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Igp csat-paper-1-geography-gist-of-ncert-climate- Igp csat-paper-1-geography-gist-of-ncert-climate- Document Transcript

  • Click Here For Integrated Guidance Programme http://upscportal.com/civilservices/online-course/integrated-free-guidance-programme Geography GIST OF N.C.E.R.T CLIMATEClimate refers to the sum total of weather west direction. This, northern part of the India liesconditions and variations over a large area for a in sub-tropical and temperate zone and the partlong period of time (more than thirty years). lying south of the Tropic of Cancer falls in theWeather refers to the state of the atmosphere over tropical zone. The tropical zone being nearer to thean area at any point of time. The elements of equ ator, ex peri ence s hi gh tempe ratu resweather and cli mate are the same, i .e. throughout the year with small daily and annualtemperatu re, atmosph eric pressu re, wi nd, range. Area north of the Tropic of Cancer beinghumidity and precipitation. You may have observed away from the equator, experiences extremethat the weather conditions fluctuate very often climate with high daily and annual range ofeven within a day. But there is some common temperature.pattern over a few weeks or months, i.e. days are Th e Himalayan Mou ntains: The to weringcool or hot, windy or calm, cloudy or bright, and wet mountain chain provides an invincible shield toor dry. On the basis of the generalized monthly protect the subcontinent from the cold northernatmospheric conditions, the year is divided into winds. The Himalayas also trap the monsoonseasons such as winter, summer or rainy seasons. winds, forcing them to shed their moisture withinDuring the summer season the desert area of the subcontinent.Rajasthan witnesses 50º temperature whereas Distribution of Land and Water: India is flankedPahalgam sector of Jammu and Kashmir has 20ºC by the India Ocean on three sides in the southtemperature. During winter nights Dras sector of and girdled by a high and continuous mountain-Jammu and Kashmir witnesses– 45ºC temperature wall in the north. As compared to the landmass,where as Thiruvananth puram has 20ºC. water heats up or cools down slowly. ThisRainfall also varies in terms of quantity and differential heating of land and sea createsdistribution in the regions of Himalaya rainfall is different air pressure zones in different seasonsin the from of snowy balls where as in the rest of in and around the Indian subcontinent. Differencepart of India it is a general rain. Again annual in air pressure causes reversal in the direction ofrainfall varies from 400ºC in the Meghalya to 10ºc monsoon winds.in Ladakh and West Rajasthan. In the coastal area Distance from the Sea: With a long coastline, largethe variation of rainfall is less. Whereas in the coastal areas have an equable climate. Areas ininner part of country the seasonal variation is the interior of India are far away from themore. Accordingly the Indians show their unity in moderating influence of the sea. Such areas havediversity in terms of food, clothing, housing and extremes of climate. That is why, the people ofculture. Mumbai and the Konkan coast have hardly anyFactors determining the climate of India idea of extremes of temperature and the seasonal rhythm of weather. On the other hand, theIndia’s climate is controlled by a number of factors seasonal contrasts in weather at places in thewhich can be broadly divided into two groups- (a) interior of the country such as Delhi, Kanpur andfactors related to location and relief, and (b) factors Amritsar affect the entire sphere of life.related to air pressure and winds. Altitude : Temperature decreases with height. Due(a) Factors related to Location and Relief to thin air, places in the mountains are coolerLatitude: You know that the Tropic of Cancer than places on the plains. For example, Agra andpasses through the central part of India in east- Darjeeling are located on the same latitude, butClick Here to Buy Full Study Kit in Hard Copy © WWW.UPSCPORTAL.COMhttp://upscportal.com/civilservices/online-course/study-kit-for-ias-pre-gs-paper-1-2012
