Koeppen’s Classification

Koeppen’s classification is based on quantitative values of temperature and precipitation.
It recognises location and points out the differences that exist between the east and west coast and between the coastal regions and interiors.
The types of climate have been defined in terms of numerical values.
The major divisions are denoted by capital letters and small letters are added to indicate other small sub-divisions. The small letter generally conveys special features of the climate.
Koeppen completed his classification scheme at two stages.
First, he identified five major groups of climate and represented by capital letters A, B, C, D and E.
Another capital letter H has been also included to represent the climate of highlands.
These five major groups of climate have been further sub-divided into a number of climatic types on the basis of temperature and precipitation differences and by adding small letters.

Humid Tropical Climate

The areas having this kind of climate occupy almost half of the earth’s surface, (over 20 per cent of the land and 40 per cent of the ocean surface).
This climatic group is bounded by the mean annual isotherm of 20°C.
The hot deserts of North Africa and Arabia lying within this area are excluded from this group because of their extreme aridity.
In this belt, temperature is more or less uniform.
Principal climatic types within this group are identified basically on the basis of their seasonal distribution of rainfall.

The Tropical Rainforest or Equatorial Climate (Af):

The climate is found in the belt extending from equator to 10°N and 10°S latitudes.
Along the windward margin of the continents, this climate may extend up to 20° North and South latitudes.
The Amazon basin, the Congo basin and the South-east Asian Island have this type of climate.
This climate has uniformly high temperature throughout the year, the annual average being about 27°C.
The daily range of temperature is in between 10°C and 25°C.
The annual range is, however, less than 5°C.
Rainfall is heavy and distributed throughout the year.
The annual average rainfall is about 250 cm.
The constantly high temperature and all the year round rainfall help to produce the most luxuriant vegetation in the region, which is known as the tropical rainforest

The Savanna Climate (Aw):

This climatic type is bounded by tropical rainforest climate toward the equator and by dry climates towards the poles.
Areas having a savanna climate are the Sudan and Veld Plateau of Africa, the tropical grasslands of northern Australia, the Llanos of the Guiana highlands of South America and the Campos of Brazil.
It represents a transitional zone which gets convectional rainfall during the summer, whereas during rest of the year it remains dry under the dominating influence of the trade winds.
The temperature is high throughout the year, the annual average temperature being about 23°C.
The annual range of temperature is 5°C to 6°C.
The annual rainfall is about 160 cm.
Wet summers alternate with dry winters.
Floods and droughts are quite common.
Duration of the rainy season and the average amount of annual rainfall decrease with the increasing distance from the equator.
Similarly annual range of temperature also increases away from the equator.
Here the tropical rainforest gives way to the savanna, the tropical grassland with scattered deciduous trees.

The Monsoon Climate (Am):

The monsoon climate is found in India, South-east Africa, Northern Australia, the Guinea Coast of West Africa and the Pacific Coast of Columbia.
The monsoon climate is characterised by seasonal reversal of wind direction associated with alternating periods of rainfall and drought.
During the summer season, humid unstable air moves from the ocean. Conditions are, therefore, conducive to rainfall.
In winter, a dry wind originating over the land blows towards the seas.
The monsoonal circulation system having reversal of wind direction develops in response to the differences in annual temperature variations between continents and oceans.
During summer, the intense heating of Central Asia produces an area of very low pressure, whereas in the Southern Hemisphere there exists the sub-tropical high pressure over the oceans.
The south-east trades flow from the high pressure to the low pressure area and are deflected to the right and reach India and south-east Asia as on-shore south and south-westerly winds.
These winds are laden with moisture and, therefore, cause heavy rainfall in these parts of the Asian Continent.
During winter, the excessive cooling in central Asia intensifies the high pressure belt and the off-shore north-east trades blow over south-east Asia.
Due to the presence of the Himalaya, these cold winds are prevented from descending into the Indian Peninsula. Temperatures are low during this season.

The Dry Climates

The dry climates have been sub-divided into the arid or desert type, and the semi-arid or steppe type. These two climatic sub-divisions have many features in common. Their differences are primarily a matter of degree.

In Koeppen’s classification, three variables have

been used in the formula to establish the boundary between dry and humid climates.

These variables are:

- Average annual temperature;
- Average annual precipitation; and
- Seasonal distribution of precipitation.

