The Koppen climate classification system is a widely-utilized vegetation-based climate classification system that was created by the German botanist and climatologist Wladimir Koppen. The Koppen climate classification system is an attempt to come up with a formula to delineate climatic boundaries in correspondence with vegetation zones or biomes across the globe.
These biomes were in the process of being formulated and mapped for the first time during the time Koppen formulated his climate classification system in 1900. Koppen published a revised edition of his Koppen climate classification system in 1918, and afterwards continued to revise his system until he passed away in 1940 (A.J. Arnfield, 2017).
Throughout history, many attempts have been made in classifying the Earth’s climates into climatic regions. The great Greek Philosopher Aristotle divided Earth into torrid, temperate and frigid zones, whose finer details are now redundant.
After this many attempts were made to classify the Earth’s climatic regions, but none were as influential as the Koppen climate classification system. The Koppen climate classification system was introduced as a map in 1928 as one co-authored with Rudolph Geiger – a student of Koppen (M. Rosenberg, 2017). Since then the Koppen climate classification system has been modified by various geographers.
The Koppen climate classification system, sometimes called the Koppen-Geiger climate classification system, is a terrestrial classification of climactic zones into five major types, which Koppen represented through the letters A, B, C, D, and E.
The present system of Koppen climate classification is based on the classification of climactic zones as based on both precipitation and temperature along with the corresponding vegetation. Temperature defines all the climactic zones except for B, as the determining factor for vegetation here is dryness, which can be categorized under precipitation.
Aridity however, is not determined only by precipitation and precipitation input in soil also works along with evaporation losses among plants. The five major climactic zones defined by Koppen as elucidated by Michael Pidwirmy, 2014 are –
A – Tropical Moist Climates (average temperature above 18oC in all months)
B – Dry Climates (deficient precipitation for most of the year)
C – Moist Mid-Latitude Climates with Mild Winters
D – Moist Mid-Latitude Climates with Cold Winters
E – Polar Climates (extremely cold summers and winters)
A – Tropical Moist Climates
Tropical moist climates can be found about 15 to 25 degrees latitude northwards and southwards of the equator. The distinctive feature of this climactic zone is that temperatures in these zones remain above 18 degree C all throughout the year. Annual precipitation in this climactic zone is usually above 1,500 mm.
Within this broad climactic zone, three minor climactic types also exist, whose classification is based on the seasonal distribution of rainfall in these climactic zones. Areas falling under these climactic zones usually consist of naturally dense tropical forests.
The first is Af, or tropical wet climate, where the climate is tropical with precipitation all year round. Monthly variations in temperature in these regions are less than of about 3 degree C. The extremely high humidity and surface temperatures in these regions cause cumulus and cumulonimbus clouds to form early into the afternoons everyday, resulting in a high amount of precipitation.
Second is tropical monsoon climate, designated as Am. In these regions, the annual precipitation is nearly similar to that of Af, but here most of the precipitation occurs within the 7 to 9 of the warmest months of the year. Less rainfall occurs in these regions in the rest of the year.
The third sub-division is Aw, or the tropical wet and dry climate, or the savanna climate. These climactic zones experience an extended dry season during the winter season. During the wet season, precipitation is usually less than 1,000 mm, and occurs mostly during the summer season.
B – Dry Climates
Temperature is not as much of a factor in these climactic zones as precipitation, or rather the lack of it is in these climactic zones. In these climactic zones, evaporation and transpiration exceeds the total precipitation. These climactic regions extend 20 to 35 degrees latitude northwards and southwards from the equator and are present in large continental regions in the mid-latitudes or are encircled by mountainous regions.
There are four broad sub-divisions of this climactic zone.
The first is BW, or dry arid climate, also called the true desert climate, and covers about 12 per cent of the Earth’s total land area. Areas falling under this climactic zone are habitats for xerophytic vegetation. The letters h and k are suffixed after BW to signify whether the dry arid zone is located in the sub-tropics or the mid-latitudes respectively.
