The water cycle Essay Example for Free

The water cycle Essay The water cycle is a perpetual process in which water evaporates from the various water bodies, forms clouds, descends to the earth as rain or snow and finally reaches the oceans by means of the runoff mechanism (hydrologic cycle, 2002). Storage Water cycle involves vast amounts of water. The earth contains nearly 340 million cu miles of water. Only three percent of this amount of water can be used for drinking. In other words nearly ninety seven percent of the total volume of water available on the earth is in the oceans and therefore salty. However, the water that evaporates does not contain salt and because of this rain water and snow are free of salt. Salt free fresh water is located in glaciers, lakes and rivers. Moreover, ground water is also fresh and free from salt. The earth contains nearly 8. 6 million cubic miles of fresh water. The atmosphere always contains at least 2,900 cubic miles of water in vapor. Storage of water in the rivers and lakes in the world is estimated at 29,000 cubic miles. The principle sources of fresh water are the great polar ice caps. Nearly 6. 7 million cubic miles of water is stored in the polar ice caps. Water stored in the ground is about 2 million cubic miles (Gedzelman, 2005). Evaporation When a phase change occurs by which water gets transformed from a liquid to gas, it is known as evaporation. The quantity of water that evaporates everyday from the surface of the earth is about two hundred and ninety cubic miles. In the absence of evaporation, precipitation would have rendered the atmosphere dry within ten days. The quantity of water that undergoes evaporation is dependent upon various factors like the intensity of the sunlight, plant cover and ground moisture. Evaporation is indirectly proportional to the humidity of the atmosphere. Due to the different climatic zones on the surface of the earth, the rate of evaporation varies from near zero at the poles to about thirteen feet a year over the Gulf Stream. Evaporation of water is offset by precipitation and runoff (Perlman, 2006). Precipitation A phase change that takes place in the atmosphere, whereby water vapor condenses to form clouds and falls on to the earth as rain is known as precipitation. This falling water can be either a liquid as in rain or it can be a solid like snow, ice etc. the daily average of precipitation that falls on to the earth is of the order of seventy cubic miles. About a third of this precipitated water flows into the rivers and streams, while the rest evaporates (Gedzelman, 2005). Runoff Surface runoff occurs when water flows into rivers and streams. On an average about twenty four cubic miles of water is runoff every day. If snow and ice melt rapidly or if any rainfall occurs the result is an overland flow of water. It causes a rapid increase in the water level of a river and this could result in floods. On the other hand, the ground water flow takes place through rocks and the soil. Water from rains and melting snow sweeps through the ground and reaches the water table. Subsequently, this water flows to a water table which is at a lower level. Its speed of flow though only three feet a day is almost constant (Gedzelman, 2005). Effects of Human Activity Human beings use a lot of water; it plays a vital role in their very existence. With the growing population the demand for fresh water is also increasing. A number of methods are used to obtain fresh water, such as irrigation channels, wells etc. Due to the large amount of water being extracted from ground there has been a significant lowering of water table. In some coastal areas the result has been the forcible entry of sea water. Due to global warming there is a vast change in the earth’s climate. In several regions of the world the water available is unfit for consumption. All these factors have adversely affect water cycle. In the absence of optimal usage of water there is a serious danger that severe water scarcity could transpire (Robert Carpenter, 2001). References Gedzelman, S. D. (2005). Water Cycle. Microsoft  ® Encarta  ® 2006 (DVD) . Redmond, WA: Microsoft Corporation. hydrologic cycle. (2002). Retrieved April 20, 2007, from In The New Dictionary of Cultural Literacy, Houghton Mifflin: http://www. xreferplus. com/entry/2446693 Perlman, H. (2006, Aug 28). The water cycle: Evaporation. Retrieved April 20, 2007, from http://ga. water. usgs. gov/edu/watercycleevaporation. html Robert, J. , Carpenter, S. R. (2001). Water in a changing world . Issues in ecology , 1027-1045.