CLIMATE

CLIMATE 

Climate refers to the sum total of weather conditions and variations over a large area for a long period of time. 

It is the sum total of weather conditions for larger area. Eg: for a country: 

WEATHER: 
It refers to state of atmosphere over an area at any point of time.
It is the total of weather conditions for limited area.
Eg: for a city

The elements of weather and climate are temperature, atmospheric pressure, wind, humidity and precipitation.

INDIAN CLIMATE

• The climate of India is monsoon type.
•Monsoon is derived from ‘mausim’which means season and it refers to the seasonal reversal in the wind direction during a year.
•In Asia, this type of climate is found mainly in south and south-east.

DIFFERENCES IN INDIAN CLIMATE
In summer the temperature of Rajasthan is about 50’C but in Jammu & Kashmir it’s 20’c.
In winter at J&K the temperature is -45’C but in Thiruvanantapuram its 22’C.
While precipitation is in the form of snowfall in upper parts of Himalyas, it rains over the rest of country.
Most parts receive rainfall from June to July but some like Tamil Nadu receive it even in the season of October and November.

CLIMATIC CONTROLS 
The major controls of climate are:
1. Latitude: Due to curvature the amount of solar energy received varies according to it. 

2. Altitude: As we go higher there is a decrease in temperature of 16’

3. Pressure and Wind system: As per latitude and altitude temperature and rainfall also influences the climate.

4. Distance from sea: The sea exerts moderating influence on climate, regions near sea experiences moderate climate.

5. Ocean Currents: It leads continentality which means very hot during summers and very cold during winters. 

FACTORS AFFECTING INDIAN CLIMATE

1.Latitude:

Tropic of cancer almost divides the country in two equal parts running from Rann of Kuchh to Mizoram.
The region lying in the south of tropic of cancer is tropical whereas the region in north is in sub tropical.
Therefore India receives both tropical as well as sub-tropical climate.

2. Altitude:
India has mountains in north with average height of 6000m and coast line of about 30m.
The Himalayas act as a barrier to enter winds in India from Centeral Asia.
That’s why it experiences mild winters as compare to Centeral Asia.

3.PRESSURE and WINDS
It is further devided in three parts.
•Pressure and surface winds
•Upper air circulation
•Western disturbances
Pressure and surface winds: India lies in the region of north-easterly winds which originate from northern hemispher and blow towards south but
deflected to right due to corollis force.These winds carry small silts that’s why don’t affect India’s rain.

4. Upper air circulation: Winds travel from a low pressure area to high pressure area. Air moves from Indian ocean to south-east direction crossing equator and turns right towards Indian subcontinent giving rain to it. The upper air circulation over warm oceans is called jet stream.

5.Western disturbances: During the time of winters in India cyclone formation takes place in ‘Mediterranean sea’whose winds are very powerful that after crossing Pakistan, Afghanistan they finally reach Jammu and Kashmir leads to rainfall in winters there.

The unifying influence of the monsoon on the Indian subcontinent is quite perceptible. 

The seasonal alteration of the wind systems and the associated weather conditions provide a rhythmic cycle of seasons.
Even the uncertainties of rain and uneven distribution are very much typical of the monsoon.
The Indian landscape, its animal and plant life, the people, including their festivities, revolve around this phenomenon.

Year after year, people of India from north to south and from east to west, eagerly await the arrival of the monsoon.
These monsoon winds bind the whole country by providing water to set the agricultural activities in motion.

The river valleys which carry this water also unite as a single river valley unit.
Early in the season, the windward side of the Western Ghats receives very heavy rainfall, more than 250cm.
The Deccan Plateau and parts of Madhya Pradesh also receive some amount of rain in spite of lying in the rain shadow area.
The maximum rainfall of this season is received in the north-eastern part of the country.
Rainfall in the Ganga valley decreases from the east to the west.

Rajasthan and parts of Gujarat get scanty rainfall.

The breaks in the monsoon are related to the movement of the monsoon tough.
The trough and its axis keep on moving northward or southward. When the axis of the monsoon trough lies over the plains and widespread rain occur in the Himalayan Rivers.

Mawsynram in the southern ranges of the Khasi Hills receives the highest average rainfall in the world.

Q. Why is monsoon known for its “uncertainties”?
While it causes heavy floods in one part, it may be responsible for droughts in the other.
It is often irregular in its arrival and its retreat. Hence, it sometimes disturbs the farming schedule of millions of farmers all over the country.
During October-November, the monsoon trough or the low pressure trough over the northern plains becomes weaker. This is gradually replaced by a high-pressure system.
The south-east monsoon winds weaken and start withdrawing gradually. By the beginning of the October, the monsoon withdraws from the Northern Plains.
The months of October-November form a period of transition from hot rainy season to dry winter conditions. The retreat of the monsoon is marked by clear skies and rise in temperature.
While day temperatures are high, nights are cool and pleasant.
Owing to the conditions of high temperature and humidity, the weather becomes rather oppressive during the day.

