Trewartha climate classification

The Trewartha climate classification (TCC), or the Köppen–Trewartha climate classification (KTC), is a climate classification system first published by American geographer Glenn Thomas Trewartha in 1966. It is a modified version of the Köppen–Geiger system, created to answer some of its deficiencies. The Trewartha system attempts to redefine the middle latitudes to be closer to vegetation zoning and genetic climate systems.

Scheme

Trewartha's modifications to the 1884 Köppen climate system sought to reclass the middle latitudes into three groups, according to how many months have a mean temperature of or higher:

* ''C'' (subtropical)—8 or more months;
* ''D'' (temperate)—4 to 7 months;
* ''E'' ( boreal climate)—1 to 3 months.

The tropical climates and polar climates remained the same as in the original Köppen climate classification.

The "highland" climate is ambiguously defined. Newer users of KTC generally omit this option.

Group A: Tropical climates

This is the tropical climate realm, defined the same as in Köppen's scheme (i.e., all 12 months average or above). The ''A'' climates are the realm of the winterless frost-free zone.

* Climates with no more than two dry months (defined as having less than average precipitation, same as per Köppen) are classified ''Ar''.
* 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).

Group B: Dry (arid and semi-arid) climates

''BW'' and ''BS'' mean the same as in the Köppen scheme. However, a different formula is used to quantify the aridity threshold: 10(''T'' − 10) + 3''P'', with ''T'' equaling 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, October through March in the Southern).

* If the precipitation for a given location is less than the above formula — that is, if ''P'' < 10(''T'' − 10) + 3''P'' — the climate is said to be that of a desert (''BW'').
* If it is equal to or greater than the formula but less than twice that amount, the climate is classified as steppe (''BS'').
* 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.

Group C: Subtropical climates

In the Trewartha scheme the ''C'' climate group encompasses subtropical climates, which have 8 or more months with a mean temperature of or higher. There are only two types within the ''C'' or subtropical climate group:

* ''Cs'', which is a dry-summer or Mediterranean climate;
* ''Cf'', or humid subtropical climate. ''Cw'' types occur within the ''Cf'' group and refer to subtropical monsoon climates (like much of east Asia).

Group D: Temperate and continental climates

In the Trewartha scheme the ''D'' climate group encompasses temperate climates that have 4 to 7 months with a mean temperature of or higher. ''D'' climate groups have two types:

* Oceanic (''Do''), where the coldest month has a mean temperature or higher
* Continental (''Dc''), where the coldest monthly mean temperature reaches below 0 °C, as in some interior landmasses in North America and Asia. For the continental climates (''Dc''), sometimes a third letter (''a'' or ''b'') is added to denote a hot or cold summer. ''Dca'' is used where the warmest month has a mean temperature of or higher, and ''Dcb'' is used for cool-summer temperate climates, where the warmest month has a mean temperature below 22.2 °C.

Most of Europe north of the 44th parallel exhibits a ''Do'' or ''Dc'' climate type.

Group E: Boreal climates

This represents subarctic and subpolar oceanic climate realms, defined the same as in Köppen's scheme, where 1 to 3 months have an average temperature of or above. In this climate zone there is only a short period (normally 50 to 90 days) that is frost free. In the original scheme, this group was not further divided; later, the designations ''Eo'' and ''Ec'' were created:

* ''Eo'' (maritime subarctic) signifies that the coldest month averages above .
* ''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 are no separate counterparts to the Köppen ''Dfd'', ''Dwd'', and ''Dsd'' climate types in Trewartha's scheme, but a letter can optionally be added to the end of the symbol to indicate the temperature of the coldest month ( see below).

Group F: Polar climates

This is the polar climate group, where all months have a monthly mean air temperature below . Polar climates have two subtypes, ''Ft'' (tundra) and ''Fi'' (ice cap):

* In the ''Ft'' climate type, at least one month has an average temperature above (but not above ), so that there is a brief time when the surface might be free of snow or ice and a scrub or tundra vegetation cover is possible.
* In the ''Fi'' climate type, all months have an average temperature below . This is the region of the vast deserts of perpetually frozen ocean in the North Pole, and the permanent ice plateaus of Antarctica and Greenland.

