It is estimated that by the year 2000, half the world population will live in urban environments (Porter and Brown, 1996). The US Bureau of the Census defines an area as being urbanized if a central city and its closely settled surrounding territory are of a certain size with 50,000 people and density of at least 1,000 people per square mile (Knox, 1994). A component of the definition denotes that human influence is a main aspect of urbanized areas in the process of urbanization. Unfortunately in order to create an urbanized area, a natural environment must be destroyed. Urbanization and human activity within an urban system produces many destructive and irreversible effects on natural environments such as climate change, air pollution, sediment and soil erosion, increased flooding magnitude, and loss of habitat.
Cities in an urban environment change the local climate dramatically. Temperatures are always warmer in the city than it is in the surrounding areas creating a sort of "heat-island" (Harms, 1994). In a city, the sun’s energy is not used in the same way as in open landscapes with vegetation and trees. Concrete, stone, asphalt, and roofs tend to act as solar collectors and emit and absorb heat. The burning of fossil fuels also emit greenhouse gases like carbon dioxide that heat up the atmosphere around the source and usually the source is within urban environments. Cities also tend to be cloudier, rainier, and less humid than their surrounding areas. Cities are 10 percent rainier and 10 percent cloudier and have a 25 percent lower average wind speed, 30 percent more summer fog, and 100 percent more winter fog than nonurban areas (Keller, 1996). Average relative humidity is six percent less in urban areas because cities have large impervious surfaces and little surface or soil water to exchange by evaporation with the atmosphere. The average maximum temperature difference in a city can be 3 degrees Celsius compared to its surrounding areas (Keller, 1996). Urbanization and human activity creates a microclimate that is not environmentally healthful.
Urban environments produce air pollution that harm the natural environment. Much of air pollution is concentrated in and around urban areas, where automobiles and industry emit mass amounts of waste into the environment. Visible air pollution, known as smog, is present in nearly all urbanized areas. Not only are humans affected adversely by bad air quality, animals also suffer. Air pollution can also curb vegetation growth and reduce crop yields. Air pollution from human activities harm all living creatures in the urbanized world.
Human land use affects soils in the environment and increases the potential for erosion. There is a sharp peak in the amount of soil and sediment erosion after the construction phase of urbanization. Sediment can either be blown or washed away with rain and movement. Soil can also be scraped off and lost inducing desertification. Once sensitive soil are disturbed, they may lower strengths when they are altered. This loss of strength increases the potential for landslides. This is especially true in areas of high densities of people and supporting structures such as roads, homes, and buildings. Urbanization disturbs soil and sediment which leads to erosion.
Human use of land in the urban environment has increased both the magnitude and frequency of floods. In the process of urbanization, raw land is converted and covered with pavement. This causes an increase in the amount of runoff after rainfall leading to flash floods. The rate of increase is a function of the percentage of the land that is covered with pavement and cement and the percentage of area served by storm sewers. Storm sewers are important because they allow urban runoff from impervious surfaces to reach stream channels quickly. Urban runoff can also carry polluted water from cities to streams and oceans, disturbing environments even outside the city.
In order to urbanize, natural land must be paved and turned into cities. This requires that flora and fauna either lose their homes or are relocated. Urbanization is virtually irreversible. Whole habitats are eliminated and permanent resources are depleted. Even though the consequences of human activity are unintended, the effects can be far reaching and potentially damaging (Merrifield and Swyngedouw, 1997).
Urbanization is a permanent land
use application. Urban ecological policies should clean up and rebuild
cities in balance with nature (Merrifield and Swyngedouw, 1997) rather
than destroy natural environments. With more and more people living and
moving to cities, the problem will extend beyond existing boundaries and
result in more damage to the natural environment. The effects of urbanization
on the environment are permanent and extensive and urban policy must change
in order to save what is left in the natural world.
Harms, Valerie. 1994. The National Audubon Society: Almanac of the Environment. G.P. Putnam’s Sons: New York
Keller, Edward A. 1996. Environmental Geology. Prentice Hall: Upper Saddle River.
Merrifield, Andy and Erik Swygedouw. 1997. The Urbanization of Injustice. New York University Press: New York.
Porter, Gareth and Janet Welsh
Brown. 1996. Global Environmental Politics. Westview Press: Boulder.