CBSE Class 9 Social Science Climate Chapter Notes

CLIMATE

WEATHER AND CLIMATE

(a) India has Diverse Climatic Conditions:

We can take two important elements-temperature and precipitation, and examine how they vary from place to place and season to season.

Temperature –

(i) In summer, the mercury occasionally touches 50^o C in some parts of the Rajasthan desert, whereas it may be around 20^o C in Pahalgam in Jammu and Kashmir. On a winter night, temperature at Drass in Jammu and Kashmir may be as low minus 45^o C. Tiruvananthpuram, on the other hand, may have a temperature of 20^o C.

(ii)In certain places there is a wide difference between day and night temperatures. In the Thar Desert the day temperature may rise to 50^o C, and drop down to near 15^o C the same night. On the other hand, there is hardly any difference in day and night temperatures in the Andaman and Nicobar islands or in Kerala. 

Precipitation –

There are variations not only in the form and types of precipitation but also in its amount and the seasonal distribution.

(i)While precipitation is mostly in the form of snowfall in the upper parts of Himalayas, it rains over the rest of the country.

(ii)The annual precipitation varies fro over 400 cm in Meghalaya to less than 10 cm in Ladakh and western Rajasthan.

(iii) Most parts of the country receive rainfall from June to September. But some parts like the Tamil Nadu coast get most of its rain during October and November.Coastal areas experience less contrast in temperature conditions, seasonal contrast are more in the interior of the country.

CLIMATIC CONTROLS

The climate of a place is determined by the interplay of various factors such as location, altitude, distance from the sea, pressure and winds and upper air circulation. 

(i) Due to the curvature of the earth, the amount of solar energy received varies according to latitude. As a result, air temperature decreases from the equator towards the poles.

(ii) As one goes from the surface of the earth to higher to higher altitudes, the atmosphere becomes less dense and temperature decreases. The hills are therefore cooler during summers.

(iii) The pressure and wind system any area depend on the latitude and altitude of the place. Thus it       influences the temperature and rainfall pattern.

(iv) The sea exerts a moderating influences on climate: As the distance form the sea increases, its moderating influence decreases and the people experience extreme weather conditions. This condition is known as continentality.

(v) Ocean currents along with onshore winds affect the climate of the coastal areas.

(vi) Relief too plays a major role in determining the climate of a place. High mountains act as barriers for cold or not winds; they may also cause precipitation if they are high enough and lie in the path of rain-bearing winds. The leeward side of mountains remains dry.

FACTORS AFFECTING INDIA’S CLIMATE

(a) Latitude:

Indian is situated roughly between 8^o N and  37^o N latitudes. India is divided in almost two equal parts by the tropic of cancer. The southern half lies in the tropical zone and the western half in the subtropical zone. Therefore, India’s climate has characteristics of tropical as well as subtropical climates.

(b) Altitude:

India has mountains to the north, which have an average height of about 6000 meters. The Himalayas prevent the cold winds from Central Asia from entering the subcontinent. It is because of these mountains that this subcontinent experiences comparatively milder winters as compared to Central Asia.

(c) Pressure and Winds:

India lies in the subtropical high pressure belt, thus, the winds originate from the land and move outwards towards the equatorial low pressure belt. These winds are known as northeast trade winds and are devoid of any moisture. But due to unequal heating of land and water in the summer, a low pressure develops over the interior of land masses. This low pressure attracts the winds from south of the equator. After crossing the equator the southeast trade winds get deflected and are known as southwest monsoons. The climate of India is also affected by jet streams. This is a fast flowing wind blowing in a narrow zone in the upper atmosphere. The jet streams are responsible for sudden outbreak of monsoons in Northern India. a subtropical westerly jet stream bring in the western disturbances in winter. These disturbances cause heavy snowfall on the mountains and light rains on the northwestern part of India.

THE INDIAN MONSOON

The climate of India is strongly influenced by monsoon winds. the Arabs, who had come to India as traders benefited from the reversal of the wind system as they came by sailing ships at the mercy of winds, they named this seasonal reversal of the wind system ‘monsoon’.

The monsoons are experienced in the tropical area roughly between 20^o N 20^o S. to understand the mechanism of the monsoons, the following facts are important.

