CHAPTER WORLD CLIMATE AND CLIMATE CHANGE he world climate can be studied by related them to the distribution of vegetation organising information and data on and used these values for classifying the Tclimate and synthesising them in climates. It is an empirical classification based smaller units for easy understanding, on mean annual and mean monthly description and analysis. Three broad temperature and precipitation data. He approaches have been adopted for classifying introduced the use of capital and small letters climate. They are empirical, genetic and to designate climatic groups and types. applied. Empirical classification is based on Although developed in 1918 and modified over observed data, particularly on temperature a period of time, Koeppen’s scheme is still and precipitation. Genetic classification popular and in use. attempts to organise climates according to their Koeppen recognised five major climatic causes. Applied classification is for specific groups, four of them are based on temperature purpose. and one on precipitation. Table 12.1 lists the climatic groups and their characteristics KOEPPEN’S SCHEME OF CLASSIFICATION according to Koeppen. The capital letters : A,C, D and E delineate humid climates and B dry OF CLIMATE climates. The most widely used classification of climate The climatic groups are subdivided into is the empirical climate classification scheme types, designated by small letters, based on developed by V. Koeppen. Koeppen identified seasonality of precipitation and temperature a close relationship between the distribution characteristics. The seasons of dryness are of vegetation and climate. He selected certain indicated by the small letters : f, m, w and s, values of temperature and precipitation and where f corresponds to no dry season, Table 12.1 : Climatic 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 years 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 2021-22 100 FUNDAMENTALS OF PHYSICAL GEOGRAPHY m - monsoon climate, w- winter dry season and islands of East Indies. Significant amount of s - summer dry season. The small letters a, b, rainfall occurs in every month of the year as c and d refer to the degree of severity of thunder showers in the afternoon. The temperature. The B- Dry Climates are temperature is uniformly high and the annual subdivided using the capital letters S for steppe range of temperature is negligible. The or semi-arid and W for deserts. The climatic maximum temperature on any day is around 30°C while the minimum temperature is types are listed in Table 12.2. The distribution around 20°C. Tropical evergreen forests with of climatic groups and types is shown in dense canopy cover and large biodiversity are Table 12.1. found in this climate. Table 12.2 : Climatic Types According to Koeppen Group Type Letter Code Characteristics Tropical wet Af No dry season A-Tropical Humid Climate Tropical monsoon Am Monsoonal, short dry season Tropical wet and dry Aw Winter dry season Subtropical steppe BSh Low-latitude semi arid or dry Subtropical desert BWh Low-latitude arid or dry B-Dry Climate Mid-latitude steppe BSk Mid-latitude semi arid or dry Mid-latitude desert BWk Mid-latitude arid or dry Humid subtropical Cfa No dry season, warm summer C-Warm temperate (Mid- Mediterranean Cs Dry hot summer latitude) Climates Marine west coast Cfb 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 Tundra ET No true summer E-Cold Climates Polar ice cap EF Perennial ice H-Highland Highland H Highland with snow cover Group A : Tropical Humid Climates Tropical Monsoon Climate (Am) Tropical humid climates exist between Tropic Tropical monsoon climate (Am) is found over of Cancer and Tropic of Capricorn. The sun the Indian sub-continent, North Eastern part being overhead throughout the year and the of South America and Northern Australia. presence of Inter Tropical Convergence Zone Heavy rainfall occurs mostly in summer. Winter (ITCZ) make the climate hot and humid. is dry. The detailed climatic account of this Annual range of temperature is very low and climatic type is given in the book on India: annual rainfall is high. The tropical group is Physical Environment. divided into three types, namely (i) Af- Tropical wet climate; (ii) Am - Tropical monsoon climate; Tropical Wet and Dry Climate (Aw) (iii) Aw- Tropical wet and dry climate. Tropical wet and dry climate occurs north and south of Af type climate regions. It borders with Tropical Wet Climate (Af) dry climate on the western part of the continent Tropical wet climate is found near the equator. and Cf or Cw on the eastern part. Extensive The major areas are the Amazon Basin in South Aw climate is found to the north and south of America, western equatorial