Chapter 4 Climate
Choose the correct answer from the four alternatives given below.
(i) Which one of the following places receives the highest rainfall in the world?
(ii) The wind blowing in the northern plains in summers is known as:
(a) Kaal Baisakhi
(c) TVade Winds
(d) None of the above
(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
(c) Western disturbances
(iv) Monsoon arrives in India approximately in:
(a) Early May
(b) Early July
(c) Early June
(d) Early August
(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
(c) Cool days and cold nights
Answer the following questions briefly.
(i) What are the factors affecting the climate of India?
The factors controlling the climate of India are:
- Pressure and winds (jet streams)
- Distance from the sea
- Relief or mountains
(ii) Why does India have a monsoon type of climate?
India has a monsoon type of climate because of the strong influence of the monsoon winds over the sub-continent. The summer monsoons cause heavy rainfall when they blow from sea to land. The winter monsoon winds blow from the interior of the continent to the sea and do not cause much rain. There is a seasonal reversal of the wind system ‘monsoon’.
(iii) Which part of India does experience the highest diurnal range of temperature and why?
The Thar desert experiences the highest diurnal range of temperature. This is because during the day the temperature rises to over 50°C, and at night due to the absence of the sun and lack vegetation the temperature drops to below 15°C the same night.
(iv) Which winds account for rainfall along the Malabar Coast?
Arabian Sea Branch of the South West summer Monsoons.
(v) What are jet streams and how do they affect the climate of India?
Jet streams are a narrow belt of high altitude (above 12,000 m) westerly winds in the troposphere. Their speed varies from about 110 km/h in summer to about 184 km/h in winter. A number of jet streams exist but the most constant are the mid-latitude and the sub-tropical jet stream. The jet streams located over 27°-30° north latitudes are known as subtropical westerly jet streams. These jet streams blow south of the Himalayas throughout the year except in summer. These are responsible for the western cyclonic disturbances experienced in the north and north western parts of the country. These jet streams move north of the Himalayas with the apparent migration of the sun.
During the summers at about 14°N, an easterly jet stream called the subtropical easterly jet stream blows over peninsular India.
(vi) Define monsoons. What do you understand by “break” in monsoon?
The word monsoon has been derived from the Arabic word ‘mausim’ which means season. In this season the winds blow from land to sea for 6 months and from sea to land for 6 months. The break in the monsoon rainfall refers to the dry spells when the monsoon rain takes place
only for a few days at a time. These breaks are related to the movement of the monsoon trough. When the axis of the monsoon trough lies over the plains, then the rainfall is heavier there. When the trough moves towards the Himalayas, the plains are dry but there is heavy rainfall occur over the mountains.
(vii) Why is the monsoon considered a unifying bond?
The subcontinent of India has a great variation in temperature conditions, despite the moderating influence created by other factors. The monsoons have a unifying influence as the rainfall that is caused affects the entire country. Water is thus supplied for agricultural activities as well as to the rivers for use all over the country. The monsoons thus bind the entire continent, where all wait eagerly for their arrival.
Why does the rainfall decrease from the east to the west in Northern India?
The low-pressure area in India lies in the northwest, 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 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.
Give reasons as to why:
(i) Seasonal reversal of wind direction takes place over the Indian subcontinent?
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.
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 waterbody is cool and has high pressure. This ideal temperature and pressure is 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.
During the winter season the Tamil Nadu coast receives rain from the north east 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 coat of south India, mainly the Tamil Nadu coast.
(iv) The delta region of the eastern coast is frequently struck by cyclones.
The delta region of the eastern coast is frequently struck by cyclones as the low pressure conditions over north western 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.
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.
Describe the regional variations in the climatic conditions of India with the help of suitable examples.
There is a great regional variation in the climatic conditions of India (mainly temperature and rainfall). In summer, the temperature rises above 50°C in some parts of Rajasthan while in Jammu and Kashmir it is about 20°C. The temperature in Drass during winters goes down to even minus 45°C while at Thiruvananthapuram it is 22°C.
The precipitation varies from over 400 cm in Meghalaya to less than 10 cm in Ladakh and western Rajasthan. While the precipitation in most of India is in the form of rain, the mountains experience snowfall. The larger part of the country receives rain between June to September. Parts of Tamil Nadu receive rain between November and December. Coastal regions have a moderate climate whereas areas in the interior have an extreme or continental climate.
Discuss the mechanism of monsoons.
The following facts are important to understand the mechanism of the monsoons.
- The difference in the heating and cooling rate of land and water bodies. In summer there is low pressure on the land and high pressure in the sea.
- The shift of the position of the Inter-Tropical Convergence Zone in summer over the Northern Plains (its normal position is about 5°N of the Equator).
- The presence of the high-pressure area, east of Madagascar, affects the Indian Monsoons.
- The intense heating of the Tibetan plateau in summer causing low pressure.
- The movement of the westerly and easterly jet stream over the Indian peninsular during summer.
Give an account of weather conditions and characteristics of the cold season.
During the cold season, the skies are clear, temperatures and humidity are low and the winds are feeble and variable.
The temperature is higher in the south due to the moderating influence of the sea but decreases as one goes northwards where it ranges between 10° and 15° Celsius. Frost is common in the north and there is snowfall in the higher slopes of the Himalayas. Winds blow from land to sea and are dry except when they pick up moisture from the Bay of Bengal and cause rainfall in Tamil Nadu.
A characteristic feature of the cold weather season is the low-pressure system which enters northwest India from the Mediterranean Sea. These are also known as the temperate or westerly depression cyclones and cause winter rain and snowfall in the hills/mountains. This rain is beneficial for the growth of ‘Rabi’ crops.
Give the characteristics and effects of the monsoon rainfall in India.
The monsoon rain has certain characteristics which make it unique.
(a) Monsoon winds are unreliable, as the exact time of arrival and departure is not the same year after year.
(b) The rainfall is unevenly distributed. Certain areas receive heavy rainfall (windward slopes of the Western Ghats) while in other areas the rainfall is less (Thar Desert), causing floods and droughts.
(c) The monsoon rain is concentrated within the three months (June – September) of the year while the rest of the year is more or less dry.
(d) There is a seasonal reversal of winds.
The monsoon rains are important in India and its effect can be seen when they arrive. All over the country people eagerly wait for its arrival. The farmers are ready to sow their seeds and the agricultural activities begin. Water is provided to the rivers which carry it to different parts of the country. Plants and animals rejuvenate with the coming of the monsoons. The supply of water through rivers is very important for the generation of power.
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.