Thursday, January 30, 2020
The water cycle Essay Example for Free
The water cycle Essay Directly relative to the hydrologic cycle is the effect of urbanization in the impervious cover (IC). As mentioned earlier in this paper, the lower the rate of impervious area, the higher will be the rate of water infiltration which means that water run-off is relatively low. Obviously, urbanization requires the construction of more sidewalks, driveways, parking lots and more houses which make the soil impervious. The next chapter of this paper discusses in detail the specific effects of urbanization to the hydrologic cycle. Powered by solar energy and gravity, the movement of water in our environment is a continuous cycle. The water cycle also referred to as the hydrological cycle is just one of the vital natural cycles that typically involves the changing of the states of water from liquid, vapor and ice as it moves on, above and below the surface of the earth (Gore, Pamela 2005). 1Water also transforms through the processes of vaporization or evaporation (liquid to gas), condensation (gas to liquid), melting or fusion (solid to liquid), and sublimation (gas to solid, or the reverse). The cycle involves the soil, the plants, and the bodies of water, the air and the sun. Playing an important role in the climactic patterns, changes in the hydrologic cycle are revealed in the changes in the worldÃ¢â¬â¢s climate and the seal level. As what researchers and scientists have been claiming decades ago, human intervention of which urbanization is the most evident, has played a great role in the significant changes in the cycle. In order to clearly present the validity of such claim, it is helpful for us to look back at the normal cycle of water. Figure 3. 1 shows the normal hydrologic cycle as presented by the U. S. Geological Survey. At first look, it seems that humans are not directly involved in the cycle but if we are to examine each phase of the cycle, we will be able to extract information that will link human activities to each phase of the cycle. Scientists consider the earth as a Ã¢â¬Å"closed-systemÃ¢â¬ which means that almost its entire elements contained therein just move in different cycles and that the earth neither lose nor gain significant amount of matter (Global Hydrology and Climate Center). In terms of the hydrologic cycle, water is distributed globally and recycled continuously, which is the same cycle way back millions of years ago. Figure 3. 1 The Water Cycle. Source: U. S. Geological Survey The cycle of water involves six major processes: (1) evaporation, (2) transpiration, (3) horizontal transport of water, (5) precipitation and (6) water flowing as run-off. In the process of evaporation, the liquid state of water from the surface of the bodies of water and from the soils transforms into gas or vapor. Water also transforms into gas state through the process of transpiration where a certain amount of water from the plants are released in the air through the leaves of plants. In another phase of the cycle, water also travels in the cycle as atmospheric water in a horizontal direction in forms of water droplets, ice crystals or vapor. The process of precipitation takes place in the air wherein the atmospheric vapor undergoes condensation and sublimation that will then fall to the earth as hail, snow, sleet and rain. In any of these states, 3precipitation that reaches the earth flows through one of four major routes. As suggested by the arrows in figure 1. 1, precipitation may fall down the earth and runs off to the bodies of water like ponds, wetlands and lakes. Precipitation may also follow the route of river and creeks after running off over the land. Water that runs over the land may run through as surface water while some amount will serve as groundwater. Because this amount of water was not able to infiltrate into the ground, the same will return to the atmosphere either through the process of transpiration or evaporation. Scientists define surface water as water that stands or flows on the surface of the earth and also referred to as run-off (White, Iain 2007). Current practice on considers run-off as dangerous to human health and these are usually driven out of the land surface as quickly as possible into sewers or man-made drainage systems. This practice however alters the normal hydrologic cycle as infiltration is lessened which directly affects the processes of transpiration and evaporation. Through the process of infiltration, water sips or absorbed by the ground surface of the earth and so these volume of water is called surface water. On the other hand, groundwater is that volume of run off that sips in the ground and flows through the cracks in the soil, sand and through the spaces between beds of rocks. Depending on the sizes of spaces between rocks and soil, groundwater will be stored in such spaces called aquifers. Aquifers are water-bearing rocks because of their characteristics of high porosity and permeability of which sandstones and gravels are excellent examples (Gore, Pamela 1995). In contrast, rocks, which are not porous like shale, are called aquicludes and so they cannot store water. However, highly jointed aquicludes may also become aquifers because water can also be contained in rock joints. The water that was not absorbed by the plants, or stored in aquifers will eventually into the bodies of water such as the ocean or creeks. The cycle then continues as such water then goes back to the atmosphere through evaporation or transpiration which scientists safely referred to as Evapotranspiration (ET). The amount of water is not well distributed globally as there are areas there are arid lands like Phoenix and Saudi Arabia compared to more permeable areas like some countries of Asia. This is primarily because the types and number of water reservoir of countries varies. Figure 4. 1 will give us the idea that since much of the worldÃ¢â¬â¢s water is stored in the ocean reservoir, it follows that countries which do have much of such bodies of water have the highest volume of water distribution. If we are to express figures in percentage, we will come up with 97% accounting for water in the ocean and the three percent is distributed among the reservoirs in the soils and the cryosphere in forms of ice caps and glaciers particularly in the areas of Antarctica and Greenland. It is important to note that the total amount of water in the different reservoirs remains nearly constant with the natural landscape and impervious groundcover held in its close original state (NEMO California Partnership, 1997). In the research made by NEMO National Network (California Partnership) in cooperation with the California local government units and the local Environmental Protection Agency (EPA), shallow and deep infiltration of water is 50% while 40% of the water is processed during evapotranspiration. Illustration of the relationship of water run-off and infiltration (NEMO) In this scenario, only 10% of water turns out to be run-off. As the rate of imperviousness increases due to alteration or removal of the natural groundcover, the rate of infiltration consequently decreases. This then results to a higher percentage of run-off water and a lower percentage of water processed during evapotranspiration. The question therefore is: in what ways does infiltration rate increases or decreases and how are human activities relate to this process?