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

(ii)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^o N of the equator – also known as the monsoon-trough during the monsoon season).

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

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

(v)   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. 

Changes in the pressure conditions over the southern oceans also affect the monsoons. Normally when the tropical eastern south Pacific Ocean experiences high pressure, the tropical eastern Indian Ocean experiences low pressure. The difference in pressure over Tahiti (Pacific Ocean, 18^o S/149^o W) and Darwin in northern Australia (Indian Ocean, 12^o 30’S/ 131^oE) is computed to predict the intensity of the monsoons. if the pressure differences are negative, it means below average and late monsoons.

THE MONSET OF THE MONSOON AND WITHDRAWAL

The Monsoon, unlike the trades, are not steady winds but are 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. The monsoon arrives at the southern tip of the Indian peninsula generally by the first week of June. Subsequently, it divides in to two – the Arabian Sea branch and the Bay of Bengal branch.The Arabian Sea branch reaches Mumbai about ten days later on approximately the 10^th of June. The Bay of Bengal branch arrives is Assam in the first week of June. The lofty mountain s 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-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 generally 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 or the retreat of the monsoon is a more gradual process. The withdrawal of the monsoon begins in northwestern states of India by early September. By mid-October, it withdraws completely from the northern half of the peninsula. The withdrawal from the southern half of the peninsula is fairly rapid. By early December, the monsoon has withdrawn from the rest of the country.

THE SEASONS

Four main seasons can be identified in India –

(i)    Cold weather season                                            --                                 December to February

(ii)   Hot weather season                                             --                                 March to May

(iii)  Advancing monsoon season                            --                                 June to September

(iv)  Retreating monsoon season                              --                                 October and November

(A) The Cold Weather Season (Winter):

(i) The cold weather season begins from mid-November in India and stays till February.

(ii) December and January are the coldest months in the northem part of India. The temperature decreases as one moves from south to the north.

(iii) Days are warm and the nights are cold. Frost is common in the north and the higher slopes of the Himalayas experience snowfall.

(iv) The northeast trade \winds prevail over the country. They blow from land to sea and hence, for most part of the country, it is a dry season.

(v) In the northern part of the country, a feeble high-pressure region develops, with light winds moving outwards from this area.

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

(vii) 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 the much-needed winter rains over the plains and snowfall in the mountains. Locally known as ‘mahawat’ are of immense importance for the cultivation of ‘rabi’ crops.

(viii) The northeast trade winds cause fair amount of rainfall in Chennai or the Coromandel Cast in winter.

(b) Hot weather season (Summer):

(i) Due to the apparent movement of the sun, the global heat belt shifts northward. as such, from March to May, it is not weather season in India.

(ii) Temperature increases from south to north. In peninsular India, temperatures remain lower

(iii) High temperature between 38^o C and 48^o C in the plains.

(iv) Local dust storms accompanied with light rains.

(v) Hot dry winds, ‘loo’is common in May and June.

(vi) Kerala and Kamataka coast receivers pre-monsoon showers. (Mango showers)

(vii) West Bengal and Assam are affected by northwesterly winds. (Kalbaisakhi).

(c) Advancing Monsoon (The Rainy Season):

The climate of India is described as of monsoon type. Derived from an Arabic word ‘mausim’, monsoons refer to the seasonal reversal in the wind direction through the year.

Mechanism of the Monsoon:

The word monsoon denotes a season in which the wind regime is completely reversed. The southeast winds, after crossing the equator in the Indian Ocean, take a southwesterly direction. The dry and hot land bearing trades are thus completely replaced by sea bearing winds full of moisture. This phenomenon of complete reversal of winds is confined to tropical lands lying between 20^o N and 20^o S. this phenomenon account for 75 to 90 percent of the annual rainfall just from June to September

Characteristics of the Monsoon:

(i) Almost all over the country, the rains occur from June to September.

(ii) 75% to 90% of the total annual rainfall is concentrated over this period.

(iii) There is great variation in the advance and withdrawal dates of the monsoons.

(iv) The monsoons occur in wet spell, interspersed by dry spells.

(v) The amount of rainfall also varies, causing floods and drought conditions.

