Environmental impact of reservoirs
The environmental impact of reservoirs comes under ever-increasing scrutiny as the global demand for water and energy increases and the number and size of reservoirs increases. Dams and reservoirs can be used to supply drinking water, generate hydroelectric power, increase the water supply for irrigation, provide recreational opportunities, flood control. In 1960 the construction of Llyn Celyn and the flooding of Capel Celyn provoked political uproar which continues to this day. More the construction of Three Gorges Dam and other similar projects throughout Asia and Latin America have generated considerable environmental and political debate. A dam acts as a barrier between the upstream and downstream movement of migratory river animals, such as salmon and trout; some communities have begun the practice of transporting migratory fish upstream to spawn via a barge. Rivers carry sediment down their riverbeds, allowing for the formation of depositional features such as river deltas, alluvial fans, braided rivers, oxbow lakes and coastal shores.
The construction of a dam blocks the flow of sediment downstream, leading to downstream erosion of these sedimentary depositional environments, increased sediment build-up in the reservoir. While the rate of sedimentation varies for each dam and each river all reservoirs develop a reduced water-storage capacity due to the exchange of "live storage" space for sediment. Diminished storage capacity results in decreased ability to produce hydroelectric power, reduced availability of water for irrigation, if left unaddressed, may result in the expiration of the dam and river; as all dams result in reduced sediment load downstream, a dammed river is demanding for sediment as it will not have enough sediment. This is because the rate of deposition of sediment is reduced since there is less to deposit but the rate of erosion remains nearly constant, the water flow erodes the river shores and riverbed, threatening shoreline ecosystems, deepening the riverbed, narrowing the river over time; this leads to a compromised water table, reduced water levels, homogenization of the river flow and thus reduced ecosystem variability, reduced support for wildlife, reduced amount of sediment reaching coastal plains and deltas.
This prompts coastal erosion, as beaches are unable to replenish what waves erode without the sediment deposition of supporting river systems. Downstream channel erosion of dammed rivers is related to the morphology of the riverbed, different from directly studying the amounts of sedimentation because it is subject to specific long term conditions for each river system. For example, the eroded channel could create a lower water table level in the affected area, impacting bottomland crops such as alfalfa or corn, resulting in a smaller supply. In the case of the Three Gorges Dam in China the changes described above now appears to have arrived at a new balance of erosion and sedimentation over a 10-year period in the lower reaches of the river; the impacts on the tidal region have been linked to the upstream effects of the dam. The water of a deep reservoir in temperate climates stratifies with a large volume of cold, oxygen poor water in the hypolimnion. Analysis of temperature profiles from 11 large dams in the Murray Darling Basin indicated differences between surface water and bottom water temperatures up to 16.7 degrees Celsius.
If this water is released to maintain river flow, it can cause adverse impacts on the downstream ecosystem including fish populations. Under worse case conditions, the stored water is stratified and large volumes of water are being released to the downstream river channel via bottom level outlets, depressed temperatures can be detected 250 - 350 kilometres downstream; the operators of Burrendong Dam on the Macquarie River are attempting to address thermal suppression by hanging a geotextile curtain around the existing outlet tower to force the selective release of surface water. Many dams are built for irrigation and although there is an existing dry ecosystem downstream, it is deliberately destroyed in favor of irrigated farming. After the Aswan Dam was constructed in Egypt it protected Egypt from the droughts in 1972–73 and 1983–87 that devastated East and West Africa; the dam allowed Egypt to reclaim about 840,000 hectares in the Nile Delta and along the Nile Valley, increasing the country's irrigated area by a third.
The increase was brought about both by irrigating what used to be desert and by bringing under cultivation 385,000 hectares that were natural flood retention basins. About half a million families were settled on these new lands. In many low lying developing countries the savanna and forest ecology adjacent to floodplains and river deltas are irrigated by wet season annual floods. Farmers annually plant flood recession crops, where the land is cultivated after floods recede to take advantage of the moist soil. Dams discourage this cultivation and prevent annual flooding, creating a dryer downstream ecology while providing a constant water supply for irrigation. Case studies The Lake Manatali reservoir formed by the Manantali dam in Mali, West Africa intersects the migration routes of nomadic pastoralists and withholds water from the downstream savanna; the absence of the seasonal flood cycle causes depletion of grazing land, is drying the forests on the floodplain downstream of the dam. After the construction of the Kainji Dam in Nigeria, 50 to 70 percent of the downstream area of flood-recession cropping stopped.
