CBSE Class 8 Geography Chapter 9 India: Climate Notes

CBSE Class 8 Geography Chapter 9 India: Climate

Cimate plays a decisive role in the day-to-day living conditions of the people of a region. It is the climate that determines their habits and habitats.

• The houses they live in, the crops they grow, the clothes they wear, the festivals they celebrate are all influenced by the climate.
• This makes it necessary to understand what climate is and how it shapes the lives of the people of a particular place.
• The state of the atmosphere that we observe over an area at any point in time is called Weather.

For example:

A day may be hot, cold, windy, cloudy, or rainy. However, these weather conditions fluctuate often even within a day. For example, it might be hot and sunny in the noon but after an hour, it might start raining, and it becomes a rainy day.

• However, a common pattern of atmospheric conditions can be observed over a few weeks or months, i.e., days are hot or cool, calm or windy, cloudy or bright and dry or wet.
• The sum total of weather conditions and variations over a large area for a long period of time (more than 30 years) is called the Climate
• Based on the generalised monthly atmospheric conditions prevailing in a region, the year is divided into seasons such as summer, winter, etc.

CBSE Class 8 Geography Chapter 9 India Climate Of India

India has a tropical monsoon type of climate. This is because India lies in the tropical belt and its climate is influenced by the monsoon winds which are largely confined to the Tropics, i.e., between 20°N £md 20°S.

• The main characteristics of this type of climate are relatively high summer temperatures and cold dry winters.
• However, the Himalayas in the north and the Indian Ocean in the south provide distinctive climatic conditions to India.
• The Himalayan ranges protect northern India from the cold winds of Central Asia and Siberia and give it a sub-tropical climate i.e., summers are hot winters are cool.
• The Indian Ocean in the south gives it a tropical monsoon climate more typical of the tropical zone than that of the temperate zone.
• Despite the broad unity of the monsoon type of climate, variations in climate occur in different regions of the country.

For example:

• The climatic conditions of Bihar and Uttar Pradesh in the north differ from that of Kerala and Tamil Nadu in the south; yet all of these States have a similar monsoon type of climate.
• These variations are expressed in the pattern of winds, temperature and rainfall, rhythm of seasons and the degree of wetness or dryness.
• These regional diversities are known as the subtypes of monsoon climate.

CBSE Class 8 Geography Chapter 9 India Factors Affecting The Climate Of India

The factors that affect the climate of any place are called climatic controls.

The factors that influence the climate of India axe the following:

1. Latitude

Due to the curvature of the earth, the amount of solar energy received varies according to the latitude. Consequently, temperatures generally decrease from the Equator towards the Poles.

• The Tropic of Cancer passes through the middle of the country and the northern portion lies in the warm temperate zone or commonly known as sub-tropical climate and the southern portion lies in the tropical zone.
• The warm temperate or sub-tropical climate of the northern zone gives it cold winter season and ha ot summer season.
• The southern tropical climatic zone of India is warmer than the north and does not have a clear-cut winter season.
• Similarly, the northern zone does not have the mid-day Sun almost vertically overhead during any part of the year, while the southern zone has the mid-day Sun almost vertically overhead at least twice eveiy year.
• Thus, India’s climate has the characteristics of both tropical and sub-tropical climates.

2. Altitude

As one goes from the surface to higher altitudes, the atmosphere becomes less dense and the temperature decreases.

• There is a decrease of 1°C for every 166 m rise in height.
• India has mountains to the north, which have an average height of about 6,000 m. India also has a vast coastal area where the maximum elevation is about 30 m. So the mountains are cooler than the plains.
• For example, Ooty (Udhagamandalam) has much lower temperature than Kochi, because of the altitude.

3. Winds

The winds which have an overwhelming influence on the climate of India are the monsoon winds. These winds bring rain to the entire Indian subcontinent. Tibet lies in the ‘rainshadow’ of the Himalayas so it does not get rain.

• Besides the monsoon winds, there are other winds which affect the climate of India. The hot and dry winds which blow over the plains of northern India, cause heat waves during the summers.
• Similarly, the winds blowing from the north-west during the winters cause cold waves in northern India.

4. Mountains

Mountains act as a barrier and interfere the free flow of air and thereby modify the climate. The climates on the two sides of a mountain range are so different at times that mountains become climatic divide.