 “Distribution of rainfall received from the southwest monsoons is governed mainly by the relief of the country.”

(i) The windward side of the Western Ghats receives a rainfall of over 250 cm. On other hand, the leeward side of the Western Ghats receives less than 50cm.

(ii) The heavy rainfall in the northeastern states can be attributed to the hill and mountain ranges.

(iii) Rainfall in the Northern Plains decreases westward.

Breaks in monsoons are related to the frequency and intensity of tropical depressions. They are formed at the head of the Bay of Bengal and cross over the mainland. The depressions follow the axis of the monsoon trough of the low pressure. 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 rains in the mountainous catchment area of the Himalayan Rivers.

 “Rainfall decreases from east to west in the Northern Plains while it increases in the Peninsular India”.

Pattern of Rainfall in the Northern Plains:

(i) The Northern Plains get much of their rainfall by Southwest Monsoons which strike the eastern part of the country first and give heavy rainfall there. so eastern parts of the country like Assam, Meghalaya, Bengal etc. get much rainfall.

(ii) Then the monsoons arising from the Bay of Bengal move westwards along the Himalayas. their capacity to cause rain become lesser and lesser as they move westward because they continue to become drier and drier.

Pattern of Rainfall in Peninsular India:

(i) The Peninsular India also gets much rainfall because of another branch of the South-West Monsoons which rises from the Arabian Sea. These monsoon winds first of all strike the Western Ghats and cause mu8ch rain there.

(ii) These winds while reaching the other side of the Western Ghats become dry and cause less rain. As they go on moving to the eastern side they become drier and drier and so the rain goes decreasing from west to east.

Mumbai receives rainfall in summer while Chennai has in Winter :

Mumbai receives more rainfall in summer as it is situated on the Arabian Sea coast, and receives all its rains from the Arabian Sea branch of the southwest monsoons from June to September only. Chennai receives two-third of the rainfall from the retreating southwest monsoons aided by cyclones on October to December.        

Western Rajasthan has desert type of climate:

(i) Western Rajasthan lies in the rain shadow areas of the Aravalli Mountains. (Leeward side).

(ii)  Arabian sea branch of S.W. monsoons blows parallel to the Aravalli range; hence the Aravallis fail to check it.

(ii)  By the time the Bay Bengal branch reaches here it is almost dry, moreover it lies on the leeward side of the Aravallis.

(iii) Monsoon winds become warmer and increase their capacity to hold moisture instead of causing rain.

(D) Retreating Monsoons:

During October-November, the monsoon trough of low pressure becomes weaker and is gradually replaced by high pressure. The outreach of te monsoon becomes unsustainable and it starts withdrawing gradually. this is known as the retreat of monsoon.

October Heat:

(i) The retreat of the monsoons is marked by clear skies and rise in temperature.

(ii) The land is still moist.

(iii) Owing to the conditions of high temperature and humidity, the weather become oppressive, which is known as October heat in northern India.

Cyclonic Depressions which originate over the Andaman Sea:

In October and November the shift of the low pressure from land to sea is far from smooth. the period is associated with occurrence of cyclonic depressions which  originate over the Andaman Sea.

The cyclones affect the eastern coasts of southern peninsular.

The cyclones affect the Sundarban Delta, Mahanadi, Godavari, Krishna and Kaveri deltas too.

These tropical cyclones cause heavy and widespread rain.

One adverse effect of the cyclones is, it is very often destructive. No year is found disaster free, it affects one or the other deltas of the Eastern Coast.

VARIETIES THE MONSOONS IN INDIA

At times the monsoons come in full swing, or it may fail altogether. Thus, causing the twin problems of floods and famines.

The alternation of dry and wet spells keeps on varying in intensity, frequency and the in duration.

Implications of vagaries of the monsoons:

(i) Due to the late arrival the crops dry up.

(ii)Due to excessive rains floods are caused, leading to destruction.

(iii) The amount of rain may vary causing drought conditions.

(iv) Sometimes the monsoons come early, normal or late.

(iv) The monsoons may retreat early, normal or late.

