PHYSIOGRAPHY OF WATER

India is a land of many rivers and mountains. Its geographical area of about 329 MHa is criss-crossed by a large number of small and big rivers, some of them figuring amongst the mighty rivers of the world. The rivers and mountains have a greater significance in the history of Indian cultural development, religious and spiritual life. It may not be an exaggeration to say that the rivers are the heart and soul of Indian life.

India is a union of States with a federal set up. Politically, the country is divided into 28 States and 7 Union Territories. A major part of India’s population of 1,027,015,247 (2001 census) is rural and agriculturally oriented for whom the rivers are the source of their prosperity.

PHYSIOGRAPHY:

Physiographically, India may be divided into seven well defined regions. These are:

1.	The Northern Mountains, comprising the mighty Himalayan ranges;
2.	The Great Plains, traversed by the Indus and Ganga Brahmaputra river systems. As much as one third of this lies in the arid zone of western Rajasthan. The remaining area is mostly fertile plains;
3.	The Central Highlands, consisting of a wide belt of hills running east-west starting from Aravalli ranges in the west and terminating in a steep escarpment in the east. The area lies between the Great Plains and the Deccan Plateau;
4.	The Peninsular Plateaus comprising the Western Ghats, Eastern Ghats, North Deccan Plateau, South Deccan Plateau and Eastern Plateau;
5.	The East Coast, a belt of land of about 100-130 km wide, bordering the Bay of Bengal land lying to the east of the Eastern Ghats;
6.	The West Coast, a narrow belt of land of about 10-25 km wide, nordering the Arabian Sea and lying to the west of the Western Ghats, and;
7.	The islands, comprising the coral islands of Lakshadeep in Arabian Sea and Andaman and Nicobar Islands of the Bay of Bengal.

CLIMATE:

The presence of the great mountain mass formed by the Himalayas and its spurs on the North and of the ocean on the South are the two major influences operating on the climate of India. The first poses an impenetrable barrier to the influence of cold winds from central Asia, and gives the sub-continent the elements of tropical type of climate. The second, which is the source of cool moisture-laden winds reaching India, gives it the elements of the oceanic type of climate.

India has a very great diversity and variety of climate and an even greater variety of weather conditions. The climate ranges from continental to oceanic, from extremes of heat to extremes of cold, from extreme aridity and negligible rainfall to excessive humidity and torrential rainfall. It is, therefore, necessary to avoid any genralisation as to the prevalence of any particular kind of climate, not only over the country as a whole but over major areas in it. The climatic condition influences to a great extent the water resources utilisation of the country.

RAINFALL:
Rainfall in India is dependent in differing degrees on the South-West and North-East monsoons, on shallow cyclonic depressions and disturbances and on violent local storms which form regions where cool humid winds the sea meet hot dry winds from the land and occasionally reach cyclonic dimension. Most of the rainfall in India takes place under the influence of South West monsoon between June to September except in Tamil Nadu where it is under the influence of North-East monsoon during October and November. The rainfall in India shows great variations, unequal seasonal distribution, still more unequal geographical distribution and the frequent departures from the normal. It generally exceeds 1000 mm in areas to the East of Longitude 78 degree. It extends to 2500 mm along almost the entire West Coast and Western Ghats and over most of Assam and Sub-Himalayan West Bengal. On the West of the line joining Porbandar to Delhi and thence to Ferozpur the rainfall diminishes rapidly from 500 mm to less than 150 mm in the extreme west. The Peninsula has large areas of rainfall less than 600 mm with pockets of even 500 mm. The estimate of areal average rainfall is subjective depending on the method adopted. Therefore, estimates of local rainfall over the country obtained by employing other techniques may differ, especially in a vast country like India.

TEMPERATURE:
The variations in temperature are also marked over the Indian sub-continent. During the winter seasons from November to February, due to the effect of continental winds over most of the country, the temperature decreases from South to North. The mean maximum temperature during the coldest months of December and January varies from 29 degree centigrade in some part of the peninsula to about 18 degree centigrade in the North, whereas the mean minimum varies from about 24 degree centigrade in the extreme South to below 5 degree centigrade in the North. From March to May is usually a period of continuous and rapid rise of temperature. The highest temperature occurs in North India, particularly in the desert regions of the North-West where the maximum may exceed 48 degree centigrade. With the advent of South West Monsoon in June, there is a rapid fall in the maximum temperature in the central portions of the country. The temperature is almost uniform over the area covering two thirds of the country which gets good rain. In August, there is a marked fall in temperature when the monsoon retreat from North India in September. In North-West India, in the month of November, the mean maximum temperature is below 38 degree centigrade and the mean minimum below 10 degree centigrade. In the extreme North, temperature drops below freezing point.

EVAPORATION:
Evaporation rates closely follow the climatic seasons, and reach their peak in the summer months of April and May and the central areas of the country display the highest evaporation rates during this period. With the onset of monsoon, there is a marked fall in the rate of evaporation. The annual potential evaporation ranges between 150 to 250 cm over most parts of the country. Monthly potential evaporation over the Peninsula increases from 15 cm in December to 40 cm in May. In the North-East, it varies from 6 cm in December to 20 cm in May. It rises to 40 cm in June in West Rajasthan. After the onset of monsoon potential evaporation decreases generally all over the country.

RIVERS:
India is blessed with many rivers. Twelve of them are classifled as major rivers whose total catchment area is 252.8 million heactare (M.Ha). Of the major rivers, the Ganga - Brahmaputra Meghana system is the biggest with catchment area of about 110 M.Ha which is more than 43 percent of the catchment area of all the major rivers in the country. The other major rivers with catchment area more than 10 M.Ha are Indus (32.1 M.Ha.), Godavari (31.3 M.Ha.), Krishna, (25.9 M.Ha.) and Mahanadi (14.2 M.Ha). The catchment area of medium rivers is about 25 M.Ha and Subernarekha with 1.9 M.Ha. catchment area is the largest river among the medium rivers in the country.

WATER BODIES:

Inland Water resources of the country are classified as rivers and canals; reservoirs; tanks & ponds; beels, oxbow lakes, derelict water; and brackish water. Other than rivers and canals, total water bodies cover all area of about 7 M.Ha. Of the fivers and canals, Uttar Pradesh occupies the First place with the total length of rivers and canals as 31.2 thousand km, which is about 17 percent of the total length of rivers and canals in the country. Other states following Uttar Pradesh are Jammu & Kashmir and Madhya Pradesh. Among the remaining forms of the inland water resources, tanks and ponds have maximum area (2.9 M.Ha.) followed by reservoirs (2.1 M.Ha.).

Most of the area under tanks and ponds lies in Southern States of Andhra Pradesh, Karnataka and Tamil Nadu. These states along with West Bengal, Rajasthan and Uttar Pradesh, account for 62 percent of total area under tanks and ponds in the country. As far as reservoirs are concerned, major states like Andhra Pradesh, Gujarat, Karnataka, Madhya Pradesh, Maharashtra, Orissa, Rajasman and Uttar Pradesh account for larger portion of area under reservoirs. More than 77 percent of area under beels, oxbow, lakes and derelict water lies in the states of Orissa, Uttar Pradesh and Assam. Orissa ranks first as regards the total area of brackish water and is followed by Gujarat, Kerala and West Bengal. The total area of inland water resources is, thus, unevenly distributed over the country with five states namely Orissa, Andhra Pradesh, Gujarat, Karnataka and West Bengal accounting for more than half of the country's inland water bodies.