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Wednesday, 10 October 2012

India has 'Tropical Monsoon' type of climate. The word monsoon has been derived from the Arabic word 'Mausim' which means seasonal reversal of the winds during the course of the year.
Climate of India
1.   The whole of India has a tropical monsoonal climate, since the greater part of the country lies within the trophies, and the climate is influenced by the monsoons.
2.   The position of the mountain ranges and direction of the rain-bearing winds are the two main factors that determine the climate of India
3.   Alternating seasons is the chief characteristic of India's Climate.

Factors Affecting the Climate of India:
1.   Latitude: India lies between 8 0 N and 37 0 N latitudes. The Tropic of Cancer passes through the middle of India, thus making the southern half of India in the Torrid Zone and the northern half in the Temperature Zone.
2.   Himalaya Mountains: The Himalayas play an important role in lending a sub-tropical touch to the climate of India. The lofty Himalaya Mountains form a barrier which effects the climate of India. It prevents the cold winds of north Asia from blowing into India, thus protecting it from severely cold winters. It also traps the Monsoon winds, forcing them to shed their moisture within the sub-continent.
3.   Altitude: Temperature decreases with height. Places in the mountains are cooler than places on the plains.
4.   Distance from the sea: With a long coastline, large coastal areas have an equable climate. Areas in the interior of India are far away from the moderating influence of the sea. Such areas have extremes of climate.
5.   Geographical Limits:
                     i.        Western Disturbances: The low pressure systems that originate over the eastern Mediterranean region in winter and move eastwards towards India passing over Iran, Afghanistan and Pakistan are responsible for the winter rain in northern India.
                    ii.        Conditions in the Regions Surrounding India: Temperature and pressure conditions in East Africa, Iran, Central Asia and Tibet determine the strength of the monsoons and the occasional dry spells. For example, high temperatures in East Africa may draw the monsoon winds from the Indian Ocean into that region thus, causing a dry spell.
                   iii.        Conditions over the Ocean: The weather conditions over the Indian ocean and the China Sea may be responsible for typhoons which often affect the east coast of India.
                  iv.        Jet Streams: Air currents in the upper layers of the atmosphere known as jet steams could determine the arrival of the monsoons and departure of the monsoons. The Scientists are studying the jet streams and how it may affect the climate of India but much remains to be learned about this phenomena.
Following are the climatic regions of India.
1.   Tropical Rain Forest:
                     i.        This type of climate is found on the west coastal plain and Sahyadris and in parts of Assam
                    ii.        The temperatures are high, not falling below 18.2 degree c even during winter and rising to 29 degree C in April and May, the hottest months.
                   iii.        Dense, forests and plantation agriculture with crops like tea, coffee and spices are the characteristics vegetation in the area.
2.   Tropical savanna:
                     i.        Most of the peninsula, except the semiarid zone in the leeside of the Sahyadris experiences this type of climate.
                    ii.        A long dry weather lasting through winter and early summer and high temperature remaining above 18.2 degree C even during the winter seasons and rising as high as 32 degree C in summer are the chief characteristics of this climate.
                   iii.        Nagpur has a mean temperature of 35.4 degree C for May which is the hottest month and 20.7 degree C for December the coldest month in the year.
                  iv.        The natural vegetation all over the area is savanna.
3.   Tropical Semi-Arid Steppe Climate:
                     i.        The rain-shadow belt, running southward from central Maharashtra to Tamil Nadu, in the leeside of the Sahyadris and Cardamom Hills come under this type of climate of low and uncertain rainfall.
                    ii.        Temperature varying from 20 degree C to 23.8 degree C for December and 32.8 degree C for May. Agriculturally, the climate is suitable only for dry farming and livestock rearing.
4.   Tropical and Sub-Tropical Steppe:
                     i.        This type of climate occurs over a broad crescent from Punjab to Kachchh between the Thar Desert to its west and the more humid climates of the Ganga Plain and the Peninsula to its east and south respectively.
                    ii.        The climate, therefore, is transitional between these two areas. The annual rainfall is not only low but it is also highly erratic.
5.   Tropical Desert :
                     i.        The western part of Barmer, Jaisalmer and Bikaner districts of Rajasthan and most of the part of Kachchh form the sandy wastes of the Thar which experiences a typical desert climate.
                    ii.        Ganganagar has recorded a maximum temperature of 50 degree C, the highest record.
6.   Humid Sub-Tropical With Winter:
                     i.        A large area to the south of the Himalayas, east of the tropical and sub-tropical steppe and north of the tropical savanna running in a long belt from Punjab to Assam with a south-westward extension into Rajasthan east of the Aravalli Range, has this type of climate.
                    ii.        Winers are dry except for a little rain received from the westerly depressions.
7.   Mountain Climate:
                     i.        The Himalayan and Karakoram ranges experience this type of climate with sharp contrasts between the temperatures of the sunny and shady slopes, high diurnal range of temperatures and high variability of rainfall.
                    ii.        The trans-Himalayan region, Ladakh, where the south-west monsoon fails to reach, has a dry and cold climate and a spare and stunned vegetation.
8.   Drought in India:
                     i.        The dry areas of Rajasthan and the adjoining part of Haryana and Gujarat are liable to frequent drought conditions.
                    ii.        Another area liable to frequent drought lies on the leeward side of the western Ghats.

