NCERT Solutions for Class 9 Social Science Chapter 9 - Climate

Answer:

(b) Mawsynram

Answer:

(b) Loo

Answer:

(c) Western disturbances

Answer:

(c) Early June

Answer:

(c) Cool days and cold nights.

Answer:

The climate of India is affected by the following geographical factors:
(a) Monsoon winds: India’s climate is controlled by the monsoon winds. In summers, monsoons are onshore winds. These winds cause most of the rainfall in the sub-continent. In winters, the monsoon winds blow from land to sea as N.E. Monsoons. These are dry winds.
(b) Extent of the country: India is a vast country. The northern part lies in the temperate region and experiences hot summers and cool winters. The southern part lies nearer to the equator and has a hot season throughout the year.
(c) Location of the Himalayas: The Himalayas act as a climatic barrier. This mountain wall protects India from the cold winds of Central Asia from entering India during winter. The Himalayas check the onshore S.W. Monsoons and prevent them from escaping the sub-continent, thus causing rainfall.
(d) The Indian Ocean: India lies at the head of the Indian Ocean. S.W. Monsoons originate from this ocean in summer and cause rainfall over most of the country. Cyclones also originate over this ocean.
(e) The Western disturbances: The western disturbances (cyclones) originate from the Mediterranean Sea and enter India in winter. These provide rainfall in the N.W. parts of India in winter.
(f) Distance from the sea: The coastal areas experience maritime climate. These areas have equable climate. But the areas in the interior experience extreme or continental type of climate such as N.W. India.
(g) Relief of the land: Relief influences the distribution of temperature and rainfall in India.
Mountainous areas have low temperature. The windward slopes such as Western Ghats receive heavy rainfall while the leeward slopes (Deccan Plateau) lie in the Rain-shadow and are dry.

Answer:

The Indian Sub-continent extends from 8$°$ North to 37$°$ North latitudes. So, it has a tropical location. The Himalayas provide an enclosed character to the sub-continent. The Indian Ocean in the South gives it a hot monsoon climate. As a result, India has essentially a tropical monsoon climate. The Tropic of Cancer divides the country into two halves. The northern half lies in the temperate zone while the southern half lies in the tropical zone. Hence, India has high temperatures throughout the year and most of the rain takes place in summer.

Answer:

The Thar desert has high diurnal or daily range of temperature. The difference between the daily maximum and daily minimum temperature is large. The sandy soils become heated during the day and cool down during the night.

Answer:

Malabar coast lies on the West Coast, facing the Western Ghats. The Arabian Sea branch of the monsoons are onshore moisture-laden winds and cause heavy rainfall on the western slopes of the Western Ghats and the West Coast. S.W. Monsoon winds first strike the Malabar coast causing heavy rainfall called a ‘monsoon burst’.

Answer:

Jet streams are fast flowing winds blowing in a narrow zone in the upper atmosphere. The Himalayas divide the jet streams into two parts. The westerly jet streams (27$°$–30º N) blows over the south of the Himalayas during the winter season. The easterly jet streams develop at about 14$°$N in summer. It is believed to be responsible for the sudden outbreak of monsoons in Northern India. It causes widespread storms, thunder and rainfall over India in just 8 to 10 days.

Answer:

Monsoons are seasonal winds. These change their directions with the season. Monsoon starts all of a sudden and is called the break in monsoons.

Answer:

There is a great diversity in climatic conditions of India due to differences in relief features. Examples: (a) Due to monsoon winds, India has a monsoon type of climate throughout the country. (b) The whole country is influenced by the same order of seasons. (c) The monsoonal rhythm of seasons is a great unifying force in India. (d) Monsoons control the atmospheric conditions of the country. Throughout the country, the summers are wet and the winters dry due to onshore winds. The distribution of rainfall is uneven. (e) Agriculture depends upon monsoonal rainfall resulting in a subsistence agriculture. Agriculture in India is a gamble in monsoons. (f) The folk songs like Kajari of Bhojpur and Malhar of Braj are associated with monsoonal rains. (g) Thus, monsoons provide a natural base for a uniformity throughout the country.

Answer:

The Bay of Bengal branch of monsoons move from east to west. These move up the Ganga Valley along the Himalayas. As these winds move westward, these become drier and cause less rainfall. Kolkata gets an annual rainfall of 162 cm, Patna 102 cm, Allahabad 91 cm and Delhi gets 56 cm of rainfall.

