Environmental effects
Impervious surfaces are an environmental concern because their construction initiates a chain of events that modifies urban air and water resources:
- The pavement materials seal the soil surface, eliminating rainwater infiltration and natural groundwater recharge. An article in the Seattle Times states that "while urban areas cover only 3 percent of the U.S., it is estimated that their runoff is the primary source of pollution in 13 percent of rivers, 18 percent of lakes and 32 percent of estuaries."[1]
- Some of these pollutants include excess nutrients from fertilizers; pathogens; pet waste; gasoline, motor oil and heavy metals from vehicles; high sediment loads from stream bed erosion and construction sites; and waste such as cigarette butts, 6-pack holders and plastic bags carried by surges of stormwater. In some cities, the flood waters get into combined sewers, causing them to overflow, flushing their raw sewage into streams. Polluted runoff can have many negative effects on fish, animals, plants and people.
- Impervious surfaces collect solar heat in their dense mass. When the heat is released, it raises air temperatures, producing urban "heat islands", and increasing energy consumption in buildings. The warm runoff from impervious surfaces reduces dissolved oxygen in stream water, making life difficult in aquatic ecosystems.
- Impervious pavements deprive tree roots of aeration, eliminating the "urban forest" and the canopy shade that would otherwise moderate urban climate. Because impervious surfaces displace living vegetation, they reduce ecological productivity, and interrupt atmospheric carbon cycling.
The total coverage by impervious surfaces in an area, such as a municipality or a watershed, is usually expressed as a percentage of the total land area. The coverage increases with rising urbanization. In rural areas, impervious cover may only be one or two percent. In residential areas, coverage increases from about 10 percent in low-density subdivisions to over 50 percent in multifamily communities. In industrial and commercial areas, coverage rises above 70 percent. In regional shopping centers and dense urban areas, it is over 90 percent. In the contiguous 48 states of the US, urban impervious cover adds up to 43,000 square miles (110,000 km2). Development adds 390 square miles (1,000 km2) annually. Typically, two-thirds of the cover is pavements and one-third is building roofs.[2]
https://en.wikipedia.org/wiki/Impervious_surface
Urban sprawl (also known as suburban sprawl or urban encroachment[1]) is defined as "the spreading of urban developments (such as houses and shopping centers) on undeveloped land near a city".[2] Urban sprawl has been described as the unrestricted growth in many urban areas of housing, commercial development, and roads over large expanses of land, with little concern for urban planning.[3] In addition to describing a special form of urbanization, the term also relates to the social and environmental consequences associated with this development.[4] Medieval suburbs suffered from the loss of protection of city walls, before the advent of industrial warfare. Modern disadvantages and costs include increased travel time, transport costs, pollution, and destruction of the countryside.[5] The cost of building urban infrastructure for new developments is hardly ever recouped through property taxes, amounting to a subsidy for the developers and new residents at the expense of existing property taxpayers.[6]
In Continental Europe, the term peri-urbanisation is often used to denote similar dynamics and phenomena, but the term urban sprawl is currently being used by the European Environment Agency. There is widespread disagreement about what constitutes sprawl and how to quantify it. For example, some commentators measure sprawl by residential density, using the average number of residential units per acre in a given area. Others associate it with decentralization (spread of population without a well-defined centre), discontinuity (leapfrogging development, as defined below), segregation of uses, and so forth.
The term urban sprawl is highly politicized and almost always has negative connotations. It is criticized for causing environmental degradation, intensifying segregation, and undermining the vitality of existing urban areas, and is attacked on aesthetic grounds. The pejorative meaning of the term means that few openly support urban sprawl as such. The term has become a rallying cry for managing urban growth.[7]
https://en.wikipedia.org/wiki/Urban_sprawl
A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, the drainage divide,[1] made up of a succession of elevated features, such as ridges and hills. A basin may consist of smaller basins that merge at river confluences, forming a hierarchical pattern.[2]
Other terms for a drainage basin are catchment area, catchment basin, drainage area, river basin, water basin,[3][4] and impluvium.[5][6][7] In North America, they are commonly called a watershed, though in other English-speaking places, "watershed" is used only in its original sense, that of a drainage divide.