  • Click Here For Integrated Guidance Programme http://upscportal.com/civilservices/online-course/integrated-free-guidance-programme Geographytemperature of January in Agra is 16ºC whereas Jet Stream and Upper Air Circulation: The patternit is only 4ºC in Darjeeling. of air circulation discussed above is witnessed only at the lower level of the atmosphere near theRelief: The physiography or relief of India also surface of the earth. Higher up in the loweraffects the temperature, air pressure, direction and troposphere, about three km above the surface ofspeed of wind and the amount and distribution of the earth, a different pattern of air circulation israinfall. The windward sides of Western Ghats and observed. The variations in the atmosphericAssam rece ive high rai nfal l du ring Jun e- pressure closer to the surface of the earth have noSeptember whereas the southern plateau remains role to play in the making of upper air circulation.dry to its leeward situation along the Western Ghats. All of Western and Central Asia remains under the(b) Factors Related to Air Pressure and Wind influence of westerly winds along the altitude of 9-To understand the differences in local climates of 13 km from west to east. These winds blow acrossIndia, we need to understand the mechanism of the Asian continent at latitudes north of thethe following three factors: Himal ayas rou ghly parallel to the Tibetan highlands. These are known as jet streams.(i) Distribution of air pressure and winds on the Tibetan highlands act as a barrier in the path of surface of the earth. these jet streams. As a result, jet streams get(ii) Upper air circulation caused by factors bifurcated. On of its branches blows to the north of controlling global weather and the inflow of the Tibetan highlands, while the southern branch different air masses and jet streams. blows in an eastward direction, south of the(iii)Inflow of western cyclones generally known as Himalayas. It has its mean position at 25ºN in disturbances during the winter season and February at 200-300 mb level. It is believed that tropical depressions during the south-west this southern branch of the jet stream exercise monsoon period into India, creating weather an important influence on the winter weather in conditions favourable to rainfall. India.The mechanism of these three factors can be Western Cyclonic Disturbance and Tropicalunderstood with reference to winter and summer Cyclones: The western cyclone disturbances whichseasons of the year separately. enter the Indian subcontinent from the west and the northwest during the winter months originateMechanism of Weather in the Winter over the Mediterranean Sea and are brought intoSeason India by the westerly jet stream. An increase inSurface pressure and winds: In winter months, the prevailing night temperature generallythe weather conditions over India are generally indicates an advance in the arrival of theseinfluenced by the distribution of pressure in cyclones disturbances.Central and Western Asia. A high pressure centre Tropical cyclones originate over the Bay of Bengalin the region lying to the north of the Himalayas and the Indian Ocean. These tropical cyclonesduring winter. This centre of high pressure gives have very high wind velocity and heavy rainfallrise to the flow of air at the low level from the north and hit the Tamil Nadu, Andhra Pradesh and Orissatowards the Indian subcontinent, south of the coast. Most of these cyclones are very destructivemountain range. The surface winds blowing out of due to high wind velocity and torrential rain thatthe high pressure centre over Central Asia reach accompanies it.India in the form of a dry continental air mass.These continental winds come in contact with Inter Tropical Convergence Zone (ITCZ)trade winds over northwestern India. The positionof this contact zone is not, however, stable. The Inter Tropical Convergence Zone (ITCZ)Occasionally, it may shift its position as far east is a low pressure zone located at theas the middle Ganga valley with the result that equator where trade winds converge, andwhole of northwestern and northern India up to so, it is a zone where air tends to ascend.the middle Ganga valley comes under the influence In July, the ITCZ is located around 20ºNof dry northwestern winds. latitu des (ove r th e Gangetic plain ),Click Here to Buy Full Study Kit in Hard Copy © WWW.UPSCPORTAL.COMhttp://upscportal.com/civilservices/online-course/study-kit-for-ias-pre-gs-paper-1-2012
