Of the several schemes of climatic classification, the one devised by Wladimir Koppen, a German botanist and climatologist, still remains the most widely known descriptive system.

It is a quantitative as well as empirical classification of climate. Koppen proposed his first classification in 1900, using the world vegetation map of de Candole, a French plant physiologist.

This classification scheme uses certain critical values of temperature of the warmest and the coldest months and precipitation of the wettest and the driest months.

It uses numerical values for delimiting the boundaries of different climatic regions and types. Koppen’s climatic regions in many cases coincided with the distinct vegetation regions.

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The plant classification proposed by A. de Candole in 1874 was accepted by Koppen. The following are the five principal biological groups that are largely controlled by temperature and moisture.

(A) Megatherms:

This group includes plants which require uniformly high temperature and abundant supply of moisture. The season is winterless, the average temperature of the coldest month being above 18°C.

There is at least one month of heavy precipitation. Certain areas of this belt are characterized by two rainy seasons. The characteristic vegetation is the tropical rain forest.

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(B) Xerophytes:

Plants that prefer aridity and need high temperatures, even though for a short season, are classed as Xerophytes.

This class of vegetation is found in the semi-arid steppes and hot deserts. These plants are also found in the warmer parts of the middle latitude zone. The type of vegetation varies with the soil types.

(C) Mesotherms:

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This group of vegetation consists of plants that are adapted to moderate heat and a moderate amount of moisture. Certain types of plants are not adapted to low winter temperatures, while others shun dryness of the warm season.

These plants are found in regions lying between latitudes 22° and 45°N and S. The average values of temperatures are usually below 18°C for the coldest month and 22°C for the warmest month.

(D) Microtherms:

Plants that need lower mean values of annual temperature, summers cool and short, and winters colder are called microtherms. The monthly mean temperature for the warmest month is at least 10°C and less than 22°C.

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The mean temperature for the coldest month is below 6°C. Occasional snow in winter and adequate precipitation during the warmer months suit the climatic requirements of these plants. Evergreen deciduous forests and steppes are the natural vegetation regime.

(E) Hekistotherms:

This group of vegetation comprises of plants of the snow-bound Arctic region, beyond the polar limits of tree growth. Mosses, lichens, etc. are the natural vegetation.

Not satisfied with his first scheme of climatic classification, Koppen revised and modified it several times during his own life time.

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Koppen revised his classification first in 1918, when he paid greater attention to the monthly and annual averages of temperature and precipitation, and their seasonal distribution. Thereafter several modifications were incorporated in his classification by the author himself.

The latest world map by the author himself appeared in 1931 in his book, Grundriss der Klimakunde, Berlin. Even after this the Koppen classification continued to be modified. Koppen-Geiger world climatic map was published in 1936.

However, a further modified version of Koppen’s original classification was published in 1953, which is known as Koppen-Geiger-Pohl’s classification of world climate.

In classifying climate Koppen placed reliance on his belief that the distribution of natural vegetation was the best expression of the totality of climate. Consequently, many of the climatic boundaries he selected were based on vegetation limits.

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The Koppen system recognizes five principal categories of climate; each category is designated by a capital letter as follows:

A. Humid tropical climates. Winterless climates; it is hot all seasons; all months have a mean temperature above 18°C.

B. Dry climates. In these climates evaporation exceeds precipitation; there is a constant water deficiency.

C. Humid mesothermal climates or warm temperate rainy climates. These climates have mild winters; the average temperature of the coldest month is below 18°C but above – 3°C; the average temperature of the warmest month over 10°C. In this group of climate both the seasons, winter and summer, are found.

D. Humid micro-thermal climates or cold snow-forest climates. These climates have severe winters; the average temperature of the coldest month is below -3°C and that of the warmest month exceeds 10°C.

E. Polar climates. These are summer-less climates; the warmest monthly mean is below 10°C.

It may be noticed that four of the principal categories of climatic gioups (A, C, D, E) are based on temperature characteristics, while the fifth, the B category, has precipitation as its fundamental criterion.

Each of the five categories of climatic groups has been subdivided on the basis of precipitation and temperature characteristics.