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ICSE Notes 2016 : climate of india notes

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Shashank Rr
St. Francis School ICSE, Hongasandra, Bengaluru

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-1- #04 , The Climate of India Name of Indian climate: Tropical Monsoon Climate. The term Monsoon is derived from an Arabic word Mausim meaning season. Monsoon winds are those winds which blow from sea to land in one season and from landmass towards the sea in the other season. Infact the climate of all south Asian countries are controlled by the Monsoon mechanism or South Asia has a Monsoon type of climate. The extremes of climate in India. There are certain regional variations in the climate of India based on topographic differences. The northern plains of India have continental type of climate. It is extremely hot in summer and very cold in winter. The reason is the distance of this area away from the moderating influence of the sea. In winter season the temperatures over Kashmir and many Himalayan regions fall below 0 C where as during May / June the Thar desert of India experiences severe heat with temperature rising over 50 C. The Thar desert is an extremely arid region with an annual rainfall of less than 25 cm where as Mawsynram near Cherrapunjee on the Khasi hills of Meghalaya receives as high as 1187cm of rainfall annually. The coastal regions of India have equable climate due to the moderating influence of the sea. Factors affecting the climate of India. 1. Role of Himalayas : The high wall of Himalayas along with its eastern and western offshoots act as an effective climatic barrier. It protects India from the cold and chilly winds originating from the Arctic region thus protects from severity of cold from winter. During the summer season it checks the moisture laden monsoon winds and helps in bringing plenty of rainfall to India. 2. Moderating influence of the sea: The Indian Ocean, Arabian Sea and Bay of Bengal exert a moderating influence on the coastal regions of India. These water bodies provides much needed moisture to the summer monsoons which brings plenty of rainfall to these regions. Places in the interior have continental type of climate as they are far from the moderating influence of the sea and have very hot summers and very cold dry winters. Punjab, Haryana, UP, Rajasthan, Delhi, Chandigarh, Lucknow and Jaipur are examples for such places. 3. Altitude: Due to the altitude factor, places located on the high mountains such as hill stations of Darjeeling, Nainital, Shimla, Mussoorie, Kathmandu, Paro etc remain cool through out the year. (for every 1000m of height decrease of 6 -2- C.) This is the reason for the high temperature of towns and cities on plain rather than hill stations. 4. Upper Air Circulation ( Jet Stream): it is a swiftly blowing wind at the height of 3 to 5 km above the sub tropical high pressure belt. It has two branches the Easterly and Westerly Jets. The Westerly Jet brings the Western disturbances and the Easterly Jet brings tropical depressions over the coastal regions of Andhra Pradesh, West Bengal and Tamil Nadu. Indian Climate Two basic monsoon winds control the climate of India. The South West Monsoon in summer and the North East (retreating monsoon) in winter. The monsoon winds changes their directions according to the seasons. It blows moist air from the ocean to the land in summer and blows dry air off shore in winter. Q: What are the similarities between the land and the sea breeze and the monsoon winds? Both are caused due to the differential rate of heating and cooling of land and water. Yet both reverse their direction periodically and derive their names accordingly. Q: What is the main difference between the land and the sea breeze and the monsoon winds? Ans: The land and sea breezes reverse their direction in the course of the day, land breeze at night and sea breeze during the day. But the South West and North East Monsoon winds reverse their direction only seasonally in summer and winter respectively. Q: What is the main difference between the sea breeze and the Monsoon winds? -3- Ans: the sea breeze do not bring rain fall as the period during which they blow is too short for collecting moisture from the sea, while the Monsoons, blowing from the sea brings rainfall as they blow over a sufficient length of time. Features of Indian climate. Tropical monsoon type of climate Diversity in climatic conditions Monsoon mechanism dominates the climate Presence of four distinct seasons in a year. Topical depressions or Bay Cyclones in the late monsoons. Westerly Depressions causing rainfall during winter in North India. Seasons of India The Cold Season : December to February Due to the latitudinal position of India temperature generally decreases from south to the north. The sun rays starts to fall slanting position on Indian sub continent. The average temperature is below 21 C. and very low at high altitudes. January is the coldest month. Weather conditions:Clear skies, Fine cool weather and Light northerly winds and low humidity . The north east monsoon off shore wind of winter season brings no rainfall to most parts of India except Tamil Nadu. Thus Tamil Nadu receives major part of its rain about 70 cm of rainfall during the months of October, November, December and January. Same time from Western disturbances Parts of Punjab, Haryana, Jammu & Kashmir, Himachal Pradesh, norther Rajasthan, Utharakhand and western UP receives an amount of 