  • Click Here For Integrated Guidance Programme http://upscportal.com/civilservices/online-course/integrated-free-guidance-programme Geography sometimes called the monsoon trough. This easterly jet stream steers the tropical depressions mon soon tro ugh enco urag es the into India. These depressions play a significant development of thermal low over north and role in the distribution of monsoon rainfall over northwest India. Due to the shift of ITCZ, the Indian subcontinent. The tracks of these the trade winds of the southern hemisphere depressions are the areas of highest rainfall in cross the equator between 40ºE and 60ºE India. The frequency at which these depressions longitudes and start blowing from southwest visit India, their direction and intensity, all go a to northeast due to the Coriolis force. It long way in determining the rainfall pattern during becomes southwest monsoon. In winter, the southwest monsoon period. the ITCZ moves southward, and so the The Nature of Indian Monsoon reversal of winds from northeast to south Monsoon is a familiar, though a little known and southwest, takes place. They are called climatic phenomenon. Despite the observations northeast monsoons. spread over centuries, the monsoon continues toMechanism of Weather in the Summer puzzle the scientists. Many attempts have beenSeason made to discover the exact nature and causation of monsoon, but so far, no single theory has beenSurface Pressure and Winds: As the summer sets abl e to explain the mon soon ful ly. A re alin and the sun shifts northwards, the wind breakthrough has come recently when it wascirculation over the subcontinent undergoes a studied at the global rather than at regional level.complete reversal at both, the lower as well as theupper levels. By the middle of July, the low pressure Systematic studies of the causes of rainfall in thebelt nearer the surface (termed as Inter Tropical South Asian region help to understand the causesConvergence Zone (ITCZ) shifts northwards, and salient features of the monsoon, particularlyroughly parallel to the Himalayas between 20ºN some of its important aspects, such as:and 25ºN. By this time, the westerly jet stream (i) The onset of the monsoon.withdraws from the Indian region. In fact,meteorologists have found an interrelationship (ii) Rain-bearing systems (e.g. tropical cyclones)between the northward shift of the equatorial and the relationship between their frequencytrough (ITCZ) and the withdrawal of the westerly and distribution of monsoon rainfall.jet stream from over the North Indian Plain. It is (iii) Break in the monsoon.generally believed that there is a cause and effectrelationship between the two. The ITCZ being a Onset of the Monsoonzone of low pressure attracts inflow of winds from Towards the end of the nineteenth century, it wasdifferent directions. The maritime tropical air believed that the differential heating of land andmass (mT) from the southern hemisphere, after sea during the summer months is the mechanismcrossing the equator, rushes to the low pressure which sets the stage for the monsoon winds of driftarea in the general southwesterly direction. It is towards the subcontinent. During April and Maythis moist air current which is popularly known when the sun shines vertically over the Tropic ofas the southwest monsoon. Cancer, the large landmass in the north of IndianJet Streams and Upper Air Circulation: The Ocean gets intensely heated. This causes thepattern of pressure and winds as mentioned above formation of an intense low pressure in theis formed only at the level of the troposphere. An northwestern part of the subcontinent. Since theeasterly jet stream flows over the southern part of pressure in the Indian Ocean in the south of thethe Peninsula in June, and has a maximum speed landmass is high as water gets heated slowly, theof 90 km per hour. In August, it is confined to 15ºN low attracts the southeast trades across thelatitude, and in September up to 22ºN latitudes. Equator. These conditions help in the northward shift in the position of the ITCZ. The southwestThe easterlies normally do not extend to the north monsoon may thus, be seen as a continuation ofof 30ºN latitude in the upper atmosphere. the southeast trades deflected towards the IndianEasterly Jet Stream and Tropical Cyclones: The subcontinent after crossing the Equator. TheseClick Here to Buy Full Study Kit in Hard Copy © WWW.UPSCPORTAL.COMhttp://upscportal.com/civilservices/online-course/study-kit-for-ias-pre-gs-paper-1-2012