Traditional Seasons
Indian Calender
Gregorian Calender
Season based on Monsoon: The climate of India may be described as tropical monsoon. Even northern India, lying beyond the tropical zone, acquires a tropical touch marked by the relatively high temperatures. The large size of the country and its varied relief play a crucial role in determining the climatic variations in different part of India. But the seasonal rhythm of the monsoon is apparent throughout India. It may conveniently from the basis for dividing the year into different seasons. The most characteristic feature of the monsoon is the complete reversal of winds. It eventually leads to the alternation of seasons. India is known as the "land of the endless growing season".
The year is divided into four seasons:
1.   The Cold Weather Season: (N.E. Monsoons) The Cold weather seasons starts in January. The north-east monsoon is fully established over India these seasons. the mean January day temperature in Chennai and Calicut is about 24-25 degree C while in the northern plains it is about 10-15 degree C. In December, the sunshines directly over the Trophic of Capricorn. The landmass of Asia, including the sub-continent, cools down very rapidly. There is a high pressure over the continent. The Indian Ocean, being warmer, has a relatively low pressure.
Three Reasons For Excessive Colds in North India
1.   States like Punjab, Haryana and Rajasthan being far away from the moderating influence of sea experience continental climate.
2.   The snowfall in the nearly Himalayan ranges create cold wave situation.
3.   Around February, the cold winds coming from Caspean Sea and Turkmenistan bring cold wave along with frost and fog over N. Western part of India.
N.E.Trade Winds (prevailing winds in the tropical Latitudes), blow, land to sea. These winds, being off shore do not give rain. In this season western disturbances bring light rainfall, most beneficial to the rabi crop in N.W. India. This rainfall decreases towards the east and the south. The Peninsular region of India, however does not have any well-defined cold weather season. There is hardly any seasonal change in the distribution pattern of the temperature in coastal areas because of moderating influence of sea and the proximity to equator.
2.   The Hot Weather Season: From mid March to May the sun moves over the Equator towards tropic of Cancer. By June 21, it is directly overhead the Tropic of Cancer. In March, the highest day temperatures of about 38 degree C occur in the Deccan Plateau. Therefore,
a.   Peninsular India, places south of Satpuras experience temperature between 26-32 degree C.
b.   Central India, comprising of Delhi and Madhya Pradesh experience temperature between 40-45 degree C.
c.    North-West India, comprising mainly of Rajasthan has very high temperature (45 degree C), due also to features like sandy soil, direct insulation and lack of cloud cover.

Storms During the Hot Weather Season
d.   Mango Showers (since the rain showers are good for the mango trees) occurs along the coast of Kerala.
e.   Norwester/Kalbaisakhi (Dark Clouds in the month of Baisakh) occurs in Assam and West Bengal. These are thunderstorms, accompanied with strong winds are heavy rainfall. This is good for the tea crop in Assam and the jute and rice in West Bengal. In Assam these storms are called Bardoli chherha.
f.     Loo is the name given to the hot, dry winds that blow in the Northern Plains. It is very common in Punjab, Haryana, Western Uttar Pradesh (called "aandhi") and Bihar.
g.   Blossom Shower with this shower, coffee flowers blossom in Karnataka and its nearby areas.