Dams break causing catastrophic damage to communities downstream. Dams break due to attack or natural disaster; the greatest dam bre
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form such as noise, heat or light. Pollutants, the components of pollution, can be either foreign substances/energies or occurring contaminants. Pollution is classed as point source or nonpoint source pollution. In 2015, pollution killed 9 million people in the world. Major forms of pollution include: Air pollution, light pollution, noise pollution, plastic pollution, soil contamination, radioactive contamination, thermal pollution, visual pollution, water pollution. Air pollution has always accompanied civilizations. Pollution started from prehistoric times. According to a 1983 article in the journal Science, "soot" found on ceilings of prehistoric caves provides ample evidence of the high levels of pollution, associated with inadequate ventilation of open fires." Metal forging appears to be a key turning point in the creation of significant air pollution levels outside the home.
Core samples of glaciers in Greenland indicate increases in pollution associated with Greek and Chinese metal production. The burning of coal and wood, the presence of many horses in concentrated areas made the cities the primary sources of pollution; the Industrial Revolution brought an infusion of untreated chemicals and wastes into local streams that served as the water supply. King Edward I of England banned the burning of sea-coal by proclamation in London in 1272, after its smoke became a problem, it was the industrial revolution. London recorded one of the earlier extreme cases of water quality problems with the Great Stink on the Thames of 1858, which led to construction of the London sewerage system soon afterward. Pollution issues escalated as population growth far exceeded viability of neighborhoods to handle their waste problem. Reformers began to clean water. In 1870, the sanitary conditions in Berlin were among the worst in Europe. August Bebel recalled conditions before a modern sewer system was built in the late 1870s: "Waste-water from the houses collected in the gutters running alongside the curbs and emitted a fearsome smell.
There were no public toilets in the squares. Visitors women became desperate when nature called. In the public buildings the sanitary facilities were unbelievably primitive.... As a metropolis, Berlin did not emerge from a state of barbarism into civilization until after 1870."The primitive conditions were intolerable for a world national capital, the Imperial German government brought in its scientists and urban planners to not only solve the deficiencies, but to forge Berlin as the world's model city. A British expert in 1906 concluded that Berlin represented "the most complete application of science and method of public life," adding "it is a marvel of civic administration, the most modern and most organized city that there is."The emergence of great factories and consumption of immense quantities of coal gave rise to unprecedented air pollution and the large volume of industrial chemical discharges added to the growing load of untreated human waste. Chicago and Cincinnati were the first two American cities to enact laws ensuring cleaner air in 1881.
Pollution became a major issue in the United States in the early twentieth century, as progressive reformers took issue with air pollution caused by coal burning, water pollution caused by bad sanitation, street pollution caused by the 3 million horses who worked in American cities in 1900, generating large quantities of urine and manure. As historian Martin Melosi notes, The generation that first saw automobiles replacing the horses saw cars as "miracles of cleanliness.". By the 1940s, automobile-caused smog was a major issue in Los Angeles. Other cities followed around the country until early in the 20th century, when the short lived Office of Air Pollution was created under the Department of the Interior. Extreme smog events were experienced by the cities of Los Angeles and Donora, Pennsylvania in the late 1940s, serving as another public reminder. Air pollution would continue to be a problem in England later during the industrial revolution, extending into the recent past with the Great Smog of 1952.