A drainage basin's boundaries are determined by watershed delineation, a common task in environmental engineering and science.
In a closed drainage basin, or endorheic basin, rather than flowing to the ocean, water converges toward the interior of the basin, known as a sink, which may be a permanent lake, a dry lake, or a point where surface water is lost underground.[8]
Drainage basins are similar but not identical to hydrologic unit code, which are drainage areas delineated so as to nest into a multi-level hierarchical drainage system. Hydrologic units are defined to allow multiple inlets, outlets, or sinks. In a strict sense, all drainage basins are hydrologic units but not all hydrologic units are drainage basins.[8]
https://en.wikipedia.org/wiki/Drainage_basin
Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs in the vadose zone below plant roots and is often expressed as a flux to the water table surface. Groundwater recharge also encompasses water moving away from the water table farther into the saturated zone.[1] Recharge occurs both naturally (through the water cycle) and through anthropogenic processes (i.e., "artificial groundwater recharge"), where rainwater and or reclaimed water is routed to the subsurface.
The most common methods to estimate recharge rates are: chloride mass balance (CMB); soil physics methods; environmental and isotopic tracers; groundwater-level fluctuation methods; water balance (WB) methods (including groundwater models (GMs)); and the estimation of baseflow (BF) to rivers.[2]
https://en.wikipedia.org/wiki/Groundwater_recharge
An urban heat island (UHI) is an urban area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference is usually larger at night than during the day,[1] and is most apparent when winds are weak. UHI is most noticeable during the summer and winter. The main cause of the UHI effect is from the modification of land surfaces.[2][3] A study has shown that heat islands can be affected by proximity to different types of land cover, so that proximity to barren land causes urban land to become hotter and proximity to vegetation makes it cooler.[4] Waste heat generated by energy usage is a secondary contributor.[5] As a population center grows, it tends to expand its area and increase its average temperature. The term heat island is also used; the term can be used to refer to any area that is relatively hotter than the surrounding, but generally refers to human-disturbed areas.[6]
Monthly rainfall is greater downwind of cities, partially due to the UHI. Increases in heat within urban centers increases the length of growing seasons and decreases the occurrence of weak tornadoes. The UHI decreases air quality by increasing the production of pollutants such as ozone, and decreases water quality as warmer waters flow into area streams and put stress on their ecosystems.
Not all cities have a distinct urban heat island, and the heat island characteristics depend strongly on the background climate of the area in which the city is located.[7] Effects within a city can vary significantly depending on local environmental conditions. Heat can be reduced by tree cover and green space, which act as sources of shade and promote evaporative cooling.[8] Other options include green roofs, passive daytime radiative cooling applications, and the use of lighter-colored surfaces and less absorptive building materials in urban areas, to reflect more sunlight and absorb less heat.[9][10][11]
Climate change is not the cause of urban heat islands but it is causing more frequent and more intense heat waves which in turn amplify the urban heat island effect in cities.[12]: 993 Compact, dense urban development may increase the urban heat island effect, leading to higher temperatures and increased exposure.[13]
https://en.wikipedia.org/wiki/Urban_heat_island
In geotechnical engineering, soil compaction is the process in which stress applied to a soil causes densification as air is displaced from the pores between the soil grains. When stress is applied that causes densification due to water (or other liquid) being displaced from between the soil grains, then consolidation, not compaction, has occurred. Normally, compaction is the result of heavy machinery compressing the soil, but it can also occur due to the passage of, for example, animal feet.
In soil science and agronomy, soil compaction is usually a combination of both engineering compaction and consolidation, so may occur due to a lack of water in the soil, the applied stress being internal suction due to water evaporation[1] as well as due to passage of animal feet. Affected soils become less able to absorb rainfall, thus increasing runoff and erosion. Plants have difficulty in compacted soil because the mineral grains are pressed together, leaving little space for air and water, which are essential for root growth. Burrowing animals also find it a hostile environment, because the denser soil is more difficult to penetrate. The ability of a soil to recover from this type of compaction depends on climate, mineralogy and fauna. Soils with high shrink-swell capacity, such as vertisols, recover quickly from compaction where moisture conditions are variable (dry spells shrink the soil, causing it to crack). But clays such as kaolinite, which do not crack as they dry, cannot recover from compaction on their own unless they host ground-dwelling animals such as earthworms — the Cecil soil series is an example.
