9 Geography NCERT Chapter 4 PDF

4 C LIMATE I n the last two chapters you have read about The climate of India is described as the the landforms and the drainage of ‘monsoon’ type. In Asia, this type of climate our country. These ar...

4 C LIMATE I n the last two chapters you have read about The climate of India is described as the the landforms and the drainage of ‘monsoon’ type. In Asia, this type of climate our country. These are the two of the three is found mainly in the south and the southeast. basic elements that one learns about the natural Despite an overall unity in the general pattern, environment of any area. In this chapter you there are perceptible regional variations in will learn about the third, that is, the climatic conditions within the country. Let us atmospheric conditions that prevail over our take two important elements – temperature and country. Why do we wear woollens in December precipitation, and examine how they vary from or why it is hot and uncomfortable in the month place to place and season to season. of May, and why it rains in June - July? The In summer, the mercury occasionally answers to all these questions can be found out touches 50°C in some parts of the Rajasthan by studying about the climate of India. desert, whereas it may be around 20°C in Climate refers to the sum total of weather Pahalgam in Jammu and Kashmir. On a winter conditions and variations over a large area for night, temperature at Drass in Jammu and a long period of time (more than thirty years). Kashmir may be as low as minus 45°C. Weather refers to the state of the atmosphere Thiruvananthapuram, on the other hand, may over an area at any point of time. The elements have a temperature of 22°C. of weather and climate are the same, i.e. temperature, atmospheric pressure, wind, In certain places there is a wide difference between day and night humidity and precipitation. You may have temperatures. In the Thar Desert the day observed that the weather conditions fluctuate temperature may rise to 50°C, and drop down very often even within a day. But there is some to near 15°C the same night. On the other hand, common pattern over a few weeks or months, there is hardly any difference in day and night i.e. days are cool or hot, windy or calm, cloudy temperatures in the Andaman and Nicobar islands or in Kerala. or bright, and wet or dry. On the basis of the generalised monthly atmospheric conditions, Let us now look at precipitation. There are the year is divided into seasons such as winter, variations not only in the form and types of summer or rainy seasons. The world is divided into a number of precipitation but also in its amount and the climatic regions. Do you know what type of seasonal distribution. While precipitation is climate India has and why it is so? We will mostly in the form of snowfall in the upper parts learn about it in this chapter. of Himalayas, it rains over the rest of the country. The annual precipitation varies from The word monsoon is over 400 cm in Meghalaya to less than 10 cm derived from the Arabic word ‘mausim’ which literally means season. in Ladakh and western Rajasthan. Most parts ‘Monsoon’ refers to the seasonal reversal in the of the country receive rainfall from June to wind direction during a year. September. But some parts like the Tamil Nadu Rationalised 2023-24 coast gets a large portion of its rain during October and November. Why most of the world’s deserts are In general, coastal areas experience less located in the western margins of continents in the subtropics? contrasts in temperature conditions. Seasonal contrasts are more in the interior of the Finally, relief too plays a major role in country. There is decrease in rainfall generally determining the climate of a place. High mountains from east to west in the Northern Plains. These act as barriers for cold or hot winds; they may variations have given rise to variety in lives of also cause precipitation if they are high enough people – in terms of the food they eat, the and lie in the path of rain-bearing winds. The clothes they wear and also the kind of houses leeward side of mountains remains relatively dry. they live in. Why the houses in Rajasthan have thick FACTORS AFFECTING INDIA’S CLIMATE walls