Köppen climate classification

Wladimir Köppen designed this system in the late 19^th century to describe climate types in parts of the world. As he was a botanist, his system was particularly designed to describe the types of climates in which certain types of plants would grow.

Places are given a two or three-letter designation to describe their climates. The first letter gives you the broad classification, the second describes rainfall distribution, and the third (if there is a third) describes the level of heat. Where there are temperature thresholds given, they refer to mean temperatures (i.e. averages from over the whole 24-hour day), not mean maximum temperatures.

Classifications

• A: tropical: every month of the year has a mean temperature of 18°C or above, with significant precipitation
  • Af: rainforest (at least 60mm of rain every month of the year)
  • Am: monsoon (less than 60mm of rain in the driest month, but more than 100 minus 4% of annual rainfall)
  • Aw or As: savannah (less than 60mm of rain and less than that threshold in that driest month). w if it’s winter that’s dry; s if it’s summer that’s dry.
• B: arid: characterised by low precipitation, as determined by some complicated formula
  • W: desert: if rainfall is less than 50% the number given by the complicated formula
  • S: steppe, or semi-arid: if rainfall is between 50–100% the number given by the complicated formula
  • an optional third letter
    • h: hot: either an annual mean temp above 18°C, or no month below 0 or -3°C¹²
    • k: cold: either an annual mean temp below 18°C, or at least one month with an average temp below 0 or -3°C;² by the latter definition there are very few cold deserts, although cold steppes are more common¹
  • there can be a fourth letter of n used predominantly by Chilean meteorologists, to describe arid climates with significant wintertime fog despite little actual rainfall (fog = niebla in Spanish)
• C: temperate: the coldest month of the year has a mean temperature between 18°C and 0 or -3°C,² and at least one month has a mean above 10°C
  • the first letter describes rainfall distribution over the year
    • s: dry-summer, or Mediterranean: the wettest month of winter sees at least 3x as much rain as the driest month of summer
    • w: dry-winter, or monsoon: the driest month of winter sees less than 10% the rainfall of the wettest month of summer
    • f: climates that are neither dry-summer nor dry-winter climates
  • the second letter describes temperatures
    • a: the warmest month has a mean temperature above 22°C
    • b: at least four months a year average above 10°C, but the warmest one averages less than 22°C
    • c: only one to three months of the year average above 10°C, but no month averages below 0 or -3°C²
• D: continental: at least one month has a mean temperature below 0° or -3°C,² and at least one month has a mean temperature above 10°C
  • the first letter describes rainfall distribution over the year (same criteria as for C climates)
    • s: dry-summer: the wettest month of winter sees at least 3x as much rain as the driest month of summer
    • w: dry-winter: the driest month of winter sees less than 10% the rainfall of the wettest month of summer
    • f: climates that are neither dry-summer nor dry-winter climates
  • the second letter describes temperatures (mostly the same as for C climates, with one extra option)
    • a: at least four months a year average above 10°C, and the warmest month has a mean temperature above 22°C
    • b: at least four months a year average above 10°C, but the warmest one averages less than 22°C
    • c: only one to three months of the year average above 10°C
    • d: the coldest month averages below -38°C, and only one to three months of the year average above 10°C
• E: polar: every month of the year has an average temperature below 10°C
  • ET: tundra: the warmest month has an average temperature between 0° and 10°
  • EF: every month has an average temperature below 0°C

Descriptions and Examples

A: Tropical

Af: Rainforest

These occur close to the equator, and are found particularly in the Amazon rainforest basin, maritime southeast Asia, and the Pacific Islands. Days are roughly the same length throughout the year. Some places are truly aseasonal; others do have some seasonal variation but just not enough to trigger any thresholds to get into a different category. Some examples: Singapore, Kuala Lumpur (Malaysia), Kampala (Uganda), Salvador (Brazil), Suva (Fiji)

Am: Monsoon

Monsoon climates have a pronounced “rainier” season but the “dry” season is still a little rainy. Some examples: Jakarta (Indonesia), Cairns (Australia), Miami (USA), Recife (Brazil), Chittagong (Bangladesh), Yangon (Myanmar), Zanzibar City (Tanzania)

