Urban sprawl is the spreading out of a city and its suburbs into rural land. One characteristic that defines urban sprawl is low population density. Residential neighborhoods, for example, tend to have a low-population density: Homes are primarily single-family and are built on lots larger than those found in the city. In addition, commercial buildings in low-density areas tend to be one story and farther apart, often increasing the distance that people must travel between their destinations.
Single-use zoning is common in urban sprawl areas. Under single-use zoning, land tracts are only used for commercial, residential, or industrial building; as a result, homes, as well as work and recreational sites, are often separated by distances that are too far to walk. Instead, people typically travel by automobile.
In the United States, the number of people living in the suburbs doubled between 1950 and 2000. During this time, commercial businesses took advantage of more space and the easy access to roads and moved farther away from city centers. In 1900, 40% of the U.S. population lived in urban areas, while 60% lived in rural parts of the country. Today, 70% of the U.S. population lives in the cities or suburbs.
Since 1970, 1.23 billion urban residents have been added to the global urban population. The United Nations estimates that there are 2.5 billion urban residents globally, and that Asia accounts for 1.2 billion people in this category. Europe has about 535 million urban residents.
Urban sprawl has negative environmental and health effects on both humans and animals. Conservationists concerned with urban sprawl's effects on the environment tend to focus on the amount of land that has been urbanized and the loss of natural habitat. In contrast, city planners' main concerns are transportation and the lack of pedestrian-friendly areas.
Negative aspects of urban sprawl, such as traffic congestion problems, pollution, and the loss of rural land, have been documented and studied for decades. For instance, air pollution (the contamination of air by smoke and harmful gases released by automobile exhausts, industrial emissions, or burning rubbish), is known to cause allergies and breathing difficulties.
Other problems are just starting to be recognized as serious global issues. For example, some metropolitan areas are continuing to grow and spread, without attempts being made to renovate buildings in the smaller, concentrated population centers. In addition, as urban sprawl expands, people must travel farther to their destinations; the subsequent increase in the use of motor vehicles raises the resulting amount of emissions and pollution. Carbon monoxide emissions occur nationwide, but are much higher in cities, where 85-95% of emissions come from vehicle exhausts.
Smog (a type of air pollution that results when sunlight reacts with the emissions from vehicles and industry) may occur in areas with heavy traffic. Smog may be especially heavy in populated areas, such as Los Angeles, that contain busy freeways and are surrounded by mountains. The first recognized episodes of smog occurred in Los Angeles in the summer of 1943: At the time, visibility was only three blocks, and residents suffered from respiratory discomfort, burning eyes, nausea, and vomiting. The smog event was called a "gas attack" and was incorrectly blamed on a nearby butadiene (chemical) plant. Conditions did not improve, however, after the plant was shut down. Los Angeles began its air pollution control program in 1945. Industrial pollutants also contribute to smog and air pollution. In 1948, a cloud of smog formed over Donora, Pennsylvania, killing 20 people and sickening more than one-third of the population.
The U.S. Environmental Protection Agency (EPA) has established 188 Hazardous Air Pollutants (HAPs), which have short- and long-term health outcomes, including respiratory, neurological, immune, and reproductive effects. Many HAPs are also known to cause adverse effects in fish and animal species; toxicity in fish and a reproductive decline in bird species are direct results from exposure to common HAPs.
Today, urban sprawl is a global issue, as worldwide land use rapidly changes with development. Rural and open space is being used to increase urban areas. This practice results in a loss of natural vegetation, wildlife habitats, and agricultural land. Water quality may also be affected: Since many surfaces are covered with pavement, rain is not absorbed into the ground and the run-off picks up pollutants from roads. Nonpoint source (NPS) pollution is a form of runoff that picks up whatever pollutants may be on the ground. These materials may be fertilizers and insecticides from agriculture, oil and toxic chemicals from roads, and bacteria from livestock and faulty septic systems. Consequently, bodies of water may become polluted.
Along with environmental costs, sprawl's monetary costs to local and state governments may be high. To support new developments and inhabitants, governments must invest in infrastructure: New schools, streets, utilities, and other services must be built to connect widely-spread populations.
Land planners try to balance the loss of rural lands by creating greenbelts, or green wedges, of undeveloped land in the urban landscape. These undeveloped areas help restore balance to the climate and reduce air pollution; they also provide natural habitats for plants and animals. In addition, urban greenbelts often provide biking and hiking trails for recreational purposes.
General: In the United States, the number of people living in the suburbs doubled between 1950 and 2000. Commercial businesses took advantage of more space and easily-accessible car routes by moving farther away from city centers. Forty percent of the U.S. population lived in urban areas in 1900, while 60% lived in rural parts of the country. Today, 70% of U.S. residents live in the suburbs or cities. Since 1970, 1.23 billion people have been added to the global urban population. The United Nations estimates that there are 2.5 billion urban residents globally, and that Asia accounts for 1.2 billion people in this category. Europe has about 535 million urban residents.