and flat roofs? Why is it that the houses in the Tarai region and in Goa and Mangalore have sloping roofs? Latitude Why houses in Assam are built on stilts? The Tropic of Cancer passes through the middle of the country from the Rann of Kuchchh in the CLIMATIC CONTROLS west to Mizoram in the east. Almost half of the country, lying south of the Tropic of Cancer, There are six major controls of the climate of belongs to the tropical area. All the remaining any place. They are: latitude, altitude, area, north of the Tropic, lies in the sub-tropics. pressure and wind system, distance from Therefore, India’s climate has characteristics of the sea (continentality), ocean currents and tropical as well as subtropical climates. relief features. Due to the curvature of the earth, the Altitude amount of solar energy received varies according to latitude. As a result, air India has mountains to the north, which have temperature generally decreases from the an average height of about 6,000 metres. India equator towards the poles. As one goes from also has a vast coastal area where the the surface of the earth to higher altitudes, maximum elevation is about 30 metres. The the atmosphere becomes less dense and Himalayas prevent the cold winds from Central temperature decreases. The hills are therefore Asia from entering the subcontinent. It is cooler during summers. The pressure and because of these mountains that this wind system of any area depend on the subcontinent experiences comparatively latitude and altitude of the place. Thus it milder winters as compared to central Asia. influences the temperature and rainfall pattern. The sea exerts a moderating influence Pressure and Winds on climate: As the distance from the sea The climate and associated weather conditions increases, its moderating influence decreases in India are governed by the following and the people experience extreme weather atmospheric conditions: conditions. This condition is known as P rressur essur essuree and sur face winds; surface continentality (i.e. very hot during summers Upper air circulation; and and very cold during winters). Ocean currents Wester n cyclonic disturbances and along with onshore winds affect the climate of tropical cyclones cyclones. the coastal areas, For example, any coastal area with warm or cold currents flowing past India lies in the region of north easterly it, will be warmed or cooled if the winds are winds. These winds originate from the onshore. subtropical high-pressure belt of the northern CLIMATE 27 Rationalised 2023-24 hemisphere. They blow southwards, get advancing monsoon and the retreating deflected to the right due to the Coriolis force, monsoon with some regional variations. and move towards the equatorial low-pressure area. Generally, these winds carry little The Cold Weather Season (Winter) moisture as they originate and blow over land. The cold weather season begins from mid- Therefore, they bring little or no rain. Hence, November in northern India and stays till India should have been an arid land, but it is February. December and January are the not so. Let us see why? coldest months in the northern part of India. The temperature decreases from south to the Coriolis force: An apparent force caused by the north. The average temperature of Chennai, on earth’s rotation. The Coriolis force is responsible for deflecting winds towards the right in the northern the eastern coast, is between 24°– 25° Celsius, hemisphere and towards the left in the southern while in the northern plains, it ranges between hemisphere. This is also known as ‘Ferrel’s Law’. 10°C and 15° Celsius. Days are warm and nights are cold. Frost is common in the north The pressure and wind conditions over and the higher slopes of the Himalayas India are unique. During winter, there is a experience snowfall. high-pressure area north of the Himalayas. During this season, the northeast trade Cold dry winds blow from this region to the winds prevail over the country. They blow from low-pressure areas over the oceans to the land to sea and hence, for most part of the country, it is a dry season. Some amount of south. In summer, a low-pressure area rainfall occurs on the Tamil Nadu coast from develops over interior Asia, as well as, over