NCERT Textbook - World Climate and Climate Change | Geography (Prelims) by Valor Academy - UPSC PDF Download

 Page 1


WORLD CLIMATE AND
CLIMATE CHANGE
T
he world climate can be studied by
organising information and data on
climate and synthesising them in
smaller units for easy understanding,
description and analysis. Three broad
approaches have been adopted for classifying
climate. They are empirical, genetic and
applied. Empirical classification is based on
observed data, particularly on temperature
and precipitation. Genetic classification
attempts to organise climates according to their
causes. Applied classification is for specific
purpose.
KOEPPEN’S SCHEME OF CLASSIFICATION
OF CLIMATE
The most widely used classification of climate
is the empirical climate classification scheme
developed by V. Koeppen. Koeppen identified
a close relationship between the distribution
of vegetation and climate. He selected certain
values of temperature and precipitation and
related them to the distribution of vegetation
and used these values for classifying the
climates.  It is an empirical classification based
on mean annual and mean monthly
temperature and precipitation data. He
introduced the use of capital and small letters
to designate climatic groups and types.
Although developed in 1918 and modified over
a period of time, Koeppen’s scheme is still
popular and in use.
Koeppen recognised five major climatic
groups, four of them are based on temperature
and one on precipitation. Table 11.1 lists the
climatic groups and their characteristics
according to Koeppen. The capital letters :  A,C,
D and E delineate humid climates and B dry
climates.
The climatic groups are subdivided into
types, designated by small letters, based on
seasonality of precipitation and temperature
characteristics. The seasons of dryness are
indicated by the small letters : f, m, w and s,
where f corresponds to no dry season,
Table 11.1 : 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
CHAPTER
2024-25
Page 2


WORLD CLIMATE AND
CLIMATE CHANGE
T
he world climate can be studied by
organising information and data on
climate and synthesising them in
smaller units for easy understanding,
description and analysis. Three broad
approaches have been adopted for classifying
climate. They are empirical, genetic and
applied. Empirical classification is based on
observed data, particularly on temperature
and precipitation. Genetic classification
attempts to organise climates according to their
causes. Applied classification is for specific
purpose.
KOEPPEN’S SCHEME OF CLASSIFICATION
OF CLIMATE
The most widely used classification of climate
is the empirical climate classification scheme
developed by V. Koeppen. Koeppen identified
a close relationship between the distribution
of vegetation and climate. He selected certain
values of temperature and precipitation and
related them to the distribution of vegetation
and used these values for classifying the
climates.  It is an empirical classification based
on mean annual and mean monthly
temperature and precipitation data. He
introduced the use of capital and small letters
to designate climatic groups and types.
Although developed in 1918 and modified over
a period of time, Koeppen’s scheme is still
popular and in use.
Koeppen recognised five major climatic
groups, four of them are based on temperature
and one on precipitation. Table 11.1 lists the
climatic groups and their characteristics
according to Koeppen. The capital letters :  A,C,
D and E delineate humid climates and B dry
climates.
The climatic groups are subdivided into
types, designated by small letters, based on
seasonality of precipitation and temperature
characteristics. The seasons of dryness are
indicated by the small letters : f, m, w and s,
where f corresponds to no dry season,
Table 11.1 : 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
CHAPTER
2024-25
FUNDAMENTALS OF PHYSICAL GEOGRAPHY 92
m - monsoon climate, w- winter dry season and
s - summer dry season. The small letters a, b,
c and d refer to the degree of severity of
temperature. The B- Dry Climates are
subdivided using the capital letters S for steppe
or semi-arid and W for deserts. The climatic
types are listed in Table 11.2. The distribution
of climatic groups and types is shown in
Table 11.1.
Group A : Tropical Humid Climates
Tropical humid climates exist between Tropic
of Cancer and Tropic of Capricorn. The sun
being overhead throughout the year and the
presence of Inter Tropical Convergence Zone
(ITCZ) make the climate hot and humid.
Annual range of temperature is very low and
annual rainfall is high. The tropical group is
divided into three types, namely (i) Af- Tropical
wet climate; (ii) Am - Tropical monsoon climate;
(iii) Aw- Tropical wet and dry climate.
Tropical Wet Climate (Af)
Tropical wet climate is found near the equator.
The major areas are the Amazon Basin in South
America, western equatorial Africa and the
islands of East Indies. Significant amount of
rainfall occurs in every month of the year as
thunder showers in the afternoon. The
temperature is uniformly high and the annual
range of temperature is negligible. The
maximum temperature on any day is around
30°C while the minimum temperature is
around 20°C. Tropical evergreen forests with
dense canopy cover and large biodiversity are
found in this climate.
Tropical Monsoon Climate (Am)
Tropical monsoon climate (Am) is found over
the Indian sub-continent, North Eastern part
of South America and Northern Australia.
Heavy rainfall occurs mostly in summer. Winter
is dry. The detailed climatic account of this
climatic type is given in the book on India:
Physical Environment.
