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The various climatic regions of India are :
Tropical Rainy Climate Region
This region has consistently even temperature, which stays above 180 C even in December, April and May are the hottest months, the temperature varying from 180 C to 270 C. July and August are the coolest months, with copious rainfall. The average rainfall exceeds 250 cm, which encourages wet evergreen forests. The western coastal strip, Western Ghats, south of Bombay, Meghalaya, western Nagaland and Tripura come in this climatic region.
Shillong rainfall patternTropical Savanna Region
The chief feature of this climate is the long dry period. Temperatures even in winter stay above 180 C, and in summer may even go up to 460C. Rainfall, except in the south eastern parts, is in summer about 100 cm. In the south eastern parts, the retreating monsoons bring sufficient rains. A major part of the southern peninsula, except the arid tract lying east of the Western Ghats, northeastern Gujarat, south Bihar. major parts of Madhya Pradesh, Orissa, northern Andhra Pradesh, eastern Maharashtra, and eastern Tamilnadu coast come under this region.
Tropical Steppes Region
The average temperature is over 27o C, the lowest temperature being about 230C. April and May are the hottest months, when temperature may rise over 300C. Average rainfall being less than 75 cm, the region comprises a part of the famine zone of the country. The southwest monsoons bring rain to this region. This region comprises the rain shadow areas lying east of the Western Ghats and covers Karnataka, interior Tamilnadu, western Andhra Pradesh, and central Maharashtra.
Sub-Tropical Steppe Region
The average temperature rises over 270 C, and as high as 480 C is recorded during summer. Rainfall from the southwest monsoons, averages between 50 and 75 cm. It often fails, leading to widespread drought conditions. This region comprises tracts stretching from the Punjab to Kutch and Saurashtra and encompassing western Rajasthan and northern Gujarat.
Tropical Desert Region
The summer temperature rises over 480C, while in winter it goes down to 10C. May and June are the hottest months. Average rainfall is 12.5 cm and very unreliable. Excessive evaporation during summer and intense cold during winter hinder crop production except through river irrigation. Western Rajasthan and parts of Kutch, which are purely sandy plains, come in this region.
Humid Sub-Tropical Region
Summer temperatures are 460C to 480C. Average rainfall, mostly from summer monsoons, is about 62.5 cm, which increases to over 250 cm in the east. Winters are virtually dry. This region is spread over the foothills of the Himalayas, eastern Rajasthan, plains of U.P., Bihar, northern Bengal, part of Assam and Arunachal Pradesh.
The average temperature in June is 150C to 170C, in winter it goes below 80C. On the northern slopes of the Himalayas, the rainfall is scanty, about 8-10 cm, but the western slopes enjoy a heavy rainfall of over 250 cm. The entire Himalayan belt comprising both the trans-Himalayas and the main Himalayas come under this region.
About 12% of India's area receives less than 61 cm rainfall on an average, and only 8% receives more than 250 cm. Drought conditions occur on account of the erratic nature of the Indian monsoons.
Drought CycleWith long dry spells accompanied by high temperature, The intensity of drought varies from year to year. It is generally more frequent in areas having low rainfall. The driest parts which are liable to drought lie in Rajasthan, adjoining Haryana and parts of Gujarat. These are areas of recurrent drought. Another area liable to frequent drought lies on the leeward side of the Western Ghats.The Irrigation Commission (1962) has identified drought affected areas as those areas with a rainfall of less than 10 cm; where even 75% of this rainfall is not received in 20% or more areas, and where irrigation is less than 30% of the cropped area. Of the total gross cultivated areas of the country, about 56 million hectares are subject to poor and unpredictable rainfall. Poor rainfall leads to drought in a little over 1 million sq. km.
Areas affected by droughtDrought Regions: There are certain well defined tracts of drought. These are :
(i) The desert and the semi-arid regions, comprising approximately 0.6 million sq. km., form a rectangle from Ahmedabad to Kanpur on one side and Kanpur to Jalandhar on the other. Rainfall in this region is below 7.5 cm and at places below 4cm. Some of these areas, where irrigation is not provided are among the worst famine tracts.
(ii) East of the Western Ghats, to a width of 300 km. The region extends all along the Krishna river almost to within 80 km from the coast. This region accounts for 0.7 million sq. km.
(iii) Scattered pockets of drought, comprises Tirunelveli district south of Vaigai river, Coimbatore area (in Tamilnadu), Saurashtra and Kutch (Gujarat), Mirzapur and Palamau (U.P.), Purulia district (West Bengal), Kalahandi (Orissa). These pockets total an area of 0.1 million sq. km.