these winds as, here they blow from sea to land. northwestern India. This causes a complete In the northern part of the country, a feeble reversal of the direction of winds during high-pressure region develops, with light winds summer. Air moves from the high-pressure moving outwards from this area. Influenced by area over the southern Indian Ocean, in a the relief, these winds blow through the Ganga south-easterly direction, crosses the equator, valley from the west and the northwest. The and turns right towards the low-pressure areas weather is normally marked by clear sky, low over the Indian subcontinent. These are known temperatures and low humidity and feeble, as the Southwest Monsoon winds. These winds variable winds. blow over the warm oceans, gather moisture A characteristic feature of the cold weather and bring widespread rainfall over the season over the northern plains is the inflow of mainland of India. cyclonic disturbances from the west and the northwest. These low-pressure systems, originate over the Mediterranean Sea and THE S EASONS western Asia and move into India, along with The monsoon type of climate is characterised the westerly flow. They cause the much-needed by a distinct seasonal pattern. The weather winter rains over the plains and snowfall in the conditions greatly change from one season to mountains. Although the total amount of the other. These changes are particularly winter rainfall locally known as ‘mahawat’ is noticeable in the interior parts of the country. small, they are of immense importance for the The coastal areas do not experience much cultivation of ‘rabi’ crops. variation in temperature though there is The peninsular region does not have a well- variation in rainfall pattern. How many seasons defined cold season. There is hardly any are experienced in your place? Four main noticeable seasonal change in temperature seasons can be identified in India – the cold pattern during winters due to the moderating weather season, the hot weather season, the influence of the sea. 28 CONTEMPORARY INDIA-I Rationalised 2023-24  Figure 4.1 : Advancing Monsoon CLIMATE 29 Rationalised 2023-24 The Hot Weather Season (Summer) Advancing Monsoon (The Rainy Season) Due to the apparent northward movement of By early June, the low-pressure condition over the sun, the global heat belt shifts northwards. the northern plains intensifies. It attracts, the As such, from March to May, it is hot weather trade winds of the southern hemisphere. These season in India. The influence of the shifting of south-east trade winds originate over the the heat belt can be seen clearly from warm subtropical areas of the southern oceans. temperature recordings taken during March- They cross the equator and blow in a south- May at different latitudes. In March, the highest westerly direction entering the Indian peninsula as the south-west monsoon. As these winds temperature is about 38° Celsius, recorded on blow over warm oceans, they bring abundant the Deccan plateau. In April, temperatures in moisture to the subcontinent. These winds are Gujarat and Madhya Pradesh are around 42° strong and blow at an average velocity of 30 Celsius. In May, temperature of 45° Celsius is km per hour. With the exception of the extreme common in the northwestern parts of the north-west, the monsoon winds cover the country. In peninsular India, temperatures country in about a month. remain lower due to the moderating influence The inflow of the south-west monsoon into of the oceans. India brings about a total change in the The summer months experience rising weather. Early in the season, the windward temperature and falling air pressure in the side of the Western Ghats receives very heavy northern part of the country. Towards the end rainfall, more than 250 cm. The Deccan of May, an elongated low-pressure area Plateau and parts of Madhya Pradesh also develops in the region extending from the Thar receive some amount of rain in spite of lying Desert in the northwest to Patna and in the rain shadow area. The maximum rainfall Chotanagpur plateau in the east and of this season is received in the north-eastern southeast. Circulation of air begins to set in part of the country. Mawsynram in the southern ranges of the