                The South-West Monsoon Season: This season begins in June and lasts until September. The low pressure which existed over Norther Plain is further intensified. It is strong enough to attract the moisture bearing winds from the Indian Ocean.
Facts about S.W. Monsoon
0.   The bulk of rainfall is received during this season in almost every part of India except Tamil Nadu.
1.   The amount of rainfall received depends on the relief of the region.
2.   The rain is unreliable and there are dry intervals.
                The S.E Trade Winds from the Southern Hemisphere are drawn into India as the S.W. Monsoon Winds after they cross the Equator. Due to the triangular shape of India, the S.W.Monsoon Winds are divided into branches - the Arabian Sea Branch and the Bay of Bengal Branch.
                The Arabian Sea Branch: It gives very heavy rainfall, more than 200 cm, to the windward side of Western Ghats. The Deccan Plateau, which lies on the leeward side of the Western Ghats, receives less than 150 cm of rainfall. Further east, rainfall decreases for eg, Hyderabad gets less than 100 cm while Chennai gets even less than 40 cm of rainfall. It does not give much rain to Rajasthan because of Aravali Ranges lie parallel to the direction of winds and hence condensation does not occur. Therefore, Rajasthan gets less than 25 cm rainfall. These winds advance northwards, attracted to the low pressure in India. Punjab at the foothill of the Shiwalik, get Relief Rainfall.
                Bay of Bengal Branch: The Bay of Bengal Branch which also blows from the southwest direction, is deflected by the Arakhan Mountains of Myanmar and the N.E. Hills of India (Garo, Khasi and Jaintia) towards genetic plain. The delta of Ganga-Brahmaputra and the wind-ward side of the N.E. Hills of India get heavy rain. For example, Cherrapunji on the windward side gets 2500 cm of rainfall, while Shillong on the leeward slope gets about 250 cm. The rainfall decreases as the winds reach the eastern Himalayas and blow westward into the Ganga Plain, attracted by the low pressure in Punjab and Rajasthan.
                The Retreating of S.W. Monsoon Season: This season lasts through October to December. The temperature in the Northern Plains begins to decrease as the Sun's rays no longer fall directly at the Tropic of Cancer. In September, the Sun shine directly at the Equator. The low pressure over the Northern Plain is not longer strong enough to attract the Monsoon Winds into the heart of India. By the end of September, the Monsoon winds are drawn only upto Punjab, by mid-October upto the Central India and by the early November upto Souther India. Thus, the S.W. Monsoon winds seem to withdraw in stages during this season. That is why this season is known as Retreating S.W. Monsoon season.

This season is marked by cyclones in the Bay of Bengal. They hit the east coast of India and Bangladesh causing widespread damage to life, property and crops.
Difference between the Retreating S.W. Monsoon and North East Monsoon
1.   They blow during the months of October to December
2.   This is a season of transition between the hot, rainy season and the cold, dry season
3.   Characterised by oppressive head and humidity known as "October Heat"
4.   They blow in the S.W. direction but are not strong enough to blow right into the Norther Plain.
5.   The withdraw in stages which results in decreasing rain
1.   They blow during the months of January to mid March.
2.   This is the cold weather season
3.   This is a very pleasant season with low temperatures, low humidity, clear skies.
4.   These winds blow in N.E direction from the land to the sea.
5.   They do not give rain.

Rainfall is the important element of Indian economy. Although the monsoons affect most part of India, the amount of rainfall varies from heavy to scanty on different parts. There is great regional and temporal variation in the distribution of rainfall. Over 80% of the annual rainfall is received in the four rainy months of June to September. The average annual rainfall is about 125 cm, but it has great spatial variations.
a.   Areas of Heavy Rainfall (Over 200cm) : The highest rainfall occurs in west costs, on the western Ghats as well as the Sub-Himalayan areas in North East and Meghalaya Hills. Assam, West Bengal, West Coast and Southern slopes of eastern Himalayas.
b.   Areas of Moderately Heavy Rainfall (100-200 cm) : This rainfall occurs in Southern Parts of Gujarat, East Tamil Nadu, North-eastern Peninsular, Western Ghats, eastern Maharashtra, Madhya Pradesh, Orrisa, the middle Ganga valley.
c.    Areas of Less Rainfall (50-100 cm) : Upper Ganga valley, eastern Rajasthan, Punjab, Southern Plateau of Karnataka, Andhra Pradessh and Tamil Nadu.
d.   Areas of Scanty Rainfall (Less than 50 cm) : Northern part of Kashmir, Western Rajasthan, Punjab and Deccan Plateau. The two significant features of India's rainfall is that
i. in the north India, rainfall decreases westwards and ii. in Peninsular India, except Tamil Nadu, it decreases eastward.
Facts About Indian Monsoon
  • Rainfall occurs in summer
  • Rainfall is erratic and unpredictable
  • Rainfall is unevenly distributed
  • Rainfall affects Indian economy

