Chapter 4 - Climate

In this chapter, you will learn about the atmospheric conditions of India. By going through Vidyakul CBSE Notes Class 9 Geography Chapter 4 on Climate, you will get the answers to many questions such as ‘Why do we wear woolens in December’ or ‘Why is it hot and uncomfortable in the month of May’ and ‘Why it rains in June – July?’ 

Climate

Climate refers to the sum total of weather conditions and variations over a large area for a long period of time (more than thirty years).

Weather refers to the state of the atmosphere over an area at any point in time.

The elements of weather and climate are the same, i.e. temperature, atmospheric pressure, wind, humidity, and precipitation. On the basis of the monthly atmospheric conditions, the year is divided into seasons such as:

Winter

Summer

Rainy Seasons

Climatic Controls

The climate of any place depends on the following factors:

1) Latitude

The amount of solar energy received varies according to latitude due to the curvature of the earth. That’s why air temperature generally decreases from the equator towards the poles.

2) Altitude

The atmosphere becomes less dense and temperature decreases when we go to a higher altitude from the earth's surface. This is the reason why hills are cooler during summer.

3) Pressure and wind system

The pressure and wind system of any area depends on the latitude and altitude of the place. It influences the temperature and rainfall pattern.

4) Distance from the sea

The sea exerts a moderating influence on the climate. As the distance from the sea increases, its moderating influence decreases and people experience extreme weather conditions. This condition is known as continentality i.e. very hot during summers and very cold during winters.

5) Ocean currents

Ocean currents along with onshore winds affect the climate of the coastal areas. For example, any coastal area with warm or cold currents flowing past it will be warmed or cooled if the winds are onshore.

6) Relief features

Relief plays a major role in determining the climate of a place. High mountains act as barriers to cold or hot winds. They may also cause precipitation if they are high enough and lie in the path of rain-bearing winds. Precipitation is any form of moisture that falls to the earth. It includes rain, snow, hail, and sleet.

Factors Affecting India’s Climate

Latitude

The Tropic of Cancer passes through the middle of the country from the Rann of Kachchh in the west to Mizoram in the east. India’s climate has characteristics of tropical as well as subtropical climates.

Altitude

India has mountains to the north and also has a vast coastal area where the maximum elevation is about 30 meters. Owing to the mountains, the subcontinent experiences comparatively milder winters as compared to central Asia.

Pressure and Winds

The climate and weather conditions in India are governed by the following atmospheric conditions:

Pressure and surface winds

Upper air circulation

Western cyclonic disturbances and tropical cyclones

Air moves from the high-pressure area over the southern Indian Ocean, in a south-easterly direction, crosses the equator and turns right towards the low-pressure areas over the Indian subcontinent. These are known as the Southwest Monsoon winds. These winds blow over the warm oceans, gather moisture and bring widespread rainfall over the territories of India.

Jet streams are fast-flowing, narrow, meandering air currents in the atmosphere.

The Indian Monsoon

The climate of India is strongly influenced by monsoon winds. The seasonal reversal of the wind system is known as a “monsoon”. The monsoons are experienced in the tropical area roughly between 20° N and 20° S. Go through the following facts to understand the mechanism of the monsoons in a better way:

The differential heating and cooling of land and water create a low pressure on the landmass of India while the seas around experience comparatively high pressure.

The shift of the position of the Inter-Tropical Convergence Zone (ITCZ) in summer, over the Ganga plain, is also known as the monsoon trough during the monsoon season.

The presence of the high-pressure area, east of Madagascar, approximately 20°S over the Indian Ocean affects the Indian Monsoon.

The Tibetan plateau gets intensely heated during summer, which results in strong vertical air currents and the formation of low pressure over the plateau at about 9 km above sea level.

The movement of the westerly jet stream to the north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula during summer also impact the Indian Monsoon.

The changes in the pressure conditions over the southern oceans also affect the monsoons. The irregularly periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean that affects the climate of the tropics and subtropics is known as Southern Oscillation or SO.

The Onset of the Monsoon and Withdrawal

The duration of the monsoon is between 100-120 days from early June to mid-September. Around the time of its arrival, the normal rainfall increases suddenly and continues constantly for several days, which is known as the “burst” of the monsoon.