Khasi Hills receives the around this trough. highest average rainfall in the world. Rainfall A striking feature of the hot weather season in the Ganga valley decreases from the east to is the ‘loo’. These are strong, gusty, hot, dry the west. Rajasthan and parts of Gujarat get winds blowing during the day over the north scanty rainfall. and northwestern India. Sometimes they even Another phenomenon associated with the continue until late in the evening. Direct monsoon is its tendency to have ‘breaks’ in exposure to these winds may even prove to be rainfall. Thus, it has wet and dry spells. In fatal. Dust storms are very common during the other words, the monsoon rains take place month of May in northern India. These storms only for a few days at a time. They are bring temporary relief as they lower the interspersed with rainless intervals. These temperature and may bring light rain and cool breaks in monsoon are related to the breeze. This is also the season for localised movement of the monsoon trough. For thunderstorms, associated with violent winds, various reasons, the trough and its axis keep on moving northward or southward, which torrential downpours, often accompanied by determines the spatial distribution of rainfall. hail. In West Bengal, these storms are known When the axis of the monsoon trough lies over as the ‘Kaal Baisakhi’. the plains, rainfall is good in these parts. On Towards the close of the summer season, the other hand, whenever the axis shifts closer pre-monsoon showers are common especially, to the Himalayas, there are longer dry spells in Kerala and Karnataka. They help in the early in the plains, and widespread rain occur in ripening of mangoes, and are often referred to the mountainous catchment areas of the as ‘mango showers’. Himalayan rivers. These heavy rains bring in 30 CONTEMPORARY INDIA-I Rationalised 2023-24  Figure 4.2 : Retreating Monsoon CLIMATE 31 Rationalised 2023-24 their wake, devastating floods causing The low-pressure conditions, over north- damage to life and property in the plains. The western India, get transferred to the Bay of frequency and intensity of tropical Bengal by early November. This shift is depressions too, determine the amount and associated with the occurrence of cyclonic duration of monsoon rains. These depressions, which originate over the depressions form at the head of the Bay of Andaman Sea. These cyclones generally cross Bengal and cross over to the mainland. The the eastern coasts of India cause heavy and depressions follow the axis of the “monsoon widespread rain. These tropical cyclones are trough of low pressure”. The monsoon is often very destructive. The thickly populated known for its uncertainties. The alternation deltas of the Godavari, the Krishna and the of dry and wet spells vary in intensity, Kaveri are frequently struck by cyclones, which frequency and duration. While it causes heavy cause great damage to life and property. floods in one part, it may be responsible for Sometimes, these cyclones arrive at the coasts droughts in the other. It is often irregular in of Odisha, West Bengal and Bangladesh. The its arrival and its retreat. Hence, it sometimes bulk of the rainfall of the Coromandel Coast is disturbs the farming schedule of millions of derived from depressions and cyclones. farmers all over the country. D ISTRIBUTION OF R AINFALL Retreating/Post Monsoons Parts of western coast and northeastern India (The Transition Season) receive over about 400 cm of rainfall annually. During October-November, with the apparent However, it is less than 60 cm in western movement of the sun towards the south, the Rajasthan and adjoining parts of Gujarat, monsoon trough or the low-pressure trough Haryana and Punjab. Rainfall is equally low in the interior of the Deccan plateau, and east over the northern plains becomes weaker. This of the Sahyadris. Why do these regions receive is gradually replaced by a high-pressure low rainfall? A third area of low precipitation system. The south-west monsoon winds is around Leh in Jammu and Kashmir. The rest weaken and start withdrawing gradually. By of the country receives moderate rainfall. the beginning of October, the monsoon Snowfall is restricted to the Himalayan region. withdraws from