World Climate Types and Their Causes

GC Leong gives world climate its own chapter, separate from the chapter on natural vegetation and soils, and the exam treats that separation seriously. Where World Vegetation Belts and Soil Types organises the world by biome, describing climate only as far as it explains why a forest or a soil looks the way it does, this chapter treats climate as a formal system in its own right: named climate types, each with a precise temperature and rainfall regime and a precise reason it sits where it does on the map. UPSC's own real question on this chapter, from the 2024 paper, asks nothing about vegetation or soil. It describes a climate purely by its seasonal temperature and rainfall behaviour and its position on a continent, then asks which named type that is, out of four real candidates. That is the skill this note builds: reading a description of temperature range, rainfall amount and rainfall timing, and placing it correctly among the world's climate types, by name and by cause.

Why a climate needs a name and a cause

A climate classification groups places with a genuinely similar temperature and rainfall regime under one name, then explains that regime through a small set of repeating physical controls: latitude (how directly the sun strikes, hence how much the seasons vary), position on the continent (windward versus leeward, west coast versus east coast), the pressure and wind belts overhead (the equatorial low, the subtropical high, the mid-latitude westerlies), and coastal ocean currents (warm currents moisten and warm the air passing over them, cold currents dry and cool it). Once these controls are clear, most named climates stop being labels to memorise: a place under the subtropical high nearly all year is dry almost by definition, and a west coast at 50 degrees latitude, permanently in the path of the westerlies, is wet in every month almost by definition.

The most widely used formal version of this same logic is the Köppen classification, built on numerical thresholds for monthly temperature and rainfall. This note follows the same broad groups and causes without leaning on Köppen's letter codes, since UPSC tests the descriptive climate type (Mediterranean, monsoon, Siberian) rather than a label like Csa or Dfb.

The tropical climates: equatorial, monsoon and savanna

Three climate types share the deep tropics, separated almost entirely by the length and severity of the dry season.

The equatorial climate sits within about 10 degrees of the Equator, across the Amazon basin, the Congo basin, and the Malesian region running from Myanmar through Malaysia, Indonesia, the Philippines and Papua New Guinea to parts of tropical Australia. No month averages below 18°C, and annual rainfall typically runs 1,800 to 2,500 millimetres, spread with little seasonal break through the year. There is no true dry season, because the equatorial low, where the trade winds of both hemispheres converge and rise, sits over or near this belt for most of the year, keeping the air perpetually unstable and rain-bearing.

The monsoon climate covers most of South and Southeast Asia and shares the equatorial climate's heat and, often, an even higher annual rainfall total, but with one defining difference: a real dry season, usually in the low-sun half of the year. In summer, warm moist maritime air converges into the low-pressure zone that builds north of the Himalayas, producing heavy convective and orographic rain; in winter, cool dry air diverges outward from the Siberian anticyclone, the vast high-pressure cell over the frozen Asian interior, and this outflow suppresses rain for months at a stretch. A smaller, gentler version, the trade-wind littoral variety, appears on narrow windward coasts in parts of the Americas and Africa. The mechanics of the south-west monsoon over India specifically are covered in The Indian Monsoon, Made Simple; this note treats monsoon only as one named world climate type among several.

The savanna climate, also called the Sudan type after its clearest expression across the African Sudan belt, occupies roughly 8 to 20 degrees from the Equator, where the dry season runs longer than the wet one. Temperatures stay warm to hot in every month (roughly 19 to 20°C in the cool season, 24 to 27°C in the hot season), but rainfall drops to 500 to 1,750 millimetres a year, arriving almost entirely as convective thunderstorms in the high-sun half of the year. The cause is the seasonal swing of the same equatorial low that keeps the equatorial belt wet all year: as it shifts toward the summer hemisphere it drags rain-bearing convection over the savanna belt for a few months, then withdraws and leaves the belt under the descending, stable air of the subtropical high, the same system responsible for the deserts one zone further out. Africa carries the largest savanna area, with substantial belts also in the Brazilian cerrado, the Venezuelan llanos, northern Australia, and parts of South and Southeast Asia.