Africa and the the Amazon forest in Brazil and adjoining parts 2021-22 WORLD CLIMATE AND CLIMATE CHANGE 101 of Bolivia and Paraguay in South America, often causing famine. Rain occurs in short Sudan and south of Central Africa. The annual intense thundershowers in deserts and is rainfall in this climate is considerably less than ineffective in building soil moisture. Fog is that in Af and Am climate types and is variable common in coastal deserts bordering cold also. The wet season is shorter and the dry currents. Maximum temperature in the summer season is longer with the drought being more is very high. The highest shade temperature of severe. Temperature is high throughout the 58° C was recorded at Al Aziziyah, Libya on year and diurnal ranges of temperature are the 13 September 1922. The annual and diurnal greatest in the dry season. Deciduous forest and ranges of temperature are also high. tree-shredded grasslands occur in this climate. Warm Temperate (Mid-Latitude) Climates-C Dry Climates : B Warm temperate (mid-latitude) climates extend Dry climates are characterised by very low from 30° - 50° of latitude mainly on the eastern rainfall that is not adequate for the growth of and western margins of continents. These plants. These climates cover a very large area climates generally have warm summers with of the planet extending over large latitudes from mild winters. They are grouped into four types: 15° - 60° north and south of the equator. At (i) Humid subtropical, i.e. dry in winter and low latitudes, from 15° - 30°, they occur in the hot in summer (Cwa); (ii) Mediterranean (Cs); area of subtropical high where subsidence and (iii) Humid subtropical, i.e. no dry season and inversion of temperature do not produce mild winter (Cfa); (iv) Marine west coast climate rainfall. On the western margin of the (Cfb). continents, adjoining the cold current, particularly over the west coast of South Humid Subtropical Climate (Cwa) America, they extend more equatorwards and Humid subtropical climate occurs poleward of occur on the coast land. In middle latitudes, Tropic of Cancer and Capricorn, mainly in from 35° - 60° north and south of equator, they North Indian plains and South China interior are confined to the interior of continents where plains. The climate is similar to Aw climate maritime-humid winds do not reach and to except that the temperature in winter is warm. areas often surrounded by mountains. Dry climates are divided into steppe or Mediterranean Climate (Cs) semi-arid climate (BS) and desert climate (BW). They are further subdivided as subtropical As the name suggests, Mediterranean climate steppe (BSh) and subtropical desert (BWh) at occurs around Mediterranean sea, along the latitudes from 15° - 35° and mid-latitude west coast of continents in subtropical latitudes steppe (BSk) and mid-latitude desert (BWk) at between 30° - 40° latitudes e.g. — Central latitudes between 35° - 60°. California, Central Chile, along the coast in south eastern and south western Australia. Subtropical Steppe (BSh) and Subtropical These areas come under the influence of sub Desert (BWh) Climates tropical high in summer and westerly wind in winter. Hence, the climate is characterised by Subtropical steppe (BSh) and subtropical hot, dry summer and mild, rainy winter. Monthly desert (BWh) have common precipitation and average temperature in summer is around temperature characteristics. Located in the 25° C and in winter below 10°C. The annual transition zone between humid and dry precipitation ranges between 35 - 90 cm. climates, subtropical steppe receives slightly more rainfall than the desert, adequate enough Humid Subtropical (Cfa) Climate for the growth of sparse grasslands. The rainfall in both the climates is highly variable. The Humid subtropical climate lies on the eastern variability in the rainfall affects the life in the parts of the continent in subtropical latitudes. steppe much more than in the desert, more In this region the air masses are generally 2021-22 102 FUNDAMENTALS OF PHYSICAL GEOGRAPHY unstable and cause rainfall throughout the Cold Climate with Dry Winters (Dw) year. They occur in eastern United States of Cold climate with dry winter occurs mainly America, southern and eastern China, over Northeastern Asia. The development of southern Japan, northeastern Argentina, pronounced winter anti cyclone and its coastal south Africa and eastern coast of weakening in summer sets in monsoon like Australia. The annual averages of precipitation reversal of wind in this region. Poleward vary from 75-150 cm. Thunderstorms in summer temperatures are lower and winter summer and frontal precipitation in winter are temperatures are extremely low with many common.