Answer:

Mechanism of Monsoons
The N.E. trade winds are replaced by the monsoons. The S.E. trade winds of the southern hemisphere after crossing the equator become S.W. monsoons. The dry and hot winds are replaced by wet monsoons during the summer seasons. The mechanism of the monsoon is from temperature, through pressure and winds to rainfall.

Due to high temperatures, a low pressure develops over the North-West part of India. This is basically responsible for the reversal of wind direction and rise of S.W. monsoons. Thus, it was originally thought that monsoons have a thermal origin and these are surface winds. But nowadays, the meteorological data has proved that upper air winds and currents also play an important role in the mechanism of monsoons. The jet streams also affect the mechanism of monsoons. The eastern branch of jet streams is believed to be responsible for the sudden break of monsoons and cause heavy rainfall.

Answer:

The bulk of rainfall in India is received during the four months of the rainy season, i.e., June, July, August and September. This is the period of South-West monsoons blowing from sea to land. These sea to land winds are the rain giver, as these moisture-laden winds are onshore winds. The tropical cyclones add to the amount of rainfall. Easterly tropical jet streams, too, help in rains during this period.

Answer:

The Konkan Coast faces the onshore S.W. monsoons during summer. These moisture-laden winds cause heavy rainfall (more than 300 cms). But these winds do not give much rainfall on the Coromandel Coast as it lies in the rain shadow area of the Western Ghats. The Coromandel Coast receives winter rainfall from N.E. monsoons, but on the Konkan Coast, these winds are offshore and do not give any rainfall. Thus, Coromandel Coast gets rainfall in both the seasons, but the total amount is less than that of Konkan Coast. Total rainfall in Chennai is 128 cms, but it is 180 cms at Mumbai.
Tamil Nadu gets most rain from North-East monsoons in October and November. These winds after picking up moisture from the Bay of Bengal give more rain on the East Coast. Thus, Tamil Nadu gets most rain in winter when the fury of monsoons is over in most parts of the country.

Answer:

Tropical cyclones are depressions originating over the Bay of Bengal. These tropical cyclones are often very destructive. They cause heavy rains. These cyclones strike West Bengal and Bangladesh (Ganga Delta). These cross the eastern coast and affect the states of Odisha, Andhra Pradesh, Tamil Nadu and Kerala. The thickly populated deltas of Mahanadi, Godavari, Krishna and Kaveri are their targets.

Answer:

The western part of Rajasthan is a desert. It gets an annual rainfall of less than 20 cms. This is due to the following reasons:
(a) Rajasthan is under the influence of the S.W. summer monsoons. The Aravallis system lies parallel to the direction of S.W. monsoons coming from the Arabian Sea. These low mountain system is unable to check these winds. So, western Rajasthan is practically dry. The southern parts get some rainfall.
(b) This area lies at a great distance from the Bay of Bengal. The Bay of Bengal monsoons become dry and lose their moisture when they reach Rajasthan.
(c) This area is away from the Himalayan region. So it does not come under the influence of monsoons, giving rain in the sub-Himalayan region.
(d) Gujarat has high variability of rainfall. So it is a drought prone area.
(e) The leeward slopes of Western Ghats is in rain shadow area.

Answer:

Due to the vast size of India, many regional variations in climatic conditions are found. But due to the influence of monsoons, India has a broad unity of Monsoon type of climate having the same rhythm of season. Many factors like location, altitude, distance from the sea, general relief produce regional variations in pattern of winds, temperature and rainfall. The examples given below illustrate the climatic differences:
(i) Temperature: Barmer (Rajasthan) has recorded the highest day temperatures of 50$°$C in summer, and 15$°$C at night, while hilly regions like Gulmarg (Kashmir) have a day temperature of 20$°$C in June. The winter temperatures at Dras and Kargil (Leh) drops as low as –45$°$C, on the other hand Chennai may record only 20$°$C in December. The annual range of temperature is about 12$°$C at Cochin while it is about 40$°$C in Punjab. Coastal regions have almost uniform temperatures throughout the year.
(ii) Rainfall: The striking differences are found in rainfall pattern. Mawsynram (Meghalaya) with an annual rainfall of 1140 cm is the rainiest place in the world, while Jaisalmer (Rajasthan) rarely gets more than 12 cm of annual rainfall and Leh gets only 10 cm rainfall. The Western coastal plain gets rain-storms while the Coromandel coast remains dry. When the Brahmaputra valley is submerged in floods, it brings drought in Bihar.
(iii) Monsoons: The dates of onset and withdrawal of monsoons differ in various parts. The west coast gets monsoons in the first week of June, while the interior parts like Punjab receive monsoons by the first week of July.
(iv) Seasons: The southern parts of the country have uniformly high temperatures throughout the year. There is no winter season in the south. On the other hand, seasonal extremes are found in the north. In summer, a heat wave is produced, called Loo whereas, a cold wave is felt in winter.

