48 Fun Facts About Monsoons

Traditionally, how is a monsoon defined?

A seasonal reversing wind, with matching changes in rainfall, is the traditional definition; in everyday use the word now also means the rains those winds bring.

The English word "monsoon" ultimately derives from an Arabic word meaning what?

Season: monsoon goes back to Arabic mawsim, 'season', from a verb meaning 'to mark'; it named the right time of year for a voyage or a pilgrimage.

Which language did "monsoon" pass through on its way from Arabic into English?

Portuguese sailors picked up the Arabic word in the Indian Ocean as monção; English took it in the 1580s by way of early Dutch monssoen.

Monsoon rains follow the yearly north–south migration of which atmospheric feature?

The Intertropical Convergence Zone, the rain belt where the trade winds meet, shifts north and south with the sun; monsoon rains arrive where it swings over land in summer.

Why do continents warm faster than the sea in summer, setting up monsoon winds?

Land has a lower heat capacity than water, so the same sunshine warms it faster; the sea also mixes heat tens of metres down by convection, while rock and sand only conduct it slowly.

In summer, why does the air over heated land develop low pressure?

Warm air expands and rises over the heated land, lowering the pressure at the surface, so cooler, moister air from over the ocean is drawn inland to replace it.

Summer monsoon winds over India, the Guinea coast and northern Australia share which dominant directional component?

Westerly: India's and West Africa's summer monsoons blow from the southwest and northern Australia's from the northwest, so a westerly component is common to all; winter monsoons are mostly easterly and dry.

The strengthening of the Asian monsoon has been linked to the uplift of which highland region?

The Tibetan Plateau was pushed up after India collided with Asia about 50 million years ago; each summer the high plateau heats the air above it, which helps drive the Indian monsoon.

Which low-level wind crosses the equator off Africa to feed moisture into India's summer monsoon?

The Somali Jet, or Findlater Jet, is a narrow low-level stream that blows past Somalia and Oman each summer; the same winds push surface water offshore, so cold deep water wells up along the Somali coast.

During which months does India's southwest monsoon occur?

June to September: the rains reach India's southern coast at the start of June, take about six weeks to spread over the whole country, and begin to withdraw in September.

Which arid region's summer heating creates the low pressure that draws the monsoon into India?

The Thar Desert bakes in early summer and a deep low forms over it, pulling moist ocean air into India; yet the rain-bearing winds mostly pass the desert by, which is why it stays so dry.

What deflects the southeast trade winds into India's southwesterly monsoon once they cross the equator?

The Coriolis effect, a product of Earth's rotation, turns moving air to the right in the northern hemisphere, so the southeast trades swing round after crossing the equator and reach India from the southwest.

Which Indian state is the first to receive rain from the southwest monsoon?

Kerala gets the rains first because the monsoon winds coming off the sea strike its Western Ghats before any other part of the mainland.

Monsooned Malabar is which crop, left in ventilated warehouses to swell in India's moist monsoon winds?

Coffee: on the Malabar coast, dried beans are spread in ventilated warehouses for three to four months of the rains, where the damp winds make them swell, turn pale gold and lose their acidity.

Into which two arms does the southwest monsoon split at the southern tip of India?

Arabian Sea and Bay of Bengal: the Arabian Sea branch runs up the Western Ghats, while the Bay of Bengal branch swings around the bay towards the eastern Himalayas and the Ganges plain.

Which town on the southern slopes of the Khasi Hills in Meghalaya is one of the wettest places on Earth?

Mawsynram sits on the rain-facing southern slopes of the Khasi Hills, where moist Bay of Bengal monsoon air is forced up the escarpment, giving it one of the highest average annual rainfalls ever measured.

The wettest spots in India's Khasi Hills average roughly how much rain a year?

About 12 metres: the two rival villages each average between 11 and 12 metres a year, though Lloró in Colombia claims more, so the title of wettest place on Earth is disputed.