Tropical Wet and Dry Climate (Aw)
Tropical wet and dry climate occurs north and
south of Af type climate regions. It borders with
dry climate on the western part of the continent
and Cf or Cw on the eastern part. Extensive
Aw climate is found to the north and south of
the Amazon forest in Brazil and adjoining parts
Table 11.2 : Climatic Types According to Koeppen
Group Type Letter Code Characteristics
Tropical wet Af No dry season
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
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
Mediterranean Cs Dry hot summer
Marine west coast Cfb No dry season, warm and cool summer
Humid continental Df No dry season, severe winter
Subarctic Dw Winter dry and very severe
Tundra ET No true summer
Polar ice cap EF Perennial ice
Highland H Highland with snow cover
A-Tropical Humid
Climate
B-Dry Climate
C-W arm
temperate (Mid-
latitude) Climates
D-Cold Snow-
forest Climates
E-Cold Climates
H-Highland
2024-25
Page 3


WORLD CLIMATE AND
CLIMATE CHANGE
T
he world climate can be studied by
organising information and data on
climate and synthesising them in
smaller units for easy understanding,
description and analysis. Three broad
approaches have been adopted for classifying
climate. They are empirical, genetic and
applied. Empirical classification is based on
observed data, particularly on temperature
and precipitation. Genetic classification
attempts to organise climates according to their
causes. Applied classification is for specific
purpose.
KOEPPEN’S SCHEME OF CLASSIFICATION
OF CLIMATE
The most widely used classification of climate
is the empirical climate classification scheme
developed by V. Koeppen. Koeppen identified
a close relationship between the distribution
of vegetation and climate. He selected certain
values of temperature and precipitation and
related them to the distribution of vegetation
and used these values for classifying the
climates.  It is an empirical classification based
on mean annual and mean monthly
temperature and precipitation data. He
introduced the use of capital and small letters
to designate climatic groups and types.
Although developed in 1918 and modified over
a period of time, Koeppen’s scheme is still
popular and in use.
Koeppen recognised five major climatic
groups, four of them are based on temperature
and one on precipitation. Table 11.1 lists the
climatic groups and their characteristics
according to Koeppen. The capital letters :  A,C,
D and E delineate humid climates and B dry
climates.
The climatic groups are subdivided into
types, designated by small letters, based on
seasonality of precipitation and temperature
characteristics. The seasons of dryness are
indicated by the small letters : f, m, w and s,
where f corresponds to no dry season,
Table 11.1 : 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
CHAPTER
2024-25
FUNDAMENTALS OF PHYSICAL GEOGRAPHY 92
m - monsoon climate, w- winter dry season and
s - summer dry season. The small letters a, b,
c and d refer to the degree of severity of
temperature. The B- Dry Climates are
subdivided using the capital letters S for steppe
or semi-arid and W for deserts. The climatic
types are listed in Table 11.2. The distribution
of climatic groups and types is shown in
Table 11.1.
Group A : Tropical Humid Climates
Tropical humid climates exist between Tropic
of Cancer and Tropic of Capricorn. The sun
being overhead throughout the year and the
presence of Inter Tropical Convergence Zone
(ITCZ) make the climate hot and humid.
Annual range of temperature is very low and
annual rainfall is high. The tropical group is
divided into three types, namely (i) Af- Tropical
wet climate; (ii) Am - Tropical monsoon climate;
(iii) Aw- Tropical wet and dry climate.
Tropical Wet Climate (Af)
Tropical wet climate is found near the equator.
The major areas are the Amazon Basin in South
America, western equatorial Africa and the
islands of East Indies. Significant amount of
rainfall occurs in every month of the year as
thunder showers in the afternoon. The
temperature is uniformly high and the annual
range of temperature is negligible. The
maximum temperature on any day is around
30°C while the minimum temperature is
around 20°C. Tropical evergreen forests with
dense canopy cover and large biodiversity are
found in this climate.
Tropical Monsoon Climate (Am)
Tropical monsoon climate (Am) is found over
the Indian sub-continent, North Eastern part
of South America and Northern Australia.
Heavy rainfall occurs mostly in summer. Winter
is dry. The detailed climatic account of this
climatic type is given in the book on India:
Physical Environment.
Tropical Wet and Dry Climate (Aw)
Tropical wet and dry climate occurs north and
south of Af type climate regions. It borders with
dry climate on the western part of the continent
and Cf or Cw on the eastern part. Extensive
Aw climate is found to the north and south of
the Amazon forest in Brazil and adjoining parts
Table 11.2 : Climatic Types According to Koeppen
Group Type Letter Code Characteristics
Tropical wet Af No dry season
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
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
Mediterranean Cs Dry hot summer
Marine west coast Cfb No dry season, warm and cool summer
Humid continental Df No dry season, severe winter
Subarctic Dw Winter dry and very severe
Tundra ET No true summer
Polar ice cap EF Perennial ice
Highland H Highland with snow cover
A-Tropical Humid
Climate
B-Dry Climate
C-W arm
temperate (Mid-
latitude) Climates
D-Cold Snow-
forest Climates
E-Cold Climates
H-Highland
2024-25
WORLD CLIMATE AND CLIMATE CHANGE 93
of Bolivia and Paraguay in South America,
Sudan and south of Central Africa. The annual
rainfall in this climate is considerably less than
that in Af and Am climate types and is variable
also. The wet season is shorter and the dry
season is longer with the drought being more
severe. Temperature is high throughout the
year and diurnal ranges of temperature are the
greatest in the dry season. Deciduous forest and
tree-shredded grasslands occur in this climate.
