic. This means
that water warmed in the tropical regions cannot just flow north,
taking its heat with it. It stays in the Arabian Sea and the Bay of Ben-
gal, lapping at India from the west and the east. And to the subcon-
tinent’s north sits the Tibetan plateau, the highest on the planet.
The summer heat there draws the monsoon’s moisture far higher
into the atmosphere than it would otherwise be able to go, adding
mountains of cloud to the Himalayan peaks.
The monsoon is thus a mixture of necessity and chance. Given
the arrangement of sea and land and the flow of heat from equator
to pole, such a season has to exist; given the vagaries of weather
from year to year, and within the seasons themselves, it springs
surprises for good and ill. It is also, and increasingly, a mixture of
the natural and the human—as ever more humans depend on it, as
humans learn new ways of anticipating it, and as humans face up
to the climate change which will reshape it. 7The heroine waits for her lover, who is away
seeking war, wealth and adventure, to return
with the monsoon rainsT
he rainsfor which Narayanappa waits are not the whole story.
The word “monsoon” blew into English from Portuguese in the
late 16th century not because European sailors cared about the rain
on alien plains, but because when they followed Vasco da Gama
around the tip of Africa they came across a type of wind they had
never encountered, and for which they had no name.
The Portuguese monçãocomes in its turn from the Arabic, maw-
sim, which means “season”. In the Atlantic Ocean, the only one to
which the Portuguese were accustomed, winds in any given place
tend to blow in pretty much the same direction throughout the
year, though their intensities change with the season and their
prevailing direction changes with the latitude. In the Indian
Ocean, the prevailing winds flip back and forth.
This is because of the role played in the monsoon by the “inter-
tropical convergence zone” (itcz) which encircles the world close
to the equator. The itczis a zone of low pressure over the warmest
water. In all the oceans, this low pressure draws in steady winds
from the south-east known as the southern trade winds.
During the northern hemisphere’s winter, the itczsits south of
the equator in the Indian Ocean. As warmth creeps north, so does
the itcz, becoming a dynamic part of the monsoon. It ends up nes-
tled against the Himalayas, bringing the southern trades with it.
But their move from the southern hemisphere to the northern, and
the constraining effect of high pressure over Africa, sees them
twisted from south-easterlies to south-westerlies. When these
south-westerly trades pick up in late spring—wind speeds in the
Arabian Sea can double over a few weeks—the rains are on their
way to Thiruvananthapuram.Turnabout is fair play
Just as coastal breezes turn around at set of sun, when the land
cools fast and the sea stays warm, so monsoons reverse in winter.
This is true both for the South Asian monsoon and the East Asian
monsoon, which affects Indo-China, the Philippines, southern
China, Taiwan, Korea and part of Japan. As the land cools in the au-
tumn, north-easterly winds replace the south-westerlies (see map
on next page). Because the winds are mostly dry they are not so im-
portant to farmers, though they do bring rain to some parts of
southern India. But they matter a great deal to navigation, and thus
to human history. The monsoon rains feed what has always been
the most populous part of the human world. It is the monsoon
winds, though, which brought those people together to form Asia.
Winds which reverse with the seasons shaped a maritime
world stretching from the Strait of Hormuz in the north-west to the
island archipelagoes of South-East Asia, from Madagascar in the
south-west to Japan. With patience, this whole world could be tra-
versed in both directions, with vessels set fair for east and north in
summer, west and south in the winter—and with layovers en-
forced by the tropical storms called hurricanes in the Atlantic, ty-
phoons in East Asia and cyclones in the Indian Ocean (the term
comes from the Greek kukloma, the coil of a serpent). The winds of
the South Asian monsoon suppress the conditions needed for cy-
clones to form. When the monsoon is over, they come out to play.
It was a world of long-range trade where seafarers mingled
quite freely. And India sat athwart it. Before any written record, the
Bay of Bengal was the realm of floating communities of water no-
mads, with mastery of the seas and little sense of bounded space.
Their boat-dwelling descendants live on as the Moken, Orang Suku
Laut and Bajau Laut. Today they are marginalised, subjected to
ever-tightening pressure by the state to respect borders and comeThe winds that made Asia