Group H: Highland climates

Highland climates are those in which altitude plays a role in determining climate classification. Specifically, this would apply if correcting the average temperature of each month to a sea-level value—using the formula of adding for each of elevation—would cause the climate to fit into a different thermal group from 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 between , but the ''G'' or ''H'' is placed in front of the applicable thermal letter rather than replacing it. The second letter used reflects the ''corrected'' monthly temperatures, not the actual monthly temperatures.

Universal Thermal Scale

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, denoting mean monthly temperature, conform to the following scale:

Examples

A

* ''Arha'' for Kuala Lumpur, Malaysia or Colombo, Sri Lanka
* ''Arhb'' for Fort Lauderdale, Florida, United States or Ishigaki, Japan
* ''Araa'' for Suva, Fiji or Quibdó, Colombia
* ''Arab'' for Kampala, Uganda or Innisfail, Australia
* ''Arbb'' for Mamasa, Indonesia
* ''Amha'' for Manila, Philippines or Jakarta, Indonesia
* ''Amhb'' for Miami, Florida, United States or Wanning, China
* ''Amaa'' for Monrovia, Liberia or Cali, Colombia
* ''Amab'' for Cairns, Australia
* ''Ambb'' for Mérida, Venezuela or Baguio, Philippines
* ''Awha'' for Cuiabá, Brazil or Mumbai, India or Surabaya, Indonesia
* ''Awhb'' for Dhaka, Bangladesh or Naples, Florida, United States
* ''Awaa'' for Brazzaville, Republic of the Congo or Goiânia, Brazil
* ''Awab'' for Maputo, Mozambique
* ''Awbb'' for Guatemala City, Guatemala or Malanje, Angola
* ''Asha'' for Chennai, India or Mombasa, Kenya
* ''Asaa'' for Fortaleza, Brazil or Kapalua, Hawaii, United States
* ''Asab'' for Lanai City, Hawaii, United States

B

* ''BWih'' for Dallol, Ethiopia
* ''BWia'' for Khartoum, Sudan
* ''BWib'' for Tessalit, Mali or Dubai, United Arab Emirates
* ''BWil'' for Riyadh, Saudi Arabia or Phoenix, Arizona, United States
* ''BWik'' for Tikrit, Iraq
* ''BWha'' for Punto Fijo, Venezuela
* ''BWhb/BShb'' for Karachi, Pakistan
* ''BWhl'' for Alice Springs, Australia or Cairo, Egypt
* ''BWhk'' for Las Vegas, Nevada, United States or Qom, Iran
* ''BWho'' for Turpan, China or Nukus, Uzbekistan
* ''BWal'' for Lima, Peru or Iquique, Chile
* ''BWak'' for Neuquén, Argentina
* ''BWao'' for Leh, India or Yinchuan, China
* ''BWac'' for Aral, Kazakhstan or Karamay, China
* ''BWbl'' for Antofagasta, Chile or Sanaa, Yemen
* ''BWbo'' for Bamyan, Afghanistan
* ''BWbc'' for Khovd, Mongolia
* ''BWll'' for Walvis Bay, Namibia or Arequipa, Peru
* ''BWlc'' for Ölgii, Mongolia
* ''BSil'' for Dezful, Iran
* ''BSha'' for Accra, Ghana
* ''BShb'' for Luanda, Angola or Ahmedabad, India
* ''BShl'' for Piraeus, Greece
* ''BShk'' for Mashhad, Iran
* ''BSaa'' for Barquisimeto, Venezuela or Honolulu, Hawaii, United States
* ''BSab'' for Toliara, Madagascar
* ''BSal'' for Murcia, Spain or Tripoli, Libya
* ''BSak'' for Baku, Azerbaijan
* ''BSao'' for Denver, Colorado, United States or Yerevan, Armenia
* ''BSbl'' for Cochabamba, Bolivia
* ''BSbk'' for Alexandra, New Zealand
* ''BSbo'' for Kamloops, Canada
* ''BSbc'' for Ulaanbaatar, Mongolia
* ''BSbd'' for Kyzyl, Russia
* ''BSll'' for Asmara, Eritrea
* ''BSlk'' for Río Gallegos, Argentina or Lhasa, Tibet, China