The dry climates: hot desert and steppe

The hot desert climate dominates a belt roughly 15 to 30 degrees from the Equator, on the poleward side of the Hadley cell whose rising, rain-dropping air feeds the equatorial belt. By the time that air has travelled poleward and sunk back down over the subtropics, it has already lost its moisture and warmed further on the way down, arriving as the persistently dry, subsiding subtropical high that sits over these latitudes in every month. Rainfall is typically under 250 millimetres a year and wildly unreliable; monthly means run 21 to 32°C, with daily swings that can exceed 35°C because cloudless desert air radiates the day's heat back out almost as fast as it absorbed it. Britannica records Death Valley reaching 57°C and al-Aziziyah in Libya reaching a nominal 58°C, though the World Meteorological Organization later disqualified the Libyan reading, leaving Death Valley's 1913 figure as the currently recognised world record. The driest, hottest deserts sit on the western sides of continents, where the subtropical high is strongest, which is why the Sahara, the Arabian desert, the Kalahari and Australia's interior all sit on the drier western halves of their landmasses. A cooler west coast desert variant, the Atacama, the Namib, and the Moroccan Sahara, runs 15 to 21°C and foggier than interior deserts at the same latitude, chilled by an adjacent cold current even as it stays bone dry.

The steppe (semi-arid) climate forms a transitional ring around true deserts, wetter (roughly 380 to 630 millimetres a year) but still too dry for regular cultivation without irrigation. On its equatorward edge it shades into the savanna climate, picking up a small summer rainfall peak; on its poleward edge it shades into the Mediterranean climate, picking up a cooler, wetter winter from mid-latitude frontal storms. It covers the world's great semi-arid grasslands: the Central Asian and Russian steppe, the North American Great Plains, and the South American pampas margins.

The warm temperate climates: Mediterranean, China and Natal types

Two genuinely distinct warm temperate regimes sit on either side of a continent at similar latitudes, roughly 20 to 45 degrees, and confusing them is a favourite exam trap.

The Mediterranean climate occupies western continental margins between about 30 and 45 degrees: the lands ringing the Mediterranean Sea, coastal California, central Chile, South Africa's Cape region and south-western Australia. Its rhythm reverses the savanna's: hot, dry summers and cool, wet winters. In summer the subtropical high extends poleward over these coasts, bringing the same descending, rain-suppressing air that dries the deserts one band closer to the Equator; in winter that high retreats and mid-latitude frontal cyclones bring the season's rain. Annual rainfall runs 350 to 900 millimetres, drier than the humid subtropical climate on the far side of the continent, and the annual temperature range is smaller than the cool temperate climate further poleward on the same coast, since a west coast rarely receives the coldest continental air, which forms over land rather than open ocean. Only in Europe does the Mediterranean Sea itself let this climate extend far inland, since the sea basin coincides with the right latitude band; elsewhere north-south mountain ranges pin it to a narrow coastal strip.

The China type, more formally the humid subtropical climate, is the east coast counterpart at the same 20 to 35 degree band: southern and eastern China, the south-eastern United States, southern Japan and Korea, north-eastern Argentina and Uruguay, and eastern Australia. Summers are hot and genuinely humid, warmest-month averages around 27°C with daily highs often 30 to 38°C, driven by moist maritime air on the western flank of the same subtropical high that dries the Mediterranean coast on the far side of the continent. Rainfall is heavier in summer than winter, roughly 750 to over 2,000 millimetres a year in total; winter is mild (5 to 12°C, frost possible but not routine) and drier, its rain coming from frontal systems along the retreating polar front. In eastern and southern Asia this climate carries a genuinely monsoonal twist: a sharply dry winter caused by the same Siberian anticyclone that drives the true monsoon's dry season further south. This Asian variant carries a noticeably larger annual temperature range than its American or Australian counterparts for exactly that reason.

Descriptive geography gives the Southern Hemisphere expression of this same east coast climate a separate traditional name, the Natal type, after the Natal coast of South Africa, its clearest example. Britannica's own account of the humid subtropical climate confirms the type occurs symmetrically between 20 and 35 degrees in both hemispheres, so Natal, coastal eastern Australia and southern Brazil read as the same climate as southern China and the American Gulf and Atlantic coasts, carried under a Southern Hemisphere name for the same reason the China type carries a Northern Hemisphere one.