This is known as “OCTOBER HEAT”.
The low-pressure conditions, over north-western India, get transferred to the Bay of Bengal by early November.
This shift is associated with the occurrence of cyclonic depressions, which originates over the Andaman Sea.
These cyclones generally cross the eastern coasts of India cause heavy and widesprad rain.
These tropical cyclones are often very destructive.
The thickly populated deltas of the Godavari, the Krishna and the Kaveri are frequently struck by cyclones, which cause great damage to life and property.

THE SEASONS
The monsoon type of climate is characterised by a distinct seasonal pattern.
The weather conditions greatly change from one season to the other.

The coastal areas do not experience much variation in temperature though there is variation  in rainfall pattern.

Four main seasons can be identified in India-

the cold weather season,

hot weather season,

the advancing monsoon and

the retreating monsoon with some regional variations.

THE COLD WEATHER SEASON (WINTER)
1. The cold weather season begins from mid- November in northern India and stays  till February.
2. December and January are the coldest months in the northern part of India.
3. The temperature decreases from south to the north.
4. Days are warm and nights are cold.
5. Frost is common in the north and the higher slopes of Himalayas experience
snowfall.
6. The northeast trade winds blow from land to sea and hence, for most part of the
country, it is a dry season.
7. Some amount of rainfall occurs on the Tamil Nadu coast from these winds as,
here they blow from sea to land.
8. The weather is normally marked by clear sky, low temperatures and low humidity and feeble variable winds.
9. A characteristic feature of the cold weather season over the northern plains is a
the inflow of cyclonic disturbances from the west and the northwest.
10.They cause the much- needed winter rains over the plains and snowfall in the
mountains.
11.Total amount of winter rainfall locally known as ‘mahawat’ is small; they are of    immense importance for the cultivation of ‘rabi’ crops.
12. The peninsular region does not have well- defined cold season.

THE HOT WEATHER SEASON (SUMMER)
1. From March to May, it is hot weather season in India.
2. The influence of shifting of the heat belt can be seen clearly from temperature
recordings taken during March- May at different latitudes.
3. In peninsular India, temperature remain lower due to the moderating influence of the oceans.
4. The summer months experience rising temperature and falling air pressure in the
northern part of the country.
5. Towards the end of May, an elongated low pressure area develops in the region
extending from the Thar Desert in the northwest to Patna and Chotanagpur plateau
and southeast.
6. The striking feature of the hot weather season is the ‘loo’. These are strong, gusty, hot, dry winds blowing during the day over the north and northwestern India.
7. Dust storms are very common during the month of May in northern India. These  storms bring temporary relief as they lower the temperature and may bring light rain and cool breeze.
8. In West Bengal, these storms are known as ‘Kaal Baisakhi’.
9. Towards the close of the summer season, pre- monsoon showers are common
especially, in Kerala and Karnataka.

DISTRIBUTION OF RAINFALL
There are three types of rainfall :-
-Low rainfall (Less than 50 cm.)
- Average rainfall (Between 50 to 250 cm.)
- High rainfall (More than 250 cm.)

1. Parts of western coast and northern India receive over about 400 cm of rainfall
annually.
2. It is less than 60cm in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab.
3. Rainfall is equally low in the interior of Deccan plateau, and east of the Sahyadris.
4. The rest of the country receives moderate rainfall. Snowfall is restricted to the Himalayan region.

Because of the nature of monsoons, the annual rainfall is highly variable from year to year. Variability is high in the regions of low rainfall such as parts of Rajasthan, Gujarat and leeward (rain shadow area) side of the Western Ghats. While the areas of high rainfall are responsible to be affected by the floods and the areas of low rainfall are drought- prone.

SOME  IMPORTANT TERMS
1. Frost-  A state in freezing, frozen dew.

2. Loo- Strong, gusty, hot, dry winds blowing during the day over the north and northwestern India.

3. Mango showers- Pre-monsoon showers in Kerala and Karnataka help in ripening of mangoes earlier, known as monsoon showers.

4. Trough- large vacuum in between of the Himalayas and the peninsular plateau, the plains.

5. Leeward- Rain shadow area. 

6. Climate: The sum total of weather conditions and variations over a large area for a long period of time (more than thirty years) is called climate.

