Classification of the world climate
by Koeppen : -
The most widely used
classification of climate is the empirical climate classification scheme
developed by Wladimir Köppen (German geographer and meteorologist).
Koeppen identified a close
relationship between the distribution of vegetation and climate. He selected
certain values of temperature and precipitation and related them to the
distribution of vegetation and used these values for classifying the climates.
It is an empirical classification
based on mean annual and mean monthly temperature and precipitation data. He
introduced the use of capital and small letters to designate climatic groups
and types. Although developed in 1918 and modified over a period of time,
Koeppen’s scheme is still popular and in use.
The world climate can be studied
by organising information and data on climate and synthesising them in smaller
units for easy understanding, description and analysis.
Three broad approaches have been
adopted for classifying climate. They are empirical, genetic and applied.
·
Empirical classification is based on observed data,
particularly on temperature and precipitation.
·
Genetic classification attempts to organise climates
according to their causes.
·
Applied classification is for specific purpose.
Koeppen recognised five
major climatic groups; four of them are based on temperature and one on
precipitation. Table 12.1 lists the climatic groups and their characteristics
according to Koeppen. The capital letters: A, C, D and E delineate humid
climates and B dry climates.
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| Map of the Classification of the world climate by Koeppen |
Group A: Tropical Humid Climates
Tropical humid climates exist
between Tropic of Cancer and Tropic of Capricorn. The sun being overhead
throughout the year and the presence of Inter Tropical Convergence Zone (ITCZ)
make the climate hot and humid. Annual range of temperature is very low and
annual rainfall is high.
The tropical group is divided into
three types, namely (i) Af- Tropical wet climate; (ii) Am - Tropical monsoon
climate; (iii) Aw- Tropical wet and dry climate.
Tropical Wet Climate (Af)
Tropical wet climate is
found near the equator. The major areas are the Amazon Basin in South America, western
equatorial Africa and the islands of East Indies. Significant amount of
rainfall occurs in every month of the year as thunder showers in the afternoon.
The temperature is uniformly high and the annual range of temperature is
negligible. The maximum temperature on any day is around 30°C while the
minimum temperature is around 20°C. Tropical evergreen forests with dense
canopy cover and large biodiversity are found in this climate.
Tropical monsoon climate (Am) is
found over the Indian sub-continent, North Eastern part of South America
and Northern Australia. Heavy rainfall occurs mostly in summer. Winter is
dry. The detailed climatic account of this climatic type is given in the
book on India: Physical Environment.
Tropical Wet and Dry
Climate (Aw)
Tropical wet and dry climate
occurs north and south of Af type climate regions. It borders with dry
climate on the western part of the continent and Cf or Cw on the eastern
part. Extensive Aw climate is found to the north and south of the Amazon forest
in Brazil and adjoining parts of Bolivia and Paraguay in South America, Sudan
and south of Central Africa. The annual rainfall in this climate is considerably
less than that in Af and Am climate types and is variable also. The wet season
is shorter and the dry season is longer with the drought being more severe. Temperature
is high throughout the year and diurnal ranges of temperature are the greatest
in the dry season. Deciduous forest and tree-shredded grasslands occur in
this climate.
Dry climates are characterised by
very low rainfall that is not adequate for the growth of plants. These climates
cover a very large area of the planet extending over large latitudes from 15° -
60° north and south of the equator. At low latitudes, from 15° - 30°, they
occur in the area of subtropical high where subsidence and inversion of
temperature do not produce rainfall. On the western margin of the
continents, adjoining the cold current, particularly over the west coast of
South America, they extend more equatorwards and occur on the coast land. In
middle latitudes, from 35° - 60° north and south of equator, they are
confined to the interior of continents where maritime-humid winds do not reach
and to areas often surrounded by mountains.
Dry climates are divided
into steppe or semi-arid climate (BS) and desert climate (BW). They are further
subdivided as subtropical steppe (BSh) and subtropical desert (BWh) at
latitudes from 15° - 35° and mid-latitude steppe (BSk) and mid-latitude desert
(BWk) at latitudes between 35° - 60°.
Subtropical Steppe (BSh)
and Subtropical Desert (BWh) Climates
Subtropical steppe (BSh) and
subtropical desert (BWh) have common precipitation and temperature
characteristics. Located in the transition zone between humid and dry
climates, subtropical steppe receives slightly more rainfall than the desert,
adequate enough for the growth of sparse grasslands. The rainfall in both
the climates is highly variable. The variability in the rainfall affects the
life in the steppe much more than in the desert, more often causing famine.