Which town, also called Sohra, holds the records for rain in a single month and year?

Cherrapunji, officially renamed Sohra, logged more than 26 metres of rain in the twelve months from August 1860; it sits on a plateau edge where saturated monsoon air is forced up the slope and cools at once.

Which Southeast Asian river reverses its flow each year when monsoon floods swell the Mekong?

The Tonlé Sap normally drains Cambodia's great lake into the Mekong; in the monsoon the swollen Mekong pushes water back up it, and the lake spreads to several times its dry-month area.

Which staple is India's main monsoon-sown crop, planted as the rains arrive?

Rice needs heavy rainfall, which is why it is India's chief kharif, or monsoon-sown, crop; wheat, by contrast, is a rabi crop, sown after the rains and harvested in spring.

What term describes the sudden switch to rainy, humid weather when the monsoon arrives in India?

Bursting: the 'burst' of the monsoon is the abrupt switch from hot, dry weather to rain and humidity when the moist winds arrive, which the jet-stream theory links to the subtropical jet suddenly shifting north of the mountains.

By what other name is India's northeast monsoon, which follows the summer rains, known?

The retreating monsoon: as the southwest monsoon withdraws, cold dry air sweeps off the northern landmass towards the sea; blowing from the land, it leaves most of India dry through the cooler months.

Which Indian city is watered mainly by the northeast monsoon rather than the southwest one?

Chennai lies in the rain shadow of the Western Ghats during the southwest monsoon, so most of its rain comes from the northeast monsoon off the Bay of Bengal later in the year.

In which months does the northeast monsoon bring rain to southern India?

October to December: once the high-pressure system over the cooling northern landmass builds, northeasterly winds cross the Bay of Bengal and rain out over Tamil Nadu and Sri Lanka.

What is the northeast monsoon called in the Philippines?

Amihan is the Filipino name for the cool northeast monsoon of the northern winter; it gives the islands' western coasts their dry months while the eastern coasts stay rainy. The southwest monsoon is the Habagat.

What is the East Asian summer rain belt called in China?

Meiyu is China's name for the front that stalls over eastern China, Taiwan and southern Japan for weeks in early summer, until the subtropical high strengthens and shoves it north; Korea calls it Jangma, Japan Bai-u or Tsuyu.

The East Asian monsoon's spring-summer rains are referred to in several languages as what kind of rain?

Plum rain: the Chinese and Japanese names both mean 'plum rain', traditionally because the damp weeks come just as plums ripen south of the Yangtze.

Which dry, dusty trade wind is interrupted by the West African monsoon each summer?

The harmattan, the dry northeasterly off the Sahara, gives way to moist southwesterlies as the monsoon pushes north; in its own months it carries so much dust that it grounds flights and settles on ships far out in the Atlantic.

Which semi-arid African region depends on the West African monsoon for most of its rain?

The Sahel, the semi-arid strip along the Sahara's southern edge, gets most of its rain from the West African monsoon; when those rains failed from 1968 into the 1980s, drought and famine followed across the region.

What Arabic name is given to the dust walls kicked up by monsoon thunderstorms in America's Southwest?

A haboob is the wall of dust flung ahead of a collapsing thunderstorm's outflow, sometimes thousands of feet high; the name was borrowed from Sudan, where such storms are common.

Which body of water is the main low-level moisture source for the Sonoran Desert's summer monsoon?

The Gulf of California sends surges of moist air up its length into the desert; once the first rains green the Sierra Madre Occidental's forests, their transpiration adds still more.

By which other name is the North American monsoon also known?

The Arizona monsoon is one of several names, alongside the Southwest, Mexican and New Mexican monsoon; it sets in when a summer high shifts north and the prevailing winds swing round to the south, pulling in moist air.

Operation Popeye's cloud seeding tried to prolong the monsoon over which wartime supply route?

