Urban sprawl
Urban sprawl refers to the unplanned and uncontrolled expansion of urban areas, often leading to a mix of incompatible land uses and inefficient urban service provision. This phenomenon arises from various social and economic pressures, including population heterogeneity, the desire for escape from dense urban environments, and the pursuit of profit by landowners. As cities grow, particularly in developing nations, urbanization is set to intensify, with projections indicating that by 2050, 68 percent of the global population will reside in urban areas.
The environmental impacts of urban sprawl are significant, resulting in habitat destruction, changes in microclimates, and increased runoff due to impervious surfaces. While sprawl can lead to increased air and water pollution, some studies suggest that it may also alleviate pollution levels compared to densely populated urban centers. Efforts to combat sprawl, such as zoning regulations and the promotion of "smart growth," aim to create more sustainable urban environments by encouraging high-density development and reducing reliance on automobiles. These initiatives seek to enhance the quality of life by reducing travel distances and promoting mixed-use neighborhoods. Understanding urban sprawl is essential for addressing the challenges of modern urbanization and its multifaceted impacts on communities and the environment.
Urban sprawl
- DEFINITION: The uncontrolled and unregulated development that occurs outside the administrative boundaries of the zoning and land-use authority of municipalities and outside the conscious and deliberate direction of those authorities
When urban settlements become overcrowded, some individuals, businesses, and industries migrate to the fringes of the urban area, where population concentrations are less dense, but urban services remain available. The concentration and eventual diffusion of urbanization affect existing land uses, the physical environment, the survival of plant and animal species, and the aesthetics of the landscape.
Urban growth and development are usually controlled by two forces. First, municipal government authorities regulate growth through urban planning, zoning, and a variety of land-use ordinances. Second, social and economic forces combine to encourage outward growth of the urban area in one of three consistent patterns, described as concentric circle, sector, and multinuclear patterns. Urban sprawl, which is neither controlled nor regulated, often involves some break in this historic pattern. The unplanned nature of urban sprawl often results in a mix of incompatible land uses placed adjacent to one another in the same developed physical area.
The challenges presented by urbanization and urban sprawl are likely to intensify in the decades to come. In mid-2009, the world population officially became more urbanized than rural. By 2020, the world population totaled 7.821 billion people. Of those people, 56.15 percent lived in urban areas, and 43.85 percent lived in rural areas. According to United Nations projections for the year 2050, the world’s population growth will continue to be concentrated within urban areas; of that increase, most is expected to be within the cities and towns of developing nations. The United Nations estimated in 2018 that by 2050 the number of people inhabiting urban areas would be roughly 6.3 billion, constituting 68 percent of the global population.
Problems Caused by Sprawl
Sprawl results in discontinuous leapfrog or checkerboard patterns of development and strip development along transportation corridors, with skipped areas remaining undeveloped. This creates inefficiencies in providing urban services to the sprawl area. Sprawl also results in less-than-maximum utilization of existing developed land in the urban center. Instead of converting existing developed land to new uses, developers establish new developments on less expensive land in suburban areas adjacent to the existing urban area.
Urban sprawl generally increases the total amount of land affected by human activity, the number of natural areas converted to recreational uses, the amount of wasteland, and the residential, industrial, institutional, and infrastructure uses of land. Wasteland is land disturbed by humans to such an extent that natural uses cannot be restored, and future development on the land is restricted. Wastelands include soil borrow pits (areas where soil has been dug out to be taken to other locations), quarries, debris landfills, and construction material storage sites. Urban sprawl generally decreases agricultural uses and timber uses of land and decreases the amount of natural barren or rocky lands, river and stream floodplain areas, and native timber- and grasslands.
Sprawl is encouraged by a variety of social and economic forces. First, it is often a consequence of increasing heterogeneity of the urban population and is a means to limit or escape from interactions between dissimilar social, economic, and ethnic groups. Second, sprawl allows individuals and businesses to escape from the negative effects caused by concentrations of undesirable land uses—such as industrial, commercial, and low-income residential zones—and relocate to suburban areas with more pristine and affordable real estate. Third, sprawl is encouraged by landowners in suburban areas seeking to maximize profits from investments in land. Finally, sprawl permits individuals and businesses to escape taxes and regulations imposed in core urban areas.
