Köppen climate classification explained

The Köppen climate classification is one of the most widely used climate classification systems. It was developed by Wladimir Köppen, a Russian climatologist, around 1900 (with several further modifications by Köppen himself, notably in 1918 and 1936). It is based on the concept that native vegetation is the best expression of climate; thus, climate zone boundaries have been selected with vegetation distribution in mind. It combines average annual and monthly temperatures and precipitation, and the seasonality of precipitation.[1]

The scheme

Köppen climate classification scheme divides the climates into five main groups and several types and subtypes. Each particular climate type is represented by a 2 to 4 letter symbol.

GROUP A: Tropical/megathermal climates

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

GROUP B: Dry (arid and semiarid) climates

These climates are characterized by the fact that precipitation is less than potential evapotranspiration.[6] The threshold is determined as follows:

GROUP C: Temperate/mesothermal climates

These climates have an average temperature above 10 °C (50 °F) in their warmest months, and a coldest month average between -3 °C (27°F) and 18 °C (64 °F).

Some climatologists, particularly in the United States, however, prefer to observe 0 °C (32 °F) rather than -3 °C (27 °F) in the coldest month as the boundary between this group and Group D; this is done to prevent certain headland locations in or near New England - principally Cape Cod - and such nearby islands as Nantucket and Martha's Vineyard, from fitting into the Maritime Temperate category noted below; this category is alternately known as the Marine West Coast climate, and eliminating the aforementioned locations indeed confines it exclusively to places found along the western margins of the continents, at least in the Northern Hemisphere. This also moves some mid-latitude areas - such as parts of the Ohio Valley and some areas in the Mid-Atlantic States, plus parts of east-central Asia - from humid subtropical to humid continental.

GROUP D: Continental/microthermal climate

These climates have an average temperature above 10 °C (50 °F) in their warmest months, and a coldest month average below -3 °C (or 0 °C in some versions, as noted previously). These usually occur in the interiors of continents, or on their east coasts, north of 40° North latitude. In the Southern Hemisphere, Group D climates are extremely rare due to the smaller land masses in the middle latitudes and the almost complete absence of land south of 40° South latitude, existing only in some highland locations in New Zealand that have heavy winter snows.

GROUP E: Polar climates

These climates are characterized by average temperatures below 10 °C (50 °F) in all twelve months of the year:

Trewartha climate classification scheme

The Trewartha climate classification scheme is a modified version of the Köppen system. It attempts to redefine the broad climatic groups in such a way as to be closer to vegetational zoning, especially in the United States. Under the standard Köppen system western Washington and Oregon are classed into the same climate as southern California, even though the two regions have strikingly different vegetation. It also classes southern New England into the same climate as the Gulf Coast. Trewartha's modifications sought to reclass the Pacific Northwest seaboard as a different climate from California, and New England from the Gulf Coast.[18]

Criticisms of the Köppen scheme

Some climatologists have argued that Köppen's system could be improved upon. One of the most frequently-raised objections concerns the temperate Group C category, regarded by many as overbroad (it includes both Tampa, Florida and Philadelphia, Pennsylvania for example, even using 0°C/32°F as the baseline). In Applied Climatology (first edition published in 1966), John F. Griffiths proposed a new subtropical zone, encompassing those areas with a coldest month of between 6 °C (42.8 °F) and 18 °C (64.4 °F), effectively subdividing Group C into two nearly equal parts (his scheme assigns the letter B to the new zone, and identifies dry climates with an additional letter immediately following the temperature-based letter).

Another point of contention involves the dry B climates; the argument here is that their separation by Köppen into only two thermal subsets is inadequate. Those who hold this view (including Griffiths) have suggested that the dry climates be placed on the same temperature continuum as other climates, with the thermal letter being followed by an additional capital letter - S for steppe or W (or D) for desert - as applicable (Griffiths also advances an alternate formula for use as an aridity threshold: R = 160 + 9T, with R equalling the threshold, in millimeters of mean annual precipitation, and T denoting the mean annual temperature in degrees Celsius).