7. Weather: The state of the atmosphere over an area at any point of time is called weather.

8. Monsoon: This type of climate is mainly found in the south and Southeast Asia. The climate of India is of monsoon type. The seasonal reversal in wind direction during a year is called monsoon.

9. Coriolis Force: An apparent force caused by the earth’s rotation is called Coriolis Force. The winds are deflected towards right in the northern hemisphere and towards the left in the southern hemisphere due to this force. This is also known as ‘Ferrel’s Law’.

10. Jet Stream: Fast flowing and narrow air currents are called jet streams. The streams flow at high altitudes (about 12,000 feet) in the troposphere. Their speed varies from about 110 km/h in summer to 184 km/h in winter.

Western Cyclonic Disturbance:

The western cyclonic disturbances are weather phenomena of the winter months brought in by the westerly flow from the Mediterranean region.

They usually influence the weather of the north and north-western regions of India.

Inter Tropical Convergence Zone (ITCZ):

The Inter Tropical Convergence Zone (ITCZ,) is a broad trough of low pressure in equatorial latitudes.

The northeast and the southeast trade winds converge in this zone.

This zone lies more or less parallel to the equator.

 It moves north or south with the apparent movement of the sun.

CLIMATIC CONTROLS

There are six major controls of the climate of any place. They are:

Latitude, Altitude, Pressure and wind system, Distance from the sea, Ocean currents and Relief features

Factors Affecting India’s Climate

Latitude: The Indian landmass is equally divided by The Tropic of Cancer. Hence, half of India has tropical climate and another half has subtropical climate.

Altitude: While the average elevation in the coastal areas is about 30 metre, the average elevation in the north is about 6,000 metre. The Himalayas prevent the cold winds from Central Asia from entering the Indian subcontinent. Due to this, the subcontinent gets comparatively milder winters as compared to Central Asia.

Pressure and Winds: The Indian subcontinent lies in the region of north-easterly winds. These winds originate from the subtropical high-pressure belt of the northern hemisphere. After that, these winds blow towards south. They get deflected to the right due to the Coriolis force and then move towards the low pressure area near the equator.

The north-easterly winds originate and blow over the land and hence they carry very little moisture. India should have been an arid land because of these winds but that is not the case.

There is high-pressure area towards the north of the Himalayas. Cold winds from this region blow to the low pressure areas over the oceans in the south.

During summer, low-pressure area develops over interior Asia and also over northwestern India. This results in a complete reversal of the direction of winds during summer.

Air moves from the high-pressure area moves over the southern Indian Ocean in a south-easterly direction. It crosses the equator and turns right towards the low-pressure areas over the Indian subcontinent.

These winds are known as the Southwest Monsoon wind. They collect moisture from the warm oceans and bring widespread rainfall over the mainland of India.

The upper air circulation in this region is dominated by a westerly flow. Jet stream is an important component of this flow. These jet streams are called subtropical westerly jet streams because they are located approximately over 27°-30° north latitude.

The westerly jet streams are responsible for western cyclonic disturbances in the north and north-western parts of India. The subtropical westerly jet stream moves north of the Himalayas with the apparent movement of the sun.

The tropical jet stream (an easterly jet stream) blows over the Indian Peninsula; approximately over 14° north during the summer months.

NCERT Solution

Q 1.Which one of the following places receives the highest rainfall in the world?

Silchar

Cherrapunji

Mawsynram

Guwahati

Ans: (c) Mawsynram

Q 2 . The wind blowing in the northern plains in summers is known as:

Kaal Baisakhi

Trade Winds

Loo

None of the above

Ans: (c) Loo

Q 3. Which one of the following causes rainfall during winters in north-western part of India.

Cyclonic depression

Western disturbances

Retreating monsoon

Southwest monsoon

Ans; (b) Western disturbances

Q 4 . Monsoon arrives in India approximately in:

Early May

Early June

Early July

Early August

Ans: (b) Early June

Q 5. Which one of the following characterizes the cold weather season in India?

Warm days and warm nights

Warm days and cold nights

Cool days and cold nights

Cold days and warm nights

Ans: (c) Cool days and cold nights

Q 6 . What are the controls affecting the climate of India?

Ans: Latitude, Altitude and Pressure and Winds are the main factors which affect the climate of India.

Q 7 .Why does India have a monsoon type of climate?

Answer: India comes in the Inter Tropical Convergence Zone (ITCZ). This fact; in association with various other factors, like the El Nino, Jet Stream and Coriolois Force are the reasons for monsoon type of climate in India.

Q 8. Which part of India does experience the highest diurnal range of temperature and why?

Ans: Northwestern part of India experiences the highest diurnal range of temperature. This happens because of the presence of the Thar Desert and also because this region does not have the moderating influence of the ocean.

