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.Peel MC, Finlayson BL, McMahon TA (2007) Updated world map of the Köppen–Geiger climate classification. Hydrol Earth Syst Sci 11: 1633–1644 The Trewartha system attempts to redefine the middle latitudes to be closer to vegetation zoning and genetic climate systems.Bailey RG (2009) Ecosystem geography: from ecoregions to sites, 2nd edn. Springer, New York, NY
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)—1 to 3 months.
The tropical climates and polar climates remained the same as in the original Köppen climate classification.
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) + 3P, 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).Patton CP (1962) "A note on the classification of dry climate in the Köppen system". California Geographer 3: 105–112
If the precipitation for a given location is less than the above formula — that is, if P < 10(T − 10) + 3P — 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 three types within the C or subtropical climate group:
Cs, which is a dry-summer or mediterranean climate; Cf, or humid subtropical climate with no dry season; Cw, a monsoon-influenced humid subtropical climate with dry winters.
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.
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: Code Description Temperature range i Severely hot or higher h Very hot a Hot b Warm l Mild k Cool o Cold c Very cold d Severely cold e Excessively cold or below
Examples
A Arhh for Singapore or Funafuti, Tuvalu Arha for Kuala Lumpur, Malaysia or Colombo, Sri Lanka Arhb for Santos, Brazil or Fort Lauderdale, Florida, United States or Ishigaki, Japan Araa for Suva, Fiji or Quibdó, Colombia Arab for Easter Island, Chile 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 Awha for Cuiabá, Brazil or Mumbai, India or Surabaya, Indonesia Awhb for Rio de Janeiro, Brazil or 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 Almería, Spain or 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 BShh for Mossoró, Brazil BSha for Petrolina, Brazil or Accra, Ghana BShb for Luanda, Angola or Ahmedabad, India BShl for Murcia, Spain or Rivadavia, Argentina or Piraeus, Greece BShk for Mashhad, Iran BSaa for Barquisimeto, Venezuela or Honolulu, Hawaii, United States BSab for Toliara, Madagascar BSal for Tripoli, Libya BSak for Baku, Azerbaijan BSak/BSao for Boise, Idaho, United States 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 Austin, Texas, United States or Orlando, Florida, United States or Asunción, Paraguay Cfhk for Tokyo, Japan or Hangzhou, China or Dallas, Texas, United States Cfal for Buenos Aires, Argentina or Montevideo, Uruguay or Sydney, Australia or Porto Alegre, Brazil Cfak for Nashville, Tennessee, United States Cfbl for A Coruña, Spain or Auckland, New Zealand or Curitiba, Brazil Cfbk for Bilbao, Spain or Melbourne, Australia Cfll for Campos do Jordão, Brazil or Bogotá, Colombia or Quito, Ecuador Cflk for São Joaquim, Brazil or Hobart, Australia or Isles of Scilly, United Kingdom or Wellington, New Zealand Cwil for New Delhi, India Cwhl for Las Lomitas, Argentina or 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 or Baguio, Philippines Cwbk for Johannesburg, South Africa or Kunming, China Cwll for Cusco, Peru or Sucre, Bolivia Cwlk for La Paz, Bolivia or Gangtok, India Cshl for Seville, Spain or Patras, Greece Cshk for Tashkent, Uzbekistan or Urfa, Turkey Csal for Nice, France or Los Angeles, California, United States or Perth, Australia or Monte Carlo, Monaco Csak for Marseille, France or Rome, Italy or Madrid, Spain Csbl for Oeiras, Portugal or Santa Barbara, California, United States Csbk for Porto, Portugal or Santiago, Chile Csll for San Francisco, California, United States or Camariñas, Spain Cslk for Eureka, California, United States or 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 or Frankfurt, Germany or Copenhagen, Denmark or Seattle, Washington, United States or Zurich, Switzerland Dolk for Dublin, Ireland or Bergen, Norway or Stavanger, Norway or Puerto Montt, Chile or Skrova, Norway Dcho for Arak, Iran or Setif, Algeria Dcao for Seoul, South Korea or Chicago, Illinois, United States or Boston, Massachusetts, United States Dcac for Harbin, China or Orenburg, Russia Dcbo for Missoula, Montana, United States or 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 Dras, India or Fairbanks, Alaska, United States or Ardahan, Turkey Dcld for Baruunturuun, Mongolia
E Eolk for Punta Arenas, Chile or El Alto, Bolivia or Reykjavík, Iceland or Tórshavn, Faroe Islands Eolo for Tromsø, Norway or Anchorage, Alaska, United States Ecbc for Surgut, Russia Ecbd for Yakutsk, Russia or Vilyuysk, Russia or Mohe City, China 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 or Puerto Toro, Chile Ftko for Nuuk, Greenland, Denmark or Finse, Norway or Villa Las Estrellas, Antarctica, Chile Ftkc for Longyearbyen, Svalbard, Norway or Esperanza Base, Antarctica, Argentina or Provideniya, Russia or Ittoqqortoormiit, Greenland or Utqiagvik, Alaska, United States or Qaanaaq, Greenland Ftkd for Pevek, Russia or Iqaluit, Canada or Alert, Nunavut, Canada or Resolute, Nunavut, Canada Ftke for Eureka, Canada Fioo for Puncak Jaya, Indonesia Fioc for Showa Station, Antarctica