Trewartha climate classification
The Trewartha climate classification, or the Köppen–Trewartha climate classification, 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 —8 or more months;D —4 to 7 months;E —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.
This is the tropical climate realm, defined the same as in Köppen's scheme. The A climates are the realm of the winterless frost-free zone.
- Climates with no more than two dry months 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.
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 + 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.
- If the precipitation for a given location is less than the above formula — that is, if P < 10 + 3P — the climate is said to be that of a desert.
- If it is equal to or greater than the formula but less than twice that amount, the climate is classified as steppe.
- 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.
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, where the coldest month has a mean temperature or higher
- Continental, where the coldest monthly mean temperature reaches below 0 °C, as in some interior landmasses in North America and Asia. For the continental climates, sometimes a third letter 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 that is frost free. In the original scheme, this group was not further divided; later, the designations Eo and Ec were created:Eo signifies that the coldest month averages above.Ec 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.
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 and Fi :
- In the Ft climate type, at least one month has an average temperature 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:
| 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, TuvaluArha for Kuala Lumpur, Malaysia or Colombo, Sri LankaArhb for Fort Lauderdale, Florida, United States or Caraguatatuba, Brazil or Ishigaki, JapanAraa for Suva, Fiji or Quibdó, ColombiaArab for Santos, Brazil or Easter Island, Chile or Ubatuba, Brazil or Innisfail, AustraliaArbb for Mamasa, IndonesiaAmha for Manila, Philippines or Jakarta, IndonesiaAmhb for Miami, Florida, United States or Wanning, ChinaAmaa for Monrovia, Liberia or Cali, ColombiaAmab for Cairns, AustraliaAmbb for Baguio, PhilippinesAwha for Cuiabá, Brazil or Mumbai, India or Surabaya, IndonesiaAwhb for Dhaka, Bangladesh or Naples, Florida, United StatesAwaa for Brazzaville, Republic of the Congo or Goiânia, BrazilAwab for Rio de Janeiro, Brazil or Maputo, MozambiqueAwbb for Guatemala City, Guatemala or Malanje, AngolaAsha for Chennai, India or Mombasa, KenyaAsaa for Fortaleza, Brazil or Kapalua, Hawaii, United StatesAsab for Lanai City, Hawaii, United States
B
BWih for Dallol, EthiopiaBWia for Khartoum, SudanBWib for Tessalit, Mali or Dubai, United Arab EmiratesBWil for Riyadh, Saudi Arabia or Phoenix, Arizona, United StatesBWik for Tikrit, IraqBWha for Punto Fijo, VenezuelaBWhb/BShb for Karachi, PakistanBWhl for Alice Springs, Australia or Cairo, EgyptBWhk for Las Vegas, Nevada, United States or Qom, IranBWho for Turpan, China or Nukus, UzbekistanBWal for Lima, Peru or Iquique, ChileBWak for Neuquén, ArgentinaBWao for Leh, India or Yinchuan, ChinaBWac for Aral, Kazakhstan or Karamay, ChinaBWbl for Antofagasta, Chile or Sanaa, YemenBWbo for Bamyan, AfghanistanBWbc for Khovd, MongoliaBWll for Walvis Bay, Namibia or Arequipa, PeruBWlc for Ölgii, MongoliaBSil for Dezful, IranBShh for Mossoró, BrazilBSha for Petrolina, Brazil or Accra, GhanaBShb for Luanda, Angola or Ahmedabad, IndiaBShl for Rivadavia, Argentina or Piraeus, GreeceBShk for Mashhad, IranBSaa for Barquisimeto, Venezuela or Honolulu, Hawaii, United StatesBSab for Toliara, MadagascarBSal for Murcia, Spain or Tripoli, LibyaBSak for Baku, AzerbaijanBSak/''BSao for Boise, Idaho, United StatesBSao for Denver, Colorado, United States or Yerevan, ArmeniaBSbl for Cochabamba, BoliviaBSbk for Alexandra, New ZealandBSbo for Kamloops, CanadaBSbc for Ulaanbaatar, MongoliaBSbd for Kyzyl, RussiaBSll for Asmara, EritreaBSlk'' for Río Gallegos, Argentina or Lhasa, Tibet, China