The cool temperate climates: British, Laurentian and Siberian types

This trio is what the 2024 PYQ tests most directly, and the fastest way to tell them apart is two questions: which coast, and how big is the annual temperature swing.

The British type, the marine west coast climate, sits on western continental margins between roughly 35 and 60 degrees: the British Isles and coastal north-west Europe, the Pacific coast of North America from Oregon to British Columbia, southern Chile, and coastal south-eastern Australia and New Zealand. Unlike the Mediterranean belt equatorward of it, this zone lies beyond the poleward reach of the subtropical high altogether, so it sits in the path of the mid-latitude westerlies and their travelling frontal storms in every month, not just winter. The result is genuinely equable: mean annual temperatures of 7 to 13°C, an annual range of only 10 to 15°C, roughly half what the continental interior sees at the same latitude, and ample, reliable rain in every month, typically 500 to 2,500 millimetres a year. Fog is common in autumn and winter and gales are frequent, but genuine thunderstorms are rare. Where north-south mountain ranges back the coast, in the Americas, Australia and New Zealand, this climate is squeezed into a narrow strip; Europe is the exception, since its major ranges run broadly east to west rather than blocking the westerlies, letting the climate push some 2,000 kilometres inland across eastern Germany and Poland.

The Laurentian type, the humid continental climate, is the cool temperate east coast counterpart, named after the St Lawrence and Great Lakes region where it is classically expressed, found more broadly across the north-eastern United States and southern Canada, with a similar belt across north-eastern China, Korea and parts of Japan, roughly 30 to 60 degrees, in the zone where cold polar and warm tropical air routinely collide. Four sharp seasons are the hallmark: hot, sometimes humid summers with a summer rainfall maximum, and cold, often snowy winters, coldest month averaging below freezing with continuous snow cover for one to four months. Annual rainfall runs 500 to 1,250 millimetres, reasonably spread through the year with a summer peak. Because this coast, unlike a west coast, takes the full force of continental polar air sweeping down from the interior, its annual temperature range is considerably larger than the British type's at a comparable latitude, even though both sit at an ocean's edge. Eastern Asia's version of this climate carries its own monsoonal dry winter, again driven by the outflowing Siberian anticyclone.

The Siberian type, the cold continental or subarctic climate, sits north of the Laurentian belt, roughly 50 to 70 degrees, across interior Alaska and Canada, northern Scandinavia, and the breadth of Siberia. Its defining feature is the sheer severity and length of winter: mean monthly temperatures 40 to 50°C below freezing are unremarkable across interior Siberia, six to eight months of the year average below 0°C, and the frost-free season can run as short as 50 to 90 days. Summers are short but can turn genuinely warm inland, sometimes reaching 25°C, giving this climate the largest annual temperature range on Earth: over 60°C in central Siberia against roughly 30°C through most of the rest of the belt. Annual precipitation is modest, generally under 500 millimetres, falling mostly as summer rain with a persistent winter snow cover. This climate's own high-pressure engine, the Siberian anticyclone, supplies the cold, dry winter outflow that shapes the winter dry seasons of three climates already covered here (the Asian monsoon, the Asian China type, and the Asian Laurentian type), which is exactly why it sits at the centre of so many of this chapter's comparison questions.

The polar climates: tundra and ice cap

Poleward of the Siberian type, tree growth stops altogether. The tundra climate runs roughly 60 to 75 degrees, along the Arctic coasts of North America and Eurasia and the fringes of Greenland: winters are long and bitterly cold, six to ten months below freezing in the far north, but the defining constraint is a short, cool summer rather than extreme winter cold, since even the warmest month averages below 10°C, too cool for tree growth even where enough rain falls. Annual precipitation is modest, generally under 350 millimetres, and much of the ground stays permanently frozen as permafrost, thawing only in a shallow active layer each summer. World Vegetation Belts and Soil Types covers what actually grows on that thawed layer; this note stops at the climate figures that define the zone. Beyond the tundra lies the ice cap climate, where even the warmest month stays below freezing, so no real summer thaw occurs: the Antarctic interior and the Greenland ice sheet are its main expressions, effectively polar deserts locked under ice rather than sand.

