The Köppen climate classification divides Earth's climates into five main climate groups, with each group being divided based on patterns of seasonal precipitation and temperature. The five main groups are A (tropical), B (arid), C (temperate), D (continental), and E (polar). Each group and subgroup is represented by a letter. All climates are assigned a main group (the first letter). All climates except for those in the E group are assigned a seasonal precipitation subgroup (the second letter). For example, Af indicates a tropical rainforest climate. The system assigns a temperature subgroup for all groups other than those in the A group, indicated by the third letter for climates in B, C, D, and the second letter for climates in E. Other examples include: Cfb indicating an oceanic climate with warm summers as indicated by the ending b, while Dwb indicates a semi-monsoonal continental climate, also with warm summers. Climates are classified based on specific criteria unique to each climate type.
The Köppen climate classification is the most widely used climate classification scheme. It was first published by German-Russian climatologist Wladimir Köppen (1846–1940) in 1884, with several later modifications by Köppen, notably in 1918 and 1936. Later, German climatologist Rudolf Geiger (1894–1981) introduced some changes to the classification system in 1954 and 1961, which is thus sometimes called the Köppen–Geiger climate classification.
As Köppen designed the system based on his experience as a botanist, his main climate groups represent a classification by vegetation type. In addition to identifying climates, the system can be used to analyze ecosystem conditions and identify the main types of vegetation within climates. Due to its association with the plant life of a given region, the system is useful in predicting future changes of plant life within that region.
[[File:Koppen-Geiger Map v2 World 1991–2020.svg|thumb|center|upright=3|Köppen–Geiger climate map 1991–2020
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Overview
{|class="wikitable plainlist" style="margin:auto;"
|+ Köppen climate classification scheme symbols description table
!scope="col"| 1st
!scope="col"| 2nd
!scope="col"| 3rd
|-
! scope="row" | A (Tropical)
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- f (Rainforest)
- m (Monsoon)
- w (Savanna, dry winter)
- s (Savanna, dry summer)
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|-
! scope="row" | B (Dry)
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- W (Arid desert)
- S (Semi-arid steppe)
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- h (Hot)
- k (Cold)
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! scope="row" | C (Temperate)
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- w (Dry winter)
- f (No dry season)
- s (Dry summer)
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- a (Hot summer)
- b (Warm summer)
- c (Cold summer)
|-
! scope="row" | D (Continental)
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- w (Dry winter)
- f (No dry season)
- s (Dry summer)
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- a (Hot summer)
- b (Warm summer)
- c (Cold summer)
- d (Very cold winter)
|-
! scope="row" | E (Polar)
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- T (Tundra)
- F (Ice cap)
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|}
The Köppen climate classification scheme divides climates into five main climate groups: A (tropical), B (arid), C (temperate), D (continental), and E (polar). The second letter indicates the seasonal precipitation type, while the third letter indicates the level of heat. Summers are defined as the six-month period that is warmer either from April to September or October to March, while winter is the six-month period that is cooler.
- BWh = Hot desert climate
- BWk = Cold desert climate
- BSh = Hot semi-arid climate
- BSk = Cold semi-arid climate
Group C: Temperate climates
thumb|right|[[Cornwall, UK, has a temperate oceanic climate]]
Temperate climates have the coldest month averaging between
Some of the places with this climate are indeed uniformly and monotonously wet throughout the year (e.g., the northwest Pacific coast of South and Central America, from Ecuador to Costa Rica; see, for instance, Andagoya, Colombia, Miami), but in many cases, the period of higher sun and longer days is distinctly wettest (as at Palembang, Indonesia) or the time of lower sun and shorter days may have more rain (as at Sitiawan, Malaysia). Among these places, some have a pure equatorial climate (Balikpapan, Kuala Lumpur, Kuching, Lae, Medan, Paramaribo, Pontianak, and Singapore) with the dominant ITCZ aerological mechanism and no cyclones or a subequatorial climate with occasional hurricanes (Davao, Ratnapura, Victoria).