DISTRIBUTION OF PRECIPITATION IN THE COUNTRY

Areas of Heavy rainfall: Areas which get rainfall of 200 cms and above are Assam, the Ganga Delta, the Western Ghats and the Western Coastal regions and the mountainous regions of Himachal Pradesh.

areas of Moderate Rainfall: Areas which get annual rainfall between 100 cms to 200 cms are Madhya Pradesh, Orissa, Chhota Nagpur, Western Bengal, Bihar, Eastern U.P , North-Eastern Punjab; Eastern parts of Tamil Nadu and Eastern slopes of Western Ghats receive moderate rainfall.

Areas with Low Rainfall: Areas receiving annual rainfall between 50 cms to 100 cms are the Deccan Plateau, Western U.P, South-Eastern Punjab, Eastern Rajasthan and parts of Kashmir get low rainfall.

Areas with Scanty Rainfall: Areas which get less than 50 cms rainfall annually are western Rajasthan, Kutch, Southeastern parts of Haryana, Northeastern Kashmir get scanty rainfall.

                                                   Figure : Seasonal Rainfall (June-September)

Consequences of the Uneven Precipitation in India :

(i)  If there is too much rain in certain areas they cause floods and havoc all around. many grown up crops,villages, railway lines are washed away resulting in great loss of men and money.

(ii) If there are not sufficient rains even then people are doomed because of drought and hunger. Many people begin to starve and die of hunger. Standing crops dry away thereby bringing doom to the farmers.

Uneven distribution rainfall is due to:

(A) Relief / Orography                      (B) Wind direction

(C) Location                                      (D) Low pressure axis.

Relief / orography largely govern the distribution of rainfall. For instance, the windward side of the Western Ghats registers a rainfall of 250cms. on the other hand, the leeward side of this ghat is hardly able to receive 50cms.

Again, the heavy rainfall in the northwestern states can be attributed to their hilly ranges and the eastern Himalayas.

Western Rajasthan gets scanty rain because the Arabian Sea branch of the monsoon blows parallel to the Aravallis.

Rainfall in the north decreases from east to west. Kolkata situated near the sea receive about 120 cm, Patna 102cm, Allahabad 91cm, and Delhi 56 cm.

 MONSOON AS A UNIFYING BOND

(i)There is great diversity in the climatic conditions due to location, extent and relief features.

(ii) But these diversities are subdued by the monsoons, which prevails over the whole country.

(iii) This water scarcity is felt all over country.

(iv)Thus the arrival of the monsoon is most welcome; it changes the Indian landscape, gives impetus to agricultural activities, the total life of the Indian people revolves around the monsoons, including festivals.

 IMPORTANT POINTS TO REMEMBER

(a) Mango showers:

(i) Mango showers are pre-monsoon showers.

(ii)This phenomenon is observed in Kerala and coastal Kamataka.

(iii) The mango showers help in the early ripening of, mangoes.

(b) Kalbaisakhi:

Kalbaisakhi means the violent black clouds of the month of Baisakh. This is the name given to the north-westerly and northerly winds in Bengal and Assam. These winds cause very heavy rains and distraction.

(c) Chennai receives more rain in winter:

(i)  The northeast winds pick up moisture while crossing Bay of Bengal. these winds are onshore in the winter season.

(ii) In the summer Chennai lies in the rain-shadow of the Western Ghats, moreover the winds are offshore, therefore receives less rainfall.

(d) Break or burst of the monsoon:

The sudden approach of the moisture laden winds is associated with violent thunder and lightening. This is known as “break” or “burst” of the monsoons. The first ‘break’ of monsoons on the south-west-coast of India is around 1^st June.

(e) Southern Oscillation:

The pressure systems of Pacific and Indian Oceans are interrelated. When the pressure is high in the pacific, there is low pressure in the Indian Ocean. The winds move from high pressure to low pressure and vice-versa. This causes shifting of winds across the equator in different seasons. this is known as the southern oscillation.

(f) EI Nino Southern Oscillations :

A feature connected with Southern Oscillation is the EI Nino, a warm ocean current that flows past the Peruvian Coast, in place of the cold Peruvian current, every 2 to 5 years. the changes in pressure conditions are connected to the EI Nino, the phenomenon is referred to as ENSO (EI Nino Southern Oscillations).

(g) Mawsynram receives the highest rainfall in the world:

(i)  Mawsynram is situated at the head of a funnel shaped valley in the Khasi hills.

