Urbanization

1 Introduction.

Changes in the environment which eventually affect bio diversity are usually as a result of population increases affecting the carrying capacity, technology meant to increase efficiency and productivity using artificial means and so on. A description of what constitutes the environment is relative in terms of distance or space. More importantly however, is the immediate environment, which directly affects the immediate populations more than those, which are further from the area.

The effects of the environment resulting to a resident of an urban center may affect both rural and urban populations but the incidence is more on urban populations than on rural populations and vice versa. To have a more detailed analysis of the environmental issues and their effects on both classes of populations, we have to go over the pressures affecting both environments and their impacts both locally and widespread i.e. Indiscriminate.

2. Environmental effects of urban centers or cities.

A city is an urban area, differentiated from a town, village, or hamlet by size, population density, importance, or legal status. In most parts of the world cities are generally substantial and nearly always have an urban core.

A rural area therefore simply means outside the limits of any incorporated or unincorpated city, town, village, or any other designated residential or commercial area such as a subdivision, a business or shopping center, or community development. It is usually characterised by farms of other forms of activities, which require large tracts of land such as ranching.

As late as 1900, there were barely 43 cities in the world exceeding 500,000 population, of which only 16 exceeded 1,000,000. Since 1950 the number of large cities has increased very rapidly (about 400 exceed 1,000,000). Metropolitan areas have grown to form even larger agglomerations and some very large urban areas with populations in the tens of millions have emerged. For example, Calcutta, Bombay, Cairo, Jakarta and Seoul are each expected to be in the 15-20 million people range. The environment in large urban areas has deteriorated and resulted in an increased incidence of diseases and ailments.

The effects of urban development can be defined by many factors. The most important of these factors relate to air quality, the availability of safe water supplies, provisions for sanitation and waste management and provision of land for expansion to accommodate increases in population and the planning process for the same. Effects of these factors may be far reaching but some are felt more in the urban centers than in rural areas. To have a more detailed look of these factors and their issues, we have to look into them one by one.

2.1 Urban centers and air quality issues.

Local effects of urban air pollution which don't affect rural populations as such.

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.

The burning of fossil fuels emits 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 non urban areas.

Compared to rural surfaces, city surfaces absorb and store significantly more solar radiation. Specifically during the summer months, the buildings, pavement, and concrete of the city absorb and store solar radiation. The concreted city surfaces have both great thermal capacity and conductivity, so that heat is stored during the day and released at night. Because of the high water runoff in the city, less of this energy is used for evaporation. In contrast, the countryside, the presence of evaporation and transpiration results in relatively lower temperatures during the day and night. This results in what is referred

to as the heat island effect.The presence of pollutants over the city enhances the heat island effect. H2O, CO2, and other pollutants enhance the surface temperature through convection and radiation processes.

Widespread effects of urban air pollution which also affect rural populations.

Ozone depletion which occurs when the natural balance between the production and destruction of stratospheric ozone is tipped in favour of destruction has been linked such as CFC's, bromine etc. which are mainly emitted

from industries and domestic effluents located in urban centers.

With respect to rural areas, air pollution from urban centres which results in Ozone depletion can curb vegetation growth and reduce crop yields. Ozone depletion results in increased UV radiation. Physiological and developmental processes of plants are affected by UV radiation, even by the amount of UVB in present-day sunlight. Despite mechanisms to reduce or repair these effects and a limited ability to adapt to increased levels of UV, plant growth can be directly affected by UV radiation.

Also, exposure to solar UV radiation has been shown to affect both orientation mechanisms and motility in phytoplankton, resulting in reduced survival rates for these organisms. Scientists have demonstrated a direct reduction in phytoplankton production due to ozone depletion-related increases in UV radiation. One study has indicated a 6-12% reduction in the marginal ice zone. This affects fish populations which are the mainstay of some rural populations as phytoplankton form the foundation of aquatic food webs.

Solar UV radiation has been found to cause damage to early developmental stages of fish, shrimp, crab, amphibians and other animals. The most severe effects are decreased reproductive capacity and impaired larval development. Even at current levels, solar UV radiation is a limiting factor, and small increases in UV exposure could result in significant reduction in the size of the population of animals that eat these smaller creatures.

Effects of the urban air pollution also affect populations of residents across the board