Studying urban sprawl: New technologies show that the earth's landscape and its atmosphere are changing as urban sprawl increases. One of the latest technologies in use is the Defense Meteorological Satellite Program's Operational Linescan System (DMSP-OLS), a U.S. Department of Defense program that monitors meteorological, oceanographic, and solar-terrestrial physics environments by satellite. The DMSP-OLS also monitors light emissions from cities at night; researchers are able to overlay these "light maps" onto existing soil and vegetation maps, allowing them to determine if urbanization is having an impact on photosynthetic productivity. In areas where urbanization is intense, as much as 20 days of annual photosynthetic productivity may be lost: This result is the equivalent of turning the lights off in a greenhouse for 20 days out of the year.
A study of downtown Atlanta using satellites suggests that urban development may affect local weather conditions. When cities hold on to heat at night, low pressure areas are created. This added heat increases the chance that thunderstorms may develop.
Temporal urban mapping uses satellite data to monitor and record changes in land use on earth. Comparisons of earlier data, historical maps, and computer illustrations show how much of the earth's land has been urbanized. Such data provide fast, visual confirmation of differences in land and water use, as well as changes in the natural environment; some changes that are tracked include the depleting of rivers and the continual alteration of shorelines.
A temporal database may also be used to accurately predict patterns of change and to discover problems associated with urban growth. This process is important in order to assess the environment and to meet goals of sustainable development. Examples of national programs involved in this research include NASA's Mission to Planet Earth (MTPE) and the U.S Global Change Research Program. MTPE is dedicated to understanding and researching environmental changes on earth from the vantage point of space. The U.S Global Change Research Program and MTPE work with other organizations, including the National Oceanic and Atmospheric Administration, to further understand and support essential and complex environmental decisions.
In the past, census data was used to measure urban sprawl; however, this data was not as accurate as the details that come from visually observing the use of land. Visual data provide current, immediate information, instead of the sometimes-outdated statistics of census records. Additionally, a visual map is easier to understand and process than masses of written data. Remote sensing performed by satellites is able to detect and monitor global change on large and small scales. The Advanced Very High Resolution Radiometer (AVHRR), Landsat Thematic Mapper (TM), and the French SPOT system have successfully measured deforestation, biomass burning, and other land use changes by using similar satellite technology. These technologies have only recently been used to monitor the conversion of agricultural land to residential and commercial use. Most remote sensing data of urban areas and mapping of traditional land-use/landcover types use high-resolution image data sources like SPOT and Landsat.
Nighttime images produced by the Defense Meteorological Satellite Program's Operational Linescan System (DMSP/OLS) provide dramatic pictures of city lights as they are seen from space. Merging data from the DMSP/OLS with digitized soil maps and census data has created an early approximation of how urban land use in the United States may be reducing agricultural potential and how much productive soil is being lost to urban sprawl. The U.S. Geological Survey (USGS) states that the best available soils may be protected from development; however, in states such as California and Illinois, even the best soils are being lost at high rates because of urban growth. The USGS has used DMSP/OLS data to determine that California has lost about 16% of its best soils to urban use. Illinois has lost about 8% of its most productive soil. The second best types of soils are also being developed at a high rate. Nationwide, about two percent of the best soils have been lost to urban development.
Metropolitan areas are continuing to grow and spread. This urban sprawl may have negative environmental and health effects on humans and animals. Some of these problems are just beginning to be recognized as serious global issues. Yet, instead of remaining as small concentrated population centers, most cities and their suburbs have spread out and are still growing as more people move to the suburbs.
Urban sprawl and urbanization affects the environment in various ways. As agricultural lands, pastures, woodlands, and wetlands are being developed, researchers are noticing that this development has biological repercussions. Since the 1990s there has been a growing interest in ecology and humans' effects on the natural ecology of ecosystems. Urban sprawl has reduced and changed the ecology of the natural environments.
When land use is changed, basic elements of the ecosystem are transformed, and non-native species may be introduced. For instance, species that are highly specialized in terms of what they eat and where they live are at greater risk of extinction when change occurs in their natural environments.
As urban sprawl increases, people must travel farther to reach their destinations. More emissions and pollution occurs with the subsequent increased use of motor vehicles. Carbon monoxide emissions occur nationwide, but are much higher in cities, where 85-95% of emissions come from vehicle exhausts. Smog may also occur in areas with heavy traffic; this form of pollution may be prevalent when populated areas, such as Los Angeles, are surrounded by mountains. In addition, industrial pollutants may contribute to air pollution and smog. In 1948, a cloud of smog formed over Donora, Pennsylvania, killing 20 people and sickening more than one-third of the population.