Dry Climates : B
Dry climates are characterised by very low
rainfall that is not adequate for the growth of
plants. These climates cover a very large area
of the planet extending over large latitudes from
15° - 60° north and south of the equator. At
low latitudes, from 15° - 30°, they occur in the
area of subtropical high where subsidence and
inversion of temperature do not produce
rainfall. On the western margin of the
continents, adjoining the cold current,
particularly over the west coast of South
America, they extend more equatorwards and
occur on the coast land. In middle latitudes,
from 35° - 60° north and south of equator, they
are confined to the interior of continents where
maritime-humid winds do not reach and to
areas often surrounded by mountains.
Dry climates are divided into steppe or
semi-arid climate (BS) and desert climate (BW).
They are further subdivided as subtropical
steppe (BSh) and subtropical desert (BWh) at
latitudes from 15° - 35° and mid-latitude
steppe (BSk) and mid-latitude desert (BWk) at
latitudes between 35° - 60°.
Subtropical Steppe (BSh) and Subtropical
Desert (BWh) Climates
Subtropical steppe (BSh) and subtropical
desert (BWh) have common precipitation and
temperature characteristics. Located in the
transition zone between humid and dry
climates, subtropical steppe receives slightly
more rainfall than the desert, adequate enough
for the growth of sparse grasslands. The rainfall
in both the climates is highly variable. The
variability in the rainfall affects the life in the
steppe much more than in the desert, more
often causing famine. Rain occurs in short
intense thundershowers in deserts and is
ineffective in building soil moisture. Fog is
common in coastal deserts bordering cold
currents. Maximum temperature in the summer
is very high. The highest shade temperature of
58° C was recorded at Al Aziziyah, Libya on
13 September 1922. The annual and diurnal
ranges of temperature are also high.
Warm Temperate (Mid-Latitude) Climates-C
Warm temperate (mid-latitude) climates extend
from 30° - 50° of latitude mainly on the eastern
and western margins of continents. These
climates generally have warm summers with
mild winters. They are grouped into four types:
(i) Humid subtropical, i.e. dry in winter and
hot in summer (Cwa); (ii) Mediterranean (Cs);
(iii) Humid subtropical, i.e. no dry season and
mild winter (Cfa); (iv) Marine west coast climate
(Cfb).
Humid Subtropical Climate (Cwa)
Humid subtropical climate occurs poleward of
Tropic of Cancer and Capricorn, mainly in
North Indian plains and South China interior
plains. The climate is similar to Aw climate
except that the temperature in winter is warm.
Mediterranean Climate (Cs)
As the name suggests, Mediterranean climate
occurs around Mediterranean sea, along the
west coast of continents in subtropical latitudes
between 30° - 40° latitudes e.g. — Central
California, Central Chile, along the coast in
south eastern and south western Australia.
These areas come under the influence of sub
tropical high in summer and westerly wind in
winter. Hence, the climate is characterised by
hot, dry summer and mild, rainy winter. Monthly
average temperature in summer is around
25° C and in winter below 10°C. The annual
precipitation ranges between 35 - 90 cm.
Humid Subtropical (Cfa) Climate
Humid subtropical climate lies on the eastern
parts of the continent in subtropical latitudes.
In this region the air masses are generally
2024-25
Page 4


WORLD CLIMATE AND
CLIMATE CHANGE
T
he world climate can be studied by
organising information and data on
climate and synthesising them in
smaller units for easy understanding,
description and analysis. Three broad
approaches have been adopted for classifying
climate. They are empirical, genetic and
applied. Empirical classification is based on
observed data, particularly on temperature
and precipitation. Genetic classification
attempts to organise climates according to their
causes. Applied classification is for specific
purpose.
KOEPPEN’S SCHEME OF CLASSIFICATION
OF CLIMATE
The most widely used classification of climate
is the empirical climate classification scheme
developed by V. Koeppen. Koeppen identified
a close relationship between the distribution
of vegetation and climate. He selected certain
values of temperature and precipitation and
related them to the distribution of vegetation
and used these values for classifying the
climates.  It is an empirical classification based
on mean annual and mean monthly
temperature and precipitation data. He
introduced the use of capital and small letters
to designate climatic groups and types.
Although developed in 1918 and modified over
a period of time, Koeppen’s scheme is still
popular and in use.
