Chapter 4: Climate

Answer: (b) Mawsynram.

Answer: (b) Loo.

Answer: (c) Early June.

Answer: (b) Warm days and cold nights.

Answer: The major controls affecting the climate of India are:
(i) Latitude
(ii) Altitude
(iii) Pressure and wind system
(iv) Distance from the sea or continentality
(v) Ocean currents
(vi) Relief features

Answer: India has a monsoon type of climate because the climate of the country is strongly influenced by the monsoon winds. These winds show seasonal reversal in direction and bring most of the rainfall during a few months. India has a distinct seasonal pattern consisting of the cold weather season, hot weather season, advancing monsoon and retreating monsoon. Therefore, the climate of India is described as the monsoon type of climate.

Answer: The northwestern part of India, especially the Thar Desert region of Rajasthan, experiences the highest diurnal range of temperature. This happens because the region is far from the moderating influence of the sea and has dry sandy soil, clear skies and very little humidity. As a result, the days become very hot while the nights become comparatively cool.

Answer: The Arabian Sea branch of the south-west monsoon winds accounts for rainfall along the Malabar coast.

Answer: Monsoon refers to the seasonal reversal in wind direction during a year. In India, the monsoon winds blow from sea to land during summer and from land to sea during winter.

A “break” in monsoon means a temporary dry spell during the rainy season. The monsoon rains do not occur continuously for many months. They occur for a few days at a time and are followed by rainless intervals, which are called breaks in monsoon.

Answer: The monsoon is considered a unifying bond because it influences the climate, agriculture, vegetation, animal life and people’s activities across India. The seasonal change of winds and associated weather conditions create a rhythmic cycle of seasons. Indian agriculture depends heavily on monsoon rainfall, and people across the country eagerly wait for its arrival. The monsoon provides water for farming and supports river systems, thus binding the country together.

Answer: Rainfall decreases from the east to the west in Northern India because the Bay of Bengal branch of the south-west monsoon moves westward along the Ganga plains. As these winds move inland, they continue to lose moisture by causing rainfall. Therefore, the eastern part of the northern plains receives more rainfall, while the western part receives less rainfall.

Answer: Seasonal reversal of wind direction takes place because of the differential heating and cooling of land and water. During summer, the landmass of India heats up quickly and develops low pressure, while the surrounding seas have comparatively high pressure. Winds blow from sea to land. During winter, the land cools faster and develops high pressure, while the seas remain relatively warmer. Winds then blow from land to sea. This causes the seasonal reversal of winds.

Answer: The bulk of rainfall in India is concentrated over a few months because most of India’s rainfall is brought by the south-west monsoon. The monsoon usually arrives in early June and continues till September. Since the monsoon winds are moisture-laden and active during this short period, most rainfall occurs only during these months.

Answer: The Tamil Nadu coast receives winter rainfall because it gets rain from the retreating or north-east monsoon. During this season, winds blow from land to sea, but while crossing the Bay of Bengal they pick up moisture. When these moisture-laden winds reach the Tamil Nadu coast, they cause rainfall. Cyclonic depressions from the Bay of Bengal also contribute to winter rainfall in this region.

Answer: The delta region of the eastern coast is frequently struck by cyclones because low-pressure conditions shift to the Bay of Bengal during the retreating monsoon season. Cyclonic depressions often develop over the Andaman Sea and the Bay of Bengal. These tropical cyclones usually cross the eastern coast of India and affect the deltas of the Mahanadi, Godavari, Krishna and Kaveri, causing heavy rainfall and destruction.

Answer: Parts of Rajasthan and Gujarat are drought-prone because they receive very low and highly variable rainfall. The leeward side of the Western Ghats is drought-prone because it lies in the rain shadow area. Moist monsoon winds lose much of their moisture on the windward side of the Western Ghats, so the leeward side receives little rainfall.

Answer: India has a monsoon type of climate, but there are many regional variations in temperature and rainfall.