5 to 7 cm of rainfall. This cyclonic rainfall is beneficial to crops like wheat and barley. The Hot Season (March to mid- June) Due to the vertical rays of sun maximum temperature receives in Indian subcontinent. Very high temperatures are recorded. Weather conditions Due to excessive heat and dryness wells and tanks almost dry up, rivers shrink to narrow stream. Dust storm with strong winds is common in Punjab, Haryana and UP. They were known as Northwesters and Loo here, Kalbaisakhi in Assam and West Bengal and Mango showers in Kerala. Kalbaisakhi brings torrential rainfall and destruction to crops and property. -4- But this summer rain is good for tea in Assam, jute and rice in West Bengal and ripening of mangoes in Kerala. The Rainy Season (mid June to end of September) The intense heat prevails over the Indian subcontinent in the months of April and May causes a low pressure region. It attracts the moisture laden South East Trade winds from the southern hemisphere. On crossing the equator they deflect to their right and blow over the Indian subcontinent as the South West Monsoon winds. The South West Monsoon winds are divided as Arabian Sea branch and Bay of Bengal branch. Arabian Sea branch of South West Monsoon. The total volume of rain it brings is three times greater than the Bay of Bengal branch. The High Western Ghats force the moist air to rise quite high and precipitates around 250 to 300cm in the windward side and leeward slopes receives around 60 cm of rainfall. Further east towards Chennai receives 30 to 40 cm of rain. The wind deposits less rainfall from west to east direction. Thiruvananthapuram around 325 cm Goa 300cm Mumbai 200cm After crossing the Western Ghats the monsoon winds reaches MadhyaPradesh, Jharkhand and Orissa and brings moderate rainfall. -5- Part of it enters Narmada valley and gives a good amount of rainfall to Chotanagpur Plateau. A part of these winds goes straight to the sub- Himalayan region giving rainfall to the foothills of Western Himalayas, Eastern Punjab, Haryana and North eastern Rajasthan and meets with the Bay of Bengal Branch of South West Monsoon. The Aravalli Hills runs almost parallel to these winds direction and do not form a barrier to intercept these winds hence Thar Desert of South Eastern Rajasthan receives an amount of less than 25cm of rainfall in a year. The Bay of Bengal Branch of South West Monsoon These winds passing overt the Ganga Brahmaputra Delta, strike against the lower ranges of the Himalayas, Chittagong and Assam Hills and brings heavy rainfall in West Bengal, Arunachal Praseh and Southern slope of Khasi Jaintia Hills. Thus Cherrapunji on the windward slope of Khasi hills receives an annual rainfall of 1250cm. The Bay of Bengal branch precipitates 250 cm in Ganga delta 100cm in Patna, 50 cm at Delhi and 25cm at Indus valley. As Aravalli blocks these winds the leeward side of South western Rajasthan remains with low rain or no rain. The Duration of Monsoon in India Most parts of India 100 to 120 days Kerala Around six months Rajasthan 45 to 50 days Retreating Monsoon Season -6- This is the period of transition between the final withdrawal of the South West Monsoon and the regular setting of the North East Monsoon. Due to the apparent movement of the Sun south of equator, the low pressure area over the north western part of India weakens and the south west monsoon starts withdrawing from the subcontinent. By beginning of September the wind withdraws from Rajasthan, retreats from Punjab and Haryana by mid September and by first week of October it withdraws from most parts of North India. By mid- October it retreats from Central India and by early November The monsoon winds completely withdraws from the Indian sub continent. Tropical Cyclones The general direction of advancing monsoon is towards the north where as the retreating monsoon is towards the south. During the period of retreating Monsoon due to the local variations of heat and moisture tropical cyclones are occurred, which originates in the Andaman Sea and travels towards the west or North West in the Bay of Bengal. Strong winds accompanies with torrential rainfall experiences in the coastal region ns of Tamil Nadu and Andhra Pradesh. These rains are often destructive in nature for life and property. They usually occur in the month of October- November Weather conditions of Retreating Monsoon Clear sky, low humidity, and the weather become fresh and pleasant in the north and almost stagnant in the Deccan. This sultry and oppressive weather is known as October Heat. It is the transition between the hot rainy to cold season. Characteristics of Monsoon -7- 1. 2. 3. 4. 5. Erratic in nature Unevenly spread and sporadic Rains are orographic in nature Brings rain in summer Some of the rain occurs due to tropical depressions. Q: Why do Thar remain as a desert? There is a very little rain, less than 25 cm annually. The Arabian sea branch of South West Monsoon do not bring rainfall as the Aravallies remain parallel to these winds and fails to form a barrier to precipitate. The Bay of Bengal branch of south West Monsoon has little or no rain by the time it reaches Thar after traversing the Ganga valley. A little rain falls on the windward side and Thar on the leeward side remains as a desert as no rain. Humidity is very low in summer therefore the moisture evaporates before it could precipitate, because Thar lacks water bodies. (Please read the remaining part in your text book.)

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