Answer:

Currently, the mechanism of the monsoon is a widely-studied subject globally. In the Indian subcontinent, the mountain barriers to the north guide the flow of the monsoon winds. The Western Ghats, too, play a similar role.
To understand the mechanism of the monsoons. Certain factors are responsible for the cause of the wind-reversal.
(i) The less heat around the Arabian Sea is caused due to intensive heating during the premonsoon months.
(ii) The northernmost position of Inter-Tropical Convergence Zone (ITCZ) in summer, also known as the monsoon-trough during the monsoon season.
(iii) High Pressure on the Indian Ocean. The intensity and position of this high-pressure area over the Indian ocean affects the Indian Monsoon.
(iv) The Tibetan high-level plateau gets intensely heated during summer, which results in strong vertical air currents and the formation of high pressure over the plateau at about a kilometre above the sea level.
(v) The movement of the westerly jet streams to the north of the Himalayas and the presence of the tropical easterly jet streams over the Indian peninsula during summer.

Answer:

The Cold Season: The cold season lasts from January to February. (i) Temperature: The sun is overhead at the Tropic of Capricorn. The Indian sub-continent has winter season. January is the coldest month. The southern parts have warm conditions (20$°$C) while low temperatures (10$°$C) are found in N.W. India and the Trans-Himalayan region of Jammu and Kashmir, which are the coldest parts of India. The minimum temp. of –40$°$C are recorded at Dras or Kargil (Ladakh).
(ii) Pressure and Winds: High pressure developes over N.W. part, while a low pressure exists over the Indian Ocean. As a result, winds blow from land to sea.
(iii) Rainfall: The N.E. Monsoons being offshore winds are dry. But these winds pick up some moisture while crossing the Bay of Bengal and deliver rain to the S.E. coast of India. Some cyclones from the Mediterranean Sea cause rainfall (10–20 cm) on the Northern Plains. Leh receives snowfall.

Answer:

Characteristics of rainfall in India: The average annual rainfall in India is about 110 cms. It is estimated that more than 85% of this rainfall is received in summer. The main characteristics of summer rainfall are as follows:
(i) Monsoonal rainfall: Most of the rain is received from the S.W. summer monsoons during the period mid-June to mid-September. It is seasonal rainfall.
(ii) Uncertain rainfall: Summer rainfall is quite uncertain. Some times monsoons start early resulting in floods. Often the onset of monsoons is delayed resulting in drought. The early or late retreat of monsoons also results in severe droughts.
(iii) Unequal distribution: The rainfall is unevenly distributed over the country. About 10% of the country gets more than 200 cm of rain while 25% of the country gets less than 75 cm of rain.
(iv) Heavy rainfall: Indian rainfall is heavy. It is often said that ‘‘It pours, it never rains in India.’’ (v) Relief rainfall: The amount of rainfall is determined by the presence of mountains. High mountains force monsoons to rise and cause rainfall.
(vi) No continuity of rainfall: Summer rain is characterised by breaks or dry spells.
(vii) Variable rainfall: Most of the areas have variable rainfall, as much as 30 cm plus or minus. Due to variability in areas of low rain, famines are formed.

Answer:

Houses in Rajasthan have thick walls:
(i) During summers, extreme heat is experienced during the days. The thick walls do not allow the heat to enter inside the houses. It absorbs heat and keeps the house cool. Similarly in winter, thick walls of the houses do not allow the cold winds to enter the house, keeping it warm. Houses in Rajasthan have flat roofs:
(i) Flat roofs are considered ideal for keeping the house cold during the summer months and warm during the winter months.

Answer:

The houses in the Tarai region and in Goa and Mangalore have slopping roofs as these areas receive heavy rainfall. The slopping roof does not allow rain water to accumulate on roof-tops. Thus, slopping roofs keeps the house safe in this region.

Answer:

Houses in Assam are built on the stilts, as stilts allows the free flow of water. It also avoids wetness and danger from poisonous reptiles which can enter the houses.

Answer:

As these region are devoid of moisture and rainfall.