The arrival of the Monsoon in different parts of India

The monsoon arrives at the southern tip of the Indian peninsula generally by the 1st week of June. Subsequently, it proceeds into two – the Arabian Sea branch and the Bay of Bengal branch.

The Arabian Sea branch reaches Mumbai on approximately the 10th of June.

The Bay of Bengal branch arrives in Assam in the 1st week of June.

By mid-June, the Arabian Sea branch of the monsoon arrives over Saurashtra-Kuchchh and the central part of the country.

The Arabian Sea and the Bay of Bengal branches of the monsoon merge over the northwestern part of the Ganga plains.

Delhi receives the monsoon showers from the Bay of Bengal branch by the end of June.

By the first week of July, western Uttar Pradesh, Punjab, Haryana, and eastern Rajasthan experience the monsoon.

By mid-July, the monsoon reaches Himachal Pradesh and the rest of the country.

Withdrawal of the Monsoon

The withdrawal of the monsoon begins in the northwestern states of India by early September. By mid-October, it withdraws completely from the northern half of the peninsula. From north to south, the withdrawal of monsoon takes place from the first week of December to the first week of January. By early December, the monsoon has withdrawn from the rest of the country.

The Seasons

4 main seasons can be identified in India:

The cold weather season (Winter)

The hot weather season (Summer)

The advancing monsoon (Rainy Season)

The retreating monsoon with some regional variations (Transition Season)

Let’s discuss each of them in detail:

The Cold Weather Season (Winter)

Winter begins in mid-November in northern India and stays till February.

December and January are the coldest months in the northern part of India.

The temperature decreases from the south to the north.

Days are warm and nights are cold.

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

This season is extremely important for the cultivation of ‘rabi’ crops.

The Hot Weather Season (Summer)

From March to May, the hot weather season is observed in India. The summer months experience rising temperatures and falling air pressure in the northern part of the country. A striking feature of the hot weather season is the ‘loo’. Loo is the strong, gusty, hot, dry winds blowing during the day over north and northwestern India.

Towards the close of the summer season, pre-monsoon showers come which help in the early ripening of mangoes, and are often referred to as ‘mango showers’.

Advancing Monsoon (The Rainy Season)

South-east trade winds originate over the warm subtropical areas of the southern oceans. They cross the equator and blow in a southwesterly direction entering the Indian peninsula as the southwest monsoon. The monsoon winds cover the country for about a month. Mawsynram in the southern ranges of the Khasi Hills receives the highest average rainfall in the world.

A phenomenon associated with the monsoon is its tendency to have ‘breaks’ in rainfall. These breaks in monsoon are related to the movement of the monsoon trough. The trough and its axis keep on moving northward or southward and determine the spatial distribution of rainfall. The frequency and intensity of tropical depressions also determine the amount and duration of monsoon rains. The monsoon is known for its uncertainties. The alternation of dry and wet spells varies in intensity, frequency, and duration.

Retreating/Post Monsoons (The Transition Season)

The months of October-November form a period of transition from the hot rainy season to dry winter conditions. The retreat of the monsoon is marked by clear skies and a 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 commonly known as ‘October heat’. In the second half of October, the mercury begins to fall rapidly in northern India.

Distribution of Rainfall

Parts of the western coast and northeastern India receive over about 400 cm of rainfall annually.

Rainfall is less than 60 cm in western Rajasthan and adjoining parts of Gujarat, Haryana, and Punjab.

Rainfall is low in the interior of the Deccan plateau, and east of the Sahyadris.

Snowfall is restricted to the Himalayan region.

The annual rainfall is highly variable from year to year.

Monsoon as a Unifying Bond

The unifying influence of the monsoon on the Indian subcontinent is quite noticeable. The seasonal alteration of the wind systems and the associated weather conditions provide a rhythmic cycle of seasons. The uncertainties of rain and uneven distribution are very much typical of monsoons. Year after year, the 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 agricultural activities in motion.

Exercise

1. Choose the correct answer from the four alternatives given below.

(i) Which one of the following places receives the highest rainfall in the world?

(a) Silchar

(b) Mawsynram

(c) Cherrapunji

(d) Guwahati

Answer: Mawsynram

(ii) The wind blowing in the northern plains in summer is known as

(a) Kaal Baisakhi

(b) Loo

(c) Trade Winds

(d) None of the above

Answer: Loo

(iii) Which one of the following causes rainfall during winters in the northwestern part of India?