Awareness of atmospheric pollution spread after World War II, with fears triggered by reports of radioactive fallout from atomic warfare and testing. A non-nuclear event – the Great Smog of 1952 in London – killed at least 4000 people; this prompted some of the first major modern environmental legislation: the Clean Air Act of 1956. Pollution began to draw major public attention in the United States between the mid-1950s and early 1970s, when Congress passed the Noise Control Act, the Clean Air Act, the Clean Water Act, the National Environmental Policy Act. Severe incidents of pollution helped increase consciousness. PCB dumping in the Hudson River resulted in a ban by the EPA on consumption of its fish in 1974. National news stories in the late 1970s – the long-term dioxin contamination at Love Canal starting in 1947 and uncontrolled dumping in Valley of the Drums – led to the Superfund legislation of 1980; the pollution of industrial land gave rise to the name brownfield, a term now common in city planning.
The development of nuclear science introduced radioactive contamination, which can remain lethally radioactive for hundreds of thousands of years. Lake Karachay – named by the Worldwatch Institute as the "most polluted
A quarry is a type of open-pit mine in which dimension stone, construction aggregate, sand, gravel, or slate is excavated from the ground. The word quarry can include the underground quarrying for stone, such as Bath stone. Types of rock extracted from quarries include: Chalk China clay Cinder Clay Coal Construction aggregate Coquina Diabase Gabbro Granite Gritstone Gypsum Limestone Marble Ores Phosphate rock Quartz Sandstone Slate Many quarry stones such as marble, granite and sandstone are cut into larger slabs and removed from the quarry; the surfaces finished with varying degrees of sheen or luster. Polished slabs are cut into tiles or countertops and installed in many kinds of residential and commercial properties. Natural stone quarried from the earth is considered a luxury and tends to be a durable surface, thus desirable. Quarries in level areas with shallow groundwater or which are located close to surface water have engineering problems with drainage; the water is removed by pumping while the quarry is operational, but for high inflows more complex approaches may be required.
For example, the Coquina quarry is excavated to more than 60 feet below sea level. To reduce surface leakage, a moat lined with clay was constructed around the entire quarry. Ground water entering the pit is pumped up into the moat; as a quarry becomes deeper, water inflows increase and it becomes more expensive to lift the water higher during removal. Some water-filled quarries are worked by dredging. Many people and municipalities consider quarries to be eyesores and require various abatement methods to address problems with noise and appearance. One of the more effective and famous examples of successful quarry restoration is Butchart Gardens in Victoria, BC, Canada. A further problem is pollution of roads from trucks leaving the quarries. To control and restrain the pollution of public roads, wheel washing systems are becoming more common. Many quarries fill with water after abandonment and become lakes. Others are made into landfills. Water-filled quarries can be deep 50 ft or more, cold, so swimming in quarry lakes is not recommended.
Unexpectedly cold water can cause a swimmer's muscles to weaken. Though quarry water is very clear, submerged quarry stones and abandoned equipment make diving into these quarries dangerous. Several people drown in quarries each year. However, many inactive quarries are converted into safe swimming sites; such lakes lakes within active quarries, can provide important habitat for animals. Clay pit Coal mining Collecting fossils Gravel pit List of minerals List of rock types List of stones Miner Mountaintop removal mining Opencast mining Quarry lake Quarries
Social and environmental impact of palm oil
Palm oil, produced from the oil palm, is a basic source of income for many farmers in South East Asia and West Africa, Central America. It is locally used as a cooking oil, exported for use in many commercial food and personal care products and is converted into biofuel, it produces up to 10 times more oil per unit area than soyabeans, rapeseed or sunflowers. Oil palms produce 38% of the world's vegetable-oil output on 5% of the world’s vegetable-oil farmland. Palm oil plantations monocrops are under increasing scrutiny for their effects on the environment, including loss of carbon-sequestering, biodiverse forest land. There is concern over displacement and disruption of human and animal populations due to palm oil cultivation. An estimated 1.5 million small farmers grow the crop in Indonesia, along with about 500,000 people directly employed in the sector in Malaysia, plus those connected with related industries. As of 2006, the cumulative land area of palm oil plantations is 11,000,000 hectares.