Koeppen recognised five major climatic
groups, four of them are based on temperature
and one on precipitation. Table 11.1 lists the
climatic groups and their characteristics
according to Koeppen. The capital letters :  A,C,
D and E delineate humid climates and B dry
climates.
The climatic groups are subdivided into
types, designated by small letters, based on
seasonality of precipitation and temperature
characteristics. The seasons of dryness are
indicated by the small letters : f, m, w and s,
where f corresponds to no dry season,
Table 11.1 : 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
CHAPTER
2024-25
FUNDAMENTALS OF PHYSICAL GEOGRAPHY 92
m - monsoon climate, w- winter dry season and
s - summer dry season. The small letters a, b,
c and d refer to the degree of severity of
temperature. The B- Dry Climates are
subdivided using the capital letters S for steppe
or semi-arid and W for deserts. The climatic
types are listed in Table 11.2. The distribution
of climatic groups and types is shown in
Table 11.1.
Group A : Tropical Humid Climates
Tropical humid climates exist between Tropic
of Cancer and Tropic of Capricorn. The sun
being overhead throughout the year and the
presence of Inter Tropical Convergence Zone
(ITCZ) make the climate hot and humid.
Annual range of temperature is very low and
annual rainfall is high. The tropical group is
divided into three types, namely (i) Af- Tropical
wet climate; (ii) Am - Tropical monsoon climate;
(iii) Aw- Tropical wet and dry climate.
Tropical Wet Climate (Af)
Tropical wet climate is found near the equator.
The major areas are the Amazon Basin in South
America, western equatorial Africa and the
islands of East Indies. Significant amount of
rainfall occurs in every month of the year as
thunder showers in the afternoon. The
temperature is uniformly high and the annual
range of temperature is negligible. The
maximum temperature on any day is around
30°C while the minimum temperature is
around 20°C. Tropical evergreen forests with
dense canopy cover and large biodiversity are
found in this climate.
Tropical Monsoon Climate (Am)
Tropical monsoon climate (Am) is found over
the Indian sub-continent, North Eastern part
of South America and Northern Australia.
Heavy rainfall occurs mostly in summer. Winter
is dry. The detailed climatic account of this
climatic type is given in the book on India:
Physical Environment.
Tropical Wet and Dry Climate (Aw)
Tropical wet and dry climate occurs north and
south of Af type climate regions. It borders with
dry climate on the western part of the continent
and Cf or Cw on the eastern part. Extensive
Aw climate is found to the north and south of
the Amazon forest in Brazil and adjoining parts
Table 11.2 : Climatic Types According to Koeppen
Group Type Letter Code Characteristics
Tropical wet Af No dry season
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
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
Mediterranean Cs Dry hot summer
Marine west coast Cfb No dry season, warm and cool summer
Humid continental Df No dry season, severe winter
Subarctic Dw Winter dry and very severe
Tundra ET No true summer
Polar ice cap EF Perennial ice
Highland H Highland with snow cover
A-Tropical Humid
Climate
B-Dry Climate
C-W arm
temperate (Mid-
latitude) Climates
D-Cold Snow-
forest Climates
E-Cold Climates
H-Highland
2024-25
WORLD CLIMATE AND CLIMATE CHANGE 93
of Bolivia and Paraguay in South America,
Sudan and south of Central Africa. The annual
rainfall in this climate is considerably less than
that in Af and Am climate types and is variable
also. The wet season is shorter and the dry
season is longer with the drought being more
severe. Temperature is high throughout the
year and diurnal ranges of temperature are the
greatest in the dry season. Deciduous forest and
tree-shredded grasslands occur in this climate.
Dry Climates : B
Dry climates are characterised by very low
rainfall that is not adequate for the growth of
plants. These climates cover a very large area
of the planet extending over large latitudes from
15° - 60° north and south of the equator. At
low latitudes, from 15° - 30°, they occur in the
area of subtropical high where subsidence and
inversion of temperature do not produce
rainfall. On the western margin of the
continents, adjoining the cold current,
particularly over the west coast of South
America, they extend more equatorwards and
occur on the coast land. In middle latitudes,
from 35° - 60° north and south of equator, they
are confined to the interior of continents where
maritime-humid winds do not reach and to
areas often surrounded by mountains.
Dry climates are divided into steppe or
semi-arid climate (BS) and desert climate (BW).
They are further subdivided as subtropical
steppe (BSh) and subtropical desert (BWh) at
latitudes from 15° - 35° and mid-latitude
steppe (BSk) and mid-latitude desert (BWk) at
latitudes between 35° - 60°.
Subtropical Steppe (BSh) and Subtropical
Desert (BWh) Climates
Subtropical steppe (BSh) and subtropical
desert (BWh) have common precipitation and
temperature characteristics. Located in the
transition zone between humid and dry
climates, subtropical steppe receives slightly
more rainfall than the desert, adequate enough
for the growth of sparse grasslands. The rainfall
in both the climates is highly variable. The
variability in the rainfall affects the life in the
steppe much more than in the desert, more
often causing famine. Rain occurs in short
intense thundershowers in deserts and is
ineffective in building soil moisture. Fog is
common in coastal deserts bordering cold
currents. Maximum temperature in the summer
is very high. The highest shade temperature of
58° C was recorded at Al Aziziyah, Libya on
13 September 1922. The annual and diurnal
ranges of temperature are also high.