• Rainfall increases higher up as the moist air is forced up slope and the contact of the air stream with the colder surface.
• Heavy cloud and rainfall occurs on the windward side of a mountain.
• The rain shadow region on the leeward side experiences less rain or remains dry. The Himalayas and the Western Ghats are classical examples which display the influence of mountains on the climate.

Without the presence of the Himalayas, the monsoon winds would have blown into Central Asia and the northern part of India would have remained dry.

• The Western Ghats get heavy rainfall on western side because they stand in the way of South West Monsoon winds which come from the Arabian Sea to the Indian peninsular.
• On the other hand, the Deccan Plateau gets less rainfall as it lies in the rain shadow area of the Western Ghats.
• In Rajasthan, the Aravalli Range lies parallel to the direction of the South West Monsoon winds. So it is unable to stop the moisture laden winds.
• This makes Rajasthan a dry area. The southern hills of Assam get heavy rainfall but the northern ones do not.
• This is because the southern hills force the moisture-laden winds to shed their moisture before they proceed northwards.

5. Distance from the Sea

Areas in the interiors of India have an extreme type of climate or continental climate, whereas coastal areas have equable or maritime climate.

• The effect of land breeze and sea breeze caused by differential rate of heating and cooling of land and sea are responsible for moderate climate in coastal areas.
• Thus, areas close to the sea do not experience large variations in temperature across seasons.

For example:

Kochi experiences less variations in temperature than Agra does. This is because Kochi lies on the coast, whereas Agra is far away from the sea.

Western Disturbances

Western Disturbances are temperate cyclones, which originate in West Asia and the regions near the Mediterranean Sea and move towards India. They reach India during the winter season and bring the much-needed winter rainfall over the plains and snowfall in the mountains.

7. Jet Streams

Upper air currents in the Troposphere which determine the arrival and departure of monsoons, are known as jet streams. These currents develop in the upper layers of the atmosphere.

The westerly jet stream prevails over the North Indian Plains during the winter months, while the easterly jet stream steers the tropical depression over India. These upper air circulations play a significant role in the distribution pattern of the monsoon rainfall in the subcontinent. The highest rainfall occurs along the track of these depressions

CBSE Class 8 Geography Chapter 9 India Monsoon Phenomena And Its Mechanism

Monsoons Are Periodic Or Seasonal Winds. They Develop Because Of Differential Heating And Cooling Of The Land And The Sea. They Are Divided Into Two Wind Systems — The Summer Monsoon And The Winter Monsoon.

Summer Monsoons

In May, June and July, the plains of the Indian subcontinent are heated by the vertical rays of the sun.

• The intense heat develops a low pressure on the land. During these months, in the southern hemisphere over the Indian Ocean, a high pressure area develops.
• So, the winds blow from the Indian Ocean northward and northwestward into Asia.
• As they blow from the sea to the land, they bring heavy rainfall in some parts of the Indian subcontinent.
• The summer monsoon winds blow from south¬ west; so they are known as the ‘South-West Summer Monsoon’ or the ‘Advancing Monsoon’.

Winter Monsoons

During winter season, the conditions are just reverse of those in summers. A high pressure develops over a big landmass stretching from Central Asia up to north-west Indian plains.

• At the same time a low pressure zone develops in the Indian Ocean. As the winds blow from the land to the sea, they bring cold dry weather. They are incapable of producing rain.
• When these winds blow over seas and pass over the adjoining land, they bring some rainfall.
• The Southern Coromandel Coast (Tamil Nadu and southern tip of Andhra Pradesh) in India get rain from winter monsoons.
• The winter monsoon winds blow north-east; so the monsoon is known as the ‘North-East Winter Monsoon.’

CBSE Class 8 Geography Chapter 9 India Major Seasons In India

India has a Monsoon type of climate which has distinct seasonal pattern marked by significant change from one season to the other. These changes are clearly visible in the interior parts of the country. The coastal areas, due to the influence of the seas do not experience much variation in temperature though there occurs ‘variation in the pattern of rainfall.

Thus, the year may be divided into four principal seasons based on monsoon variations:

1. The Hot and Dry summer (March to May).
2. The Hot and Wet or Rainy Season or the
3. South-West Monsoon (June to September).
4. The Retreating South-West Monsoon (October-November).
5. The Cold and Dry Winter Season or Northeast Monsoon (December-February)

1. The Summer Season

In India, the hot season begins in March and lasts until June. The vertical rays of the Sun move towards the Tropic of Cancer during this period.

