Page No. 39
Ques.1. Choose the right answer from the four alternatives given below.
(i) Which one of the following places receives the highest rainfall in the world?
Ans. (b) Mawsynram
(ii) The wind blowing in the Northern Plains in the summers is known as:
(a) Kaal Baisakhi
(c) Trade Winds
(d) None of the above
Ans. (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
Ans. (c) Western disturbances
(iv) Monsoon arrives in India approximately in
(a) Early May
(b) Early July
(c) Early June
(d) Early August
Ans. (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
Ans. (c) Cool days and cold nights
Ques.2. Answer the following questions briefly.
(i) What are the controls affecting the climate of India?
Ans. The elements affecting the climate are:
• Pressure & Winds
• distance from the sea
• ocean currents
• Relief features.
(ii) Why does India have a monsoon type of climate?
Ans. India has a monsoon type of climate because the climate of India is governed by the monsoon winds which are limited between 20° North and 20° South.
(iii) Which part of India does experience the highest diurnal range of temperature and why?
Ans. The Indian desert located in the north-western part of India experiences the highest diurnal range of temperature because of the sand which is present there, quickly becomes hot during day and cools down rapidly during night.
(iv) Which winds account for rainfall along the Malabar Coast?
Ans. Malabar Coast gets rains from South-West Monsoon Winds.
(v) What are Jet streams and how do they affect the climate of India?
Ans. Jet streams are fast flowing, narrow, meandering air currents found in the atmosphere of some planets, including Earth. The westerly flows are responsible for the western disturbances experienced in the north and north-western parts of the country. In the months of October- November the easterly jet streams cause tropical depressions.
(vi) Define monsoons. What do you understand by “break” in monsoon?
Ans. (i) Monsoon refers to a wind system that influences large climatic regions and reverses direction seasonally.
(ii) Monsoon ‘break’ refers to the happening of wet and dry spells during the rainy season.
(iii) The monsoon rains take place only for a few days at a time.
(vii) Why is the monsoon considered a unifying bond?
Ans. The monsoon is considered a unifying bond because:
(i) The monsoon of India is highly influenced by its flora and fauna.
(ii) The water for the agricultural activities is provided by these monsoon winds.
(iii) Most of the festivals in India that are related to agricultural cycle may be known by different names in different parts of the country, but their celebration is decided by the monsoon.
(iv) The river valleys which carry this water also unite as a single river valley unit.
Ques.3. Why does the rainfall decrease from the east to the west in Northern India?
Ans. The low-pressure area in India lies in the north-west, towards which the South West Monsoon winds are attracted. After depositing moisture in south India, the Bay of Bengal branch of the South West Monsoons strikes the Khasi - Garo Hills. After causing heavy rainfall on the windward slopes, these winds turn westwards because of the presence of the lofty Himalayas. These winds then keep depositing rainfall a they go up the Ganga valley towards the low pressure area. The rainfall deposited thus keeps on decreasing as the winds proceed from east to west in Northern India, as this is the last region to be affected by the monsoons.
Ques.4. Give reasons as to why.
(i) Seasonal reversal of wind direction takes place over the Indian subcontinent?
Ans. Land and water are of different densities, so the rate of heating and cooling varies. The Indian subcontinent is surrounded by water on three sides. In summer the land mass of India is warmer than the surrounding sea, therefore there is low pressure. The sea is cooler, thereby having higher pressure. So the winds blow from sea to land.
In winter the land has high pressure while the sea has low pressure. Therefore, the winds blow towards the sea. Thus a seasonal reversal of wind direction takes place.
(ii) The bulk of rainfall in India is concentrated over a few months.
Ans. In India, the bulk of the rainfall is concentrated over a few months. The main source of rainfall is the monsoon wind which blows when there is intense low pressure on the land. The surrounding water body is cool and has high pressure. This ideal temperature and pressure are caused in May when the rain falls between June - September and it becomes cooler (high pressure). Rest of the year is practically dry.
(iii) The Tamil Nadu coast receives winter rainfall winds.
Ans. During the winter season, the Tamil Nadu coast receives rain from the northeast Monsoon which blow from land to sea. They do not cause any rain in the northern part of the country. But while crossing the Bay of Bengal they pick up moisture and cause rain on the eastern coast of South India, mainly the Tamil Nadu coast.
(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 as the low pressure conditions over northwestern India get transferred to the Bay the Bengal by early November. This shift is responsible for the occurrence of cyclonic depressions which originate over the Andaman sea. These then cross the eastern coast causing heavy widespread rain leading to great damage to life and property.