(ii) Its unique topographical location together with wind direction is responsible for causing the heaviest rainfall in the world.

(h) The rainfall decreases from South to North :

(i)  The S.W. Monsoons originates from the Indian Ocean and divides into branches due to the shape of the Indian peninsular.

(ii) Trivandrum gets above 200 cm. 

(iii) Whereas Delhi situated in the interior gets only about 50 cm.

(iv) The Arabian Sea branch strikes the Western Ghats and causes heavy rainfall.

(v) Whereas another branch of the Arabian Sea monsoon blows parallel to the Aravallis. thus jodhpur gets less than 25cms of rain.

(i) The Western Ghats receive more rain from the southwest monsoons than the Eastern Ghats because:

(i) The Arabian Sea branch of the monsoon is on shore.

(ii) These winds are forced to rise and cause heavy rains.

(iii) By the time these winds reach the east coast, most of the moisture is lost.

(iv) The winds are offshore, so they given less rain.

(v) Eastern Ghats lies on the leeward/rain-shadow area, hence it gets less rain.

(j) Indian would have been an arid land or desert if there had been no phenomena of monsoons :

(i) Indian receives 75 to 90% of the rainfall from the monsoons.

(ii) These monsoons winds occur due to the uneven heating of land and sea.

(iii) The mighty Himalayas check the two branches of southwest monsoons, the Arabian Sea branch and the Bay of Bengal branch. These, cover the whole of India thus preventing it from becoming a desert.

DIFFERENCE BETWEEN

Q.1. Define: climate and weather.

Ans. Weather: Weather refers to the state of the atmosphere at any point of time and space. It changes very frequently.

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

Q.2. What are the elements of climate and weather?

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

Q.3. How is the climate of India described as?

Ans. The climate of India is described as Monsoon type of climate.

Q.4. What is Continentality?

Ans. As the distance from the sea increases, people experience extreme weather conditions, i.e., very hot during summers and very cold during winters. This condition is known as Continentality.

Q.5. What is Coriolis force?

Ans. An apparent force caused by the earth’s rotation responsible for deflecting winds towards the right in the northern hemisphere and towards the left in the southern hemisphere. This is also known as Ferrel’s law. Eg. South-east winds become south-west winds.

Q.6. Why the climate of India is described both as tropical as well as sub-tropical?

Ans. The tropic of cancer passes through the middle of the country. Almost half of the country, lying south of the Tropic of Cancer belongs to the tropical area and the remaining area, north of tropics lies in sub-tropics. Therefore, climate of India has the characteristics of tropical as well as sub-tropical climate.

Q.7. What do you understand by the terms burst of monsoons and break in monsoons?

Ans. Burst of monsoons: the phenomena when the normal rainfall increases suddenly and continues constantly for several days are known as burst of the monsoons. Break in monsoons: Monsoons are interspersed with rainless intervals which are related to the movement of the monsoon trough. These wet and dry spells in the monsoons are known as break in monsoons.

Q.8. How western disturbances are important for the agriculture of India?

Ans. The western disturbances during the winters are of immense importance for the cultivation of rabi crop which is extensively done over the North-western part of the country.

Q.9. Why there is a change of season from winter to summer over the Indian landmass?

Ans. Because of the tilt ness and revolution of the earth, there occurs a change of season from winter to summer over the Indian landmass.

Q.10. What do you understand by the term ‘loo’?

Ans. Loo is the hot and dry speedy wind moving from west to east in the north plains of India during summer afternoons. It causes the temperature to increase to 45 to 500C, and cause tremendous loss to life due to extreme heat.

Q.11. How the withdrawal of monsoons happens in India?

Ans. During October-November, due to decrease in temperature conditions, the low pressure trough over the northern plains is replaced by high pressure system. Due to this, the monsoon winds start withdrawing from India.

Q.12. Why does western part of Western Ghats receives more rainfall than the eastern side?

Ans. Western Ghats act as a relief to the Arabian Sea branch of the monsoon winds. The western parts of the Western Ghats lie to the windward side for the monsoon winds and therefore, receive more rainfall than the eastern side which is the leeward side.