Warm Temperate (Mid-Latitude) Climates-C
Warm temperate (mid-latitude) climates extend
from 30° - 50° of latitude mainly on the eastern
and western margins of continents. These
climates generally have warm summers with
mild winters. They are grouped into four types:
(i) Humid subtropical, i.e. dry in winter and
hot in summer (Cwa); (ii) Mediterranean (Cs);
(iii) Humid subtropical, i.e. no dry season and
mild winter (Cfa); (iv) Marine west coast climate
(Cfb).
Humid Subtropical Climate (Cwa)
Humid subtropical climate occurs poleward of
Tropic of Cancer and Capricorn, mainly in
North Indian plains and South China interior
plains. The climate is similar to Aw climate
except that the temperature in winter is warm.
Mediterranean Climate (Cs)
As the name suggests, Mediterranean climate
occurs around Mediterranean sea, along the
west coast of continents in subtropical latitudes
between 30° - 40° latitudes e.g. — Central
California, Central Chile, along the coast in
south eastern and south western Australia.
These areas come under the influence of sub
tropical high in summer and westerly wind in
winter. Hence, the climate is characterised by
hot, dry summer and mild, rainy winter. Monthly
average temperature in summer is around
25° C and in winter below 10°C. The annual
precipitation ranges between 35 - 90 cm.
Humid Subtropical (Cfa) Climate
Humid subtropical climate lies on the eastern
parts of the continent in subtropical latitudes.
In this region the air masses are generally
2024-25
FUNDAMENTALS OF PHYSICAL GEOGRAPHY 94
unstable and cause rainfall throughout the
year. They occur in eastern United States of
America, southern and eastern China,
southern Japan, northeastern Argentina,
coastal south Africa and eastern coast of
Australia. The annual averages of precipitation
vary from 75-150 cm. Thunderstorms in
summer and frontal precipitation in winter are
common. Mean monthly temperature in
summer is around 27°C, and in winter it varies
from 5°-12° C. The daily range of temperature
is small.
Marine West Coast Climate (Cfb)
Marine west coast climate is located poleward
from the Mediterranean climate on the west
coast of the continents. The main areas are:
Northwestern Europe, west coast of North
America, north of California, southern Chile,
southeastern Australia and New Zealand. Due
to marine influence, the temperature is
moderate and in winter, it is warmer than for
its latitude. The mean temperature in summer
months ranges from 15°-20°C and in winter
4°-10°C. The annual and daily ranges of
temperature are small. Precipitation occurs
throughout the year. Precipitation varies
greatly from 50-250cm.
Cold Snow Forest Climates (D)
Cold snow forest climates occur in the large
continental area in the northern hemisphere
between 40°-70° north latitudes in Europe,
Asia and North America. Cold snow forest
climates are divided into two types: (i) Df- cold
climate with humid winter; (ii) Dw- cold climate
with dry winter. The severity of winter is more
pronounced in higher latitudes.
Cold Climate with Humid Winters (Df)
Cold climate with humid winter occurs
poleward of marine west coast climate and mid
latitude steppe. The winters are cold and
snowy. The frost free season is short. The
annual ranges of temperature are large. The
weather changes are abrupt and short.
Poleward, the winters are more severe.
Cold Climate with Dry Winters (Dw)
Cold climate with dry winter occurs mainly
over Northeastern Asia. The development of
pronounced winter anti cyclone and its
weakening in summer sets in monsoon like
reversal of wind in this region. Poleward
summer temperatures are lower and winter
temperatures are extremely low with many
locations experiencing below freezing point
temperatures for up to seven months in a year.
Precipitation occurs in summer. The annual
precipitation is low from 12-15 cm.
Polar Climates (E)
Polar climates exist poleward beyond 70°
latitude. Polar climates consist of two types:
(i) Tundra (ET); (ii) Ice Cap (EF).
Tundra Climate (ET)
The tundra climate (ET) is so called after the
types of vegetation, like low growing mosses,
lichens and flowering plants. This is the region
of permafrost where the sub soil is permanently
frozen. The short growing season and water
logging support only low growing plants.
During summer, the tundra regions have very
long duration of day light.
Ice Cap Climate (EF)
The ice cap climate (EF) occurs over interior
Greenland and Antartica. Even in summer, the
temperature is below freezing point. This area
receives very little precipitation. The snow and
ice get accumulated and the mounting pressure
causes the deformation of the ice sheets and
they break. They move as icebergs that float in
the Arctic and Antarctic waters. Plateau Station
, Antarctica ,79°S, portray this climate.
Highland Climates (H)
Highland climates are governed by topography.