(The term aseasonal refers to the lack in the tropical zone of large differences in daylight hours and mean monthly (or daily) temperature throughout the year. Annual cyclic changes occur in the tropics, but not as predictably as those in the temperate zone, albeit unrelated to temperature, but to water availability whether as rain, mist, soil, or groundwater. Plant response (e.g., phenology), animal (feeding, migration, reproduction, etc.), and human activities (plant sowing, harvesting, hunting, fishing, etc.) are tuned to this 'seasonality'. Indeed, in tropical South America and Central America, the rainy season, or the high water season, is called (Spanish) or (Portuguese), both meaning "winter," although it can occur in the Northern Hemisphere summer. Likewise, the dry season, or low water season, is called or , both meaning "summer," and it can occur in the Northern Hemisphere winter).
Am: Tropical monsoon climate
This type of climate results from the monsoon winds which change direction according to the seasons. This climate has a driest month (which nearly always occurs at or soon after the "winter" solstice for that side of the equator) with rainfall less than , but at least <math display="inline">100-\left (\frac{\mathrm{total\,annual\,precipitation\,(mm){25} \right)</math> of average monthly precipitation. This is the case in parts of Hawaii, northwestern Dominican Republic, Eastern Africa, southeast India and northeast Sri Lanka, and the Brazilian Northeastern Coast. In places that have this climate type, the dry season occurs during the time of high sun and longer days generally because of rain shadow effects.
Group B: Arid (desert and semi-arid) climates
thumb|[[Arid climate distribution]]
These climates are characterized by the amount of annual precipitation less than a threshold value that approximates the potential evapotranspiration.
If the annual precipitation is less than 50% of this threshold, the classification is BW (arid: desert climate); if it is in the range of 50%–100% of the threshold, the classification is BS (semi-arid: steppe climate).
A third letter can be included to indicate temperature. Here, h signifies low-latitude climate (average annual temperature above 18 °C) while k signified middle-latitude climate (average annual temperature below 18 °C).
Desert areas situated along the west coasts of continents at tropical or near-tropical locations characterized by frequent fog and low clouds, although these places rank among the driest on earth in terms of actual precipitation received, can be labeled BWn with the n denoting a climate characterized by frequent fog.
BW: Arid climates
thumb|right|Namib Desert
The desert climate or arid climate (BW) is a dry climate sub-type in which there is a severe excess of evaporation over precipitation. The typically bald, rocky, or sandy surfaces in desert climates are dry and hold little moisture, quickly evaporating the already little rainfall they receive. Covering 14.2% of Earth's land area, hot deserts are the second-most common type of climate on Earth after the Polar climate.
There are two variations of a desert climate: a hot desert climate (BWh), and a cold desert climate (BWk). To delineate "hot desert climates" from "cold desert climates", a mean annual temperature of is used as an isotherm so that a location with a BW type climate with the appropriate temperature above this isotherm is classified as "hot arid subtype" (BWh), and a location with the appropriate temperature below the isotherm is classified as "cold arid subtype" (BWk).
Most desert/arid climates receive between of rainfall annually, although some of the most consistently hot areas of Central Australia, the Sahel and Guajira Peninsula can be, due to extreme potential evapotranspiration, classed as arid with the annual rainfall as high as .
BWh: Hot deserts
Hot desert climates (BWh) are typically found under the subtropical ridge in the lower middle latitudes or the subtropics, often between 20° and 33° north and south latitudes. In these locations, stable descending air and high pressure aloft clear clouds and create hot, arid conditions with intense sunshine. Hot desert climates are found across vast areas of North Africa, West Asia, northwestern parts of the Indian subcontinent, southwestern Africa, interior Australia, the Southwestern United States, northern Mexico, the coast of Peru and Chile, parts of the Brazilian sertão and the southeastern coast of Spain. This makes hot deserts present in every continent except Antarctica. At the time of high sun (summer), scorching, desiccating heat prevails. Hot-month average temperatures are normally between , and midday readings of are common.
BWk: Cold deserts
thumb|Rare snow in the [[Atacama Desert, at elevation]]
Cold desert climates (BWk) usually feature hot (or warm in a few instances), dry summers, though summers are not typically as hot as hot desert climates. Unlike hot desert climates, cold desert climates tend to feature cold, dry winters. Snow tends to be rare in regions with this climate. The Gobi Desert in northern China and Mongolia is one example of a cold desert. Though hot in the summer, it shares the freezing winters of the rest of Inner Asia. Summers in South America's Atacama Desert are mild, with only slight temperature variations between seasons. Cold desert climates are typically found at higher altitudes than hot desert climates and are usually drier than hot desert climates. Cold desert climates are typically located in temperate zones in the 30s and 40s latitudes, usually in the leeward rain shadow of high mountains, restricting precipitation from the westerly winds.