Programs of Drought Areas: The main policy programs for drought areas should be :
(i) Conjunctive use of water from rainfall, surface, and underground.
(ii) Introduction of crop pattern which best protects them from drought and ensures a reasonable and reliable income.
(iii) developing minor irrigation works like anicuts, bandharas, tanks and dug-wells.
(iv) Lining of canals and distributaries to minimise water loss.
(v) Drip of trickle irrigation to reclaim some highly saline desert areas and to develop them for growing high value off-season crops.
(vi) Expeditious completion of continuing projects.
(vii) Dry farming methods to preserve and make the best use of available natural moisture.
India is one of the worst flood affected tropical countries. Roughly, about 25 million hectares are prone to floods. Every year floods affect an average of 7.4 million hectares, of which 3.1 million hectares is cropped area.
Cause of Flood
Nearly 60% of the flood damage in the country occurs from river flood, and 40% from heavy rainfall and cyclones. Himalayan rivers account for 60% of the total flood damage. The damage is least by Central Indian rivers. U.P. accounts for about 33% of the flood damage in the country, followed by Bihar (27%) and Punjab and Haryana (15%).
Flood Prone Areas
(1) The basin of Himalayan rivers (covering a part of the Punjab, Haryana, Himachal Pradesh, Delhi, Rajasthan, U.P., Bihar and West Bengal) gets flooded on account of overflow, erosion and inadequate drainage, steep gradients of the rivers and change in their courses. Kosi and Damodar devastate large areas. The Brahmaputra basin is subject to earthquakes and landslide, which obstruct the free flow of water.
(2) The North Western river basin comprising Jammu and Kashmir, parts of Haryana, western U.P.., Punjab and Himachal Pradesh are flooded by the tributaries of the Indus (Jhelum, Sutlej, Beas, Ravi and Chenab). In Kashmir Valley, the Jhelum is unable to carry the flood discharge. In Punjab and Haryana plains, the problem is mainly of inadequate drainage.
Flood-prone areas of India(3) The Central Indian and Peninsular river basin, covering Madhya Pradesh, Orissa, Andhra Pradesh and Maharashtra contains the Tapti, Narmada and the Chambal. In their basins, at times rainfall is excessive, causing occasional floods. Heavy floods also occur in the Godavari, Krishna and Cauvery at long intervals, In Andhra Pradesh, the Kolleru lake submerges vast areas along its fringes.
While heavy monsoonal rains cause major floods in the Himalayan regions, the coastal areas suffer from heavy rainfall in association with tropical cyclones and storm surges.
Flood Control Policy and Programmes
The national flood control policy comprises three phases :
(i) Immediate phase extends over two years and comprises collection of basic hydrological data, construction of embankments, urgent repairs, improvement of river channels, and raising of villages above flood levels.
(ii) Short-term phase concerns the next four to five years. It consists of improving surface drainage, establishing proper flood warning system, shifting or raising of villages over flood level, construction of channel diversions, more embankments and construction of raised platforms for use in times of flood emergency.
(iii) Long-term phase envisages schemes such as construction of dams or storage reservoirs for flood protection and soil conservation in the catchment of various rivers, detention basins, and digging large channel diversions.
Under the National Flood Control Programme, launched in 1954, protection measures have been taken up since second plan. Emphasis has been given to drainage and anti-waterlogging measures, Flood forecasting and warning centres have been established in some of the most flood prone areas. Flood Control Boards and River Commissions have been set up in all states to coordinate and implement
The measures. A Central Flood Control Board, at the national level, has been set up to coordinate the work of State Boards and River Commissions.
Multipurpose reservoir with specific storage for flood control have been constructed on the Mahanadi (at Hirakud), the Damodar (at Konar, Maithon. Panchet and Tilaiya); on the Sutlej (at Bhakra); on the Beas (at Pong); and on the Tapti (at Ukai), which have offered considerable protection to the lower areas of the rivers.
A number of multipurpose reservoirs, like the Bhakra Nangal on Sutlej, the Nagarjun Sagar etc., though not having any specific storage for flood moderation, have given incidental benefits of flood moderation in downstream areas. In addition, a number of flood protection works including construction of embankments, drainage channels, town protection works and raising of villages have been carried out. Flood forecasting systems have also been set up in various places.
Flash floods are a quick and sudden flood that occur in a usually dry valley. They are highly localised phenomenon and are generally caused by cloud burst during monsoons. These floods are characterised by concentrated and rapid runoff giving very high discharges over short periods of time. They generally revitalise the dead/buried drainage systems, the ephemeral streams become very active. Considerable area cultivated illegally in the bed of the buffed/dead drainage system gets inundated. The good micro-environments in low lying areas are severely affected and productivity is lost. In addition the houses, roads and bridges also collapse.
