The
Trewartha climate classification
Trewartha climate classification is a climate classification
system published by American geographer
Glenn Thomas Trewartha in
1966, and updated in 1980. It is a modified version of the 1899
Köppen system, created to answer some of the deficiencies of the
Köppen system.[1] The Trewartha system attempts to redefine the
middle latitudes to be closer to vegetation zoning and genetic climate
systems. It was considered a more true or "real world" reflection of
the global climate.[2]
The changes were seen as most effective on the large landmasses in
Asia
Asia and North America, where many areas fall into a single group (C)
in the Köppen system.[3] For example, under the standard Köppen
system, Washington and
Oregon
Oregon are classed into the same climate zone
as Southern California, even though the two regions have strikingly
different weather and vegetation. Another example was classifying
cities like
London
London in the same climate group as
Brisbane
Brisbane or New
Orleans, despite great differences in seasonal temperatures and native
plant life. [4]
Contents
1 Scheme
1.1 Group A: Tropical climates
1.2 Group B: Dry (arid and semi-arid) climates
1.3 Group C:
Subtropical
Subtropical climates
1.4 Group D:
Temperate
Temperate and continental climates
1.5 Group E: Boreal climates
1.6 Group F: Polar climates
1.7 Group H: Highland climates
2 Universal Thermal Scale
3 See also
4 References
5 External links
Scheme[edit]
Trewartha's modifications to the 1899 Koppen climate system sought to
reclass the middle latitudes into three groups: C (subtropical)—8 or
more months have a mean temperature of 10 °C (50 °F) or
higher; D temperate—4 to 7 months have a mean temperature of 10 °C
or higher; and E boreal climate—1 to 3 months have a mean
temperature of 10 °C or higher. Otherwise, the tropical climates and
polar climates remained the same as the original Köppen climate
classification.
Group A: Tropical climates[edit]
This the tropical climate realm, defined the same as in Köppen's
scheme (i.e., all 12 months average 18 °C, 64 °F, 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
60 mm, 2.4 inches, average precipitation, same as per Köppen)
are classified Ar, 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).
Group B: Dry (arid and semi-arid) climates[edit]
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(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
Northern Hemisphere and October through March in the
Southern).[5]
If the precipitation 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.
Group C:
Subtropical
Subtropical climates[edit]
In the Trewartha scheme the "C" climate group encompasses Subtropical
climates that have 8 or more months with a mean temperature of
10 °C (50 °F) or higher.
There are only two types within the "C" or subtropical climate group,
Cs which is a dry -summer or Mediterranean climate, and a Cf or humid
Subtropical
Subtropical climate. Cw types occur within the Cf group and mean
subtropical Monsoon climates (like much of east Asia).
Group D:
Temperate
Temperate and continental climates[edit]
In the Trewartha scheme the "D" climate group encompasses Temperate
climates that have 4 to 7 months with a mean temperature of
10 °C (50 °F) or higher.
"D" climate groups have two types – a Oceanic type (Do), where the
coldest month has a mean temperature 0 °C (32 °F) or
higher, and a Continental type (Dc), where the coldest monthly mean
temperature reaches below 0 °C in some interior landmasses like North
America and Asia.
For the continental climates (Dc), sometimes the third letter (a or b)
is used to denote a hot or cold summer. "Dca" is where the warmest
month has a mean temperature of 22.2 °C (72.0 °F) or
higher, and "Dcb" is used for cool summer temperate climates, where
the warmest month has a mean temperature below 22.2 °C.
Group E: Boreal climates[edit]
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 10 °C (50 °F) 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, with Eo
(maritime subarctic) signifying that the coldest month averages above
−10 °C (14 °F), 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, 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[edit]
This is the polar climate group, where all months must have a monthly
mean air temperature of below 10°C/50 F. Polar climates have two
subtypes Ft (tundra) and Fi (ice cap):
In the "Ft" climate type, at least one month has an average temperate
above 0 °C or 32 °F (but not above 10 °C), so that there
is a brief time when the surface might be free of snow or ice and a
scrub or
Tundra
Tundra vegetation cover is possible.
In the "Fi" climate type, all months have an average temperature below
0 °C, 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[edit]
Highland climates, in which altitude plays a role in determining
climate classification.[6] 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 (10.1 °F) for each
1,000 meters (3,300 ft) 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 between 500 and 2,500 meters (1,600 and 8,200 ft), 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. G stands for
glacier for instances.
Universal Thermal Scale[edit]
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
(95 °F) or higher
h — very hot: 28 to 34.9 °C (82.4 to 94.8 °F)
a — hot: 23 to 27.9 °C (73.4 to 82.2 °F)
b — warm: 18 to 22.9 °C (64.4 to 73.2 °F)
l — mild: 10 to 17.9 °C (50.0 to 64.2 °F)
k — cool: 0.1 to 9.9 °C (32.2 to 49.8 °F)
o — cold: −9.9 to 0 °C (14.2 to 32.0 °F)
c — very cold: −24.9 to −10 °C (−12.8 to 14.0 °F)
d — severely cold: −39.9 to −25 °C (−39.8 to
−13.0 °F)
e — excessively cold: −40 °C (−40 °F) or below.
Examples of the resulting designations include BWil for Riyadh, Saudi
Arabia; BWhb for Aswan, Egypt; Awha for Surabaya, Indonesia; Cfak for
Tokyo; Csll for San Francisco, California; Cfhk for Dallas, Texas,
U.S.; DObk for London; EClc for Arkhangelsk, Russia; FTkd for Barrow,
Alaska, U.S.; Cfbk for Melbourne, Australia; and FIce for Vostok
Station in Antarctica.
See also[edit]
Holdridge life zones
Holdridge life zones climate classification by three dimensions:
precipitation, humidity, and potential evapotranspiration ratio
References[edit]
^ Peel MC, Finlayson BL, McMahon TA (2007) Updated world map of the
Köppen-Geiger climate classification. Hydrol Earth Syst Sci 11:
1633–1644
^ Akin, Wallace E. (1991). Global Patterns: Climate, Vegetation, and
Soils. University of Oklahoma Press. p. 52.
ISBN 0-8061-2309-5.
^ Köppen, 1936, Trewartha & Horn 1980, Bailey 2009, Baker et al.
2010
^ Bailey RG (2009) Ecosystem geography:from ecoregions to sites, 2nd
edn. Springer, New York, NY
^ Patton CP (1962) A note on the classification of dry climate in the
Köppen system.
California
California Geographer 3: 105–112
^ McKnight, 237–40
External links[edit]
Climate classification
Climate classification revisited: from Köppen to Trewartha
Use of the Köppen–
Trewartha climate classification
Trewartha climate classification for the
People’s