The U.S. Environmental Protection Agency (EPA) has established a list of 188 Hazardous Air Pollutants (HAPs). HAPs have short- and long-term health consequences, including respiratory, neurological, immune, and reproductive effects. Many HAPs are also known to cause adverse effects in fish and animal species; toxicity in fish and a reproductive decline in bird species are direct results of exposure to common HAPs.
Global warming has been attributed to an increase in greenhouse gas emissions. Air pollutants such as carbon dioxide and methane are types of greenhouse gases that have increased through human activity.
When sprawl replaces agricultural fields, forests and open areas, the water quality often declines. This deterioration of water quality is largely due to the number of people and vehicles on the roads: Paved surfaces and polluted rainfall run-off are the contributing factors. Because more surfaces are covered with pavement, rain is not absorbed into the ground and the run-off picks up pollutants from roads; consequently, bodies of water may then become polluted.
Smart growth practices include compact development, the mixing of land uses, better pedestrian and bike amenities, the reduction of covered surfaces, and the improvement of water retention. These techniques may lessen the negative environmental effects of urban sprawl. A 2000 study on compact developments that use smart growth practices found that these neighborhoods produced 40% less water pollution than similar-sized neighborhoods that didn't incorporate smart growth practices. Additionally, residents of neighborhoods where land uses were mixed (commercial and residential) traveled 26% fewer vehicle-miles than residents in more widely-spaced neighborhoods: There was less dependence on vehicle use.
The National Award for Smart Growth Achievement is given by the U.S. Environmental Protection Agency (EPA) in recognition of communities that use smart growth principles. The EPA also offers grants to support and improve smart growth developments. The U.S. Geological Survey (USGS) is another organization leading efforts to promote smart growth planning, by providing scientific data to state and local governments.
According to the Smart Growth Network, there are 10 smart growth principles that can be applied in planning today: 1) strengthening and directing development towards communities that already exist; 2) using compact building designs; 3) encouraging uniqueness and beauty in communities; 4) creating walkable communities; 5) providing a range of housing choices for people of all income levels; 6) encouraging collaboration between the community and stakeholders in development decisions; 7) providing a variety of transportation options; 8) integrating mixed land uses into communities; 9) making development decisions fair, predictable, and cost effective; and 10) preserving natural beauty, open space, farmland, and important environmental areas.
FUTURE RESEARCH OR APPLICATIONS
Urban sprawl is seen as a global issue, as worldwide land use rapidly changes with development. Rural and open space is being used to increase urban areas. As a result, there is a loss of natural vegetation, wildlife habitats, and even agricultural lands. Water quality may also be impacted. In addition to the environmental costs of sprawl, monetary costs may also be high: New schools, streets, and other services must be built to connect widely-spread populations. Governments must expand infrastructure, such as roads and utility services, to support new developments and the people who live there.
Studies conducted by the U.S. Geological Survey (USGS) suggest that population increases in suburban and exurban counties will continue. "Exurban" refers to communities that lie beyond the suburbs, generally inhabited by wealthy individuals. Vulnerability assessments conducted by the USGS in the 1990s evaluated the potential risks of future wild land conversion into urban areas, based on the proximity of wild lands to urban growth areas.
Current temporal urban databases used in monitoring urban sprawl and other development studies are used to forecast future areas of urban growth. By applying modern mapping techniques to communities nationwide (and eventually to areas on a global scale), these temporal urban databases will be the framework for understanding urban growth. More accessible satellite imaging is needed, however, to provide global data that will help prevent the negative effects of urban sprawl. It may be possible to stop global development problems before they start, through the gathering of more data and by creating a system for planners around the globe to access the information.
The Center for Land-use Education and Research at the University of Connecticut is working with the U.S. National Aeronautics and Space Administration (NASA) on a project called NAUTILUS. This project will quickly provide city planners with satellite data, in a form that non-scientists can understand and apply to planning. NAUTILUS is one of seven Regional Earth Science Application Centers (RESACs) throughout the United States; RESACs put critical information into the hands of local and national decision-makers. As of late 2008, the NAUTILUS team is fine-tuning their remote-sensing tools in four test regions: Maine, New Jersey, Connecticut, and Massachusetts. Researchers are learning the best ways to use this satellite data to meet the needs of local officials, and in what form the information is best delivered. For example, data forms may include time-lapse animations and color-coded maps: Time-lapse animations show how land use has changed, by using data and computer illustrations for a specified length of time and then playing them back at high speeds.
NAUTILUS researchers are also using a software package called CommunityViz to allow city planners to create hypothetical futures for their cities. Virtual outcomes of possible growth scenarios, including estimates of water quality data, provide immediate feedback and help planners make more accurate decisions about the future.
The National Award for Smart Growth Achievement is given by the Environmental Protection Agency (EPA) in recognition of communities that use smart growth principles. The EPA also offers grants to support and improve smart growth developments. The U.S. Geological Survey (USGS) is another organization leading efforts to promote smart growth planning, by providing scientific data to state and local governments.
This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).
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