Flash floods can be prevented by proper vegetative cover of these areas with suitable silvopasture system.
The field bunds which are often supported by trenched should be covered with grasses on the bunds and trees in trenches. Cultivation near the ephemeral stream should be checked. The embankments of these streams should be strengthened with vegetative means. The bed of the dead/buried drainage system should never be cultivated.
How is India called a tropical country when more than half its area is outside the tropics?
Although more than half of India is outside the Tropic of Cancer, the country as whole is a separate meteorological unit in which the predominant role is played by the monsoon. The climate is best described as tropical monsoon type. The monsoon winds blow into the sub-continent after the hot weather which creates the thermal contrast between the landmass and the southern Indian Ocean. The winds are blocked by the Himalayas and made to shed their moisture on the northern plains. These plains are outside the tropics and should strictly be a sub-tropical temperate region, considering the latitudes only. However, the effect of the monsoon changes this.
Chief features of the Summer monsoon rainfall
The average annual rainfall in India is about 110 cms. It is estimated that more than 85% of this rainfall is received in summer. The main characteristics of summer rainfall are as follows:—
Significance of Monsoons in Agriculture:
(i) India is essentially an agricultural country. Indian agriculture and economy is dependent on S.W. summer monsoons. Indian agriculture is the backbone or pivot of Indian economy. It has been rightly said, ‘Indian budget is a gamble on monsoons.’
(ii) Indian rainfall is seasonal. The summer crops or Kharif crops depend on monsoons.
(iii) The failure of summer monsoons result in famines and food shortage. ‘It monsoons fail, there is a lock out in agriculture industry.’
(iv) Most of the foodgrains like Rice, Jowar, Maize etc. grown as Kharif crops depend on rainfall. Good rains have resulted in bumper crops.
(v) The amount of rainfall determines the cropping pattern. Rice, Sugarcane, Tea, Jute etc. are grown in areas with over 200 cms of rain. Dry areas have crops like millets, pulses, oil seeds, etc.
(vi) The uniform distribution of rain results in multiple cropping.
The coastal areas of India do not register any significant change in temperature even during summer and winter.
The Coastal areas have uniformly moderate temperature throughout the year. This is due to the moderating effect of the Sea. The Sea Water is heated and cooled down slowly. It can retain heat in winter and coolness in summer. The land breeze and sea breeze keep these areas warm in winter and cool in summer. As a result, the annual range of temperature is very low. There is actually no winter season. These areas have uniformly high temperatures throughout the year.
Distribution of rainfall all over India not uniform
Many regional variations are found in the distribution of annual rainfall in India. The distribution of annual rainfall shows two main trends:
(i) From the coastal areas, the rainfall decreases towards the West and North west.
(ii) The rainfall decreases towards the interior of the country.
The main factors controlling this distribution of rainfall are the presence of high mountains and the distance from the sea. The coastal areas get high rainfall. The western ghats, the Garo-Khasi hills and the Sub-Himalayan region get more than 200 cms of rainfall. But Rajasthan is dry as there is no high mountain to check S.W. Monsoons.
Western part of Rajasthan arid
The western part of Rajasthan is a desert. It gets an annual rainfall less than 20 cms. This is due to the following reasons:—
(i) Rajasthan is under the influence of S.W. Summer monsoons. The Aravallis system lies parallel to the direction of S.W. monsoons coming from Arabian Sea. So this mountain system is unable to check these winds. So western Rajasthan is practically dry. The southern parts get some rainfall.
(ii) This area lies at a great distance from the Bay of Bengal. The Bay of Bengal monsoons become dry and lost their moisture when they reach Rajasthan.
(iii) This area is away from the Himalayan region. So it does not come under the influence of monsoons giving rain in Sub-Himalayan region.
Co-efficient of variation of annual rainfall low on the West Coast of India and high in Kutch and Gujarat
The main feature of the monsoon rainfall in India is its variability from year to year. The same place gets different amounts of rainfall every year. When the actual rainfall of a place in a year deviates from its mean annual rainfall, it is known as Variability of rainfall. The variability of annual rainfall is calculated with the help of the following formula:—
Co-efficient of variation =
Indian weather with special reference to Jet streams
The mechanism of Indian weather depends upon the following factors:—
(1) Surface distribution of pressure and winds.
(2) Upper air circulation.
(3) Flow of different air masses.
(4) Western disturbances.
(5) Jet stream.