  • Click Here For Integrated Guidance Programme http://upscportal.com/civilservices/online-course/integrated-free-guidance-programme Geographywinds cross the Equator between 40ºE and 60ºE EI-Nino and the Indian Monsoonlongitudes. EI-Nino is a complex weather system thatThe shift in the position of the ITCZ is also related appears once every three to seven yearsto the phenomenon of the withdrawal of the bringing drought, floods and other weatherwesterly jet stream from its position over the north extremes to different parts of the world.Indian plain, south of the Himalayas. The easterly Th e sy stem involves o cean ic andjet stream sets in along 15ºN latitude only after atmosph eric phe nome na w ith thethe western jet stream has withdrawn itself from appearance of warm currents off the coast ofthe region. This easterly jet stream is held peru in the Eastern Pacific and affectsresponsible for the burst of the monsoon in India. weather in many places including India. EI-Entry of Monsoon into India: The southwest Nino is merely an extension of the warmmonsoon sets in over the Kerala coast by 1st June equatorial current which gets replaced temporarily by cold Peruvian current orand moves swiftly to reach Mumbai and Kolkata Humbolt current (locate these currents inbetween 10th and 13th June. By mid- July, your atlas). This current increases theso uthw e st monsoon engu lfs the enti re temperature of water on the Peruvian coastsubcontinent. by 10ºC. This results in:Rain-bearing Systems and Rainfall (i) The distortion of equatorial atmosphericDistribution circulation;There seem to be two rain-bearing systems in (ii) Irregularities in the evaporation of seaIndia. First originate in the Bay of Bengal causing water;rainfall over the plains of north India. Second is (iii) Reduction in the amount of planktonsthe Arabian Sea current of the southwest monsoon which further reduces the number ofwhich brings rain to the west coast of India. Much fish in the sea.of the rainfall along the Western Ghats isorographic as the moist air is obstructed and forced The word EI-Nino means ‘Child Christ’to rise along the Ghats. The intensity of rainfall because this cu rrent appears aro undover the west coast of India is, however, related to Christmas in December. December is a summer month in Peru (S outh erntwo factors: Hemisphere).(i) The offshore meteorological conditions. EI-Nino is used in India for forecasting long(ii) The position of the equatorial jet stream along range monsoon rainfall. In 1990-91, there the eastern coast of Africa. was a wild EI-Nino even and the onset of southwest monsoon was delayed over mostThe fre quency of the tropical depressi ons parts of the country ranging from five tooriginating from the Bay of Bengal varies from year twelve days.to year. Their paths over India are mainlydetermined by the position of ITCZ which is Break in the Monsoongenerally termed as the monsoon trough. As the During the south-west, monsoon period afteraxis of the monsoon trough oscillates, there are having rains for a few days, it rain fails to occur forfluctuations in the track and direction of these one or more weeks, it is known as break in thedepressions, and the intensity and the amount of monsoon. These dry spells are quite commonrainfall vary from year to year. The rain which during the rainy season. These breaks in thecomes in spells, displays a declining trend from different regions are due to different reasons:west to east over the west coast, and from the (i) In northern India rains are likely to fail if thesoutheast towards the northwest over the North rain-bearing storms are not very frequentIndian Plai n and the northern part of the along the monsoon trough or the ITCZ over thisPeninsula. region.Click Here to Buy Full Study Kit in Hard Copy © WWW.UPSCPORTAL.COMhttp://upscportal.com/civilservices/online-course/study-kit-for-ias-pre-gs-paper-1-2012
  • Click Here For Integrated Guidance Programme http://upscportal.com/civilservices/online-course/integrated-free-guidance-programme Geography(ii) Over the west coast the dry spells are associated (i) States like Punjab, Haryana and Rajasthan with days when winds blow parallel to the coast. bei ng far away from the moderating influenced of sea experience continentalThe Rhythm of Seasons climate.The climatic conditions of India can best be (ii) The snowfall in the nearby Himalayan rangesdescribed in terms of an annual cycle of seasons. creates cold wave situation; andThe meteorologists recognize the following fourseasons: (iii) Around February, the cold winds coming from the Caspian Sea and Turkmenistan bring(i) The cold weather season cold wave along with frost and fog over the(ii) The hot weather season northwestern parts of India.