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, 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.
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.
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.
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).
Overview
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 6-month period that is warmer either from April–September and/or October–March while winter is the 6-month period that is cooler.
Group A: tropical climates
This type of climate has an average temperature of or higher every month of the year, with significant precipitation. Af = Tropical rainforest climate; average precipitation of at least in every month. Am = Tropical monsoon climate; driest month (which nearly always occurs at or soon after the "winter" solstice for that side of the equator) with precipitation less than , but at least . Aw or As = Tropical wet and dry or savanna climate; with the driest month having precipitation less than and less than .
Group B: arid climates
This type of climate is defined by little precipitation that does not fit the polar (EF or ET) criteria of no month with an average temperature greater than .
The threshold in millimeters is determined by multiplying the average annual temperature in Celsius by 20, then adding: (a) 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 (b) 140 if 30%–70% of the total precipitation is received during the spring and summer, or (c) 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).
A third letter can be included to indicate temperature. Here, h signifies low-latitude climates (average annual temperature above ) 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. BWh = Hot desert climate BWk = Cold desert climate BSh = Hot semi-arid climate BSk = Cold semi-arid climate