Weather and Climate

Weather pertains to the condition of the atmosphere at any place at a specic time or for a short time with respect to various elements (temperature, sunshine, wind, clouds, fog, precipitation etc). This is an hour to hour, or day to day condition. On the other hand, climate is the average weather conditions throughout the year over a fairly extensive area over many years (usually 30 to 35 years) in terms of climate elements like temperature, rainfall etc.

Classification of Climate

Different parts of the world experience dierent types of climate and classiation of climate is essential for its proper understanding. Climate can be classified on the basis of temperature, rainfall, evaporation etc. Several scholars like Miller, Koeppen, orntheonite and Trewartha have tried to classify climate of the world in their own way. However, Koeppen’s classication is the most popular and wid ely accepted classiation of the world’s climates.

Koeppen’s Scheme of Classification of Climate

Wladimir Koeppen (1846-1940) was German climatologist and botanist who presented his empirical classiation of climate in 1918 and revised it in 1931 and 1936. Although developed about a century ago, Koeppen’s scheme is still popular and is widely used because of its ease of comprehension. He recognised a close relationship between vegetation and climate and based his classication on mean annual and mean monthly temperature, average monthly precipitation and related them to the distribution of vegetation. He introduced the use of capital and small letters to designate climatic groups and types.

Koeppen recognised five major climatic groups out of which four were based on temperature and one on precipitation. In addition, he treated cold climate of high lands separately. His scheme of climatic groups is given in the following table.

Table 3.2 Climate Groups According to Koeppen

Group Characteristics
A’Tropical Average temperature of the coldest month is 18’C or higher
B’Dry Climates Potential evaporation exceeds precipitation
C’Warm Temperate The average temperature of the coldest month of the (Mid-latitude) climates is higher
  than minus 3’C but below 18’C
D’Cold Snow Forest Climates The average temperature of the coldest month is minus 3′ C or below
E’Cold Climates Average temperature for all months is below 10′ C
H’High Land Cold due to elevation

In addition to above-mentioned capital letters, dry climates are subdivided using capital letters S for steppe or semi-arid and W for deserts. THe above-mentioned climatic groups are subdivided into types depending upon the seasonality of precipitation and temperature. ese subdivisions are represented by small letters.

These letters are explained as under:

  • = Hot summer, average temperature of the warmest month over 22’C
  • = Cold winters, temperature of the warmest month below 22’C c = Cold short summer season, temperature above 10’C for less than four months
  • = Rainfall throughout the year. No dry season
  • w = Dry season in winter
  • s = Dry season in summer
  • h = Average annual temperature above 18′
  • k = Cold mean annual temperature below 18’C m = Monsoon
  • t = Tundra

Details of Koeppen’s Climate types are given below

Group Type Letter Code Characteristics
A’ Tropical Humid Tropical wet Af No dry season.
  Climate Tropical Monsoon Am Monsoonal, short dry season
    Tropical wet and dry Aw Winter dry season
B’ Dry Climate Subtropical steppe BSh Low latitude semi arid or dary
    Subtropical desert BWh Low latitude arid or dry
    Mid-latitude steppe BSk Mid-latitude semi arid or dry
    Mid-latitude desert BWk Mid-latitude arid or dry
C’ Warm Humid Humid subtropical Cfa No dry season, warm summer
  Temperate Mediterranean Cs Dry hot summer, mild rainy winter
  (Mid-latitude) Climates Marine west coast C No dry season, warm and’ cool summer
D’ Cold Snow- Humid continental Df No dry season, severe winter
  forest Climates Subarctic Dw Winter dry and very severe
E’ Cold Climates Tundra ET No true summer
    Polar ice cap EF Perennial ice
H’ Highland Highland H Highland with snow cover

A’Tropical Humid Climates

These climates are found within the tropics i.e., between Tropic of Cancer in the north and Tropic of Capricorn in the south. The sun’s rays are almost vertical throughout the year and plenty of rainfall is received, as a result of which hot and humid climates prevail in this zone. ThIs group of climates is further divided into following three types of climates:

Tropical Wet Climate (Af). is type of climate is found in areas located near the equator. The major areas of this climate are the Amazon basin in South America, the Zaire Basin of Africa, and the islands of East Indies. Heavy rainfall is received throughout the year and the driest month receives more than 6 cm. of rainfall. The rainfall occurs almost everyday as thu nder showers in the aernoon. The annual range of temperature is negligible.

In several areas, the annual range of temperature is less than the daily range of temperature. The maximum temperature during the day is about 30′ C whereas the minimum temperature at night may be 20′ C. Areas of tropical wet climate are covered by tropical evergreen forests with dense canopy and large biodiversity.

Tropical Monsoon Climate (Am). This climate is dominated by monsoon winds which bring heavy rainfall in summer and winter is practically dry. This type of climate is found in the Indian sub-continent, North-Eastern part of South America and Northern Australia.

Tropical Wet and Dry Climate (Aw). This type of climate is found to the north and south of the Amazon south forest of Brazil and adjoining parts of Bolivia and Paraguay in South America, Sudan and south of Central Africa. The rain fall is variable and is much less than that in Af and Am climates. Wet season is considerably shorter than the dry season and droughts is a common phenomenon. Temperature remains high throughout the year. Deciduous forests and tree-shredded grasslands are found in this climate.

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