In 2005 the Malaysian Palm Oil Association, responsible for about half of the world's crop, estimated that they manage about half a billion perennial carbon-sequestering palm trees. Demand for palm oil is expected to climb further. Between 1967 and 2000 the area under cultivation in Indonesia expanded from less than 2,000 square kilometres to more than 30,000 square kilometres. Deforestation in Indonesia for palm oil is so rapid that a 2007 United Nations Environment Programme report said that most of the country's forest might be destroyed by 2022; the rate of forest loss has declined in the past decade. Global production is forecast at a record 46.9m tonnes in 2010, up from 45.3m in 2009, with Indonesia providing most of the increase. Oil palm provides a source of employment, it allows small landholders to participate in the cash economy and results in improvements to local infrastructure and greater access to services such as schools and health facilities. In some areas, the cultivation of oil palm has replaced traditional practices due to the higher income potential of palm oil.
However, in some cases, land has been developed by oil palm plantations without consultation or compensation of the indigenous people occupying the land. This has occurred in Papua New Guinea and Indonesia. In the Sarawak state of Malaysian Borneo, there has been debate over whether there was an appropriate level of consultation with the Long Teran Kanan community prior to the development of local land for palm oil plantations. Appropriation of native lands has led to conflict between the plantations and local residents in each of these countries. According to a 2008 report by NGOs including Friends of the Earth, palm oil companies have reportedly used force to acquire land from indigenous communities in Indonesia. Additionally, some Indonesian oil palm plantations are dependent on imported labor or undocumented immigrants, which has raised concerns about the working conditions and social impacts of these practices. In Indonesia, rising demand for palm oil and timber has led to the clearing of tropical forest land in Indonesian national parks.
According to a 2007 report published by UNEP, at the rate of deforestation at that time, an estimated 98 percent of Indonesian forest would be destroyed by 2022 due to legal and illegal logging, forest fires and the development of palm oil plantations. Malaysia, the second largest producer of palm oil has pledged to conserve a minimum of 50 percent of its total land area as forests; as of 2010, 58 percent of Malaysia was forested. Palm oil cultivation has been criticized for: Greenhouse gas emissions. Deforestation in tropical areas accounts for an estimated 10 percent of manmade CO2 emissions, is a driver toward dangerous climate change. Habitat destruction, leading to the demise of critically endangered species. Reduced biodiversity, including damage to biodiversity hotspots. Cultivating crops on land that belongs to indigenous people in the Sarawak and Kalimantan states on the island of Borneo and the Malaysian state of Sabah. In some states where oil palm is established, lax enforcement of environmental legislation leads to encroachment of plantations into riparian strips, release of pollutants such as palm oil mill effluent in the environment.
More environment-friendly practices have been developed. Among those approaches is anaerobic treatment of POME, which might allow for biogas production and electricity generation, but it is difficult to maintain optimum growth conditions for the anaerobic organisms that break down acetate to methane. Damage to peatland due to palm oil production, is claimed to contribute to environmental degradation, including four percent of global greenhouse gas emissions and eight percent of all global emissions caused annually by burning fossil fuels, due to the clearing of large areas of rainforest for palm oil plantations. Many Indonesian and Malaysian rainforests lie atop peat bogs. Forest removal and bog drainage to make way. Researchers are looking for possible solutions and ways to help the situation and have suggested that if enough land is conserved and there remain large enough areas of primary forest reserves, the effects of the palm oil industry may not have as much of an impact on wildlife and biodiversity.
Environmental groups like Greenpeace, the Roundtable on Sustainable Palm Oil, Amnesty International are taking part in advocating bans on unsustainable palm oil crops and the
Environmental impact of aviation
The environmental impact of aviation occurs because aircraft engines emit heat, noise and gases which contribute to climate change and global dimming. Airplanes emit particles and gases such as carbon dioxide, water vapor, carbon monoxide, nitrogen oxides, sulfur oxides and black carbon which interact among themselves and with the atmosphere. Despite emission reductions from automobiles and more fuel-efficient and less polluting turbofan and turboprop engines, the rapid growth of air travel in the past years contributes to an increase in total pollution attributable to aviation. From 1992 to 2005, passenger kilometers increased 5.2 percent per year. In the European Union, greenhouse gas emissions from aviation increased by 87 percent between 1990 and 2006. Comprehensive research shows that despite anticipated efficiency innovations to airframes, engines and flight operations, there is no end in sight many decades out, to rapid growth in CO2 emissions from air travel and air freight, due to projected continual growth in air travel.