The second is BS, or dry semi-arid climate, also referred to as steppe climate. This forms a sort of grassland climate that is present in about 14 per cent of the Earth’s surface. Regions coming under dry semi-arid climate or BS receives more precipitation than the regions under the dry arid climate or BW, which is mainly due to mid-latitude cyclones or due to the inter-tropical convergence zone.
The letters h and k are suffixed in a similar way to BW zones to define the location of the climactic zone in the sub-tropics or in the mid-latitudes respectively.
C – Moist Sub-tropical Mid-latitude Climates
In this climactic zone summers are usually warm and humid while winters are mild. These climactic zones extend 30 to 50 degrees latitude northwards and southwards from the equator and are present mainly at the eastern and western extremes of most continents. Summer months feature many convective thunderstorms and winter months feature some mid-latitude cyclones. Three subdivisions exist for this form of climactic zone.
The first is the humid sub-tropical climate or Cfa, where summers are hot and humid with frequent thunderstorms. The winters are comparatively mild and precipitation during this period occurs due to mid-latitude cyclones, like in southeastern USA for example.
The second is the Cfb marine climates that are usually found on the western coasts of continents. The climate here is largely humid with a hot and dry summer. Winters are mild, although accompanied with heavy precipitation due to mid-latitude cyclones. Third is the Mediterranean climactic zone or Cs, where rainfall mostly occurs during the mild winters due to the mid-latitude cyclones.
Precipitation during the summer months in this climactic zone can be extremely scanty. Areas falling under this climactic zone can include locations in Portland, Oregon and California for example.
D – Moist Continental Mid-latitude Climates
In moist continental mid-latitude climates, summers are warm and can also be cool while winters are cold. The regions with moist continental mid-latitude climates are usually located pole wards from the moist sub-tropical mid-latitude climates or C climates. Average temperatures in the warmest months are usually more than 10 degrees C, while temperatures in the coldest months can be less than minus 3 degrees C.
Winters in these regions can be bitterly cold, with strong winds and snowstorms that flow from the Continental Polar and the Arctic air masses. There are three sub-divisions in this form of Koppen climate classification, namely, Dw – with dry winters, Ds – with dry summers, and Df – with precipitation all year round.
E – Polar Climates
In Polar climates, temperatures are low all year round with the warmest month having temperatures less than 10 degrees C. Polar climates occur on the northern coastal areas of Asia, Europe and North America and on Greenland and Antarctica. Polar climates have two sub-divisions.
The first is ET or Polar Tundra in which soil occurs as permanently frozen as permafrost extending hundreds of meters in depth. Most vegetation found here occurs in the form of dwarf trees, woody shrubs, lichens and mosses. The second is EF or Polar Ice Caps, which have a surface that is permanently covered with ice or snow.
Determining Factors For Koppen Climate Classification
The factors that influence the climactic characteristics of these regions include latitudinal position and amount of solar radiation received, air masses, air pressure (with high and low pressure zones), wind patterns, heat exchange with the ocean, topographical features (such as mountains), land and sea distribution, and altitude.
The greatest influence on these climactic zones is exerted by solar radiation, air masses and air pressure in terms of high and low pressure zones (M. Pidwirmy, 2014); making heat and its resulting effects a primary determinant of global climactic zones in the Koppen climate classification.
The model however, does not take extremes of weather into account substantively, such as extremes of temperature, temporary wind patterns, cloud cover or number of days of sunshine for example. The Koppen climate classification system serves as a general guide to larger climactic zones on Earth. However, the system is not accountable in terms of instantaneous or micro climactic aberrations or shifts, and represents general classificatory categories of world climate.
The Koppen-Geiger climate classification as we have described has in one of its proceeding modifications, been modified into the Koppen-Trewartha climate classification. This scheme takes into account observed and prospective climactic changes on Earth based on reliable variability exhibited by types of land surfaces.
With the scheme provided in the Koppen-Trewartha climate classification, it is possible to model simulations of the period between 1900 and 2099. Based on this, the Intergovernmental Panel on Climate Change (IPCC) in its 4th Assessment, projected 16 global climate models continuing into the near future. In this assessment, the average annual mean surface temperature over the Arctic landmasses is expected to witness an increase of 3.1, 4.6 and 5.3oC (S. Feng et al., 2011).