In summer, the temperature may rise to about 50°C in parts of the Rajasthan desert, while it may be around 20°C in Pahalgam in Jammu and Kashmir. In winter, the temperature at Drass may fall to about -45°C, while Thiruvananthapuram may have a temperature of about 20°C.

There are also large variations in rainfall. Mawsynram in Meghalaya receives very heavy rainfall, while parts of Rajasthan and Ladakh receive very little rainfall. Coastal areas such as Mumbai and Chennai have a moderate climate because of the influence of the sea, while interior areas experience extreme temperatures. These examples show the regional variations in India’s climate.

Answer: The cold weather season begins from mid-November in northern India and continues till February. December and January are the coldest months. The temperature decreases from south to north. Chennai has average winter temperatures of about 24°C to 25°C, while the northern plains have temperatures around 10°C to 15°C.

During this season, days are usually warm and nights are cold. Frost is common in the northern plains, and the higher slopes of the Himalayas receive snowfall. The north-east trade winds blow from land to sea, so most parts of the country remain dry. However, Tamil Nadu receives some rainfall from these winds after they pass over the Bay of Bengal. Western cyclonic disturbances also bring winter rain to north-western India and snowfall to the mountains.

Answer: The monsoon rainfall in India has several important characteristics. It is seasonal and occurs mainly between June and September. The monsoon arrives suddenly with a rapid increase in rainfall, known as the burst of the monsoon. It does not rain continuously; instead, rainfall occurs in wet spells separated by dry intervals called breaks.

The monsoon rainfall is unevenly distributed. The windward side of the Western Ghats and north-eastern India receive heavy rainfall, while Rajasthan, Gujarat, Ladakh and the leeward side of the Western Ghats receive low rainfall. The amount of rainfall also varies from year to year.

The monsoon has major effects on India. It supports agriculture, fills rivers, lakes and reservoirs, and influences the cropping pattern. A good monsoon helps agricultural production, while a weak or delayed monsoon can cause droughts. Excessive rainfall may cause floods in some regions.

Answer: This is a map-based activity. Students should mark areas of very high rainfall, areas of very low rainfall and the direction of the south-west monsoon on an outline map of India using the textbook map or an atlas.

Guidance: Areas receiving rainfall over 400 cm are mainly found in parts of Meghalaya and the western coast. Areas receiving less than 20 cm of rainfall are mainly found in western Rajasthan and parts of Ladakh. The south-west monsoon should be shown entering India from the Arabian Sea branch and the Bay of Bengal branch.

NCERT Activity: This is a local study activity. Students should collect examples of seasonal songs, dances, festivals and food preparations from their own region and compare them with other regions of India to identify similarities and differences.

NCERT Activity: Students should collect photographs of rural houses and clothing from different regions and observe their connection with climate and relief. For example, houses in heavy rainfall areas often have sloping roofs, desert regions use thick walls and light clothing, and cold mountain regions use woollen clothing and compact houses.

Answer: Jet streams are narrow belts of high-altitude westerly winds in the troposphere. They blow at a height of about 12,000 metres and have very high speed. Over India, the subtropical westerly jet stream blows south of the Himalayas in winter and brings western cyclonic disturbances to north and north-western India. In summer, it shifts north of the Himalayas, and the tropical easterly jet stream influences the monsoon over the Indian peninsula.

Answer: The mechanism of monsoon depends on several factors:
(i) Differential heating and cooling of land and water creates low pressure over India in summer and comparatively high pressure over the surrounding seas.
(ii) The Inter-Tropical Convergence Zone shifts northwards over the Ganga plain during summer and acts as the monsoon trough.
(iii) A high-pressure area develops east of Madagascar over the Indian Ocean, affecting the Indian monsoon.
(iv) The Tibetan Plateau heats up strongly during summer, creating strong vertical air currents.
(v) The westerly jet stream shifts north of the Himalayas, and the tropical easterly jet stream develops over the Indian peninsula.