Köppen climate classification explained

The Köppen climate classification is one of the most widely used climate classification systems. It was first published by Russian German climatologist Wladimir Köppen in 1884, with several later modifications by Köppen himself, notably in 1918 and 1936. Later, German climatologist Rudolf Geiger collaborated with Köppen on changes to the classification system, which is thus sometimes referred to as the Köppen - Geiger climate classification system.The system 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]

Scheme

The Köppen climate classification scheme divides climates into five main groups, each having 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 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.[1] The threshold is determined as follows:

GROUP C: Temperate/mesothermal climates

These climates have an average temperature above 10°C in their warmest months (April to September in northern hemisphere), and a coldest month average between -3°C and 18°C.

Some climatologists, particularly in the United States, however, prefer to observe 0°C rather than -3°C 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 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 between 40°-60° South latitude, existing only in some highland locations.

GROUP E: Polar climates

See main article: Polar climate. These climates are characterized by average temperatures below 10°C in all twelve months of the year:

GROUP H: Alpine climates

See main article: Alpine climate. The Alpine climates are considered to be part of group E.

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 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 and 18°C, 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, 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 latitude in the landmass interiors, the two lines crossing at or near the east coasts of both Asia and North America.

Trewartha climate classification scheme

The Trewartha climate classification scheme is a modified version of the Köppen system, as an answer to some of its deficiencies. 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 weather and vegetation. The Köppen system 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.[9]

This the tropical climate realm, defined the same as in Köppen's scheme (i.e., all 12 months average 18 °C or above). Climates with no more than two dry months (defined as having less than 60 mm average precipitation, same as per Köppen) are classified Ar (instead of Köppen's Af), while others are classified Aw if the dry season is at the time of low sun/short days or As if the dry season is at the time of high sun/long days. There was no specific monsoon climate identifier in the original scheme, but Am was added later, with the same parameters as Köppen's (except that at least three months, rather than one, must have less than 60 mm average precipitation).

BW and BS mean the same as in the Köppen scheme, with the Köppen BWn climate sometimes being designated BM (the M standing for "marine"). However, a different formula is used to quantify the aridity threshold: 10 X (T - 10) + 3P, with T equalling the mean annual temperature in degrees Celsius and P denoting the percentage of total precipitation received in the six high-sun months (April through September in the Northern Hemisphere and October through March in the Southern). If the precipition for a given location is less than the above formula, its climate is said to be that of a desert (BW); if it is equal to or greater than the above formula but less than twice that amount, the climate is classified as steppe (BS); and if the precipitation is more than double the value of the formula the climate is not in Group B. Unlike in Köppen's scheme, no thermal subsets exist within this group in Trewartha's, unless the Universal Thermal Scale (see below) is used.

In the Trewartha scheme this category encompasses subtropical realm climates only (8 or more months above 10 °C). Cs and Cw have the same meanings as they do in Köppen's scheme, but the subtropical climate with no distinct dry season is designated Cr instead of Köppen's Cf (and for Cs the average annual precipitation must be less than 890mm in addition to the driest summer month having less than 30 mm precipitation and being less than one-third as wet as the wettest winter month).

This group represents cold continental realms (4 to 7 months above 10 °C). Maritime temperate climates (most of Köppen's Cfb and Cwb climates, though some of these would fit into Trewartha's Cr and Cw respectively) are denoted DO in the Trewartha classification (although some places (like Halifax) near the east coasts of both North America and Asia actually qualify as DO climates in Trewartha's scheme when they fit into Cfa/Cwa rather than Cfb/Cwb in Köppen's), while continental climates are represented as DCa (Köppen Dfa, Dwa, Dsa) and DCb (Köppen Dfb, Dwb, Dsb). For the continental climates, sometimes the third letter (a or b) is omitted and DC is simply used instead, and occasionally a precipitational seasonality letter is added to both the maritime and continental climates (r, w, or s, as applicable). The dividing point between the maritime and continental climates is 0 °C in the coldest month, rather than the Köppen value of -3 °C (as noted in the section on the Köppen scheme, however, some climatologists - particularly in the United States - now observe 0 °C in the coldest month as the equatorward limit of the continental climates in that scheme as well).

This represents Ice realms, defined the same as in Köppen's scheme (1 to 3 months with average temperatures of 10 °C or above; Köppen Cfc, Dfc, Dwc, Dsc, Dfd, Dwd). In the original scheme, this group was not further divided; later, the designations EO and EC were created, with EO (maritime subarctic) signifying that the coldest month averages above -10 °C, while EC (continental subarctic or "boreal") means that at least one month has an average temperature of -10 °C or below. As in Group D, a third letter can be added to indicate seasonality of precipitation. There is no separate counterpart to the Köppen Dfd/Dwd climate in Trewartha's scheme.

This is the polar climate group, split into FT (Köppen ET) and FI (Köppen EF).

Highland climates, in which altitude plays a role in determining climate classification.[1] Specifically, this would apply if correcting the average temperature of each month to a sea-level value using the formula of adding 5.6 °C for each 1,000 meters of elevation would result in the climate fitting into a different thermal group than that into which the actual monthly temperatures place it. Sometimes G is used instead of H if the above is true and the altitude is 500 meters or higher but lower than 2,500 meters; but the G or H is placed in front of the applicable thermal letter rather than replacing it - and the second letter used reflects the corrected monthly temperatures, not the actual monthly temperatures.

An option exists to include information on both the warmest and coldest months for every climate by adding a third and fourth letter, respectively. The letters used conform to the following scale:
i - severely hot: Mean monthly temperature 35°C or higher
h - very hot: 28C34.9C
a - hot: 23C27.9C
b - warm: 18C22.9C
l - mild: 10C17.9C
k - cool: 0.1C9.9C
o - cold: -9.9C0C
c - very cold: -24.9C-10C
d - severely cold: -39.9C-25C
e - excessively cold: -40°C or below.
Examples of the resulting designations include Afaa for Surabaya, Indonesia, BWhl for Aswan, Egypt, Crhk for Dallas, Texas, DOlk for London, EClc for Arkhangelsk, Russia, and FTkd for Barrow, Alaska.

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.[10]

Other maps

All maps use the >0°C definition for temperate climates

See also

External links

Climate records

Notes and References

  1. Book: McKnight, Tom L; Hess, Darrel. 2000. Climate Zones and Types. Physical Geography: A Landscape Appreciation. Upper Saddle River, NJ. Prentice Hall. 0-13-020263-0.
  2. Book: Linacre, Edward. Bart Geerts. Climates and Weather Explained. Routledge. London. 1997. 379. 0-415-12519-7.
  3. Web site: CHAPTER 7: Introduction to the Atmosphere. physicalgeography.net. 2008-07-15.
  4. Book: Tapper, Andrew. Tapper. Nigel. The weather and climate of Australia and New Zealand. 1996. Oxford University Press. Melbourne, Australia. 0195533933. First. Gray, Kathleen. 300.
  5. Web site: Statistics for AUS WA.Perth.Airport RMY. EnergyPlus. U.S. Department of Energy. 2009-01-19.
  6. Web site: Climate classification of São Paulo state. Instituto Agronômico de Campinas.
  7. Web site: Statistics for AUS QLD.Brisbane RMY. EnergyPlus. U.S. Department of Energy. 2009-01-19.
  8. Web site: ClClimatological Information for Juliaca, Peru. Hong Kong Observatory.
  9. Book: Akin, Wallace E.. 1991. Global Patterns: Climate, Vegetation, and Soils. 52. University of Oklahoma Press. 0-8061-2309-5.
  10. 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. 3. 2006MetZe..15..259K.