A third idea is to create a maritime polar or EM zone within Group E to separate relatively mild marine locations (such as Ushuaia, Argentina and the outer Aleutian Islands) from the colder, continental tundra climates. Specific proposals vary; some advocate setting a coldest-month parameter, such as -7 °C (19.4 °F), while others support assigning the new designation to areas with an average annual temperature of above 0 °C.

The accuracy of the 10 °C warmest-month line as the start of the polar climates has also been questioned; Otto Nordenskiöld, for example, devised an alternate formula: W = 9 - 0.1 C, with W representing the average temperature of the warmest month and C that of the coldest month, both in degrees Celsius (for instance, if the coldest month averaged -20 °C, a warmest-month average of 11 °C or higher would be necessary to prevent the climate from being polar). This boundary does appear to more closely follow the tree line, or the latitude poleward of which trees cannot grow, than the 10 °C warmest-month isotherm; the former tends to run poleward of the latter near the western margins of the continents, but at a lower latitide in the landmass interiors, the two lines crossing at or near the east coasts of both Asia and North America.

World Map of the Köppen-Geiger climate classification for the period 1951-2000

Based on recent data sets from the Climatic Research Unit (CRU) of the University of East Anglia and the Global Precipitation Climatology Centre (GPCC) at the German Weather Service, a new digital Köppen-Geiger world map on climate classification for the second half of the 20th century has been compiled.[20]

External links

Climate records

Notes and References

  1. Book: McKnight, Tom L; Hess, Darrel. 2000. Climate Zones and Types: The Köppen System. Physical Geography: A Landscape Appreciation. 200–1. Upper Saddle River, NJ. Prentice Hall. 0-13-020263-0.
  2. McKnight & Hess, pp. 205-8, "Climate Zones and Types: Tropical Wet Climate (Af)"
  3. McKnight & Hess, p. 208, "Climate Zones and Types: Tropical Monsoon Climate (Am)"
  4. McKnight & Hess, pp. 208-11, "Climate Zones and Types: Tropical Savanna Climate (Aw)"
  5. Web site: CHAPTER 7: Introduction to the Atmosphere. physicalgeography.net. 2008-07-15.
  6. McKnight & Hess, pp. 212-1, "Climate Zones and Types: Dry Climates (Zone B)"
  7. McKnight & Hess, pp. 221-3, "Climate Zones and Types: Mediterranean Climate (Csa, Csb)"
  8. Web site: Statistics for AUS WA.Perth.Airport RMY. EnergyPlus. U.S. Department of Energy. 2009-01-19.
  9. McKnight & Hess, pp. 223-6, "Climate Zones and Types: Dry Humid Subtropical Climate (Cfa, Cwa)"
  10. Web site: Statistics for AUS QLD.Brisbane RMY. EnergyPlus. U.S. Department of Energy. 2009-01-19.
  11. McKnight & Hess, pp. 226-9, "Climate Zones and Types: Marine West Coast Climate (Cfb, Cfc)"
  12. Web site: Statistics for AUS ACT.Canberra.Airport RMY. EnergyPlus. U.S. Department of Energy. 2009-01-19.
  13. McKnight & Hess
  14. McKnight & Hess, pp. 231-2, "Climate Zones and Types: Humid Continental Climate (Dfa, Dfb, Dwa, Dwb)"
  15. McKnight & Hess, pp. 232-5, "Climate Zones and Types: Subarctic Climate (Dfc, Dfd, Dwc, Dwd)"
  16. McKnight & Hess, pp. 235-7, "Climate Zones and Types: Tundra Climate (ET)"
  17. McKnight & Hess, pp. 237, "Climate Zones and Types: Ice Cap Climate (EF)"
  18. Book: Akin, Wallace E.. 1991. Global Patterns: Climate, Vegetation, and Soils. 52. University of Oklahoma Press. 0-8061-2309-5.
  19. McKnight & Hess, pp. 237-40, "Climate Zones and Types: Highland Climate (Zone H) "
  20. Kottek, M., J. Grieser, C. Beck, B. Rudolf, and F. Rubel. 2006. World Map of the Köppen-Geiger climate classification updated. Meteorol. Z.. 15. 259–263. 10.1127/0941-2948/2006/0130.