Water Resource of India
Water resources of a country constitute one of its vital assets. Of all the planet’s renewable resources, water has a unique place. It is essential for sustaining all forms of life, food production, economic development, and for general well being. It is aptly called as life as well universal solvent because of no substitute for most of its uses, difficult to de-pollute, expensive to transport, and it is truly a unique gift to mankind from nature. Water is also one of the most manageable of the natural resources as it is capable of diversion, transport, storage, and recycling. All these properties impart to water its great utility for human beings. The surface water and groundwater resources of the country play a major role in agriculture, hydropower generation, livestock production, industrial activities, forestry, fisheries, navigation, recreational activities, etc. (National Water Policy,2000) in the planning and operation of systems. Water allocation priorities should be broadly as: (i) drinking water, (ii) irrigation, (iii) hydropower, (iv) ecology (v) agro-industries and non-agricultural industries and (vi) navigation.
Rainfall in India is dependent on the south-west and north-east monsoons, on shallow cyclonic depressions and disturbances and on local storms. Most of it takes place under the influence of south-west monsoon between June and September except in Tamil Nadu, where it is under the influence of north-east monsoon during October and November. The long-term average annual rainfall for the country is 1160 mm, which is the highest anywhere in the world for a country of comparable size (Lal, 2000). India has good average annual precipitation, but its poor distribution in space and time has led to the scarcity of groundwater in many areas. The highest rainfall in India of about 11,690 mm is recorded at Mousinram near Cherrapunji in Meghalaya in the northeast. (Bose and Saxena, 2001). The other places like Jaisalmer, Rajasthan in the west, which receives marely150 mm of rain. Though the average rainfall is adequate, nearly three-quarters of the rain pours down in less than 120 days, from June to September. As much as 21% of the area of the country receives less than 750 mm of rain annually while 15% receives rainfall in excess of 1500 mm. Precipitation generally exceeds 1000 mm in areas to the east of Longitude 78°E. It reaches nearly to 2500 mm along almost the entire west coast and over most of Assam and Sub-Himalayan West Bengal. Large areas of peninsular India receive rainfall less than 600 mm. Annual rainfall of less than 500 mm is experienced in western Rajasthan and adjoining parts of Gujarat, Haryana and Punjab.
Rainfall is equally low in the interior of the Deccan plateau, east of the Sahyadris. A third area of low precipitation is around Leh in Kashmir. (Kumar Rupa et.al, 2005)
The average annual rainfall in the country is 1170 mm (Fig.No.1.1), which correspond to an annual precipitation of 4000 billion cubic meters (BCM). Out of this volume of precipitation, 1869 BCM appears as average annual flow in rivers. Due to various constraints, only 1123 BCM is assessed as the average annual utilizable water (690 BCM from surface water and 433 BCM from groundwater). The present total water use is 643 BCM of which 83% is for irrigation. This is projected to grow to 813 BCM by 2010, 1093 BCM by 2025 and 1447 BCM 2050, against utilizable quantum of 1123 BCM. (Fig No.1.2)