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Köppen climate classification

The Köppen climate classification is one of the most widely used climate classification systems. It was first published by German-Russian climatologist Wladimir Köppen (1846–1940) in 1884,[1][2] with several later modifications by Köppen, notably in 1918 and 1936.[3][4] 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.[5][6]

The Köppen climate classification divides 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. For example, Cfb indicates an oceanic climate with warm summers as indicated by the ending b. Climates are classified based on specific criteria unique to each climate type.[7]

As Köppen designed the system based on his experience as a botanist, his main climate groups are based on the types of vegetation occurring in a given climate classification region. 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.[8]

The Köppen climate classification system was modified further within the Trewartha climate classification system in 1966 (revised in 1980). The Trewartha system sought to create a more refined middle latitude climate zone, which was one of the criticisms of the Köppen system (the climate group C was too general).[9]: 200–1 

Köppen–Geiger climate map 1991–2020[8]

Overview

The Köppen climate classification scheme divides climates into five main climate groups: A (tropical), B (arid), C (temperate), D (continental), and E (polar).[11] The second letter indicates the seasonal precipitation type, while the third letter indicates the level of heat.[12] Summers are defined as the six-month period that is warmer either from April to September and/or October to March, while winter is the six-month period that is cooler.[8][10]

Group A: Tropical climates

Tropical climates have an average temperature of 18 °C (64.4 °F) or higher every month of the year, with significant precipitation.[8][10]

Group B: Desert and semi-arid climates

Desert and semi-arid climates are defined by low precipitation in a region that does not fit the polar (EF or ET) criteria of no month with an average temperature greater than 10 °C (50 °F).

The precipitation threshold in millimeters is determined by multiplying the average annual temperature in Celsius by 20, then adding:

  1. 280 if 70% or more of the total precipitation is in the spring and summer months (April–September in the Northern Hemisphere, or October–March in the Southern), or
  2. 140 if 30%–70% of the total precipitation is received during the spring and summer, or
  3. 0 if less than 30% of the total precipitation is received during the spring and summer.

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).[8][10]

A third letter can be included to indicate temperature. Here, h signifies low-latitude climates (average annual temperature above 18 °C (64.4 °F)) while k signifies middle-latitude climates (average annual temperature less than 18 °C). In addition, n is used to denote a climate characterized by frequent fog and H for high altitudes.[13][14][15]

Group C: Temperate climates

Temperate climates have the coldest month averaging between 0 °C (32 °F)[10] (or −3 °C (26.6 °F))[7] and 18 °C (64.4 °F) and at least one month averaging above 10 °C (50 °F).[10][7] For the distribution of precipitation in locations that both satisfy a dry summer (Cs) and a dry winter (Cw), a location is considered to have a wet summer (Cw) when more precipitation falls within the summer months than the winter months while a location is considered to have a dry summer (Cs) when more precipitation falls within the winter months.[10] This additional criterion applies to locations that satisfies both Ds and Dw as well.[10]

Group D: Continental climates

Continental climates have at least one month averaging below 0 °C (32 °F) (or −3 °C (26.6 °F)) and at least one month averaging above 10 °C (50 °F).[10][7]

Group E: Polar and alpine climates

Polar and alpine climates has every month of the year with an average temperature below 10 °C (50 °F).[8][10]

Group A: Tropical/megathermal climates

Tropical climate distribution

Tropical climates are characterized by constant high temperatures (at sea level and low elevations); all 12 months of the year have average temperatures of 18 °C (64.4 °F) or higher; and generally high annual precipitation. They are subdivided as follows:

Af: Tropical rainforest climate

All 12 months have an average precipitation of at least 60 mm (2.4 in). These climates usually occur within 10° latitude of the equator. This climate has no natural seasons in terms of thermal and moisture changes.[9] When it is dominated most of the year by the doldrums low-pressure system due to the presence of the Intertropical Convergence Zone (ITCZ) and when there are no cyclones then the climate is qualified as equatorial. When the trade winds dominate most of the year, the climate is a tropical trade-wind rainforest climate.[16]

Examples