In high mountains, large changes in mean
temperature occur over short distances.
Precipitation types and intensity also vary
spatially across high lands. There is vertical
zonation of layering of climatic types with
elevation in the mountain environment.
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WORLD CLIMATE AND
CLIMATE CHANGE
T
he world climate can be studied by
organising information and data on
climate and synthesising them in
smaller units for easy understanding,
description and analysis. Three broad
approaches have been adopted for classifying
climate. They are empirical, genetic and
applied. Empirical classification is based on
observed data, particularly on temperature
and precipitation. Genetic classification
attempts to organise climates according to their
causes. Applied classification is for specific
purpose.
KOEPPEN’S SCHEME OF CLASSIFICATION
OF CLIMATE
The most widely used classification of climate
is the empirical climate classification scheme
developed by V. Koeppen. Koeppen identified
a close relationship between the distribution
of vegetation and climate. He selected certain
values of temperature and precipitation and
related them to the distribution of vegetation
and used these values for classifying the
climates.  It is an empirical classification based
on mean annual and mean monthly
temperature and precipitation data. He
introduced the use of capital and small letters
to designate climatic groups and types.
Although developed in 1918 and modified over
a period of time, Koeppen’s scheme is still
popular and in use.
Koeppen recognised five major climatic
groups, four of them are based on temperature
and one on precipitation. Table 11.1 lists the
climatic groups and their characteristics
according to Koeppen. The capital letters :  A,C,
D and E delineate humid climates and B dry
climates.
The climatic groups are subdivided into
types, designated by small letters, based on
seasonality of precipitation and temperature
characteristics. The seasons of dryness are
indicated by the small letters : f, m, w and s,
where f corresponds to no dry season,
Table 11.1 : 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
CHAPTER
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FUNDAMENTALS OF PHYSICAL GEOGRAPHY 92
m - monsoon climate, w- winter dry season and
s - summer dry season. The small letters a, b,
c and d refer to the degree of severity of
temperature. The B- Dry Climates are
subdivided using the capital letters S for steppe
or semi-arid and W for deserts. The climatic
types are listed in Table 11.2. The distribution
of climatic groups and types is shown in
Table 11.1.
Group A : Tropical Humid Climates
Tropical humid climates exist between Tropic
of Cancer and Tropic of Capricorn. The sun
being overhead throughout the year and the
presence of Inter Tropical Convergence Zone
(ITCZ) make the climate hot and humid.
Annual range of temperature is very low and
annual rainfall is high. The tropical group is
divided into three types, namely (i) Af- Tropical
wet climate; (ii) Am - Tropical monsoon climate;
(iii) Aw- Tropical wet and dry climate.
Tropical Wet Climate (Af)
Tropical wet climate is found near the equator.
The major areas are the Amazon Basin in South
America, western equatorial Africa and the
islands of East Indies. Significant amount of
rainfall occurs in every month of the year as
thunder showers in the afternoon. The
temperature is uniformly high and the annual
range of temperature is negligible. The
maximum temperature on any day is around
30°C while the minimum temperature is
around 20°C. Tropical evergreen forests with
dense canopy cover and large biodiversity are
found in this climate.
Tropical Monsoon Climate (Am)
Tropical monsoon climate (Am) is found over
the Indian sub-continent, North Eastern part
of South America and Northern Australia.
Heavy rainfall occurs mostly in summer. Winter
is dry. The detailed climatic account of this
climatic type is given in the book on India:
Physical Environment.
Tropical Wet and Dry Climate (Aw)
Tropical wet and dry climate occurs north and
south of Af type climate regions. It borders with
dry climate on the western part of the continent
and Cf or Cw on the eastern part. Extensive
Aw climate is found to the north and south of
the Amazon forest in Brazil and adjoining parts
Table 11.2 : Climatic Types According to Koeppen
Group Type Letter Code Characteristics
Tropical wet Af No dry season
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
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
Mediterranean Cs Dry hot summer
Marine west coast Cfb No dry season, warm and cool summer
Humid continental Df No dry season, severe winter
Subarctic Dw Winter dry and very severe
Tundra ET No true summer
Polar ice cap EF Perennial ice
Highland H Highland with snow cover
A-Tropical Humid
Climate
B-Dry Climate
C-W arm
temperate (Mid-
latitude) Climates
D-Cold Snow-
forest Climates
E-Cold Climates
H-Highland
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WORLD CLIMATE AND CLIMATE CHANGE 93
of Bolivia and Paraguay in South America,
Sudan and south of Central Africa. The annual
rainfall in this climate is considerably less than
that in Af and Am climate types and is variable
also. The wet season is shorter and the dry
season is longer with the drought being more
severe. Temperature is high throughout the
year and diurnal ranges of temperature are the
greatest in the dry season. Deciduous forest and
tree-shredded grasslands occur in this climate.