BS: Semi-arid (steppe) climates
thumb|upright=1.6|Regions with semi-arid climates
A semi-arid or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi-arid climates, depending on variables such as temperature, and they give rise to different biomes.
BSh: Hot semi-arid
Hot semi-arid climates (type "BSh") tend to be located from the high teens to mid-30s latitudes of the tropics and subtropics, typically in proximity to regions with a tropical savanna climate or a humid subtropical climate. These climates tend to have hot, or sometimes extremely hot, summers and warm to cool winters, with some to minimal precipitation. Hot semi-arid climates are most commonly found around the fringes of subtropical deserts.
BSk: Cold semi-arid
Cold semi-arid climates (type "BSk") tend to be located in elevated portions of temperate zones generally from the mid-30s to low 50s latitudes, typically bordering a humid continental climate or a Mediterranean climate. They are also typically found in continental interiors some distance from large bodies of water. Cold semi-arid climates usually feature warm to hot dry summers, though their summers are typically not quite as hot as those of hot semi-arid climates. Unlike hot semi-arid climates, areas with cold semi-arid climates tend to have cold and possibly freezing winters. These areas usually see some snowfall during the winter, though snowfall is much lower than at locations at similar latitudes with more humid climates.
Group C: Temperate/mesothermal climates
thumb|upright=1.5|[[Temperate climate distribution]]
In the Köppen climate system, temperate climates are defined as having an average temperature above (or , as noted previously) in their coldest month but below . The average temperature of roughly coincides with the equatorward limit of frozen ground and snow cover lasting for a month or more.
The second letter indicates the precipitation pattern—w indicates dry winters (driest winter month average precipitation less than one-tenth wettest summer month average precipitation). s indicates at least three times as much rain in the wettest month of winter as in the driest month of summer. f means significant precipitation in all seasons (neither above-mentioned set of conditions fulfilled). These climates are in the polar front region in winter, and thus have moderate temperatures and changeable, rainy weather. Summers are hot and dry, due to the domination of the subtropical high-pressure systems, except in the immediate coastal areas, where summers are milder due to the nearby presence of cold ocean currents that may bring fog but prevent rain.
Group E: Polar climates
thumb|upright=1.5|[[Polar climate distribution]]
In the Köppen climate system, polar climates are defined as the warmest temperature of any month being below . Polar climates are further divided into two types, tundra climates and icecap climates:
ET: Tundra climate
Tundra climate (ET): warmest month has an average temperature between and . These climates occur on the northern edges of the North American and Eurasian land masses (generally north of 70 °N although they may be found farther south depending on local conditions), and on nearby islands. ET climates are also found on some islands near the Antarctic Convergence, and at high elevations outside the polar regions, above the tree line.
EF: Ice cap climate
thumb|right|[[Denman Glacier, Antarctica]]
Ice cap climate (EF): this climate is dominant in Antarctica, inner Greenland, and summits of many high mountains, even at lower latitudes. Monthly average temperatures never exceed .
Ecological significance
Biomass
The Köppen climate classification is based on the empirical relationship between climate and vegetation. This classification provides an efficient way to describe climatic conditions defined by temperature and precipitation and their seasonality with a single metric. Because climatic conditions identified by the Köppen classification are ecologically relevant, it has been widely used to map the geographic distribution of long-term climate and associated ecosystem conditions.
Climate change
Over recent years, there has been an increasing interest in using the classification to identify changes in climate and potential changes in vegetation over time.
In 2015, a Nanjing University paper published in Scientific Reports analyzing climate classifications found that between 1950 and 2010, approximately 5.7% of all land area worldwide had moved from wetter and colder classifications to drier and hotter classifications. The authors also found that the change "cannot be explained as natural variations but are driven by anthropogenic factors".
A 2018 study provides detailed maps for present and future Köppen-Geiger climate classification maps at 1-km resolution.
Other Köppen climate maps
All maps use the ≥ definition for the temperate-continental border.