1.   Though the jet streams go a long way in explaining the origin of monsoon some questions remain unanswered. The great variation in the amount of rainfall both spatially and temporally, the high degree of uncertainty related to the date of arrival etc. are unexplained. Meteorologists have been trying to explain these phenomena from different angles relating to wide variety of generalisation. They have been monitoring huge high pressure or anticyclone zones that form a few kilometers below the jet streams. This ridge hovers over south Goa. It has been noticed that if the ridge moves towards karwar in Karnataka it does not augur well for the monsoon. This high-pressure zone, it is reasoned, blocks the low flowing south westerly monsoon from intensifying over the west coast. When it is not positioned well, several meteorologists remain skeptical about the monsoon's performance.
2.   The unusual cooling of surface temperatures over the Arabian Sea by as much as 3 to 4 degrees before the onset of monsoon is another curious phenomenon. This is due to the cool Somali current. It pushes the cool waters of the Indian Ocean towards the Arabian Sea and the drop in temperature seen to have an impact on the progress of the rains.
3.   Just before the monsoon sets over south-east Asia the atmosphere pressure over the Indian Ocean drops. Simultaneously about 10,000 kilometers away in the South Pacific there is rise in pressure, when the rain is over, this reverses. This phenomena called southern oscillations is key indicator of the south-west monsoon. When the pressure over Indian Ocean is lower than normal it augurs well for the good monsoon.
Global Atmospheric Research Programme and Monex
The World Meteorological Organisation (WMO) and the International council of Scientific Union (ICSU) organized a Global Atmospheric Research Programme (GARP) in 1969. Under the aegis of this programme, a Global Weather Experiment was conducted for one full year beginning on 1 December 1978. it was one of the biggest ever international experiments, on a global scale, for observing the earth's atmosphere from land and ocean based data collection platforms, and by weather satellites, which now monitor the restless atmosphere, was launched after several years of intensive preparations and planning. Some idea of the dimensions of the experiment may be gleaned from the fact that in May of 1979 as many as fifty two research ships were deployed over the tropical oceans between 10oN and 10oS, While 104 aircraft missions were successfully completed over different parts of the Pacific, the Atlantic and the Indian Ocean. Of considerable interest to India was a special programme of the Global Weather Experiment. This was the Monsoon Experiment (MONEX). Its purpose was to study the influence of monsoon winds on the general circulation of the atmosphere. In view of its economic impact, the Indian scientists were naturally interested in improving their capacity to predict the vagaries of this seasonal phenomenon, which occurs year after over the landmasses of Asia and parts of Africa.

In view of its seasonal characteristics, the monsoon experiment (MONEX) was designed to have three components:-
1.   Winter MONEX from 1 December 1978 to 5 March 1979 to cover the eastern Indian Ocean and the Pacific along with the land areas adjoining Malaysia and Indonesia.
2.   Summer MONEX from 1 May to 31 August 1979 which covered the eastern coast of Africa, the Arabian Sea and the Bay of Bengal together with the adjacent landmass. It also covered the Indian Ocean in the belt extending from 10oN to 10oS.
3.   A West African Monsoon Experiment (WAMEX) over western and central parts of Africa from 1 May to 31 August 1979
International MONEX Management Centers (IMMC) were set up in Kuala Lumper and in New Delhi to supervise the winter and summer components of the experiment. A large number of scientists from different countries came and worked at these Centers to plan and implement this international project.
Change is the law of nature. It is continuous process that goes on uninterruptedly involving phenomena, big and small, material and non-material and make over physical and socio-cultural environment. It is a process present everywhere with variations in terms of magnitude, intensity and scale. Change can be gradual or slow process like the evolution of land forms and organism and it can be as sudden and swift as volcanic eruptions, tsunamis, earthquakes and lightening etc. Similarly, it may remain confined to a smaller area occurring within a few seconds like hailstorms, tornadoes and dust storm, and it can also have global dimensions such as global warming and depletion of the ozone layer. Besides, these changes have different meaning for different people. It depends upon the perspective one takes while trying to understand them. From the perspective of nature, changes are value-neutral. But from the human perspective, these are value-loaded. There are some changes that are desirable and good like the changes of season, ripening of fruits, while there are others like earthquake, floods and wars that are considered bad and undesirable.

Classification of Natural Disasters
Broadly natural disasters can be classified under the following four categories:
  • Blizzards
  • Thunder-storms
  • Lightening
  • Tornadoes
  • Tropical cyclone
  • Drought
  • Hailstorm
  • Frost, Heat, wave
  • Cold Wave
  • Earthquakes
  • Volcanic eruptions
  • Landslides
  • Avalanches
  • Subsidence
  • Soil Erosion
  • Floods
  • Tidal Waves Ocean
  • Stormsurge
  • Tsunami
  • Insect Infection
  • Viral diseases like bird flu, dengue, AIDS etc

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