the Northern Plains. Owing to the nature of monsoons, the The months of October-November form a annual rainfall is highly variable from year to period of transition from hot rainy season to year. Variability is high in the regions of low dry winter conditions. The retreat of the rainfall, such as parts of Rajasthan, Gujarat monsoon is marked by clear skies and rise in and the leeward side of the Western Ghats. As such, while areas of high rainfall are liable to be affected by floods, areas of low rainfall are Mawsynram, the wettest drought-prone (Figure 4.3). place on the earth is also reputed for its stalagmite and stalactite caves. MONSOON AS A U NIFYING B OND temperature. While day temperatures are You have already known the way the Himalayas high, nights are cool and pleasant. The land protect the subcontinent from extremely cold is still moist. Owing to the conditions of high winds from central Asia. This enables northern temperature and humidity, the weather India to have uniformly higher temperatures becomes rather oppressive during the day. compared to other areas on the same latitudes. This is commonly known as ‘October heat’. In Similarly, the Peninsular plateau, under the the second half of October, the mercury begins influence of the sea from three sides, has to fall rapidly in northern India. moderate temperatures. Despite such 32 CONTEMPORARY INDIA-I Rationalised 2023-24  Figure 4.3 : Annual Rainfall CLIMATE 33 Rationalised 2023-24 34 CONTEMPORARY INDIA-I Activity (i) On the basis of the news items above, find out the names of places and the seasons described. (ii) Compare the rainfall description of Chennai and Mumbai and explain the reasons for the difference. (iii) Evaluate flood as a disaster with the help of a case study. Rationalised 2023-24 moderating influences, there are great entire agricultural calendar and the life of the variations in the temperature conditions. people, including their festivities, revolve Nevertheless, the unifying influence of the around this phenomenon. Year after year, monsoon on the Indian subcontinent is quite people of India from north to south and from perceptible. The seasonal alteration of the wind east to west, eagerly await the arrival of the systems and the associated weather conditions monsoon. These monsoon winds bind the provide a rhythmic cycle of seasons. Even the whole country by providing water to set the uncertainties of rain and uneven distribution agricultural activities in motion. The river are very much typical of the monsoons. The valleys which carry this water also unite as a Indian landscape, its animal and plant life, its single river valley unit. E XERCISE 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 (c) Cherrapunji (b) Mawsynram (d) Guwahati (ii) The wind blowing in the northern plains in summers is known as: (a) Kaal Baisakhi (c) Trade Winds (b) Loo (d) None of the above (iii) Monsoon arrives in India approximately in: (a) Early May (c) Early June (b) Early July (d) Early August (iv) 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 2. Answer the following questions briefly. (i) What are the controls affecting the climate of India? (ii) Why does India have a monsoon type of climate? (iii) Which part of India does experience the highest diurnal range of temperature and why? (iv) Which winds account for rainfall along the Malabar coast? (v) Define monsoons. What do you understand by “break” in monsoon? (vi) Why is the monsoon considered a unifying bond? 3. Why does the rainfall decrease from the east to the west in Northern India. CLIMATE 35 Rationalised 2023-24  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. (iii) The Tamil Nadu coast receives winter rainfall. (iv) The delta region of the eastern coast is frequently struck by cyclones. (v) Parts of Rajasthan, Gujarat and the leeward side of the Western Ghats are drought-prone. 5. Describe the regional variations in the climatic conditions of India with the help of suitable examples. 6. Give an account of weather conditions and characteristics of the cold season. 