Q.13. Which region in India will experience highest diurnal range of temperature?

Ans. Rajasthan experience highest diurnal range of temperature. 

 [Diurnal range of temperature = max. temperature of the day – min. temperature of the day] 

 [Monthly range of temperature = max. temperature of the month – min. temp. of the month]

 [Annual range of temperature = max. temp. of the year – min. temp. of the year]

Q.14. Name the winds which cause rainfall along the Malabar Coast and Coromandal Coast.

Ans. Malabar Coast: South-west monsoon winds Coromandal Coast: North-east winds

Q.15. Define the following winds:

Ans. Kalbaisakh: kalbaisakh are locally formed thunderstorms during the summer evenings in Assam and West Bengal and cause heavy rainfall with violent winds in the adjoining areas.

Mango showers: The pre-monsoon showers occurring on the coastal regions of Kerela and Karnataka and beneficial

to the ripening of mango fruit are called Mango showers.

Q.16. Why Tiruvananthapuram has equable climate?

Ans. Because Tiruvananthapuram is located nearer to the sea therefore, it experience equable type of climate throughout the year i.e., neither too hot nor too cold.

Q.17. Why does western Rajasthan obtain scanty rainfall?

Ans. Western Rajasthan obtain scanty rainfall because the Arabian sea branch of the monsoon winds move parallel to the Aravalli range without shedding any orographic rainfall. Moreover, the high temperature in Rajasthan does not allow the winds to condense to form clouds.

Q.18. Why is it that the heaviest rainfall of the world occurs at Shillong plateau (in Mawsynram)?

Ans. The heaviest rainfall of the world occurs in Mawsynram because it is situated in funnel shaped Garo, Khasi and Jaintia hills. A part of the bay of Bengal branch of the monsoon winds gets trapped into these hills and shed all its moisture here.

Q.19. How can you say that Himalayas act as an important climatic divide for India?

Ans. The predominant land feature which divides the climates of the regions on its both sides is known as climatic divide. Himalayas act as an important climatic divide for India as:

a. They do not allow the cold winds from Central Asia to enter India.

b. Also, they do not allow the monsoon winds to cross the Indian landmass.

c. They help in shedding orographic rainfall in the northern parts of the country.

Q.20. Why is Kolkata rainier in July than in June unlike Shillong which is rainier in June than in July?

Ans. The Bay of Bengal branch of the monsoon winds move from east to west direction. Monsoon arrive India in the early month of June. Shillong being located in East is rainier in June than that of Kolkata which is to the west of Shillong.

Q.21. Why does Delhi receive more rain than Jodhpur?

Ans. Delhi gets the collective monsoon from the Arabian Sea Branch as well as Bay of Bengal branch where as Jodhpur get very scanty rainfall only from the Arabian Sea branch. Therefore, Delhi is rainier than Jodhpur.

Q.22. How is the climate of India described as? Explain it.

Ans. A. The climate of India is described as the ‘monsoon’ type.

B. monsoon is the seasonal reversal in the wind system during the year.

C. This type of climate if found mainly in South and Southeast Asia.

D. The word monsoon is derived from the Arabic word ‘mausim’ which literally means season.

Q.23.Why does the Coromandal Coast (Tamil Nadu) receives winter rainfall?

OR

Where do we experience winter monsoons and why?

Ans. Coromandal coast (Tamil Nadu) receives winter rainfall from the North-east monsoon winds. These winds blow from land to sea and therefore, are generally dry in nature. They absorb moisture passing over Bay of Bengal and cause rainfall on the Tamil Nadu coast during winter.

Q.24. What do you understand by ITCZ?

Ans. * Inter-tropical Convergence Zone or ITCZ, is a broad trough of low pressure in equatorial latitudes.

• This is the area where northeast and southeast trade winds converge.

• This convergence zone lies more or less parallel to the equator but moves northwards or southwards with the movement of the sun.

Q.25. Explain the features of “October Heat”.

Ans. Monsoon retreat is marked by clear skies and rise in temperature. Day temperatures are high, nights are cool and pleasant. Owing to the conditions of high temperature and humidity, weather becomes rather oppressive during the day. This is commonly known as ‘October Heat’.

Q.26. What is Southern Oscillation ?

