Quantity of Water
Water is the earth's foremost problem. Of the earth's water, 99 per cent is not available for direct use by humans. Salinity and the form in which it is available and location, (glaciers, ice caps) are the primary reasons for such a state of affairs. For 1.0 per cent of the world's water, the entire humanity is in competition.
More than 97 per cent of the water on the earth is salt water. This is not directly used by the humankind. The remaining 3 per cent is freshwater. The quantity of water directly available for human consumption is 0.014 per cent to the total. The rest is found in some seas, lakes, rivers, glaciers and icecaps as well as underground.
Surface water is about 230,250 ckm, of which freshwater lakes hold 125,000 ckm, saline lakes and backwaters 104,000 ckm and rivers and fountains 1,250 ckm. Groundwater is about 8.41 million ckm, of which soil humidity is 67,000 ckm, sub-groundwater and deep water 417,000 ckm. While the groundwater accounts for less than one per cent of the total water (in fact, 0.625 per cent), the surface water accounts for a negligible proportion only (0.0171 per cent). Ice and glaciers account for 2.15 per cent of the total waters (or 29.18 million ckm) while atmosphere for 0.001 per cent (13,000 ckm).
Freshwater Sources: Most freshwater is locked up in ice. It is stored also as the groundwater in great quantities. Only the remaining fraction of freshwater is directly available to us as the useful part of the freshwater from the lakes and the rivers. These water bodies are discussed in great detail in the following pages.
(1) Icecaps and Glaciers: Of the world's freshwater, 77 per cent is in solid form in the icecaps. The poles are covered by the icecaps. Antarctica and Greenland are entirely covered by ice. A portion of these flow as the glaciers. Thus, the freshwater is found locked up for a thickness of several thousand metres in the ice covering the polar regions. In these regions, the precipitation is also in the form of snow. As the ice does not melt even during the summer in these parts, the ice becomes solid and becomes the rocks of ice and icebergs. About 29 million cubic kilometre of water is in the form of ice.
River Flows: The surface waters flowing in the rivers are the most useful for us. The waters of the rivers are received primarily from precipitation. Sometimes, the rains gather as snow or ice and turn into surface waters in summer or spring seasons. About 60 per cent of the total geographical area of the world is made of river basins. There are several large rivers such as the Amazon and Congo draining the equatorial region. In the South and Southeast Asian regions, there are equally large rivers as those of the Indus, Ganges, Hwango and Irrawady. There are no large rivers in the temperate region as are found in the tropical areas. Yet, because of the special climatic features of this region, the rivers here are perennial. Examples are the Thames, Rhine and Volga. Due primarily to local conditions, streams that run once in several years are formed in the tropical deserts.
A majority of the people live depending on the river waters. But, the quantum of water in the rivers changes with the seasons. As a result, for some months in a year, there may be water scarcities. Groundwater comes in useful during these months.
(A) Underground Water: In dense forest areas, much groundwater is gathered. The forests of the tropics, temperate areas and also Taiga regions possess much groundwater. In semi-arid regions also the groundwater is gathered due to rains. Such groundwater aquifers are found in Australia, in the provinces of Queensland, New South Wales and Victoria. Water emerges from the rocks beneath the surface as artesian springs. Groundwater is also found in abundance in the coastal areas. During the times of scarcities, the groundwater of the coastal area is greatly used by the people living along the coast. At times, the groundwater is so very highly exploited that the sea water intrudes down below. As a result, the wells along the coast yield salt water. In most areas of the city of Chennai, there is such a situation.
Water Recharge: All the freshwaters mentioned above can be recharged. Yet, the water withdrawn is much more than what is recharged and hence over the years these sources become dried up. When the quantum of water declines in the water bodies, there generally arises a scarcity. With scarcity, the quality also goes down. Particularly, the freshwater loses its quality through contamination and pollution.
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