(a) Cyclonic depression

(b) Retreating monsoon

(c) Western disturbances

(d) Southwest monsoon

Answer: Western disturbances

(iv) Monsoon arrives in India approximately in

(a) Early May

(b) Early July

(c) Early June

(d) Early August

Answer: Early June

(v) Which one of the following characterizes the cold-weather season in India?

(a) Warm days and warm nights

(b) Warm days and cold nights

(c) Cool days and cold nights

(d) Cold days and warm nights

Answer: Warm days and cold nights.

2. Answer the following questions briefly.

(i) What are the factors affecting the climate of India?

Answer: The factors affecting the climate of India are

1. Latitude

2. Altitude

3. Pressure and Winds

(ii) Why does India have a monsoon-type of climate?

Answer: The climate of India is described as the ‘monsoon’ type. Monsoon refers to the seasonal reversal in the wind direction during a year.

The monsoon type of climate is characterized by a distinct seasonal pattern. The weather conditions greatly change from one season to the other. These changes are particularly noticeable in the interior parts of the country. The coastal areas do not experience much variation in temperature, though there is variation in the rainfall pattern.

Four main seasons can be identified in India – the cold weather season, the hot weather season, the advancing monsoon, and the retreating monsoon with some regional variations.

The climate of India is strongly influenced by monsoon winds. The duration of the monsoon is between 100-120 days from early June to mid-September.

(iii) Which part of India does experience the highest diurnal range of temperature and why?

Answer: The regions experiencing this phenomenon are in the northwestern part of India. The reason behind this effect is the Thar desert. Moreover, this region does not have an ocean to moderate the temperature.

(iv) Which winds account for rainfall along the Malabar Coast?

Answer: Southwest monsoon winds are responsible for rainfall along the Malabar Coast.

(v) What are Jet streams, and how do they affect the climate of India?

Answer: Jet Streams are a narrow belt of high altitude (above 12,000 m) westerly winds in the troposphere. Their speed varies from about 110 km/h in summer to about 184 km/h in winter. A number of separate jet streams have been identified. The most constant is the mid-latitude and subtropical jet stream. They cause depression during the monsoon season.

(vi) Define monsoons. What do you understand by “break” in monsoon?

Answer: Breaks in monsoon are related to the movement of the monsoon trough. For various reasons, the trough and its axis keep on moving northward or southward, which determines the spatial distribution of rainfall. When the axis of the monsoon trough lies over the plains, rainfall is good in these parts. On the other hand, whenever the axis shifts closer to the Himalayas, there are longer dry spells in the plains, and widespread rain occurs in the mountainous catchment areas of the Himalayan rivers.

(vii) Why is the monsoon considered a unifying bond?

Answer: 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 monsoons. The Indian landscape, its animal and plant life, its entire agricultural calendar, and the life of the people (including their festivities) revolve around this phenomenon. Year after year, the 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 agricultural activities in motion. The river valleys which carry this water also unite as a single river valley unit.

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

Answer: As they move in that direction, the winds lose the moisture content. Hence, the reason for the reduction in rainfall.

4. Give reasons as to why.

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

Answer:

1. Seasonal change in wind direction due to pressure difference.

2. El Nino plays a major role.

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

Answer: Rainfall is dependent on the South West Monsoon winds; it rapidly progresses and covers large swathes of the country by July.

(iii) The Tamil Nadu coast receives winter rainfall.

Answer: It is because of North-East monsoon winds.

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

Answer: The Bay of Bengal faces frequent pressure changes.

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

Answer: Because they fall in the rain shadow region of the Aravali Mountains.

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

Answer:

The cold weather season begins in mid-November in northern India and stays till February. December and January are the coldest months in the northern part of India. The temperature decreases from south to north. The average temperature of Chennai, on the eastern coast, is between 24°-25° Celsius, while in the northern plains, it ranges between 10°C and 15° Celsius. Days are warm, and nights are cold. Frost is common in the north, and the higher slopes of the Himalayas experience snowfall.