7. Give the characteristics and effects of the monsoon rainfall in India. M AP S KILLS 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. P ROJECT /A CTIVITY (i) Find out which songs, dances, festivals and special food preparations are associated with certain seasons in your region. Do they have some commonality with other regions of India? (ii) Collect photographs of typical rural houses, and clothing of people from different regions of India. Examine whether they reflect any relationship with the climatic condition and relief of the area. FOR DOING IT YOURSELF Figure 1 : Temperature and Rainfall of Delhi 1. In Table-I, the average mean monthly temperatures and amounts of rainfall of 10 representative stations have been given. It is for you to study on your own and convert them into ‘temperature and rainfall’ graphs. A glance at these visual representations will help you to grasp instantly the smilarities and differences between them. One such graph (Figure 1) is already prepared for you. See if you can arrive at some broad generalisations about our diverse climatic conditions. We hope you are in for a great joy of learning. Do the following activities. 2. Re-arrange the 10 stations in two different sequences: 36 CONTEMPORARY INDIA-I Rationalised 2023-24  (i) According to their distance from the equator. (ii) According to their altitude above mean sealevel. 3. (i) Name two rainiest stations. (ii) Name two driest stations. (iii) Two stations with most equable climate. (iv) Two stations with most extreme climate. (v) Two stations influenced by retreating monsoons. (vi) The two hottest stations in the months of (a) February (b) April (c) May (d) June Table I Stations Latitude Altitude J a n. F e b. M a r. Apr. M a y. J u n. J u l. A u g. S e p. O c t. N o v. D e c. A n n u a l (Metres) Rainfall Temperature (°C) 20.5 22.7 25.2 27.1 26.7 24.2 23.0 23.0 23.1 22.9 18.9 20.2 Bengaluru 12°58'N 909 Rainfall (cm) 0.7 0.9 1.1 4.5 10.7 7.1 11.1 13.7 16.4 15.3 6.1 1.3 88.9 Temperature (°C) 24.4 24.4 26.7 28.3 30.0 28.9 27.2 27.2 27.2 27.8 27.2 25.0 Mumbai 19° N 11 Rainfall (cm) 0.2 0.2 – – 1.8 50.6 61.0 36.9 26.9 4.8 1.0 – 183.4 Temperature (°C) 19.6 22.0 27.1 30.1 30.4 29.9 28.9 28.7 28.9 27.6 23.4 19.7 Kolkata 22°34' N 6 Rainfall (cm) 1.2 2.8 3.4 5.1 13.4 29.0 33.1 33.4 25.3 12.7 2.7 0.4 162.5 Temperature (°C) 14.4 16.7 23.3 30.0 33.3 33.3 30.0 29.4 28.9 25.6 19.4 15.6 Delhi 29° N 219 Rainfall (cm) 2.5 1.5 1.3 1.0 1.8 7.4 19.3 17.8 11.9 1.3 0.2 1.0 67.0 Temperature (°C) 16.8 19.2 26.6 29.8 33.3 33.9 31.3 29.0 20.1 27.0 20.1 14.9 Jodhpur 26°18' N 224 Rainfall (cm) 0.5 0.6 0.3 0.3 1.0 3.1 10.8 13.1 5.7 0.8 0.2 0.2 36.6 Temperature (°C) 24.5 25.7 27.7 30.4 33.0 32.5 31.0 30.2 29.8 28.0 25.9 24.7 Chennai 13°4' N 7 Rainfall (cm) 4.6 1.3 1.3 1.8 3.8 4.5 8.7 11.3 11.9 30.6 35.0 13.9 128.6 Temperature (°C) 21.5 23.9 28.3 32.7 35.5 32.0 27.7 27.3 27.9 26.7 23.1 20.7 Nagpur 21°9' N 312 Rainfall (cm) 1.1 2.3 1.7 1.6 2.1 22.2 37.6 28.6 18.5 5.5 2.0 1.0 124.2 Temperature (°C) 9.8 11.3 15.9 18.5 19.2 20.5 21.1 20.9 20.0 17.2 13.3 10.4 Shillong 24°34' N 1461 Rainfall (cm) 1.4 2.9 5.6 14.6 29.5 47.6 35.9 34.3 30.2 18.8 3.8 0.6 225.3 Temperature (°C) 26.7 27.3 28.3 28.7 28.6 26.6 26.2 2.6.2 26.5 26.7 26.6 26.5 Thiruvananthapuram 8°29' N 61 Rainfall (cm) 2.3 2.1 3.7 10.6 20.8 35.6 22.3 14.6 13.8 27.3 20.6 7.5 181.2 Temperature (°C) – 8.5 – 7.2 – 0.6 6.1 10.0 14.4 17.2 16.1 12.2 6.1 0.0 – 5.6 Leh 34° N 34°N 3506 Rainfall (cm) 1.0 0.8 0.8 0.5 0.5 0.5 1.3 1.3 0.8 0.5 – 0.5 8.5 CLIMATE 37 Rationalised 2023-24 4. Now find out (i) Why are Thiruvananthapuram and Shillong rainier in June than in July? (ii) Why is July rainier in Mumbai than in Thiruvananthapuram? (iii) Why are southwest monsoons less rainy in Chennai? (iv) Why is Shillong rainier than Kolkata? (v) Why is Kolkata rainier in July than in June unlike Shillong which is rainier in June than in July? (vi) Why does Delhi receive more rain than Jodhpur? 5. Now think why — Thiruvananthapuram has equable climate? — Chennai has more rains only after the fury of monsoon is over in most parts of the country? — Jodhpur has a hot desert type of climate? — Leh has moderate precipitation almost throughut the year? — while in Delhi and Jodhpur most of the rain is confined to nearly three months, in Thiruvananthapuram and Shillong it is almost nine months of the year? 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. 38 CONTEMPORARY INDIA-I Rationalised 2023-24