The Ho Chi Minh Trail through Laos was the target: from 1967 to 1972 US aircraft secretly seeded clouds to keep the rain falling into the dry months, so that sodden roads would stop North Vietnam's supply trucks.

Tree rings link the 15th-century decline of which Southeast Asian city to long droughts broken by violent monsoons?

Angkor: tree rings from southern Vietnam record decades of drought in the 14th and 15th centuries, interrupted by monsoons fierce enough to wreck the canals and reservoirs the Khmer capital relied on.

What is the Australian monsoon commonly called?

The Wet is northern Australia's name for its monsoon months, when moist ocean air is drawn over the hot land and brings downpours, lightning shows and cyclones; the rest of the year is the Dry.

What do northern Australians call the hot, humid weeks before the monsoon rains arrive?

The build-up is Darwin's name for the run-up to the monsoon, when heat and humidity climb steadily as moist air is drawn over the hot land; relief usually comes when the rains arrive around December.

Which pressure system sends cold, dry air south across Asia each year as the winter monsoon?

The Siberian High forms as the continent's interior chills in winter; air spills out of it across East Asia and, as northerly winds, over India, which is why the winter monsoon is cold and dry.

How does an El Niño year usually affect India's southwest monsoon?

It weakens it, causing droughts in many El Niño years, because the Pacific's shifted circulation leaves air sinking over India; but the link is loose, and some strong El Niños have passed with normal rains.

Which 1999-discovered climate pattern explains why the 1997 El Niño caused no drought in India?

The Indian Ocean Dipole, identified in 1999, was in a strong positive phase in 1997 and offset El Niño's drying; adding the related EQUINOO effect also explains failed forecasts like the 2002 drought.

Attempts to predict India's monsoon rainfall began after which disaster?

The Great Famine of 1876–1878 followed a failed monsoon; in the 1880s India's first chief meteorologist, Henry Blanford, began forecasting the rains from how much snow had fallen on the mountains to the north.

Which Greek navigator is credited with discovering the monsoon route across the Arabian Sea to India?

Hippalus: the first-century Periplus of the Erythraean Sea credits the pilot Hippalus with discovering the open-sea route from Arabia to India on the southwest monsoon, which Greek sailors then named after him.

Exceptional monsoon rains in 2022 brought floods that killed more than 1,700 people in which country?

Pakistan: the 2022 monsoon dumped several times the usual rain on parts of the country, and the floods that followed affected about 33 million people.

Which Indian megacity was brought to a standstill by monsoon floods in July 2005?

Mumbai: on 26 July 2005 the city recorded 944 mm of rain in 24 hours; the suburban trains stopped, the airport shut for more than a day and many commuters had to walk home through the floodwater.

Which cloud type towers thousands of metres over the hot land to unleash the monsoon's violent thunderstorms?

Cumulonimbus clouds form as moist monsoon air turns unstable over the heated land; the heat released as their vapour condenses drives the towers higher still, feeding the violent thunderstorms of the monsoon's onset.

Which director general of observatories in India identified and named the Southern Oscillation?

Sir Gilbert Walker, who took charge in 1904 and set out to predict monsoon failures, sifted worldwide weather records and found a pressure seesaw across the Indian and Pacific oceans, which he named the Southern Oscillation.

The Southern Oscillation Index measures the pressure difference between Darwin and which island?

Tahiti and Darwin anchor the index; the oscillation turned out to be the atmospheric side of El Niño and La Niña, so together they are called ENSO.

Which prized South Asian timber tree stands leafless through the dry months before the monsoon?

Teak is deciduous: its big leaves fall during the dry months, and new foliage emerges only when the first monsoon rains arrive.

Which low-pressure band runs from northwest India to the Bay of Bengal during the monsoon?

The monsoon trough is that east–west band of low pressure from Rajasthan to the head of the Bay of Bengal; rain belts follow it, and when it shifts north to the Himalayan foothills a 'break' sets in.