• By 21st June it is directly over the Tropic of Cancer.
• In most parts of India, temperature ranges between 30° and 32°C. The highest day temperatures increase as the heat belt moves further north.
• In northwestern part of India, temperatures around 48°C are not uncommon.
• In south India, the hot weather is not as intense as in north India. The moderating influence of the oceans together with the Peninsular situation of south India keeps the temperatures lower than that in north India.
• The temperatures, therefore, remain between 26°C and 32°C in south India.
• There is some respite from the heat in the coastal regions due to the influence of the sea. Plateaus and hills are also relatively cool because of the elevation.
• A striking feature of the hot weather season is the strong and dusty winds, called loo, which blow during daytime over northern and north¬ western India.
• These winds have a temperature range between 45°C and 50°C which is hot enough to cause heat strokes.
• There are occasional tomado-like dust storms in Punjab and Haiyana and Uttar Pradesh.
• The thunderstorms accompanied with strong winds and heavy rainfalloccur in Assam and West Bengal.

These local winds are known as Kalbaisakhi which means ‘the calamity of the beings in the month of Baisakh’. In Assam, these storms are known as Bardoli Chheerha.

Receeding Monsoon:

2. The Rainy Monsoon Season

The South-West monsoon season is the season of general rainfall. This season lasts from June to September. The differential heating of land and sea during the summer months causes the monsoon winds to drift towards the subcontinent.

• The large landmass to the north of the Indian Ocean gets intensely heated during April and May.
• This causes the formation of an intense low system in the north-western part of the Indian subcontinent.
• Since the pressure in the ocean to the south of the landmass is high, it attracts the South East (S.E.) Trade winds which prevail in the southern hemisphere.
• These S.E. Trade winds after crossing the Equator are deflected towards the right because of the Coriolis force and reach the west coast as South-West Monsoon. These winds bring heavy rainfall accompanied by violent thunder and lightning.
• This sudden violent onset of rainfall in the first week of June is termed as the Burst ofthe Monsoon. The first State to receive the monsoon showers is Kerala, and also the last to see its withdrawal.

As a result of the tapering topography of peninsular Indi,a the South-West Monsoon winds divide into two branches:

1. The Arabian Sea Branch
2. The Bay of Bengal Branch.

1. The Arabian Sea Branch:

The Arabian Sea branch enters the landmass after blowing over a vast open sea. It hits the Kerala coast in the first week of June.

• It causes heavy rainfall in the western coastal areas and the western slopes of the Western Ghats. Tamil Nadu gets less rainfall because it lies in the rain shadow of the Western Ghats.
• The Arabian Sea branch of the monsoon moves along western coastal plain and spreads over Central and northern India.

2. Bay of Bengal branch:

The Bay of Bengal branch gets deflected towards the Ganga-Brahmaputra delta by the Arakan Yoma range (Myanmar).

• Since it cannot cross the Himalayas, it moves westwards and brings rainfall along the Ganga plains. Thus, these two branches of the south-west monsoon cause rains in most parts of India.

3. Retreating Monsoon

The South-West Monsoon starts retreating from northern India in early October. Hence, the months of October and November are known for the retreating monsoon.

• This is caused by the high pressure in north-western India that leads to reversal in the direction of the monsoon winds. These winds now blow from the north-east to the south-west and are known as the retreating monsoon.
• These are land winds and don’t give rain except to coastal areas ofthe eastern coastal plain.
• They cause cyclonic rainfall along with strong winds to coastal Tamil Nadu and Andhra Pradesh.
• The retreat of the monsoon is marked by clear skies and drop in night temperature. The land remains moist.
• The combination ofhigh temperature and humidity gives rise to an oppressive weather.
• This is commonly known as ‘October heat’. The day temperature rises due to clear skies. These winds give way to the NE Monsoons by December.

4. The Cold and Dry Winter Season

The cold weather season commences at the end of November and continues till March. The skies are relatively clear with dry weather. Night temperatures are low, specially in northern India, but the days are pleasantly warm.