(iii) The southwest monsoon season The Peninsular region of India, however, does not have any well-defined cold weather season. There(iv) The retreating monsoon season. is hardly any seasonal change in the distribution pattern of the temperature in coastal areas Some Famous Local Storms of Hot because of moderating influence of the sea and Weather Season the proximity to equator. For example, the mean (i) Mango Shower: Towards the end of max imum temperature for Jan uary at summer. There are pre-monsoon showers Thiruvanantapuram is as high as 31ºC, and for which are a common phenomena in Kerala June, it is 29.5ºC. Temperatures at the hills of and coastal areas of Karnataka. Locally, they Western Ghats remain comparatively low. are known as mango showers since they help Pressure and Winds: By the end of December (22nd in the early ripening of mangoes. December), the sun shines vertically over the (ii) Blossom Shower: With this shower, coffee Tropic of Capricorn in the southern hemisphere. flowers blossom in Kerala and nearby areas. The weather in this season is characterized by (iii) Nor Westers: These are dreaded evening feeble high pressure conditions over the northern thunderstorms in Bengal and Assam. Their plain. In south India, the air pressure is slightly notorious nature can be understood from the lower. The isobars of 1019 mb and 1013 mb pass local nomenclature of ‘Kalbaisakhi’, a through northwe st I ndia and far sou th, calamity of the month of Baisakh. These respectively. showers are useful for tea, Jute and rice As a result, winds start blowing from northwestern cultivation. In Assam, these storms are high pressure zone to the low air pressure zone known as “Bordoiseela”. over the Indian Ocean in the south. (iv) Loo: Hot, dry and oppressing winds Due to low pressure gradient, the light winds with blowing in the Northern plains from Punjab a low velocity of about 3-5 km per hour begin to to Bihar with higher intensity between Delhi blow outwards. By and large, the topography of the and Patna. region influences the wind direction. They are westerly or northwesterly down the Ganga Valley.The Cold Weather Season They become northerly in the Ganga-BrahamputraTemperature: Usually, the cold weather season delta. Free from the influence of topography, theysets in by mid-November in northern India. are clearly northeasterly over the Bay of Bengal.December and January are the coldest months in During the winters, the weather in India isthe northern plain. The mean daily temperature pleasant. The pleasant weather conditions,remains below 21ºC over most parts of northern however, at intervals, get disturbed by shallowIndia. The night temperature may be quite low, cyclonic depressions originating over the eastsometimes going below freezing point in Punjab Medirranean Sea and travelling eastwards acrossand Rajasthan. West Asia, Iran, Afghanistan and Pakistan beforeThere are three main reasons for the excessive the reach the northwestern parts of India. On theircold in north India during this season: way, the moisture content gets augmented from Click Here to Buy Full Study Kit in Hard Copy © WWW.UPSCPORTAL.COM http://upscportal.com/civilservices/online-course/study-kit-for-ias-pre-gs-paper-1-2012
  • Click Here For Integrated Guidance Programme http://upscportal.com/civilservices/online-course/integrated-free-guidance-programme Geographythe Caspian Sea in the north and the Persian Gulf moves further north, and in the north-western partin the south. of India, temperatures around 48ºC are not uncommon.Role of Westerly Jet Stream The hot weather season in south India is mild andRainfall: Winter monsoons do not cause rainfall not so intense as found in north India. Theas they move from land to the sea. It is because Pe ninsular situati on o f so uth Indi a wi thfirstly, they have little humidity; and secondly, due moderating effect of the oceans keeps theto anti cyclonic circulation on land, the possibility temperatures lower than that prevailing in northof rainfall from them reduces. So, most parts of India. So, temperatures remain between 26ºC andIndia do not have rainfall in the winter season. 