This is because international aviation emissions have escaped international regulation up to the ICAO triennial conference in October 2016 agreed on the CORSIA offset scheme. In addition, due to low or non-existent taxes on aviation fuel, air travel enjoys a competitive advantage over other transportation modes due to lower fares. Unless market constraints are put in place, growth in aviation emissions will result in the sector's emissions amounting to all or nearly all of the annual global CO2 emissions budget by mid-century, if climate change is to be held to a temperature increase of 2 °C or less. There is an ongoing debate about possible taxation of air travel and the inclusion of aviation in an emissions trading scheme, with a view to ensuring that the total external costs of aviation are taken into account. Like all human activities involving combustion, most forms of aviation release carbon dioxide and other greenhouse gases into the Earth's atmosphere, contributing to the acceleration of global warming and ocean acidification.
These concerns are highlighted by its rate of growth. Globally, about 8.3 million people fly daily, twice the total in 1999. U. S. airlines alone burned about 16.2 billion gallons of fuel during the twelve months between October 2013 and September 2014. In addition to the CO2 released by most aircraft in flight through the burning of fuels such as Jet-A or Avgas, the aviation industry contributes greenhouse gas emissions from ground airport vehicles and those used by passengers and staff to access airports, as well as through emissions generated by the production of energy used in airport buildings, the manufacture of aircraft and the construction of airport infrastructure. While the principal greenhouse gas emission from powered aircraft in flight is CO2, other emissions may include nitric oxide and nitrogen dioxide, water vapour and particulates, sulfur oxides, carbon monoxide, incompletely burned hydrocarbons and radicals such as hydroxyl, depending on the type of aircraft in use. Emissions weighting factor i.e. the factor by which aviation CO2 emissions should be multiplied to get the CO2-equivalent emissions for annual fleet average conditions is in the range 1.3–2.9.
In 1999 the contribution of civil aircraft-in-flight to global CO2 emissions was estimated to be around two percent. However, in the cases of high-altitude airliners which fly near or in the stratosphere, non-CO2 altitude-sensitive effects may increase the total impact on anthropogenic climate change significantly. A 2007 report from Environmental Change Institute / Oxford University posits a range closer to four percent cumulative effect. Subsonic aircraft-in-flight contribute to climate change in four ways: CO2 emissions from aircraft-in-flight are the most significant and best understood element of aviation's total contribution to climate change; the level and effects of CO2 emissions are believed to be broadly the same regardless of altitude. In 1992, emissions of CO2 from aircraft were estimated at around two percent of all such anthropogenic emissions, that year the atmospheric concentration of CO2 attributable to aviation was around one percent of the total anthropogenic increase since the industrial revolution, having accumulated over just the last 50 years.
At the high altitudes flown by large jet airliners around the tropopause, emissions of NOx are effective in forming ozone in the upper troposphere. High altitude NOx emissions result in greater concentrations of O3 than surface NOx emissions, these in turn have a greater global warming effect; the effect of O3 surface concentrations are regional and local, but it becomes well mixed globally at mid and upper tropospheric levels. NOx emissions reduce ambient levels of methane, another greenhouse gas, resulting in a climate cooling effect, but this effect does not offset the O3 forming effect of NOx emissions. It is now believed that aircraft sulfur and water emissions in the stratosphere tend to deplete O3 offsetting the NOx-induced O3 increases; these effects have not been quantified. This problem does not apply to aircraft that fly lower in the troposphere, such as light aircraft or many commuter aircraft. One of the products of burning hydrocarbons with oxygen is a greenhouse gas. Water vapour produced by aircraft engines at high altitude
Human overpopulation occurs when the ecological footprint of a human population in a specific geographical location exceeds the carrying capacity of the place occupied by that group. Overpopulation can further be viewed, in a long term perspective, as existing if a population cannot be maintained given the rapid depletion of non-renewable resources or given the degradation of the capacity of the environment to give support to the population. Changes in lifestyle could reverse overpopulated status without a large population reduction; the term human overpopulation refers to the relationship between the entire human population and its environment: the Earth, or to smaller geographical areas such as countries. Overpopulation can result from an increase in births, a decline in mortality rates, an increase in immigration, or an unsustainable biome and depletion of resources, it is possible for sparsely populated areas to be overpopulated if the area has a meagre or non-existent capability to sustain life.