Ans.* Changes in the pressure conditions over the Southern ocean also effect monsoons. Normally, when the tropical eastern South Pacific ocean experience high pressure, the tropical eastern South Indian Ocean experience low pressure.

• But, in certain years, the usually prevailing pressure conditions are reversed; it results in low pressure on the eastern pacific ocean, in comparison to the eastern Indian Ocean.

• This periodic change in pressure conditions are known as Southern Oscillation or SO.

Q.27. What is orographic rainfall? Where in India do we experience this type of rainfall?

Ans. OROGRAPHIC RAINFALL - Rainfall that occurs when moisture laden air is forced to rise over a mountain range. As the air rises, it cools. The amount of moisture that air can hold decreases with decreasing temperature. So the water vapour in the rising airstream condenses, and rain falls on the windward side of the mountain. The air descending on the leeward side contains less moisture, resulting in a rainshadow where there is little or no rain. On the western coastal plains (western side of the western ghats) we experience orographic rainfall.

Q.28. Explain the variation in terms of climate from place to place and season to season that is observed in India.

Ans. I. TEMPERATURE

(a) According to Seasons

i> In summer, temperature occasionally rises to 500C or more in some parts of Rajasthan. On the other hand, it is around 200C in Pahalgam in Jammu and Kashmir.

ii> On a winter night, temperature at Drass in Jammu and Kashmir is as low as -450C at night.

iii> On the other hand, Thiruvanthapuram experience temperature of 200C.

(b) According to Day and Night

Certain places have wide difference between day and night temperatures.

i> In Rajasthan, the day temperature rises to 500C and comes down to near freezing point the same night.

ii> On the other hand, there is hardly any difference in day and night temperatures in the Andaman and Nicobar Islands.

II. PRECIPITATION

(a) Forms and types of Precipitation

i> Precipitation is mainly in the form of snowfall in the Himalayas.

ii> It is only in the form of water droplets over the rest of the country.

(b) Annual Variations in Rainfall

i> Annual precipitation varies from over 400 cm in Meghalaya to less than 10cm in Ladakh and Western Rajasthan.

ii> Most parts of the country receive rainfalls from June to September from advancing monsoons.

iii> Tamil Nadu coast get most of its rains during November and December from retreating monsoons.

Q.29. Explain the six major climatic controls with reference to India.

Ans. A. LATITUDE

Due to curvature of earth, the amount of solar energy received on the earth varies from latitude to latitude. This results in decrease of temperature from equator to poles.

Reference to India – Tropic of Cancer passing through India divides the country into tropical and sub- tropical zones. Hence, temperature remains high throughout the year in South India (tropical zone) while they are high in summer and low in winter in North India (sub-tropical zone).

B. ALTITUDE

With increase in altitudes, the atmosphere goes on becoming less dense and temperature goes on decreasing.

Reference to India- though, Udagamandalam (Ooty) lies in low latitude area (tropical zone) but the climatic conditions are different from the adjoining regions because it is located at high altitude.

C. PRESSURE AND WINDS

The pressure and wind system exert influence on the climate of any place because they control the temperature and rainfall pattern.

Reference to India- Upper air circulation winds, western disturbances, tropical cyclones, monsoons etc. govern the climate and associated weather conditions in India.

D. DISTANCE FROM THE SEA

Sea exerts a moderating effect on climate. Distance from the sea or Continentality is a major factor in determining the climate of a place.

Reference to India- temperature remains uniform at Mumbai throughout the year where as at Delhi winter and summer temperature vary from 50C to 450C.

E. OCEAN CURRENTS

Ocean currents along with on-shore winds influence climate of coastal regions.

Reference to India- warm currents along the coastal region of India influence the climate of the adjoining areas.

F. PHYSIOGRAPHY

Relief (physiography) plays a major role in determining the climate of a place.

Reference to India- Himalayas donot allow the cold winds from Central Asia to enter India, neither allows monsoon winds to cross India. Also, relief also helps in orographic rainfall in many parts of the country.

Q.30. What are Jet streams? How do they affect the climate of India ?

Ans. Jet streams are a narrow belt of high altitude (above 12000m) westerly winds in the troposphere located approximately over 270-300 N latitude. Their speed varies from about 110km/h in summer to about 184 km/h in winter.