(v) Parts of Rajasthan, Gujarat and the leeward side of the Western Ghats are drought-prone.
Ans. Relief/Mountains play an important role in the distribution of rainfall in India. The moisture laden winds (South West Monsoons) cause heavy rain on the windward slopes of the Western Ghats and Khasi-Garo hills. As the winds cross over to the leeward slopes, there is less rainfall as most of it has been deposited on the slope facing the winds. All the area on the leeward side is deprived of rain and is drought prone. Rajasthan also lies in the rain shadow of the Aravalli hills.
Ques.5. Describe the regional variations in the climatic conditions of India with the help of suitable examples.
Ans. There is regional variation in the climatic conditions of India. Temperature and Precipitation vary from place to place and season to season.
• During the summer season, the temperature rises up to 50°C in parts of Rajasthan, whereas it may be around 20°C in Pahalgam in Kashmir.
• During the winter season at night the temperature in Drass in Kashmir may be minus 45°C, whereas in Thiruvananthapuram in Kerala may have a temperature of 20°C.
• In Andaman Islands, the difference between the temperatures of day and night may be hardly 7° - 8°C.
• Coastal areas experience less contrast in the temperature, whereas seasonal contrasts are more in the interior of the country.
• There is decrease in rainfall generally from east to west in the northern plains.
• Most parts of India receive rainfall from June - September, whereas some parts like the Tamil Nadu coast gets a large portion of its rain during October and November.
Ques.6. Discuss the mechanism of monsoons.
Ans. Following are the factors responsible for the mechanism of monsoons:
• 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 Inter Tropical Convergence Zone (ITCZ) is normally positioned about 5°N of the equator. During summer, it shifts over the Ganga plains. It is also known as the monsoon trough during the monsoon season.
• The high pressure area, east of Madagascar is approximately 20°S over the Indian Ocean. This area affects the Indian Monsoon.
• The Tibetan plateau gets intensely heated during summer. This leads in strong vertical air currents and formation of high pressure over the plateau. This high pressure zone is about 9 km above the sea level.
• The westerly jet stream moves to the north of the Himalayas, and the tropical easterly jet stream moves over the Indian Peninsula during summer.
• The periodic change in pressure conditions between Pacific Ocean and the Indian Ocean, also known as the 'Southern Oscillation' or 'SO' also affects the monsoon.
• The difference in pressure over Tahiti and Darwin is computed to predict the intensity of the monsoons. Tahiti (18°S/149°W) lies in the Pacific Ocean and Darwin (12°30'S/131°E) lies in northern Australia. If the pressure differences are negative, it means a below average and late monsoon.
Ques.7. Give an account of weather conditions and characteristics of the cold season.
Ans. Following are the features of the cold season:
• The winter season begins from mid-November and continues till February; in northern India.
• December and January are the coldest months in the northern part of India.
• The temperature ranges between 10°-15°C in the northern plains, while it ranges between 24°-25°C in Chennai.
• Days are warm and nights are cold.
• Frost is common in the north and the higher slopes of the Himalayas experience snowfall.
• The northeast trade winds prevail over the country in this season. As these winds blow from land to sea, most parts of the country experience a dry season.
• The weather is usually marked by clear sky, low temperatures and low humidity and weak 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.
• The winter rainfall is in small amount but is very important for the rabi crop. This rainfall is locally known as mahawat.
• The peninsular region does not have a well-defined cold season due to the moderating influence of the sea.
Ques.8. Give the characteristics and effects of the monsoon rainfall in India.
Ans. Characteristics of the monsoon rainfall in India:
• The duration of the monsoon varies from 100 to 120 days from early June to mid-September.
• The normal rainfall suddenly increases, around the time of its arrival and continues regularly for several days. This is called the ‘burst' of the monsoon.
• They are distinguished from the pre-monsoon showers because of their increase in rainfall amount and regularity.
• The monsoon arrives at the southern tip of the Indian Peninsular generally by the first week of June.
• The rainfall is unevenly distributed across the country.
Effects of the monsoon rainfall in India:
• Agriculture in India largely depends on Indian monsoons for water. Late, Low or excessive rains have a negative impact on crops.
• Due to uneven distribution of rainfall across the country, there are few places that are drought prone and few are flood affected.
• The monsoon provides India with a diverse climatic pattern. Hence, in spite of the presence of great regional variations, it has a unifying influence upon the country and its people.