32ºC. Due to altitude, the temperatures in the hillsHowever, there are some exceptions to it: of Western Ghats remain below 25ºC. In the coastal(i) In northwe stern In dia, some we ak regions, the north-south extent of isotherms temperate cyclones from the Mediterranean parallel to the coast confirms that temperature sea cause rainfall in Punjab, Haryana, Delhi does not decrease from north to south rather it and western Uttar Pradesh. Although the increases from the coast to the interior. The mean amount is meager, it is highly beneficial for daily minimum temperature during the summer rabi crops. The precipitation is in the form of months also remains quite high and rarely goes snowfall in the lower Himalayas. It is this below 26ºC. snow that sustains the flow of water in the Himalayan Rivers during the summer Pressure and Winds: The summer months are a months. The precipitation goes on decreasing period of excessive heat and falling air pressure from west to east in the plains and from north in the northern half of the country. Because of the to south in the mountains. The average heating of the subcontinent, the ITCZ moves winter rainfall in Delhi is around 53 mm. In northwards occupying a position centred at 25ºN Punjab and Bihar, rainfall remains between in July. Roughly, this elongated low pressure 25 mm and 18 mm respectively. monsoon trough extends over the Thar desert in(ii) Central parts of India and northern parts of the north-west to Patna and Chotanagpur plateau southern Peninsula also get winter rainfall in the east-southeast. The location of the ITCZ occasionally. attracts a surface circulation of the winds which are southwesterly on the west coast as well as along(iii) Arunachal Pradesh and Assam in the the coast of West Bengal and Bangladesh. They are northeastern parts of India also have rains easterly or southeasterly over north Bengal and between 25 mm and 50 mm during these Bihar. It has been discussed earlier that these winter months. currents of southwesterly monsoon are in reality(iv) During October and November, northeast ‘displaced’ equatorial westerlies. The influx of these monsoon while crossing over the Bay of winds by mid-June brings about a change in the Bengal, pick up moisture and causes weather towards the rainy season. torrential rainfall over the Tamil Nadu coast, sou thern An dhra Pradesh , so uthe ast In the heart of the ITCZ in the northwest, the dry Karnataka and southeast Kerala. and hot winds known as ‘Loo’, blow in the afternoon, and very often, they continue to well into midnight.The Hot Weather Season Dust storms in the evening are very commonTemperature: With the apparent northward during May in Punjab, Haryana, Eastern Rajasthanmovement of the sun towards the Tropic of Cancer and Uttar Pradesh. These temporary storms bringin March, temperatures start rising in north India. a welcome respite from the oppressing heat sinceApril, May and June are the months of summer in they bring with them light rains and a pleasantnorth India. In most parts of India, temperatures cool breeze. Occasionally, The moisture-ladenrecorded are between 30º-32ºC. In March, the winds are attracted towards the periphery of thehighest day temperature of about 38ºC occurs in trough. A sudden contact between dry and moistthe Deccan Plateau while in April, temperature air masses gives rise to local storms of greatranging between 38ºC and 43ºC are found in intensity. These local storms are associated withGujarat and Madhya Pradesh. In May, the heat belt violent winds, torrential rains and even hailstorms. Click Here to Buy Full Study Kit in Hard Copy © WWW.UPSCPORTAL.COM http://upscportal.com/civilservices/online-course/study-kit-for-ias-pre-gs-paper-1-2012
  • Click Here For Integrated Guidance Programme http://upscportal.com/civilservices/online-course/integrated-free-guidance-programme GeographyThe Southwest Monsoon Season of low rainfall is known as the rain-shadow area. Find out the rainfall at Kozhikode,As a result of rapid increase of temperature in May Mangalore, Pune and Bangalore and note theover the northwestern plains, the low pressure difference.conditions over there get further intensified. Byearly June, they are powerful enough to attract (ii) Another branch of the Arabian sea monsoonthe trade winds of Southern Hemisphere coming strikes the coast north of Mumbai. Movingfrom the Indian Ocean/ These southeast trade along the Narmada and Tapi river valleys,winds cross the equator and enter the Bay of Bengal these winds cause rainfall in extensive areasand the Arabian Sea, only to be caught up in the of central India. The Chotanagpur plateauair circulation over India. Passing over the gets 15 cm rainfall from this part of theequatorial