Some researchers contend that the sprawl problem is overstated. In the United States, for example, urban land in 2018 represented less than 2 percent of the nation’s total land area and housed more than 82 percent of the population. By contrast, about 5 percent of the nation’s land is protected from development under the 1964 Wilderness Act.
Environmental Impacts
The first significant impact of urban sprawl on the environment is the abnormal greening of the physical area. In most cases, total greening is reduced through the destruction of forests, grasslands, and floodplains to make way for development. This decreases the number and variety of species able to occupy the space and creates microclimate effects, such as regional warming. However, in some cases, total greening is increased through irrigation and the introduction of cultivated lawns, orchards, and other plantings in areas that are naturally arid or barren. This results in the introduction of new species into the environment, increased pollen counts, and a variety of microclimate effects, such as increases in regional humidity. In either case, the presprawl natural is dramatically changed, with resulting negative impacts on plant and animal species displaced by or unable to adapt to the new environment.
In the course of sprawl development, existing natural ecosystems are destroyed while presprawl plants and animals are killed, displaced, or replaced. Most presprawl wildlife retreats in the face of development. However, some species are able to adapt to the sprawl environment and find the mix of land uses, the dispersion of human activities, and the residue of human activity conducive to their survival. Among the wildlife that benefits are scavengers, such as pigeons, rats, raccoons, and opossums; vermin hunters, such as falcons, foxes, and coyotes; and foragers, such as deer, squirrels, and rabbits. Benefiting plant species include all those that homestead on disturbed soil or wasteland or that thrive in the open sunlight of most new suburban developments.
Sprawl reduces the amount of productive agricultural land and economically important forests. Productive agricultural land and forests are lost either by the development of the land for residential, industrial, or institutional uses or by the transformation of productive farms and forests into hobby farms and parkland in an effort to preserve green space without preserving the productive purpose of the agricultural lands or forestland.
Finally, sprawl increases the total amount of land surface that is impervious to rainfall penetration. Roadways, parking lots, slab building foundations, and other paved areas increase rainwater runoff and the possibility of flooding, soil erosion, and ecosystem destruction.
Impacts on Air and Water Resources
Other consequences of urban sprawl include increases in noise, light pollution, land area devoted to highways and roads, and public-utility impacts as land is cleared for underground water, sewer, and utility pipes and for aboveground utility cables.
The impact of sprawl on air and water resources is both negative and positive. The increase in human population that accompanies sprawl increases the concentration of significant amounts of unnatural substances in the soil, water, and air and also produces abnormally high concentrations of natural substances at levels that may cause undesirable health effects, corrosion, and ecological change. However, studies also indicate that the population dispersal associated with sprawl actually reduces air pollution by dispersing both the mobile and stationary sources of pollutants. Increases in air pollution from automobiles associated with sprawl may be less than the air pollution produced by traffic gridlock, mass-transit buses, and trains in denser urban areas.
Subsurface water supplies and surface watercourses are less affected by sprawl than by denser patterns of development. Denser urban development increases the demands on water resources, runoff and the possibility of flooding, and the likelihood that watercourses will be channeled and hardened by concrete and other construction materials. Denser urban development, and the increase in paved surfaces that comes with it, also make it more difficult for subsurface water to replenish itself.
Limiting Sprawl
Many municipalities attempt to limit sprawl by refusing to extend essential services such as water lines, sewer lines, and road systems outside their municipal boundaries. Rural areas may attempt to limit sprawl through zoning restrictions on development, farmland protection ordinances, environmental impact regulations, and special development-impact fees levied on new development to recover the public costs associated with constructing roads, schools, and other facilities necessary to provide services to the newly developed areas.
In North America, a movement toward “smart growth” has emerged as a sustainable middle ground between sprawl and zero growth. Smart growth emphasizes high-density neighborhoods and reduced car use. It occurs not on a city’s periphery but at its heart, where urban land is redeveloped to provide a mix of residential, retail, and office uses. The intent of this clustered development is to enable residents to work and shop near their homes. Reduced travel distances between people’s residences and their workplaces and the sites of their leisure activities enable city dwellers to walk, bike, or use public transportation to reach their destinations. From 2005 to 2015, the Environmental Protection Agency (EPA) presented national achievement awards to communities across the United States which stood out as excellent examples of the smart growth ideals. The EPA continued highlighting community examples of smart growth and providing tools and resources to help communities implement more sustainable methods into the 2020s.
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