(i) The Desert Climate (BWh):

The chief feature of any desert climate is the scarcity of water.
This happens where evaporation exceeds precipitation.
Aridity or dryness is not simply a matter of low precipitation, but of the ‘effective precipitation’.
For example, 25 cm of precipitation may be sufficient to support the forest cover in Scandinavia where evaporation is less in the cool moist air.
But the same amount of rainfall in Iran can support only a sparse vegetative cover because evaporation is very high in hot dry air.
Hence, no specific amount of precipitation can serve as a universal boundary for dry climates.
The arid deserts lie in the low-latitudes close to the Tropic of Cancer and the Tropic of Capricorn.
The Sahara, the Arabia, the Thar, South-western USA, South-western Africa and central Australia have this type of climate.
This climate is dominated by the subsidence of air masses and marked stability of the sub-tropical anti-cyclones and hence, nearly rainless.
Precipitation is not only scanty but is also very erratic.
The cloudless sky and low humidity allow a great amount of solar radiation to reach the ground during the day and permit rapid terrestrial radiation at night.
Consequently, low-latitude deserts in the interior of the continents have the highest daily ranges of temperature on the earth, which is more than 15°C.
Average annual temperature is about 38°C.
Tropical deserts located along the west coast of continents reveal marked influence of cold ocean currents on their climates.
For example, Atacama in Peru and Chile and the Namibia in south-west Africa have lower annual average as well as annual and diurnal ranges of temperature compared to other locations at similar latitudes, but in other parts.
However, these areas receive the lowest annual rainfall totals in the world despite their location adjacent to the oceans.
In fact, the aridity in this part is intensified because of the cold off-shore waters which chill the air and further stabilise it.

(ii) The Steppe (BSk/BSh):

Unlike the low-latitude deserts, the steppes are not controlled by the subsiding air masses of the sub-tropical anti-cyclones.
Instead, these are dry lands principally because of their position in the deep interiors of large land masses away from the oceanic influences.
In addition, presence of mountain barriers across the paths of the prevailing winds further restricts maritime influences.
The middle latitude deserts have steppe climates and are, therefore, most widespread in North America and Eurasia.
This climatic type is characterised by meagre and unreliable precipitation like the tropical deserts.
However, annual average (21°C) and annual ranges of temperature (13°C) are a comparatively lower.
The annual rainfall is 30 cm.
Steppes located on the poleward side on the deserts receive maximum rainfall during the cool season, while those located towards the equator receive it during the warm season.

Warm temperate Climates

This climatic group is sub-divided into the Mediterranean, China and West European climatic types. The coldest month is below-18°C, but temperature never goes below-30°C. The warmest month records temperature over 10°C.

(i) The Mediterranean Climate (Cs):

This climate is found along the west coasts of continents between 30° and 45° latitudes.
It is bounded by the arid steppe on the equatorward side and the marine west European climate on the poleward side.
Areas around the Mediterranean sea, central California, central Chile, southern part of South Africa and south-eastern and southern-western parts of Australia experience this climate.
As there is seasonal shift of pressure belts with the annual movements of the sun, these areas come under the influence of subtropical high-pressure conditions during summer, and cyclonic low-pressure conditions during winter.
Summers are, therefore, warm and dry, temperature remains in between 20°C and 27°C.
Winters are mild with temperature ranging between 4°C and 10°C.
The annual range of temperature is about 10° to 17°C.
Rainfall is moderate and varies between 40 and 60 centimetres.
Most of the rainfall occurs in the winter season.

(ii) The Humid Subtropical Climate or the China Type (Cwa/Cfa):

The humid subtropical climate is found along the eastern coasts of continents between 25° and 45° latitudes.
It occurs in the southern-eastern United States, Uruguay, Argentina, southern Brazil, eastern China, southern Japan and eastern coastal belt of Australia.
Summers are hot and humid. Winters are mild.
The average annual temperature is 20°C and the average annual range of temperature is about 17°C.
Yearly precipitation totals area usually more than 100 centimetres.
It is well distributed throughout the year.
These areas experience dreaded hurricanes and typhoons, mostly in late summer and autumn.

