NCERT Solutions Class 9 Social Science Chapter 4 Climate

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: (b) Mawsynram

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

(a) Kaal Baisakhi

(b) Loo

(c) Trade Winds

Answer: (b) Loo

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

(a) Cyclonic depression

(b) Retreating monsoon

(c) Western disturbances

(d) Southwest monsoon

Answer: (c) Western disturbances

(iv) Monsoon arrives in India approximately in:

(a) Early May

(b) Early July

(c) Early June

(d) Early August

Answer: (c) Early June

(v) Which one of the following characterises 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: (c) Cool days and cold nights

2. Answer the following questions briefly.

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

Answer: Latitude, altitude, air pressure and wind system, distance from the sea, ocean currents, and relief features are the main controls affecting the climate of India.

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

Answer: The climate of India is monsoon type because it is highly influenced by the Monsoon Winds. Following are the factors responsible for these monsoons.

   The Tibetan plateau gets intensely heated during summers.

   The shift of the position of Inter Tropical Convergence Zone (ITCZ).

   Presence of high pressure in the east of Madagascar.

   Movement of westerly jet streams to the north of Himalayas and the presence of tropical

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

Ans. Diurnal range of temperature is high in the deserts like western India especially in Thar Desert a part of Rajasthan and interior parts of Rann of Kutch in Gujarat. Being arid and semi arid, it temperature goes upto 50˚C in the daytime, while 15˚C at night. This happens because during the day time, sand absorbs heat very fast and at the same time loses heat very fast at night.

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

(v) 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 in the troposphere. Over India, these jet streams blow south of the Himalayas, all through the year except in summer. The western cyclonic disturbances experienced in the north and north-western parts of the country are brought in by this westerly flow. In summer, the subtropical westerly jet stream moves north of the Himalayas with the apparent movement of the sun. An easterly jet stream, called the sub-tropical easterly jet stream blows over peninsular India, approximately over 14°N during the summer months. These jet streams are amongst one of the major factors in determining the movement of monsoons winds towards India sub-continent.

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

Answer: The seasonal reversal in wind direction during a year is called monsoon. They blow from the southwest in summer and from the northeast in winter in India and Indian Subcontinent.

July and August, the principal monsoon months in India, account for nearly 75 percent of the annual rainfall over a major part of the country. In certain years, the monsoonal weather in some regions is interrupted by long periods of sparse rainfall called break-monsoons. This unseasonal weather is disastrous for crops, and it is responsible for severe droughts and famines.

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

Answer: The Monsoon is considered as a unifying bond in India because its landscape, its flora and fauna, etc., are highly influenced by the monsoon. The entire agricultural calendar in India is governed by the monsoon. Many festivals in India are related to agricultural and monsoon season. These festivals are known by different names in different parts of the country, but their celebration is decided by the monsoon. In spite of having great variation in climatic conditions monsoon unifies the climate in India.

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

Answer:  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. The high temperature on the land also increases the moisture holding capacity of the winds and makes them dry. So, the amount of rainfall decreases when moving to the west.

4. Give reasons as to why.

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

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

Answer: The bulk of rainfall in India is concentrated over a few months because of the intensified low pressure conditions in India attract the moisture bearing winds coming from the Indian Ocean. 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 mainly June to August for 100-120 days.

(iii) The Tamil Nadu coast receives winter rainfall.

Ans. The Tamil Nadu coast receives winter rainfall because of the North-East Monsoon winds. When the monsoon winds reverse, they are dry. When they move over the Bay of Bengal, they pick up some moisture. these moist winds are hindered by the Eastern Ghats and give away the rainfall to Tamil Nadu coast during winter.

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

Ans. The delta region of the eastern coast is frequently struck by cyclones because of the shift of the pressure conditions with the change of the seasons. More cyclones form in the Bay of Bengal than in the Arabian Sea. As such, the eastern coast is more prone to cyclones and about 80 per cent of the total cyclones generated in the Indian Ocean strike the east coast of India. There are two definite seasons of tropical cyclones in the North Indian Ocean. One is from May to June and the other from mid- September to mid-December.