As and Aw: Savanna

These are real “wet-and-dry” climates, and tend to be the most widespread type of tropical climate, covering swathes of the world just poleward of the equator in Latin America, Africa, southeast Asia and northern Australia. For example: Caracas (Venezuela), Brasília (Brazil), Lagos (Nigeria), Kinshasa (DRC), Mumbai (India), Bangkok (Thai­land), Ho Chi Minh City (Vietnam), Darwin (Australia)

B: Arid

BWh: hot desert

These climates are very dry, and every month has a mean temperature above 18°C. Huge parts of Australia, Pakistan/Afghanistan/Iran, Arabia, Africa and smaller parts of the Americas (the Peruvian coastline, Baja California, and parts of northern Mexico and the American Southwest) fit this climate type.

BWk: cold desert

Using the “at least one month with a mean temp below 18°C” definition, this climate region extends across large parts of Central Asia, southern Argentina and northern Chile, with smaller pieces elsewhere.

BSh: hot semi-arid

These places are dry, but not as dry as hot deserts; like those, though, every month in these parts of the world averages above 18°C. Some examples: Monterrey (Mexico), Alicante (Spain), Nicosia (Cyprus), Dakar (Senegal), Mogadishu (Somalia), Lahore (Pakistan)

BSk: cold semi-arid

Again, dry but not as dry as deserts. “Cold” just means “not every month averages 18°C+”; some are still comparatively pretty warm (like Zacatecas, Mexico), while others are seriously cold, especially in winter (like Ulaanbaatar, Mongolia). Some other examples: Denver (USA), Yerevan (Armenia), Kabul (Afghanistan), Tianjin (China)

C: Temperate

Csa: hot-summer mediterranean

These are more common on the western sides of continents, and are characterised by hot, dry summers and winters that are not freezing cold. Very very common around the Mediterranean basin, hence the name. Some examples: Los Angeles (USA), Madrid (Spain), Rome (Italy), Beirut (Lebanon), Perth and Adelaide (Australia)

Csb: warm-summer mediterranean

These tend to be adjacent to hot-summer areas, but without a month with a mean temperature above 22°C, they can only be “warm-summer” areas. Some examples: San Francisco and Seattle (USA), Cape Town (South Africa), Porto (Portugal), Salamanca (Spain)

Csc: cold-summer mediterranean

This is a rare climate type that exists in high-altitude areas adjacent to warm-summer mediterranean areas (like parts of the Pacific Northwest, the Andes and Tasmania). Most of the year is cold (average temperatures of 0–10°C). For three months or less in the summer, temperatures rise above 10°C.

Cfa: humid subtropical

These areas tend to be more common on continents’ east coasts. They aren’t significantly rainier in either summer or winter, with warmer summers on average than oceanic areas. The wintertime average temperature is allowed to be anywhere between 0° and 18°C, so some huge variation there. Some examples: Atlanta (USA), Buenos Aires (Argen­ti­na), Milan (Italy), Durban (South Africa), Shanghai (China), Tokyo (Japan), Sydney and Brisbane (Australia).

Cfb: oceanic / subtropical highlands

These areas are slightly cooler than humid subtropical areas, either due to a more poleward latitude or elevation. Some examples: Vancouver (Canada), Bogotá (Colombia), London (UK), Berlin (Germany), Port Elizabeth (South Africa), Melbourne and Hobart (Australia), Auckland and Wellington (NZ)

Cfc: subpolar oceanic

Another rare climate type occurring poleward again of oceanic climates, especially on islands or windswept coasts. Most of the year is cold (average temperatures of 0–10°C). For three months or less in the summer, temperatures rise above 10°C. Some examples: Punta Arenas (Chile), Reykjavík (Iceland)

Cwa: monsoon-influenced humid subtropical

These areas are not warm enough in the winter to be classified as tropical, but do share the summertime raininess of nearby tropical areas. Some examples: Guadalajara (Mexico), Córdoba (Argentina), Lusaka (Zambia), Delhi (India), Hong Kong, Hanoi (Vietnam), Busan (South Korea)

Cwb: subtropical highlands (part B) / monsoon-influenced temperate oceanic climate

These areas are similar to Cwa ones but slightly cooler in the summer, often due to higher elevation. Some examples: Mexico City, Cusco (Peru), Johannesburg (South Africa), Nairobi (Kenya), Kunming (China)

Cwc: cold subtropical highlands / monsoon-influenced subpolar oceanic

This is a very rare climate type found in very high-altitude areas, mostly in the Andes and small parts of SE Asia. Again, most of the year is cold (average temperatures of 0–10°C). In the summer, mean temperatures rise above 10°C for three months or less, and it’s also considerably rainier than the winter.