(iii) The Marine West European Climate (Cwb/Cfb):

The climate is found along the western coasts of continents from about 40° and 65° north and south latitudes.
This climate is dominated by the on-shore flow of oceanic air.
Under the influence of maritime air masses, the areas under Cwb/Cfb experience mild winters, cool summers and ample amount of rainfall throughout the year.
This climate is found most widely in Europe, where in the absence of any mountain barrier running north-south, the movement of cool maritime air is not restricted.
In North and South America, this climate is found only in narrow belt, along the cost, because of the presence of mountain barriers.
Besides these areas, New Zealand and south-eastern tip of Australia also experience this climate.
Weather remains highly variable and unpredictable throughout the year under the influence of cyclonic low pressure system.
The average annual rainfall is about 140 centimetres.
The winters are rainier than the summers.

Cold Snow forest Climates (D)

Humid mid-latitude climates having low temperatures have been sub-divided into the taiga climate, the cool east coast, and the continental climates.

(i) The Taiga Climate (Dwd/Dwe/Dfe):

This climatic type has been named after the coniferous forest cover found in the region.
This climatic region covers broad expenses from Western Alaska to Newfoundland in North America, and from Norway to the Kamchetka Peninsula in Eurasia.
The climate is dominated by continental polar air masses.
The summers are short with average temperature 15°C.
The winters are long and very cold. Minimum temperature may be as low as -50°C (recorded at Verkhoyansk in January).
The precipitation is low and concentrated in warmer months.
Despite its small amount, it is sufficient for tree growth because evaporation is less.
The vegetation associated with this climatic type is the soft-wood coniferous forest.

(ii) The Cool East Coast Climate (Dwa):

This climate is found in areas located along the north-eastern coast of the United States, northern China, Japan, Korea and lower Danube plains.
The summers are long, hot and humid under the influence of tropical maritime air masses.
Average summer temperature is 25°C. The winters are cold and the average winter temperature ranges between -40°C and 0°C. Precipitation is variable.
Summer rainfall is characteristic and is convectional in nature.
In winter, precipitation is usually less than in summer, and falls mostly in the form of snow.

(iii) The Continental Climate (Dfa):

The climatic region is situated in the interior parts of the big continents between the Taiga and the mid-latitude deserts.
In Eurasia, it spreads from Poland and Baltic States to the central Russian Plain.
Beyond the Ural mountains, the belt is narrow and runs along the 55° parallel.
In North America this climate is found in the northern states of the United States and in the southern parts of the central states of Canada.
Temperature is usually higher than those of the Taiga type climate, but is lower than those of the cool east coast climate.
Summers are short and warm, temperature being in between 10°C and 21°C. Winters are long.
Temperature goes down below freezing point.
Precipitation is variable and comes mostly in summer as rainfall.
Winter precipitation is in the form of snow.

The Cold / Polar Climate (E)

Polar climates are those in which the mean temperature of the warmest month is below 10°C. These are thus characterised by the absence of a warm period and by long cold conditions. This climatic group has been sub-divided into two types—the Tundra Climate in which the warmest month has a temperature above freezing point but is less than 10°C; and the Ice-caps climate in which the warmest month has temperature below 0°C.

(i) The Tundra Climate (Et):

It is found almost exclusively in the Northern Hemisphere occupying the coastal fringes of the Arctic Ocean and many Arctic islands and the ice-free shores of Iceland and Greenland.
Winters are severe but summers are cool.
Annual temperature ranges are high.
Precipitation is in small amount.
Temperature of the warmest month does rise above 0°C, but never above 10°C.
As such, the ground may be free from snow, but for a short period.
The 10°C summer isotherm thus marks the equatorward limit of the Tundra as well as the Poleward limit of tree growth.
Only sparse vegetation is possible which comprises grasses, mosses and lichens.

(ii) The Ice-cap Climate (Ef):

The Ice-cap climate does not have a single monthly mean above 0°C. Consequently, the growth of vegetation is prohibited and it is a region of permanent ice and snow.

Climate of Highlands

In mountainous regions, altitude and insolation play important roles in controlling temperature and precipitation.
On high mountains the effect of high altitude is almost the same as that of high latitudes on the globe.
This may be revealed by altitudinal zonation of vegetation from foot of the mountains to their tops.
In Highland Climate high insolation, low temperature, low air pressure, large diurnal ranges of temperature and relatively large amount of precipitation at higher altitudes are common.
This type of climate is found in the Alps, the Himalayas, the Tibetan Plateau, the Rockies and the Andes.

Koeppen’s Classification

Humid Tropical Climate

The Dry Climates

Warm temperate Climates

Cold Snow forest Climates (D)

The Cold / Polar Climate (E)

Climate of Highlands

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