Before soils can be compacted in the field, some laboratory tests are required to determine their engineering properties. Among various properties, the maximum dry density and the optimum moisture content are vital and specify the required density to be compacted in the field.[2]
https://en.wikipedia.org/wiki/Soil_compaction
Soil sealing or soil surface sealing is the loss of soil resources due to the covering of land for housing, roads or other construction work.[1] Covering or replacing the topsoil with impervious materials like asphalt and cement as a result of urban development and infrastructure construction paired with compaction of the underlying soil layers results in the mostly irreversible loss of relevant soil ecosystem services.[2][3][4]
https://en.wikipedia.org/wiki/Soil_sealing
Land consumption as part of human resource consumption is the conversion of land with healthy soil and intact habitats into areas for industrial agriculture, traffic (road building) and especially urban human settlements. More formally, the EEA[1] has identified three land consuming activities:
- The expansion of built-up area which can be directly measured;
- the absolute extent of land that is subject to exploitation by agriculture, forestry or other economic activities; and
- the over-intensive exploitation of land that is used for agriculture and forestry.
In all of those respects, land consumption is equivalent to typical land use in industrialized regions and civilizations.
Since often aforementioned conversion activities are virtually irreversible, the term land loss is also used. From 1990 to 2000, 1.4 million hectares (3.5×106 acres) of open space were consumed in the U.S.[2] In Germany, land is being consumed at a rate of more than 70 hectares (170 acres) every day (~250 thousand hectares (620,000 acres) per 10 years).[3] In European Union, land take is estimated approximately about to 1.2 million hectares in 21 EU countries over the period 1990–2006.[4]
Urban growth reduces open space in and around cities, impacting biodiversity and ecosystem services
— McDonald et al.[2]
Land loss can also happen due to natural factors, like erosion or desertification - nevertheless most of those can also eventually be tracked back to human activities. Another slightly different interpretation of the term is the forced displacement or compulsory acquisition of a native people or settlers from their original land due to land grabbing, etc. Again, in most cases, this will be due to economic reasons like search for profitable investment and commodification of natural resources.
Reducing global land loss, which progresses at an alarming rate, is vital since the land footprint, the area required both domestically and abroad to produce the goods and services consumed by a country or region, can be much larger than the land actually used or even available in the country itself.[3][5]
While land prices have surged in the first few years of the 21st century, land consumption economy still lacks environmental full-cost accounting to add the long-term costs of environmental degradation.
Consequences of land consumption
The major effects of land conversion for economic growth are:
- Land degradation
- Habitat loss – built-up areas support only particularly adapted species
- Soil degradation – loss or contamination of top soil by civilization waste and general pollution
- Soil compaction – buildings, heavy machinery and vehicle traffic compact the soil to a degree that macrobiotic soil life is eradicated
- Impervious surfaces – asphalt and concrete seal off the soil from the atmosphere and disrupt natural water and biogeochemical cycles
See also
References
Nationally, 1.4 million ha of open space was lost, and the amount lost in a given city was correlated with population growth
About 60 per cent of the land used to meet European demand is located outside the EU. This makes Europe the continent that is most dependent on land beyond its borders to sustain its lifestyle, its agricultural industry and its hunger for energy.
- "The true cost of consumption - The EU's land footprint" (PDF). FOE Europe. 2016.
The European Union uses more than its fair share of global land. In 2010, the amount of land used to satisfy our consumption, solely of agricultural goods and services, amounted to 269 million hectares – that's 43% more agricultural land than is available within the EU itself and an area almost the size of France and Italy used outside of our borders.
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https://en.wikipedia.org/wiki/Land_consumption
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