warm currents, they bring with them branch. Thereafter, they enter the Gangamoisture in abundance. After crossing the equator, plains and mingle with the Bay of Bengalthey follow a southwesterly direction. That is why branch.they are known as southwest monsoons. (iii) A third branch of this monsoon wind strikesThe rain in the southwest monsoon season begins the Saurashtra Peninsula and the Kachchh.rather abruptly. One result of the first rain is that It then passes over west Rajasthan and alongit brings down the temperature substantially. This the Aravallis, causing only a scanty rainfall.sudden onset of the moisture-laden winds In Punjab and Haryana, it too jokns the Bayassociated with violent thunder and lightening, is of Bengal branch. These two branches,often termed as the “break” or “burst” of the reinforced by each other, cause rains in themonsoons. The monsoon may burst in the first western Himalayas.week of June in the coastal areas of Kerala, Monsoon Winds of the Bay of BengalKarnataka, Goa and Maharashtra while in theinterior parts of the country; it may be delayed to The Bay of Bengal branch strikes the coast ofthe first week of July. The day temperature Myanmar and part of southeast Bangladesh. Butregisters a decline of 5ºC to 8ºC between mid-June the Arakan Hills along the coast of Myanmar deflectand mid-July. a big portion of this branch towards the Indian subcontinent. The monsoon, therefore, entersAs the se w inds approach the l and, the ir West Bengal and Bangladesh from south andsouthwesterly direction is modified by the relief southeast instead of from the south-westerlyand thermal low pressure over the northwest India. direction. From here, this branch splits into twoThe monsoon approaches the landmass in two under the influence of the Himalayas and thebranches: thermal low is northwest India. Its one branch(i) The Arabian Sea branch moves westward along the Ganga plains reaching as far as the Punjab plains. The other branch moves(ii) The Bay of Bengal branch. up the Brahmaputra valley in the north and theMonsoon Winds of the Arabian Sea northeast, causing widespread rains. Its sub- branch strikes the Garo and Khasi hills ofThe monsoon winds originating over the Arabian Meghalya. Mawsynram, located on the crest ofSea further split into three branches: Khasi hills, receives the highest average annual(i) Its one branch is obstructed by the Western rainfall in the world. Ghats. These winds climb the slopes of the Western Ghats from 900-1200 m. Soon, they Here it is important to know why the Tamil Nadu become cool, and as a result, the windward coast remains dry during this season. There are side of the Sahyadris and Western Coastal two factors responsible for it: Plain receive very heavy rainfall ranging (i) The Tamil Nadu coast is situated parallel to between 250 cm and 400 cm. After crossing the Bay of Bengal branch of southwest the Western Ghats, these winds descend and monsoon. get heated up. This reduces humidity in the winds. As a result, these winds cause little (ii) It lies in the rain shadow area of the Arabian rainfall east of the Western Ghats. This region Sea branch of the south-west monsoon. Click Here to Buy Full Study Kit in Hard Copy © WWW.UPSCPORTAL.COM http://upscportal.com/civilservices/online-course/study-kit-for-ias-pre-gs-paper-1-2012
  • Click Here For Integrated Guidance Programme http://upscportal.com/civilservices/online-course/integrated-free-guidance-programme GeographyCharacteristics of Monsoonal Rainfall southward in response to the southward march of the sun. The monsoon retreats from the western(i) Rainfall recei ved from the sou thwe st Rajasthan by the first week of September. It monsoons is seasonal in character, which withdraws from Rajasthan, Gujarat, Western occurs between June and September. Ganga plain and the Central Highlands by the end(ii) Monsoonal rainfall is largely governed by relief of the month. By the beginning of October, the low or topography. For instance the windward side pressures covers northern parts of the Bay of of the Western Ghats register a rainfall of Bengal and by early November, it moves over over 250 cm. Again, the heavy rainfall in the Karnataka and Tamil Nadu. By the middle of northeastern states can be attributed to their December, the centre of low pressure is completely hill ranges and the Eastern Himalayas. removed from the Peninsula.