Rain occurs in short intense thundershowers in deserts and is ineffective in
building soil moisture. Fog is common in coastal deserts bordering
cold currents. Maximum temperature in the summer is very high. The
highest shade temperature of 58° C was recorded at Al Aziziyah, Libya on
13 September 1922. The annual and diurnal ranges of temperature are also
high.
Warm temperate (mid-latitude)
climates extend from 30° - 50° of latitude mainly on the eastern and western
margins of continents. These climates generally have warm summers with mild
winters. They are grouped into four types: (i) Humid subtropical, i.e.
dry in winter and hot in summer (Cwa); (ii) Mediterranean (Cs); (iii) Humid
subtropical, i.e. no dry season and mild winter (Cfa); (iv) Marine west coast
climate (Cfb).
Humid Subtropical
Climate (Cwa)
Humid subtropical climate occurs
poleward of Tropic of Cancer and Capricorn, mainly in North Indian plains and
South China interior plains. The climate is similar to Aw climate except that
the temperature in winter is warm.
As the name suggests,
Mediterranean climate occurs around Mediterranean sea, along the west coast of
continents in subtropical latitudes between 30° - 40° latitudes e.g. — Central
California, Central Chile, along the coast in south eastern and south western
Australia. These areas come under the influence of sub-tropical high in summer
and westerly wind in winter. Hence, the climate is characterized by hot, dry summer and mild, rainy
winter. Monthly average temperature in summer is around 25° C and in winter
below 10°C. The annual precipitation ranges between 35 - 90 cm.
Humid subtropical climate lies on
the eastern parts of the continent in subtropical latitudes. In this region the
air masses are generally unstable and cause rainfall throughout the year.
They occur in eastern United States of America, southern and eastern China,
southern Japan, northeastern Argentina, coastal South Africa and eastern coast
of Australia. The annual averages of precipitation vary from 75-150 cm.
Thunderstorms in summer and frontal precipitation in winter is common. Mean
monthly temperature in summer is around 27°C, and in winter it varies from
5°-12° C. The daily range of temperature is small.
Marine west coast climate is
located poleward from the Mediterranean climate on the west coast of the
continents. The main areas are: Northwestern Europe, west coast of North
America, north of California, southern Chile, southeastern Australia and
New Zealand. Due to marine influence, the temperature is moderate and in
winter, it is warmer than for its latitude. The mean temperature in summer
months ranges from 15°-20°C and in winter 4°-10°C. The annual and daily ranges
of temperature are small. Precipitation occurs throughout the year.
Precipitation varies greatly from 50-250cm.
Cold snow forest climates occur in
the large continental area in the northern hemisphere between 40°-70° north
latitudes in Europe, Asia and North America. Cold snow forest climates are
divided into two types: (i) Df- cold climate with humid winter; (ii) Dw- cold climate
with dry winter. The severity of winter is more pronounced in higher latitudes.
Cold Climate with Humid
Winters (Df)
Cold climate with humid winter
occurs poleward of marine west coast climate and mid latitude steppe. The
winters are cold and snowy. The frost free season is short. The annual ranges
of temperature are large. The weather changes are abrupt and short. Poleward,
the winters are more severe.
Cold Climate with Dry
Winters (Dw)
Cold climate with dry winter
occurs mainly over Northeastern Asia. The development of pronounced winter anti
cyclone and its weakening in summer sets in monsoon like reversal of wind in
this region. Poleward summer temperatures are lower and winter temperatures are
extremely low with many locations experiencing below freezing point
temperatures for up to seven months in a year. Precipitation occurs in summer.
The annual precipitation is low from 12-15 cm.
Polar climates exist poleward
beyond 70° latitude. Polar climates consist of two types: (i) Tundra (ET); (ii)
Ice Cap (EF).
Tundra Climate (ET)
The tundra climate (ET) is so
called after the types of vegetation, like low growing mosses, lichens and
flowering plants. This is the region of permafrost where the sub soil is
permanently frozen. The short growing season and water logging support only low
growing plants. During summer, the tundra regions have very long duration of
day light.
Ice Cap Climate (EF)
The ice cap climate (EF) occurs
over interior Greenland and Antarctica. Even in summer, the temperature is
below freezing point. This area receives very little precipitation. The snow
and ice get accumulated and the mounting pressure causes the deformation
of the ice sheets and they break. They move as icebergs that float in the
Arctic and Antarctic waters. Plateau Station, Antarctica, 79°S, portray this
climate.
Highland climates are governed by
topography. In high mountains, large changes in mean temperature occur over
short distances. Precipitation types and intensity also vary spatially across
high lands. There is vertical zonation of layering of climatic types with
elevation in the mountain environment.
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