In March, the highest temperature is about 38° Celsius, recorded on the Deccan plateau. In April, temperatures in Gujarat and Madhya Pradesh are around 42° Celsius. In May, the temperature of 45° Celsius is common in the northwestern parts of the country. In peninsular India, temperatures remain lower due to the moderating influence of the oceans.

6. Discuss the mechanisms of the monsoon.

Answer: 

(a) The differential heating and cooling of land and water create a low pressure on the landmass of India while the seas around experience comparatively high pressure. 

(b) The shift of the position of Inter Tropical Convergence Zone (ITCZ) in summer over the Ganga Plain. (This is the equatorial trough, normally positioned about 5°N of the equator. It is also known as the monsoon trough during the monsoon season.)

(c) The presence of the high-pressure area, east of Madagascar, approximately at 20°S over the Indian Ocean. The intensity and position of this high-pressure area affect the Indian Monsoon. 

(d) The Tibetan Plateau gets intensely heated during summer, which results in strong vertical air currents and the formation of low pressure over the plateau at about 9 km above sea level. 

(e) The movement of the westerly jet stream to the north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula during summer.

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

Answer: The cold weather season begins in mid-November in northern India and stays till February. December and January are the coldest months in the northern part of India. The temperature decreases as we go from the south to the north. The average temperature in Chennai, on the eastern coast, is between 24°-25° Celsius. At the same time, in the northern plains, it ranges between 10°C and 15° Celsius. Here, the days are warm, and the nights are cold. Frost is common in the north, and the higher slopes of the Himalayas experience snowfall. During this season, the northeast trade winds prevail over the country. They blow from land to sea, and hence, for the most part of the country, it is a dry season. Some amount of rainfall occurs on the Tamil Nadu coast from these winds as here they blow from sea to land. In the northern part of the country, a feeble high-pressure region develops, with light winds moving outwards from this area. Influenced by the relief, these winds blow through the Ganga Valley from the west and the northwest. The weather is normally marked by clear sky, low temperatures and low humidity, and feeble, variable winds. A characteristic feature of the cold weather season over the northern plains is the inflow of cyclonic disturbances from the west and the northwest. These low-pressure systems originate over the Mediterranean Sea and western Asia and move into India along with the westerly flow. They cause much-needed winter rains over the plains and snowfall in the mountains. Although the total amount of winter rainfall (locally known as ‘Mahawat’) is small, they are of immense importance for the cultivation of ‘rabi’ crops. The peninsular region does not have a well-defined cold season. There is hardly any noticeable seasonal change in temperature patterns during winters due to the moderating influence of the sea.

8. Give the characteristics and effects of the monsoon rainfall in India.

Answer: The Monsoon, unlike the trades, is not a steady wind but is pulsating in nature, affected by different atmospheric conditions encountered by it on its way over the warm tropical seas. The duration of the monsoon is between 100-120 days from early June to mid-September. Around the time of its arrival, the normal rainfall increases suddenly and constantly continues for several days. This is known as the ‘burst’ of the monsoon and can be distinguished from the pre-monsoon showers. The monsoon arrives at the southern tip of the Indian peninsula, generally by the first week of June. Subsequently, it proceeds into two: the Arabian Sea branch and the Bay of Bengal branch. The Arabian Sea branch reaches Mumbai about ten days later on approximately the 10th of June. This is a fairly rapid advance. The Bay of Bengal branch also advances rapidly and arrives in Assam in the first week of June. The lofty mountains cause the monsoon winds to deflect towards the west over the Ganga Plains. By mid-June, the Arabian Sea branch of the monsoon arrives over Saurashtra-Kachchh and the central part of the country. The Arabian Sea and the Bay of Bengal branches of the monsoon merge over the northwestern part of the Ganga Plains. Delhi generally receives the monsoon showers from the Bay of Bengal branch by the end of June (tentative date is 29th of June). By the first week of July, western Uttar Pradesh, Punjab, Haryana, and eastern Rajasthan experience the monsoon. By mid-July, the monsoon reaches Himachal Pradesh and the rest of the country.

Frequently Asked Questions 

What is an ocean current?

An ocean current is a continuous movement of ocean water from one place to another.

What are the types of wind zones of the Earth?

The Earth contains five major wind zones: polar easterlies, westerlies, horse latitudes, trade winds, and doldrums.

What is differential heating?

Differential heating is the disparity in heating of air over land versus water