D: continental

Dfa: hot-summer humid continental

These are characterised by very cold winters, hot summers and rain all year round, and exist only in the northern hemisphere because the southern hemisphere doesn’t have any continents large enough to develop these kinds of temperature extremes. Some examples: Chicago (USA), Toronto and Montreal (Canada), Bucharest (Romania), Vol­go­grad (Russia), Sapporo (Japan)

Dfb: warm-summer humid continental

These tend to be located immediately poleward of Dfa areas, with cooler summers compared to them. Quite widespread in Canada (e.g. Edmonton, Winnipeg, Ottawa, Quebec City, Halifax) and northern and eastern Europe (e.g. Moscow, Kyiv, Warsaw, St Petersburg, Tallinn, Vilnius, Stockholm).

Dfc: subarctic

Pretty damn cold all year round, although no month has an average temp below -38°C (…at least that’s something?). Neither summer nor winter are particularly dry here. Found in some parts of high-altitude or far-northern Europe and North America.

Dfd: extremely cold subarctic

Horribad winters (at least one month has an average temperature below -38°C). Only found in Siberia.

Dwa: monsoon-influenced hot-summer humid continental

This is very similar to the Dfa type but in eastern Asia, the Siberian land mass causes dry winters while the summer can still be rainy from the monsoon further south. Examples: Beijing (China), Seoul (South Korea)

Dwb: monsoon-influenced warm-summer humid continental

Like Dwa climates but a little cooler. Examples: Calgary (Canada), Vladivostok (Russia)

Dwc: monsoon-influenced subarctic

Like Dfc, but with rainier summers and/or drier winters. Found more in high-altitude parts of Asia.

Dwd: monsoon-influenced extremely cold subarctic

Like Dfd, and only in Siberia as well.

Dsa: Mediterranean-influenced hot-summer humid continental

This climate type exists at high elevation near Csa areas. Seems to occur particularly in mountainous parts of western Asia and also Salt Lake City (USA).

Dsb: Mediterranean-influenced warm-summer humid continental

Similar to Dsa but even more poleward or at even higher latitudes, to make them cooler again.

Dsc: Mediterranean-influenced subarctic

Like Dfc, but with rainier winters and/or drier summers. Found in Alaska (including Anchorage) and parts of far-eastern Russia.

Dsd: Mediterranean-influenced extremely cold subarctic

Like Dfd except I'm not sure anywhere actually exists with this climate type, even in Siberia.

E: polar and alpine

ET: tundra

These are very cold places, where the warmest month of the year has an average temp somewhere between 0° and 10°C. Tends to occur at very very high altitude, or on islands or coastal areas either very far north or very far south, e.g. northern Canada, Greenland, the Falkland Islands.

EF: ice caps

No month has an average temperature above freezing. Occurs in Antarctica and inland Greenland, and also at extremely high altitudes (like the top of the Himalayas).

Comparison to Trewartha

Some feel that the Köppen system’s “C” (temperate) classification is much too broad, seeing as it includes areas with wintertime mean temperatures of anywhere from just above freezing (like New York City) to 17.9°C (like São Paulo). Considering Köppen’s original intention to design a system around what types of plants will grow, perhaps this makes sense. However, Amer­i­can geographer Glenn Thomas Trewartha decided to create an alternative system in the 1960s which replaced the two categories of “C” and “D” with three, more finely-grained, categories (plus some other tinkering and simplifications). That system doesn’t really seem to have caught on much beyond the United States (and to be honest… I’m not even sure how much it’s used there…), but it is referred to as the Trewartha system.