(iii) The monsoon rainfall has a declining trend The retreating southwest monsoon season is with increasing distance from the sea. marked by clear skies and rise in temperature. Kol kata receive s 119 cm during the The land is still moist. Owing to the conditions of southwest monsoon period, Patna 105 cm, high temperature and humidity, the weather Allahabad 76 cm and Delhi 56 cm. becomes rather oppressive. This is commonly(iv) The monsoon rains occur in wet spells of few known as the ‘October heat’. In the second half of days, duration at a time. The wet spells are October, the mercury begins to fall rapidly, interspersed with rainless interval known as particularly in northern India. The weather in the ‘breaks’. These breaks in rainfall are related retreating monsoon is dry in north India but it is to the cyclonic depressions mainly formed at associated with rain in the eastern part of the the head of the Bay of Bengal, and their Peninsula. Here, October and November are the crossing into the mainland. Besides the rainiest months of the year. frequency and intensity of these depressions, The widespread rain in this season is associated the passage followed by them determines the with the passage of cyclonic depressions which spatial distribution of rainfall. originate over the Andaman Sea and manage to(v) The summer rainfall comes in a heavy cross the eastern coast of the southern Peninsula. downpour leading to considerable run off and These tropical cyclones are very destructive. The soil erosion. thickly populated deltas of the Godavari, Krishna and Kaveri are their preferred targets. Every year(vi) Monsoons play a pivotal role in the agrarian cyclones bring disaster here. A few cyclonic storms economy of India because over three-fourths also strike the coast of West Bengal, Bangladesh of the total rain in the country is received and Myanmar. A bulk of the rainfall of the during the southwest monsoon season. Coromon dal coast is derived fro m th ese(vii) Its spatial distribution is also uneven which depressions and cyclones. Such cyclonic storms ranges from 12 cm to more than 250 cm. are less frequent in the Arabian Sea.(viii) The beginning of the rains sometimes is Distribution of Rainfall considerably delayed over the whole or a part The average annual rainfall in India is about 125 of the country. cm, but it has great spatial variations.(ix) The rains sometimes end considerably Areas of High Rainfall: The highest rainfall occurs earlier than usual, causing great damage to along the west coast, on the Western Ghats, as standing crops and making the sowing of well as in the sub-Himalayan areas is the winter crops difficult. northeast and the hills of Meghalaya. Here theSeason of Retreating Monsoon rainfall exceeds 200 cm. In some parts of Khasi and Jaintia hills, the rainfall exceeds 1,000 cm.The months of October and November are known In the Brahmaputra valley and the adjoining hills.for retreating monsoons. By the end of September, The rainfall is less then 200 cm.the southwest monsoon becomes weak as the lowpressure trough of the Ganga plain starts moving Areas of Medium Rainfall: Rainfall between 100- Click Here to Buy Full Study Kit in Hard Copy © WWW.UPSCPORTAL.COM http://upscportal.com/civilservices/online-course/study-kit-for-ias-pre-gs-paper-1-2012
  • Click Here For Integrated Guidance Programme http://upscportal.com/civilservices/online-course/integrated-free-guidance-programme Geography200 cm is received in the southern parts of Gujarat,east Tamil Nadu, northeastern Peninsula coveringOrissa, Jharkhand, Bihar, eastern MadhyaPradesh, northern Ganga plain along the sub-Himalayas and the Cachar Valley and Manipur.Seasons Months Months (According to the (According to the India Calendar) Indian Calendar)Vasanta Chaitra-Vaisakha March-AprilGrishma Jyaistha-Asadha May-JuneVarsha Sravana-Bhadra July-AugustSharada Asvina-Kartika September-OctoberHemanta Margashirsa-Pausa November-DecemberShishira Magha-Phalguna January-FebruaryAreas of Low Rainfall: Western Uttar Pradesh,Delhi, Haryana. Punjab, Jammu and Kashmir,eastern Rajasthan, Gujarat and Deccan Plateaureceive rainfall between 50-100 cm.Areas of Inadequate Rainfall: Parts of thePe ninsula, especially in A ndhra Pradesh,Karnataka and Maharashtra, Ladakh and most ofwestern Rajasthan receive rainfall below 50 cm.Snowfall is restricted to the Himalayan region.Click Here to Buy Full Study Kit in Hard Copy © WWW.UPSCPORTAL.COMhttp://upscportal.com/civilservices/online-course/study-kit-for-ias-pre-gs-paper-1-2012