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

Answer:  Rainfall in India is influenced by location as well as relief features. Areas situated in the direction of the monsoon winds receive more rainfall. Rajasthan and Gujarat lie on the leeward side of Aravalli Range, which deflects the Arabian Sea branch, leaving the region rainless. The Arabian Sea branch of the South-West Monsoon winds carries lots of moisture when it strike with the windward side of the Western Ghats and give heavy rainfall, but it becomes drier and descends the Western Ghats.

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

Answer: The two important elements of climate are temperature and precipitation. They vary from place to place and season to season and decide climate of the place. There is a sharp contrast in the climate of India. For example:     In summer, the mercury occasionally touches 50°C in some parts of the Rajasthan desert, whereas it may be around 20°C in Pahalgam in Jammu and Kashmir. On a winter night, temperature at Drass in Jammu and Kashmir may be as low as minus 45°C. Thiruvananthapuram, on the other hand, may have a temperature of 22°C. The annual precipitation varies from over 400 cm in Meghalaya to less than 10 cm in Ladakh and western Rajasthan. Parts of Jammu and Kashmir receive precipitation in the form of snow and most of the other parts receive rainfall. The North India and the western India receive rainfall by south-west monsoon winds, but the Eastern Coastal plains receive the rainfall due to the northeast monsoon winds.

6. Discuss the mechanism of monsoons.

Answer: The Monsoon winds are the seasonal winds. The duration of the monsoon is between 100-120 days from early June to mid-September. It 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 northern mountains cause the monsoon winds to deflect towards the west over the Ganga plains. By mid-June, the Arabian Sea and the Bay of Bengal branches of the monsoon merge over the northwestern part of the Ganga plains. 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. By early December, the monsoon has withdrawn from the rest of the country. The shift in the low pressure conditions from north-western plains to the Bay of Bengal causes cyclones and rains in the Coromandel Coast.

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

Ans. the important characteristics of the winter season are as follows:

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

ii.   January is the coldest months in the northern part of India.

iii.   The temperature decreases from south to the north.

iv.       Days are warm and nights are cold.

vi.   The northeast Trade winds prevail over the country. They are dry as they blow from land to sea.

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

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

ix.   A characteristic feature of the cold weather season over the northern plains is the inflow of the Western cyclonic disturbances from the west and the northwest.

x.   The total amount of winter rainfall locally known as ‘mahawat’ is small and is very important for the cultivation of ‘rabi’ crops.

xi.   The peninsular region does not have a well defined cold season due to the moderating influence of the sea.

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

i.   The monsoon rainfall in India is uneven and uncertain.

ii.   Rainy season has a longer spell in the eastern parts of the country whereas the northwest gets rains for barely two months.

iii.   The duration of the rainy season is longer in the south than in the north.

iv.   Monsoons are not steady. Rainy days are interspersed with rainless days.

v.   Heavy down pour result into the flooded rivers causing heavy damage to life and property.

vi.   A dry spell would cause as much misery as the river floods.

vii.   The arrival and departure of monsoons is uncertain. So is the extent of rainfall in any given rainy season.

viii.  These characteristics of monsoon have a very destabilising effect on Indian economy that continues to be predominantly agricultural and dependent on rainfed irrigation.

MAP SKILLS

On an outline map of India, show the following. (i) Areas receiving rainfall over 400 cm.

(ii) Areas receiving less than 20 cm of rainfall.

(iii) The direction of the south-west monsoon over India

Answer: Leh, Delhi, Jodhpur, Shillong, Kolkata, Nagpur, Mumbai, Chennai, Bengaluru, Thriuvanantpuram.

vi) Two stations most influenced by the Bay of Bengal branch of south-west monsoons. Answer: Shillong and Kolkata

d)  June – Jodhpur and Delhi

Answer: Tiruvanantapuram has equable climate due to the following

In spite of these facts see carefully if there are strong evidences to conclude that the monsoons still provide a very strong framework lending overall climatic unity to the whole country.

Answer: The seasonal reversal of monsoon winds and the associated weather conditions provide a rhythmic cycle of seasons. Monsoon rains are unevenly distributed over the space and time and typically uncertain. The Indian landforms, flora, fauna, agriculture, the people, and their festivities, all revolve around the monsoon. Indian farmers and other people eagerly await the arrival of the monsoon. It binds the whole country by providing water for irrigation as well as for industrial and domestic purposes, which sets all agricultural activities and economic activities in motion. That is why the monsoon is considered a unifying bond.