CLIMATIC CLASSIFICATION

Climate of a place can be defined as the average weather conditions over a substantially long period of time. Weather, on the other hand is defined as atmospheric conditions of temperature, pressure, humidity, wind circulations etc. at a particular point of time. While climate is fairly constant over a long period of time. While climate is fairly constant over a long period of time.

Classification of climates

On the basis of empiricism and genetics, the climate of the world is classified into various types. Statistical data is used for empirical classification and the genesis of climatic phenomena and climatic variations are used for genetic classification. Climatic classifications are closely corelated with categorization of biomes as climate is a major influencer on climate. The schemes propounded by W Koppen and C Thornwaite is most commonly studied.

Koppen’s Climatic Classification

It is quantitative as well as empirical classification of climate. Koppen proposed the classification using the world vegetation ma of De Condole. This classification scheme used certain critical values of temperature of the warmest and coldest months and precipitation of the wettest and the driest months. It uses numerical values of temperature of the warmest and coldest months and precipitation of the wettest and driest months. It used numerical values for delimiting the boundaries of different climatic regions and types. As identified by Candolle, Koppen used five major vegetation zones namely Megatherms, Xerophytes, Hekistotherms, Mesotherms, Mesotherms.

Megatherms

This group includes plants plants, which require uniformly high temperature and abundant supply of moisture. The season is winterless, the average temperature of the coldest month being above 18ºC. There is atleast one month of heavy precipitation. Certain areas of this belt are characterised by two rainy seasons. The characteristic vegetation is the tropical rain forest.

Xerophytes

Plants that prefer aridity  and need high temperatures, even though for a short season, are known as xerophytes. This class of vegetation is found in the warmer part of the middle latitude zone. The type of vegetation varies with soil types.

Hekistotherms

This group of vegetation comprises of plants of the snowbound Arctic region, beyond the polar limits.  Mosses, Lichens etc. are the natural vegetation.

Mesotherms

This group of vegetation consists of plants that are adapted to moderate moderate heat and a moderate amount of moisture. Certain types of plants are not adapted to low winter temperatures. These plants are found in regions lying between latitudes 22ºC for the warmest month.

Microtherms

Plants that need lower mean values of annual temperature cool and short summers and colder winter are called Microtherms. The monthly mean temperature for the warmest month is atleast 10ºC and less than 22ºC. The mean temperature for the coldest month is below 6ºC.  Evergreen deciduous forests and steppes are the natural vegetation regime.

Based on the vegetation zones, Koppen divided the world climate into five principal types

1. A climate Represents humid tropical climate characterised by winterless seasons, warm and moist conditions throughout the year.
2. B climate Represents dry climate where evaporation exceeds precipitation and there is water deficit.
3. C climate Humid warm temperature climate having mild winters, average temperature of the coldest and warmest months being 3ºC and above 10ºC.
4. D climate Humid cold forest climate, characterised by severe winters, average temperature of coldest and warmest months being 3ºC and above 10ºC respectively.
5. E climate Includes polar climates characterised by summerless seasons, average temperatures of warmest month below 10ºC.

 

Advantage Koppen’s Classification  

Koppen used the temperature and precipitation statistics in his classification of the climate. These two weather elements are easy to measure. Because of this quality, these elements are most widely and frequently used. Since, Koppen’s classification is based on statistical parameters, each climatic region can be precisely defined. Another advance of this classification is that it is possible to assign a given place to a particular climatic sub-group only on the basis  of certain easily acquired statistics about an area’s temperature and precipitation.

Another unique feature of the Koppen’s system is that it uses a shorthand code of letters for the climate types, so that repetition of descriptive terms becomes unnecessary.

Limitations of Koppen’s Classification

Koppen’s based his classification on the mean monthly values of temperature and precipitation. By these statistics, the most potent factor of precipitation can only be estimated rather than measured accurately. This makes comparison from one locality to another rather difficult.

Another major drawback is that it is empirical and the therefore, is based on facts and observations. The causative factors of climate have been totally ignored. Thus, the air masses, which form the very basis of modern climatology, could not find any place in Koppen’s classification. Lastly, the letter symbols used by Koppen in his climate classification provide an international shorthand describing climatic regions that are rather difficult to characterize in words.

Thornwaite’s Classification (CLIMATIC CLASSIFICATION)

C.W Thornwaite, an American climatologist presented his first scheme classification of climates of North America and later he modified it to present his second raised scheme in1948. His scheme is complex and empirical in nature.

Thornhwaite’s 1931 Classification

CW Thornwaite in 1931, devised a complex and empirical classification, which is very close to Koppen’s scheme. It also attempts to define climatic boundaries quantitatively and is based on plant associations. This classification also employs on plant associations. The classification also employs combination of letter symbols to designate the climatic types, its sub divisions and other groups. However, Thornwaite’s classification is based on precipitation effectiveness and thermal efficiency (temperature efficiency).

Thornhwaite’s 1948 Classification

In 1948, Thornwaite proposed a new classification of climate, which is his most valuable contribution. His second contribution is based on the concept of potential evapotranspiration, which represents the amount of moisture that would be transferred to the atmosphere by evaporation of liquid or solid water plus transpiration from living tissues, principally plants if it were available. The Potential Evapotranspiration is calculated from he mean monthly temperature, with corrections for the day length.

Merits of Thornwaite’s Climatic Classification

• The scheme is based on empiricism and boundaries of different climates have been determined on the basis of quantitative parameters.
• Vegetation has been made on a basis of identification of climatic zones
• Various letters used to designate different climates makes it easier to understand
• It has yielded a more number of climatic types
• The classification of climate on the basis of four indices becomes quite elaborate.

Criticism

• The schemes has not incorporated causative factors of climate for classifying the climate of the world
• There is non-availability of data of evaporation for all places
• No precise world map of climates could be made on the basis of four indices
• The formulas devised by him require regular data, which is not always available

Lately, Thornwaite developed the concept of the soil moisture balance and he preferred to use it as the foundation of his climatic system. He said that the soil moisture balance represents availability of moisture for plants and an assessment of the availability of surplus moisture to supply stream flow and ground water. This concept implies that precipitation alone does not indicate the amount of water actually available to plants. The amount and availability of soil moisture to also affected.