Advocates of population moderation cite issues like quality of life, carrying capacity, risk of starvation as a basis to argue for population decline. Scientists suggest that the human impact on the environment as a result of overpopulation, profligate consumption and proliferation of technology has pushed the planet into a new geological epoch known as the Anthropocene. Human population has been rising continuously since the end of the Black Death, around the year 1350, although the most significant increase has been since the 1950s due to medical advancements and increases in agricultural productivity; the rate of population growth has been declining since the 1980s, while the absolute total numbers are increasing. Recent rate increases in several countries enjoying steady declines are apparently contributing to continued growth in total numbers; as pointed out by Hans Rosling, the critical factor is that the population is not "just growing", but that the growth ratio reached its peak and the total population is now growing much slower.
The UN population forecast of 2017 was predicting "near end of high fertility" globally and anticipating that by 2030 over ⅔ of world population will be living in countries with fertility below the replacement level. And for total world population to stabilize between 10-12 billion people by year 2100; the United Nations has expressed concerns on continued population growth in sub-Saharan Africa. Recent research has demonstrated; as of April 14, 2019 the world's human population is estimated to be 7.699 billion. Or, 7,622,106,064 on May 14, 2018 and the United States Census Bureau calculates 7,472,985,269 for that same date, and over 7 billion by the United Nations. Most contemporary estimates for the carrying capacity of the Earth under existing conditions are between 4 billion and 16 billion. Depending on which estimate is used, human overpopulation may or may not have occurred; the rapid recent increase in human population is causing some concern. The population is expected to reach between 8 and 10.5 billion between the years 2040 and 2050.
In 2017, the United Nations increased the medium variant projections to 9.8 billion for 2050 and 11.2 billion for 2100. The recent rapid increase in human population over the past three centuries has raised concerns that the planet may not be able to sustain present or future numbers of inhabitants; the InterAcademy Panel Statement on Population Growth, circa 1994, stated that many environmental problems, such as rising levels of atmospheric carbon dioxide, global warming, pollution, are aggravated by the population expansion. Other problems associated with overpopulation include the increased demand for resources such as fresh water and food and malnutrition, consumption of natural resources faster than the rate of regeneration, a deterioration in living conditions. Wealthy but populated territories like Britain rely on food imports from overseas; this was felt during the World Wars when, despite food efficiency initiatives like "dig for victory" and food rationing, Britain needed to fight to secure import routes.
However, many believe that waste and over-consumption by wealthy nations, is putting more strain on the environment than overpopulation. In spite of concerns about overpopulation, widespread in developed countries, the number of people living in extreme poverty globally shows a stable decline though the population has grown seven-fold over the last 200 years. Child mortality has declined, which in turn has led to reduced birth rates, thus slowing overall population growth; the global number of famine-related deaths have declined, food supply per person has increased with population growth. Most countries have no direct policy of limiting their birth rates, but the rates have still fallen due to education about family planning and increasing access to birth control and contraception. Concern about overpopulation is an ancient topic. Tertullian was a resident of the city of Carthage in the second century CE, when the population of the world was about 190 million, he notably said: "What most meets our view is our teeming population.
