Koppen Climate Classification – A Brief History
A widely-used vegetation-based climate classification system, the Koppen climate classification system, was created by Wladimir Koppen, a German botanist, and climatologist. The classification system attempts to derive a formula to categorize vegetation zones or biomes across the globe, in accordance with their climatic boundaries.
In 1900, the climatic classification was a novel concept. In 1918, Koppen revised his classification system and republished, and continued revising the system until his death in 1940.
Introduced as a map in 1928, the Koppen climate classification system was co-authored by Koppen’s student Rudolph Geiger. Various geographers have modified and utilized this classification since its first publication by Koppen and Geiger.
Image Credits: Wikipedia
What is the Koppen Climate Classification System?
A land-based classification of climatic zones, the Koppen classification system divides the earth into five major types, represented with the letters A, B, C, D, and E. Presently, the system utilizes both precipitation and temperature, as well as corresponding vegetation, to categorize biomes across the world. All zones except Zone B can be defined by temperature because the determining criteria for the vegetation in this zone are dryness, which falls under precipitation.
The Five Zones
A – Tropical Moist Climates
About 15-25º latitude northwards and southwards of the equator are the tropical, moist climates. The temperature in these areas remains above 18ºC throughout the year, and the annual rainfall in this region is about 1500mm. Three types of climatic variation may be found within the Tropical Moist Climate region:
- Af, or tropical wet climate, where precipitation occurs year-round. Variations in temperature are less than 3ºC. Humidity is extremely high and the surface temperature results in the formation of cumulus and cumulonimbus clouds in the early afternoon time, daily. This results in high rainfall.
- Am, or tropical monsoon climate, where annual rainfall is similar to that of Af, but precipitation usually occurs within the 7-9 of the warmest months of the year. During the rest of the year, there is less precipitation.
- Aw, or the tropical wet and dry climate, also known as the savanna climate, where there is an extended dry season during the winter. During the wet season, rainfall is less than 1000mm, occurring mainly in the summertime
B – Dry Climates
Evaporation and transpiration play a greater role in shaping the vegetative state than temperature, here. The regions extend 20-35º latitude northwards and southwards from the equator. There are four subdivisions within this region:
- BW or dry, arid climate, or true desert climate, spans about 12 percent of the Earth’s total land. Xerophytic vegetation usually grows in this climatic zone. The letters h and k are used as suffixes after BW to represent whether the zone is subtropical (h) or mid-latitudinal (k).
- BS or dry, semi-arid climate, which is also referred to as steppe climate, spans about 14 percent of the Earth’s land and makes up grassland type climate. These regions receive more rainfall than their BW counterparts because of mid-latitude cyclones and areas of inter-tropical convergence. Here, the letters h and k are again suffixed to note the region.
C – Moist Mid-Latitude Climates with Mild Winters
These zones typically face hot and humid summers and mild winters. Extending between 30-50º latitude northwards and southwards from the equator, these regions are typically the eastern and western extremes of each continent. Sometimes, summer months may feature convective thunderstorms, and winter months may feature mid-latitudinal cyclones. The climatic classification is further broken into three types:
- Cfa, or humid sub-tropical climate, in which summers are sweltering and humid, with frequent thunderstorms. Winters are milder in comparison, and precipitation occurs due to mid-latitude cyclones.
- Cfb or marine climates are usually on the western coasts of each continent. These areas are generally humid, with a hot and dry summer. While winters are milder, they come with heavy rainfall due to mid-latitude cyclones.
- Cs or the Mediterranean climatic zones are where precipitation is heaviest during the winters due to mid-latitude cyclones. There is hardly any rainfall during the summer. Examples include Portland, Oregon or California.
D – Moist Mid-Latitude Climates with Cold Winters
Summers are typically warm but can also be cool, while winters are cold. These regions are typically situated towards the poles from C regions. During the summer months, average temperatures climb above 10º Celsius, while in the colder months it can be less than 3º Celsius.
The wintertime in this region is usually biting cold, with strong winds and the possibility of snowstorms coming in from the Continental Polar and the Arctic air masses. This Koppen climate classification is further divided into three subsections:
- Dw, which denotes dry winters
- Ds, which denotes dry summers
- Df, for year-round rainfall
E – Polar Climates
Temperatures are usually low all year round in the Polar climatic regions. The warmest months see temperatures less than 10º Celsius. Usually occurring in the northern coastal regions of North America, Asia, Europe, and in Greenland and Antarctica, these climates are divided into two categories:
- ET, or Polar Tundra, where soil remains permanently frozen as permafrost and can be hundreds of meters deep. The only vegetation in this region consists of lichen, mosses, dwarf trees, and woody shrubs.
- EF, or Polar Ice Caps are the second category, in which the surface is permanently covered in ice or snow.
How are these classifications determined?
Classification depends on their latitudinal position, the amount of solar radiation each region receives, the air masses, high and low-pressure zones, patterns of wind, exchange of heat with the ocean, the spread of land and sea, the topography, and altitude.
It is important to note that the model does not account for extreme weather conditions substantively, and is intended to serve as a general guide to the overarching climatic zones on the planet. This system cannot account for instantaneous, micro-climatic shifts.
Since its publication and updates, the Koppen-Geiger classification has been updated to the Koppen-Trewartha classification system, to account for observed and prospective climate changes, based on the variation on land surfaces.