The exam trap: telling four look-alike climates apart

UPSC's real 2024 question on this chapter is built on exactly this confusion: it describes a climate purely by its temperature range, rainfall pattern and position on a continent, then asks the candidate to name it correctly against three plausible alternatives. All four candidates (British type, China type, Mediterranean, Siberian) are perfectly real climates at broadly similar latitudes, so a vague, half-remembered sense of "cool, rainy, temperate" is not enough; the exam is testing whether the seasonal pattern of temperature and rainfall, read carefully, points to one and only one of the four.

The working method is to ask three questions in order. First, which coast: west points toward British type or Mediterranean, east points toward China type or Siberian type. Second, how big is the annual temperature swing: small (10 to 15°C) points to British type, genuinely large points to Siberian type, and Mediterranean and China type sit in between. Third, when does the rain fall: rain in every month with no dry season is British type; a hot, bone-dry summer against a cooler wet winter is Mediterranean; a wet, thundery summer against a mild but drier winter is China type; a short, modest summer rain season against a long, largely dry, savagely cold winter is Siberian type. Running any exam description through these three questions in order, rather than pattern-matching on a single remembered adjective like "mild" or "wet", resolves most of this chapter's trickier statements.

Quick revision points

• This chapter is the formal climate classification itself (named types, causes, distribution), not the vegetation/soil chapter; see World Vegetation Belts and Soil Types for what grows in each zone rather than re-deriving it here.
• Equatorial: within about 10 degrees of the Equator, no month below 18°C, 1,800 to 2,500 mm rain spread evenly all year, no real dry season (Amazon, Congo, Malesia).
• Monsoon: South and Southeast Asia, heavy summer rain from maritime air converging north of the Himalayas, a real dry winter from Siberian anticyclone outflow; Indian monsoon mechanics specifically are covered in The Indian Monsoon, Made Simple.
• Savanna (Sudan type): 8 to 20 degrees from the Equator, warm all year, rain concentrated in the high-sun season as the ITCZ shifts through, dry season longer than wet; largest belt in Africa.
• Hot desert: 15 to 30 degrees, under the subtropical high all year, under 250 mm rain typically, most extreme on west coasts; cool, foggy west coast desert variant (Atacama, Namib) from adjacent cold currents.
• Steppe: transitional ring around true deserts, 380 to 630 mm rain, shades into savanna equatorward and Mediterranean poleward.
• Mediterranean: west coast, 30 to 45 degrees, hot dry summer under the poleward-extended subtropical high, cool wet winter from frontal cyclones; 350 to 900 mm rain, smaller annual temperature range than British type.
• China type (humid subtropical): east coast, 20 to 35 degrees, hot humid summer (around 27°C average), mild winter, summer rain maximum, monsoon variant in Asia has a sharply dry winter from the Siberian anticyclone. Natal type is the same climate's Southern Hemisphere name (Natal, South Africa; also coastal eastern Australia, southern Brazil).
• British type (marine west coast): west coast, 35 to 60 degrees, beyond the subtropical high's reach, rain in every month, small annual temperature range (10 to 15°C), mild winters, cool summers.
• Laurentian type (humid continental): east coast counterpart of British type, 30 to 60 degrees, four sharp seasons, cold snowy winters, summer rain maximum, larger annual range than British type at the same latitude.
• Siberian type (cold continental/subarctic): 50 to 70 degrees, brutally cold long winters, short mild summers, the largest annual temperature range on Earth (over 60°C in central Siberia); its own anticyclone drives the winter dry seasons of the monsoon, China type and Laurentian type climates further south.
• Tundra: 60 to 75 degrees, warmest month below 10°C, permafrost, under about 350 mm rain. Ice cap: warmest month below freezing, no real summer thaw, Antarctica and interior Greenland.
• The exam trap: separate British type, Mediterranean, China type and Siberian type by coast (west vs east), size of annual temperature range (small to large in that order for the first three, largest for Siberian), and rainfall season (all year, dry summer, wet summer with dry winter, short summer rain against a long cold dry winter).