C

* ''Cfhl'' for Houston, Texas, United States or Orlando, Florida, United States
* ''Cfhk'' for Hangzhou, China or Dallas, Texas, United States
* ''Cfal'' for Buenos Aires, Argentina or Sydney, Australia
* ''Cfak'' for Nashville, Tennessee, United States or Tokyo, Japan
* ''Cfbl'' for Auckland, New Zealand or Curitiba, Brazil
* ''Cfbk'' for Bilbao, Spain or Melbourne, Australia
* ''Cfll'' for Bogotá, Colombia or Quito, Ecuador
* ''Cflk'' for São Joaquim, Brazil or Hobart, Australia, Isles of Scilly, United Kingdom or Wellington, New Zealand
* ''Cwhl'' for Islamabad, Pakistan or Hanoi, Vietnam
* ''Cwhk'' for Chongqing, China
* ''Cwal'' for São Paulo, Brazil or Córdoba, Argentina or Guadalajara, Mexico
* ''Cwak'' for Chengdu, China or Changwon, South Korea
* ''Cwbl'' for Mexico City, Mexico or Addis Ababa, Ethiopia
* ''Cwbk'' for Kunming, China or Gangtok, India
* ''Cwll'' for Cusco, Peru or Sucre, Bolivia
* ''Cwlk'' for Campos do Jordão, Brazil
* ''Cshl'' for Seville, Spain or Patras, Greece
* ''Cshk'' for Tashkent, Uzbekistan or Urfa, Turkey
* ''Csal'' for Faro, Portugal or Funchal, Portugal
* ''Csak'' for Marseille, France or Rome, Italy or Madrid, Spain
* ''Csbl'' for Cape Town, South Africa or Los Angeles, California, United States
* ''Csbk'' for Sintra, Portugal or Linares, Chile
* ''Csll'' for San Francisco, California, United States or Oakland, California, United States
* ''Cslk'' for Concepción, Chile

D

* ''Dohk'' for Diyarbakır, Turkey or Kermanshah, Iran
* ''Doak'' for New York City, New York, United States or Milan, Italy
* ''Dobk'' for London, United Kingdom or Vancouver, Canada
* ''Dolk'' for Bergen, Norway or Stavanger, Norway or Puerto Montt, Chile
* ''Dcho'' for Arak, Iran
* ''Dcao'' for Seoul, South Korea or Chicago, Illinois, United States
* ''Dcac'' for Harbin, China or Orenburg, Russia
* ''Dcbo'' for Klagenfurt, Austria or Helsinki, Finland
* ''Dcbc'' for Quebec City, Canada or Novosibirsk, Russia
* ''Dcbd'' for Hulunbuir, China or Chegdomyn, Russia
* ''Dclo'' for Cortina d'Ampezzo, Italy or Juneau, Alaska, United States
* ''Dclc'' for Fairbanks, Alaska, United States or Ardahan, Turkey
* ''Dcld'' for Baruunturuun, Mongolia

E

* ''Eolk'' for Punta Arenas, Chile or Reykjavík, Iceland
* ''Eolo'' for Tromsø, Norway or Anchorage, Alaska, United States
* ''Ecbc'' for Surgut, Russia
* ''Ecbd'' for Vilyuysk, Russia or Mohe City, China
* ''Ecbe'' (historically) for Yakutsk, Russia
* ''Eclc'' for Karasjok, Norway or Whitehorse, Canada
* ''Ecld'' for Yellowknife, Canada or Norilsk, Russia
* ''Ecle'' for Verkhoyansk, Russia or Oymyakon, Russia

F

* ''Ftkk'' for Ushuaia, Argentina or Puerto Williams, Chile
* ''Ftko'' for Nuuk, Greenland, Denmark or Finse, Norway
* ''Ftkc'' for Provideniya, Russia or Ittoqqortoormiit, Greenland
* ''Ftkd'' for Pevek, Russia or Iqaluit, Canada
* ''Fioo'' for Puncak Jaya, Indonesia
* ''Fioc'' for Showa Station, Antarctica
* ''Fiod'' for Ushakov Island, Russia or McMurdo Station, Antarctica
* ''Ficd'' for Mount Everest, China/Nepal
* ''Fice'' for Summit Camp, Greenland
* ''Fide'' for Vostok Station, Antarctica, Russia

See also

* Holdridge life zones climate classification by three dimensions: precipitation, humidity, and potential evapotranspiration ratio
* Köppen climate classification

References

{{reflist

External links

Use of the Köppen–Trewartha climate classification for the People’s Republic of China

Climate and weather classification systems