Q 9. Which winds account for rainfall along the Malabar Coast?

Ans: Monsoon winds

Q10 .What are Jet streams and how do they affect the climate of India?

Answer: Fast flowing and narrow air currents are called jet streams.

The streams flow at high altitudes (about 12,000 feet) in the troposphere.

The westerly jet streams are responsible for western cyclonic disturbances in the north and north-western parts of India.

The subtropical westerly jet stream moves north of the Himalayas with the apparent movement of the sun.

The tropical jet stream (an easterly jet stream) blows over the Indian Peninsula; approximately over 14° north during the summer months.

Q11. Define monsoons. What do you understand by “break” in monsoon?

Ans: The seasonal reversal in wind direction during a year is called monsoon. Monsoon tends to have ‘breaks’ in rainfall; which means that there are wet and dry spells in between. The monsoon rains take place only for a few days at a time and then come the rainless intervals.

Q12 .Why is the monsoon considered a unifying bond?

Answer: Although there are wide variations in weather patterns across India, the monsoon brings some unifying influences on India. The Indian landscape, its flora and fauna, etc. are highly influenced by the monsoon. The entire agricultural calendar in India is governed by the monsoon. Most of the festivals in India are related to agricultural cycle. These festivals may be known by different names in different parts of the country, but their celebration is decided by the monsoon. It is also said that the river valleys which carry the rainwater also unite as a single river valley unit. Due to these reasons, monsoon is often a great unifying factor in India.

Q 13.Why does the rainfall decrease from the east to the west in Northern India?

Ans: The Bay of Bengal branch of the monsoon winds moves towards northeast and return westwards covering the northern plains.

While they move towards west, their moisture contains tends to reduce with subsequent rains.

Hence the rainfall decreases from east to west in northern India.

Q14.Give reasons as to why

(a)Seasonal reversal of wind direction takes place over the Indian subcontinent?

Ans: Seasonal reversal of wind direction over the Indian subcontinent takes place due to pressure differential. El Nino has major role to play in the seasonal reversal of wind direction over the Indian subcontinent.

(b)The bulk of rainfall in India is concentrated over a few months.

Ans: The monsoon begins from the first week of June and advances quite rapidly to cover almost the whole country by mid-July. Hence, the bulk of rainfall in India is concentrated over the months of a few months; mainly June to August.

(c)The Tamil Nadu coast receives winter rainfall.

Ans: The Tami Nadu coast receives winter rainfall because of movement of low-pressure conditions to the Bay of Bengal.

(d)The delta region of the eastern coast is frequently struck by cyclones.

Ans: The Bay of Bengal is the centre of various pressure changes and hence there is always a chance of development of cyclone. Due to this, the delta region of the eastern coast is frequently struck by cyclones.

(e) Parts of Rajasthan, Gujarat and the leeward side of the Western Ghats are drought-prone.

Ans: The parts fall in the rain shadow area of the Aravalli. Hence, they are drought prone.

Q15. Describe the regional variations in the climatic conditions of India with the help of suitable examples.

Ans: Indian Peninsular shows wide variations in climatic conditions across various regions. For example; during winter season, the temperature goes into negative in the Himalayan region.

In the northwestern India, temperatures can range between zero degree to 15°C during winter.

During the same season, the temperature in Chennai remains a comfortable 25°C. The same variation can be seen in summer as well, while the temperature in Rajasthan can hover around 47°C, it is a comfortable 30°C in Chennai.

Q 16. Discuss the mechanism of monsoons.

Ans: The low-pressure condition over the northern plains intensifies by the beginning of June.

It attracts the trade winds from the southern hemisphere.

These south-east trade winds cross the equator and blow in a south-westerly direction to enter the Indian peninsula as the south-west monsoon.

These winds bring abundant moisture to the subcontinent.

Q17. Give an account of weather conditions and characteristics of the cold season.

Ans: The temperature ranges between 10°-15°C in the northern plains.

The weather is usually marked by clear sky, low temperatures and low humidity and feeble variable winds.

The inflow of the cyclonic disturbances from the west and the northwest is a characteristic feature of the cold weather over the northern plains.

These low-pressure systems originate over the Mediterranean Sea and Western Asia and move into India. They cause winter rains over the plains and snowfall in the mountains.

Q 18. Give the characteristics and effects of the monsoon rainfall in India.

Ans: Monsoon tends to have ‘breaks’ in rainfall; which means that there are wet and dry spells in between. The monsoon is famous for its uncertainties. It may cause heavy floods in one part of the country, and may be responsible for droughts in other part. Because of its uncertain behaviour, it sometimes disturbs the farming schedule in India. This affects millions of farmers all over the country.