Our numbers are burdensome to the world, which can hardly support us.... In deed and famine, wars, earthquakes have to be regarded as a remedy for nations, as the means of pruning the luxuriance of the human race." Before that, Plato and others broached the topic as well. Throughout recorded history, population growth has been slow despite high birth rates, due to war and other diseases, high infant mortalit
Urban sprawl or suburban sprawl refers to the unrestricted growth in many urban areas of housing, commercial development, roads over large expanses of land, with little concern for urban planning. In addition to describing a particular form of urbanization, the term relates to the social and environmental consequences associated with this development. In Continental Europe the term "peri-urbanisation" is used to denote similar dynamics and phenomena, although the term urban sprawl is being used by the European Environment Agency. There is widespread disagreement about how to quantify it. For example, some commentators measure sprawl only with the average number of residential units per acre in a given area, but others associate it with decentralization, segregation of uses, so forth. The term urban sprawl is politicized, always has negative connotations, it is criticized for causing environmental degradation, intensifying segregation and undermining the vitality of existing urban areas and attacked on aesthetic grounds.
Due to the pejorative meaning of the term, few support urban sprawl as such. The term has become a rallying cry for managing urban growth. Definitions of sprawl vary. Batty et al. defined sprawl as "uncoordinated growth: the expansion of community without concern for its consequences, in short, incremental urban growth, regarded unsustainable." Bhatta et al. wrote in 2010 that despite a dispute over the precise definition of sprawl there is a "general consensus that urban sprawl is characterized by unplanned and uneven pattern of growth, driven by multitude of processes and leading to inefficient resource utilization." Reid Ewing has shown that sprawl has been characterized as urban developments exhibiting at least one of the following characteristics: low-density or single-use development, strip development, scattered development, and/or leapfrog development. He argued that a better way to identify sprawl was to use indicators rather than characteristics because this was a more flexible and less arbitrary method.
He proposed using "accessibility" and "functional open space" as indicators. Ewing's approach has been criticized for assuming that sprawl is defined by negative characteristics. What constitutes sprawl may be considered a matter of degree and will always be somewhat subjective under many definitions of the term. Ewing has argued that suburban development does not, per se constitute sprawl depending on the form it takes, although Gordon & Richardson have argued that the term is sometimes used synonymously with suburbanization in a pejorative way. Metropolitan Los Angeles for example, despite popular notions of being an sprawling city, is the densest metropolitan region in the US, being denser than the New York metropolitan area and the San Francisco Bay Area. Most of metropolitan Los Angeles is built at more uniform low to moderate density, leading to a much higher overall density for the entire region; this is in contrast to cities such as New York, San Francisco or Chicago which have compact, high-density cores but are surrounded by large areas of low density.
The international cases of sprawl draw into question the definition of the term and what conditions are necessary for urban growth to be considered sprawl. Metropolitan regions such Greater Mexico City, Delhi National Capital Region and Beijing, are regarded as sprawling despite being dense and mixed use. Despite the lack of a clear agreed upon description of what defines sprawl most definitions associate the following characteristics with sprawl; this refers to a situation where commercial, residential and industrial areas are separated from one another. Large tracts of land are devoted to a single use and are segregated from one another by open space, infrastructure, or other barriers; as a result, the places where people live, work and recreate are far from one another to the extent that walking, transit use and bicycling are impractical, so all these activities require a car. The degree to which different land uses are mixed together is used as an indicator of sprawl in studies of the subject.
Job sprawl is another land use symptom of urban car-dependent communities. It is defined as low-density, geographically spread-out patterns of employment, where the majority of jobs in a given metropolitan area are located outside of the main city's central business district, in the suburban periphery, it is the result of urban disinvestment, the geographic freedom of employment location allowed by predominantly car-dependent commuting patterns of many American suburbs, many companies' desire to locate in low-density areas that are more affordable and offer potential for expansion. Spatial mismatch is related to economic environmental justice. Spatial mismatch is defined as the situation where poor urban, predominantly minority citizens are left without easy access to entry-level jobs, as a result of increasing job sprawl and limited transportation options to facilitate a reverse commute to the suburbs. Job sprawl has been measured in various ways, it has been shown to be a growing trend in America's metropolitan areas.
The Brookings Institution has published multiple articles on the topic. In 2005, author Michael Stoll defined job sprawl as jobs located more than 5-mile radius from the CBD, measured the concept based on year 2000