Dry Climates : B
Dry climates are characterised by very low
rainfall that is not adequate for the growth of
plants. These climates cover a very large area
of the planet extending over large latitudes from
15° - 60° north and south of the equator. At
low latitudes, from 15° - 30°, they occur in the
area of subtropical high where subsidence and
inversion of temperature do not produce
rainfall. On the western margin of the
continents, adjoining the cold current,
particularly over the west coast of South
America, they extend more equatorwards and
occur on the coast land. In middle latitudes,
from 35° - 60° north and south of equator, they
are confined to the interior of continents where
maritime-humid winds do not reach and to
areas often surrounded by mountains.
Dry climates are divided into steppe or
semi-arid climate (BS) and desert climate (BW).
They are further subdivided as subtropical
steppe (BSh) and subtropical desert (BWh) at
latitudes from 15° - 35° and mid-latitude
steppe (BSk) and mid-latitude desert (BWk) at
latitudes between 35° - 60°.
Subtropical Steppe (BSh) and Subtropical
Desert (BWh) Climates
Subtropical steppe (BSh) and subtropical
desert (BWh) have common precipitation and
temperature characteristics. Located in the
transition zone between humid and dry
climates, subtropical steppe receives slightly
more rainfall than the desert, adequate enough
for the growth of sparse grasslands. The rainfall
in both the climates is highly variable. The
variability in the rainfall affects the life in the
steppe much more than in the desert, more
often causing famine. Rain occurs in short
intense thundershowers in deserts and is
ineffective in building soil moisture. Fog is
common in coastal deserts bordering cold
currents. Maximum temperature in the summer
is very high. The highest shade temperature of
58° C was recorded at Al Aziziyah, Libya on
13 September 1922. The annual and diurnal
ranges of temperature are also high.
Warm Temperate (Mid-Latitude) Climates-C
Warm temperate (mid-latitude) climates extend
from 30° - 50° of latitude mainly on the eastern
and western margins of continents. These
climates generally have warm summers with
mild winters. They are grouped into four types:
(i) Humid subtropical, i.e. dry in winter and
hot in summer (Cwa); (ii) Mediterranean (Cs);
(iii) Humid subtropical, i.e. no dry season and
mild winter (Cfa); (iv) Marine west coast climate
(Cfb).
Humid Subtropical Climate (Cwa)
Humid subtropical climate occurs poleward of
Tropic of Cancer and Capricorn, mainly in
North Indian plains and South China interior
plains. The climate is similar to Aw climate
except that the temperature in winter is warm.
Mediterranean Climate (Cs)
As the name suggests, Mediterranean climate
occurs around Mediterranean sea, along the
west coast of continents in subtropical latitudes
between 30° - 40° latitudes e.g. — Central
California, Central Chile, along the coast in
south eastern and south western Australia.
These areas come under the influence of sub
tropical high in summer and westerly wind in
winter. Hence, the climate is characterised by
hot, dry summer and mild, rainy winter. Monthly
average temperature in summer is around
25° C and in winter below 10°C. The annual
precipitation ranges between 35 - 90 cm.
Humid Subtropical (Cfa) Climate
Humid subtropical climate lies on the eastern
parts of the continent in subtropical latitudes.
In this region the air masses are generally
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FUNDAMENTALS OF PHYSICAL GEOGRAPHY 94
unstable and cause rainfall throughout the
year. They occur in eastern United States of
America, southern and eastern China,
southern Japan, northeastern Argentina,
coastal south Africa and eastern coast of
Australia. The annual averages of precipitation
vary from 75-150 cm. Thunderstorms in
summer and frontal precipitation in winter are
common. Mean monthly temperature in
summer is around 27°C, and in winter it varies
from 5°-12° C. The daily range of temperature
is small.
Marine West Coast Climate (Cfb)
Marine west coast climate is located poleward
from the Mediterranean climate on the west
coast of the continents. The main areas are:
Northwestern Europe, west coast of North
America, north of California, southern Chile,
southeastern Australia and New Zealand. Due
to marine influence, the temperature is
moderate and in winter, it is warmer than for
its latitude. The mean temperature in summer
months ranges from 15°-20°C and in winter
4°-10°C. The annual and daily ranges of
temperature are small. Precipitation occurs
throughout the year. Precipitation varies
greatly from 50-250cm.
Cold Snow Forest Climates (D)
Cold snow forest climates occur in the large
continental area in the northern hemisphere
between 40°-70° north latitudes in Europe,
Asia and North America. Cold snow forest
climates are divided into two types: (i) Df- cold
climate with humid winter; (ii) Dw- cold climate
with dry winter. The severity of winter is more
pronounced in higher latitudes.
Cold Climate with Humid Winters (Df)
Cold climate with humid winter occurs
poleward of marine west coast climate and mid
latitude steppe. The winters are cold and
snowy. The frost free season is short. The
annual ranges of temperature are large. The
weather changes are abrupt and short.
Poleward, the winters are more severe.