Westerly Jet stream -  Westerly jet stream is an upper air circulation moving from west to east direction. In India, it is effective during winter as it remains north of Himalayan range. It causes the western disturbances to enter India and cause rainfall/snowfall in north and north-western parts of India.

Easterly Jet stream- Easterly jet stream is an upper air circulation moving from east to west direction. In India, it is effective in summer as it remains south of Himalayan range. It causes tropical cyclones to enter India.

Q.31. Explain the route followed by the monsoon winds over the Indian landmass.

Ans. ONSET OF THE MONSOON

Monsoon winds are pulsating in nature. The monsoon arrives at the southern tip of the Indian peninsula generally by the first week of June. From here, it divides itself into two – the Arabian sea branch and the Bay of Bengal Branch.

• The Arabian Sea Branch reaches Mumbai about ten days later on 10 June.

• The Bay of Bengal branch also advances rapidly and arrives in Assam in the first week of June. On reaching the Eastern Himalayas, it is deflected towards the west over the Ganga plains.

• By mid June, The Arabian Sea branch of the monsoon arrives over the Saurashtra-Kutch region and the Central part of the country.

• The Arabian Sea branch and the Bay of Bengal branches of the monsoon merge over the north-western part of the Ganga plains.

RETREAT OF THE MONSOON

• Withdrawal or retreat of the monsoon is a more gradual process than the onset.

• It begins in the western parts of northwestern states of India by early September.

• Withdrawal from the southern half of the country is fairly rapid.

• By early December, withdrawal of the monsoon has taken place from the rest of the country.

Q.32. Write down the characteristic features of the:
Ans.1. HOT WEATHER SEASON

· Due to the northward movement of the sun, the global heat belt shifts northward. It is the hot weather season in India from March to May.
· In Peninsular India, temperature remains lower due to the moderating influence of the seas on three sides whereas it goes as high as 480C in the northwestern parts of the country.
· Summer months experience rising temperature and falling air pressure in the northern part of the country. An elongated low pressure area develops in the region.
· Strong, hot, dry winds known as loo blow during the day over the northern India. Other winds like Kalbaisakh and mango showers are also common in different parts of the country.

2. COLD WEATHER SEASON
· The cold weather season begins from mid-November in northern India and stays till February.
· Temperature decreases from North to South. December and January are the coldest months. Average temperature of Chennai is 240 to 250C whereas it ranges in 100-150C.
· Days are warm and nights are cold. Frost is common in the north.
· Northeast winds from land to sea prevail over the country from land to sea.
· North east winds and western disturbances bring rainfall in different parts of the country during winters.
· The peninsular India does not have a well defined cold season. There is hardly any noticeable seasonal change in temperature pattern due to the influence of the sea.

Q.33. How the monsoons are distributed all over India?
Ans. HEAVY RAINFALL REGIONS
Annual rainfall of over 400 cm is received over parts of western coast and north-eastern India.

SCANTY RAINFALL REGIONS
a. It is less than 60cm in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab.
b. Rainfall is also low in the interior of the Deccan plateau, east of the Sahayadris.
c. A third area of low precipitation is around Leh in Jammu and Kashmir

MODERATE RAINFALL REGIONS
a. The rest of the country receives moderate rainfall.
b. Snowfall is restricted to the Himalayan region.

Q.34. How can you say that monsoons are uncertain in nature?
Ans. Vagaries of monsoon are the result of variable nature of annual rainfall. Annual rainfall is highly variable from year to year.
· Variability is high in the regions of low rainfall. These regions are parts of Rajasthan, Gujarat, and the leeward side of the Western Ghats.
· Areas of high rainfall are almost affected by floods.
· Areas of low rainfall are drought prone.

Q.35. “The nature of monsoons is highly variable, still they are considered as a unifying bond.” How?
· Ans. 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 the monsoons.
· The Indian landscape, its animal and plant life, its entire agricultural calendar and the life of people, including their festivities, revolve around this phenonmenon.
· Year after year, people of India eagerly await the arrival of the monsoon.
· The monsoon affects the people of India uniformly. Therefore, it is known as a unifying bond.