C
Cfhl for Houston, Texas, United States or Orlando, Florida, United States or Asunción, ParaguayCfhk for Hangzhou, China or Dallas, Texas, United StatesCfal for Buenos Aires, Argentina or Montevideo, Uruguay or Sydney, Australia or Porto Alegre, BrazilCfak for Nashville, Tennessee, United States or Tokyo, JapanCfbl for Auckland, New Zealand or Curitiba, BrazilCfbk for Bilbao, Spain or Melbourne, AustraliaCfll for Campos do Jordão, Brazil or Bogotá, Colombia or Quito, EcuadorCflk for São Joaquim, Brazil or Hobart, Australia or Isles of Scilly, United Kingdom or Wellington, New ZealandCwhl for Las Lomitas, Argentina or Islamabad, Pakistan or Hanoi, Vietnam or New Delhi, IndiaCwhk for Chongqing, ChinaCwal for São Paulo, Brazil or Córdoba, Argentina or Guadalajara, MexicoCwak for Chengdu, China or Changwon, South KoreaCwbl for Mexico City, Mexico or Addis Ababa, EthiopiaCwbk for Johannesburg, South Africa or Kunming, China or Gangtok, IndiaCwll for Cusco, Peru or Sucre, BoliviaCwlk for La Paz, BoliviaCshl for Seville, Spain or Patras, GreeceCshk for Tashkent, Uzbekistan or Urfa, TurkeyCsal for Los Angeles, California, United States or Funchal, PortugalCsak for Marseille, France or Rome, Italy or Madrid, SpainCsbl for Oeiras, Portugal or Santa Barbara, California, United StatesCsbk for Porto, Portugal or Santiago, ChileCsll for San Francisco, California, United States or Camariñas, SpainCslk for Eureka, California, United States or Concepción, Chile
D
Dohk for Diyarbakır, Turkey or Kermanshah, IranDoak for New York City, New York, United States or Milan, ItalyDobk for London, United Kingdom or Vancouver, Canada or Frankfurt, Germany or Seattle, Washington, United States or Zurich, SwitzerlandDolk for Dublin, Ireland or Bergen, Norway or Stavanger, Norway or Puerto Montt, ChileDcho for Arak, IranDcao for Seoul, South Korea or Chicago, Illinois, United States or Boston, Massachusetts, United StatesDcac for Harbin, China or Orenburg, RussiaDcbo for Missoula, Montana, United States or Klagenfurt, Austria or Helsinki, FinlandDcbc for Quebec City, Canada or Novosibirsk, RussiaDcbd for Hulunbuir, China or Chegdomyn, RussiaDclo for Cortina d'Ampezzo, Italy or Juneau, Alaska, United StatesDclc for Dras, India or Fairbanks, Alaska, United States or Ardahan, TurkeyDcld for Baruunturuun, Mongolia
E
Eolk for Punta Arenas, Chile or El Alto, Bolivia or Reykjavík, Iceland or Potosí, BoliviaEolo for Tromsø, Norway or Anchorage, Alaska, United StatesEcbc for Surgut, RussiaEcbd for Yakutsk, Russia or Vilyuysk, Russia or Mohe City, ChinaEclc for Karasjok, Norway or Whitehorse, CanadaEcld for Yellowknife, Canada or Norilsk, RussiaEcle for Verkhoyansk, Russia or Oymyakon, Russia
F
Ftkk for Ushuaia, Argentina or Puerto Williams, ChileFtko for Nuuk, Greenland, Denmark or Finse, Norway or Villa Las Estrellas, Antarctica, ChileFtkc for Longyearbyen, Svalbard, Norway or Provideniya, Russia or Ittoqqortoormiit, Greenland or Utqiagvik, Alaska, Alaska, United States or Qaanaaq, GreenlandFtkd for Pevek, Russia or Iqaluit, Canada or Alert, Nunavut, Canada or Resolute, Nunavut, CanadaFtke for Eureka, CanadaFioo for Puncak Jaya, IndonesiaFioc for Showa Station, AntarcticaFiod for Ushakov Island, Russia or McMurdo Station, AntarcticaFicd for Mount Everest, China/NepalFice for Summit Camp, GreenlandFide for Concordia Station, Antarctica, France and Italy or Vostok Station, Antarctica, Russia