Cold Climate with Dry Winters (Dw)
Cold climate with dry winter occurs mainly
over Northeastern Asia. The development of
pronounced winter anti cyclone and its
weakening in summer sets in monsoon like
reversal of wind in this region. Poleward
summer temperatures are lower and winter
temperatures are extremely low with many
locations experiencing below freezing point
temperatures for up to seven months in a year.
Precipitation occurs in summer. The annual
precipitation is low from 12-15 cm.
Polar Climates (E)
Polar climates exist poleward beyond 70°
latitude. Polar climates consist of two types:
(i) Tundra (ET); (ii) Ice Cap (EF).
Tundra Climate (ET)
The tundra climate (ET) is so called after the
types of vegetation, like low growing mosses,
lichens and flowering plants. This is the region
of permafrost where the sub soil is permanently
frozen. The short growing season and water
logging support only low growing plants.
During summer, the tundra regions have very
long duration of day light.
Ice Cap Climate (EF)
The ice cap climate (EF) occurs over interior
Greenland and Antartica. Even in summer, the
temperature is below freezing point. This area
receives very little precipitation. The snow and
ice get accumulated and the mounting pressure
causes the deformation of the ice sheets and
they break. They move as icebergs that float in
the Arctic and Antarctic waters. Plateau Station
, Antarctica ,79°S, portray this climate.
Highland Climates (H)
Highland climates are governed by topography.
In high mountains, large changes in mean
temperature occur over short distances.
Precipitation types and intensity also vary
spatially across high lands. There is vertical
zonation of layering of climatic types with
elevation in the mountain environment.
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WORLD CLIMATE AND CLIMATE CHANGE 95
CLIMATE CHANGE
The earlier chapters on climate summarised
our understanding of climate as it prevails now.
The type of climate we experience now might
be prevailing over the last 10,000 years with
minor and occasionally wide fluctuations. The
planet earth has witnessed many variations in
climate since the beginning.  Geological records
show alteration of glacial and inter-glacial
periods. The geomorphological features,
especially in high altitudes and high latitudes,
exhibit traces of advances and retreats of
glaciers. The sediment deposits in glacial lakes
also reveal the occurrence of warm and cold
periods. The rings in the trees provide clues
about wet and dry periods. Historical records
describe the vagaries in climate. All these
evidences indicate that change in climate is a
natural and continuous process.
India also witnessed alternate wet and dry
periods. Archaeological findings show that the
Rajasthan desert experienced wet and cool
climate around 8,000 B.C. The period 3,000-
1,700 B.C. had higher rainfall. From about
2,000-1,700 B.C., this region was the centre
of the Harappan civilisation. Dry conditions
accentuated since then.
In the geological past, the earth was warm
some 500-300 million years ago, through the
Cambrian, Ordovician and Silurian periods.
During the Pleistocene epoch, glacial and
inter-glacial periods occurred, the last major
peak glacial period was about 18,000 years
ago. The present inter-glacial period started
10,000 years ago.
Climate in the recent past
Variability in climate occurs all the time. The
nineties decade of the last century witnessed
extreme weather events. The 1990s recorded
the warmest temperature of the century and
some of the worst floods around the world. The
worst devastating drought in the Sahel region,
south of the Sahara desert, from 1967-1977
is one such variability. During the 1930s,
severe drought occurred in southwestern Great
Plains of the United States, described as the
dust bowl. Historical records of crop yield or
crop failures, of floods and migration of people
tell about the effects of changing climate. A
number of times Europe witnessed warm, wet,
cold and dry periods, the significant episodes
were the warm and dry conditions in the tenth
and eleventh centuries, when the Vikings
settled in Greenland. Europe witnessed “Little
Ice Age” from 1550 to about 1850. From about
1885-1940 world temperature showed an
upward trend. After 1940, the rate of increase
in temperature slowed down.
Causes of Climate Change
The causes for climate change are many. They
can be grouped into astronomical and
terrestrial causes. The astronomical causes are
the changes in solar output associated with
sunspot activities. Sunspots are dark and
cooler patches on the sun which increase and
decrease in a cyclical manner. According to
some meteorologists, when the number of
sunspots increase, cooler and wetter weather
and greater storminess occur. A decrease in
sunspot numbers is associated with warm and
drier conditions. Yet, these findings are not
statistically significant.
An another astronomical theory is
Millankovitch oscillations, which infer cycles
in the variations in the earth’s orbital
characteristics around the sun, the wobbling
of the earth and the changes in the earth’s axial
tilt. All these alter the amount of insolation
received from the sun, which in turn, might
have a bearing on the climate.
Volcanism is considered as another cause
for climate change. Volcanic eruption throws
up lots of aerosols into the atmosphere. These
aerosols remain in the atmosphere for a
considerable period of time reducing the sun’s
radiation reaching the Earth’s surface. After the
recent Pinatoba and El Cion volcanic
eruptions, the average temperature of the earth
fell to some extent for some years.
The most important anthropogenic effect
on the climate is the increasing trend in the
concentration of greenhouse gases in the
atmosphere which is likely to cause global
warming.
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