• The mean temperature in the northern plains is below 20°C and gets even lower in Himachal Pradesh, Jammu and Kashmir, Punjab and Haryana.
• In winter season, January is usually the coldest month. The temperature remains quite low during the winter months over the Indian sub-continent. The temperatures decrease from south to north.
• Temperatures fall below freezing point in the higher reaches of the Himalayas. Dras Valley near Kargil in Ladakh records minimum temperature of-45°C. It is the coldest place in India.

The excessive cold in north India during this season is due to the following reasons:

In the month of February, the cold winds from the Caspian Sea and Turkmenistan bring cold wave over the northwestern parts of India;

• Punjab, Haryana and Rajasthan experience sub-tropical type of climate with high variation in summer and winter temperatures. Since, they are located far away from the sea, they do not experience moderating influence of the sea.
• The snowfall in the nearby Himalayan ranges creates cold wave situation.
• In Peninsular India, the average temperature lies between 20°C to 25°C and it does not have any well defined cold weather season.
• The coastal areas hardly experience any seasonal change in the distribution pattern of temperature due to the moderating influence of the sea and proximity to the Equator.
• During this season, the north east trade winds prevail over the country. These winds blow from land to sea and hence, for most parts of the country it is dry season.
• However, when these winds pass over Bay of Bengal they pick up some moisture and cause some amount of rainfall on the Coromandel Coast.
• As these winds blow from north-east to south-west, they are called the North-East Monsoon.

Distribution of Rainfall

The distribution of rainfall in India is determined by the following:

1.  The pressure conditions and the direction of the relief features;
2. The direction of the winds bearing moisture.
3. Cyclonic depression is determined by the pressure gradient.

India can be divided into four rainfall regions:

1. Heavy Rainfall Region:

• This region experiences more than 200 cm of rainfall annually and includes the following areas.
• The windward side of the Western Ghats like the Western Coastal Plains and the slopes of the Western Ghats.
• Meghalaya Hills (Garo, Khasi and Jaintia), the southern slopes of Eastern Himalayas, Assam, Arunachal Pradesh and West Bengal.

2. Moderate Rainfall Region:

• This region receives rainfall ranging from 100 cm to 200 cm a year.
• The followingareas are includedinthis region:
• The northern part of Andhra Pradesh, the southern part of Tamil Nadu.
• Middle Ganga Valley, some portions of Western Ghats, Eastern Maharashtra, Madhya Pradesh, Odisha.

3. Low Rainfall Region:

• The rainfall in this region is scarce, vaiying from 50 to 100 cm. The areas of scanty rainfall are:
• Parts of the Deccan Plateau comprising the regions of Karnataka, Andhra Pradesh and Tamil Nadu.
• Eastern Rajasthan, Punjab, Haryana and Kashmir.

4. Scanty Rainfall Region:

These areas get the least rainfall, i.e., less than 50 cm annually. Desert and semi-desert areas are included in this

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The following areas come in this region:

• Leh in Ladakh, Southern Punjab and Western Rajasthan.
• The rain shadow regions of the Western Ghats lying in the Deccan Plateau.

Impact of Monsoon

Rains occur for over three months and the rest of the year is mostly dry. Seventy per cent of annual rainfall occurs in the rainy season. It has the following impact:

• The rains are mainly of relief type. The windward slopes of the mountains get more rainfall than the leeward side. So some areas get rainfall and other areas get either less or no rainfall.
• Only a small portion ofthe rainfall is received from sources other than the monsoon, like cyclonic rainfall and convectional rainfall.
• The quantity and the time of occurrence of rainfall cannot be predicted as the rainfall is erratic. It is because ofthis uncertainty that sometimes there are floods and sometimes droughts.
• India has an agrarian economy dependent on rainfall. A good monsoon ensures higher agricultural output and boosts Indian economy.
• A good rainfall increases the ground water level and replenishes the reservoirs, lakes and tanks. This not only benefits irrigation but also improves hydrolectric power production. Some cities like Mumbai totally depend on the South West Monsoon for water.
•  Monsoons are celebrated through many festivals in India to thank nature for the rains and a good harvest. Some of these are Harela (Uttarakhand), Onam (Kerala), Nariyal Poomima (Maharashtra), Hemis (Ladakh), Minjar (Himachal Pradesh) and Adi Perukku (Tamil Nadu).
• Pongal, Baisakhi are festivals that revolve around a good harvest as a result of good rainfall.