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Erosion Reference library
Encyclopedia of Global Change
...it becomes concentrated into flow paths, its velocity increases, and it is able to cut small channels or rills into the land surface. Dense rill networks can be formed on bare farmland during intense rainstorms; they are also a feature of slopes left bare of vegetation for several months at a time, such as road cuttings, embankments, industrial sites, and residential areas left bare while construction work is in progress. In many situations, rill channels do not cut very deeply because the underlying material is less weathered, more compact, and therefore...
Building Decay Reference library
Encyclopedia of Global Change
...the service life of many building materials. Allied with other good environmental management practices, such as the improvement of air quality, better management of groundwater resources, and reduction of traffic-related impacts such as de-icing salt applications, such strategies should help to conserve buildings and engineering structures by reducing materials decay. See also Air Quality . Addleson, L. , and C. Rice . Performance of Materials in Buildings . Oxford: Butterworth Heinemann, 1991. A readable summary of important properties. Baer, N. S. , and ...
Erosion Reference library
The Oxford Companion to Global Change
...runoff over the land surface is reduced. The percentage of the annual rainfall contributing to runoff varies from less than 1% in densely vegetated areas to nearly 60% in urban areas and on bare soil. By determining the fate of the rainfall, the vegetation cover directly influences the erosion by raindrop impact and surface runoff. Raindrop Impact Raindrop impact on bare soil is a powerful agent of particle detachment. Norman Hudson ( 1934–1996 ) carried out a simple but classic experiment in the 1950s in Zimbabwe to show the importance of covering the soil...
Biological Feedback Reference library
The Oxford Companion to Global Change
...warming at high latitudes decreases the effects of snow albedo and causes regional warming. Evidence from studies of past glacial-interglacial cycles suggests that a cooler and drier climate leads to less vegetation cover on the land surface, which in turn leads to an increase in bare soil and thus dustiness. Iron-containing dust from the land is transported by wind over the oceans, where it acts as a fertilizer to phytoplankton, causing a bloom which removes CO 2 from the atmosphere, leading to a cooler and drier climate. There is also evidence that the...
Catastrophist–cornucopian Debate Reference library
Encyclopedia of Global Change
...of health, wealth, and happiness, but of population always growing to the limits of bare subsistence, its growth ever checked by one or the other of two means Malthus recognized: “misery and vice.” The arguments of the essay differ in several ways from those of modern environmental catastrophists. Malthus saw crises of subsistence not as a looming future consequence of excessive growth but as a factor constantly in operation, something that had always been a part of human life and always would be. He did not directly address environmental change as a constraint...
Catastrophist-Cornucopian Debate Reference library
The Oxford Companion to Global Change
...of health, wealth, and happiness, but of population always approaching the limits of bare subsistence, its growth ever checked by one of the two means Malthus recognized, misery and vice. The arguments of the Essay differ in several ways from those of modern environmental catastrophists. Malthus saw crises of subsistence not as a looming future consequence of excessive growth but as a factor constantly in operation, something that had always been a part of human life and always would be. He did not directly address environmental change as a constraint on...
Mangroves Reference library
Encyclopedia of Global Change
...proceeds, mangrove zones will tend to migrate landward, invading a low-lying hinterland. In humid regions they will invade backing rainforest or formerly freshwater swamps, as on the Mamberano delta in Irian Jaya, while in drier areas they will colonize backing salt marsh and bare saline flats, as at Port Adelaide in South Australia. As this migration proceeds, it is likely that some mangrove species will become more abundant and extensive, while others will diminish or even disappear. In many places the landward migration of mangroves in response to a...
Modeling of Natural Systems Reference library
Encyclopedia of Global Change
...worldwide. The sparse vegetation natural to arid and semiarid areas can easily be removed as a result of relatively minor changes in the climate, or by direct influence of human activity such as overgrazing or poor agricultural practices. Removal of vegetation and exposure of bare soil decreases soil water storage because of increased runoff and increased albedo. Less moisture available at the surface means decreased latent heat flux, leading to an increase in surface temperature. On the other hand, the increased albedo produces a net radiative loss. In...
Mangroves Reference library
The Oxford Companion to Global Change
...proceeds, mangrove zones will tend to migrate landward, invading a low-lying hinterland. In humid regions they will invade backing rainforest or formerly freshwater swamps, as on the Mamberamo delta in Irian Jaya, while in drier areas they will colonize backing salt marsh and bare saline flats, as at Port Adelaide in South Australia. As this migration proceeds, it is likely that some mangrove species will become more abundant and extensive, while others will diminish or even disappear. In many places the landward migration of mangroves in response to a...
Deserts Reference library
Encyclopedia of Global Change
...from more consistent temperate environments. Second, many geomorphologic processes in deserts and drylands tend to be characterized by significant periods of quiescence, punctuated by abrupt episodes of activity. Thus areas cleared of natural vegetation by grazing pressures, or bare in the period immediately following harvesting, are particularly susceptible to rapid erosion from high-intensity rainstorms or windy conditions. Third, the remarkable growth of urban areas in deserts and drylands since World War II has placed significant pressures on limited...
Deserts Reference library
The Oxford Companion to Global Change
...from temperate environments that enjoy more consistent conditions. Second, many geomorphologic processes in deserts and drylands are characterized by significant periods of quiescence, punctuated by abrupt episodes of activity. Areas cleared of natural vegetation by grazing, or bare in the period immediately following harvesting, are thus particularly susceptible to rapid erosion by high-intensity rainstorms or strong winds. Third, the rapid growth of urban areas in deserts and drylands since World War II has placed significant pressures on limited water...
Tundra Reference library
Encyclopedia of Global Change
...of 45 centimeters. Assume that the soil below this depth is supersaturated permafrost and yields upon thawing, on a volume basis, 50 percent excess water and 50 percent saturated soil. If the top 15 centimeters were removed, the equilibrium thickness of the active layer, under the bare ground conditions, might increase to 60 centimeters. Since only 30 centimeters of the original layer remains, 60 centimeters of the permafrost must thaw before the active layer can thicken to 60 centimeters, since 30 centimeters of supernatant water will be released. Thus, the...
Sea Ice Reference library
Encyclopedia of Global Change
...smooth first-year ice the pools are initially very shallow, forming in minor depressions. Their shape becomes more fixed as they melt their way down into the ice through preferential absorption of solar radiation by the water, which has an albedo of 0.1 compared with 0.6–0.7 for bare ice. Eventually the pools can drain off into the sea, over floe edges, through existing cracks, or by melting a thaw hole through the ice. Sea Ice. Figure 2a. Seasonal Change in Extent of Sea Ice in Arctic, Excluding Ice Coverage of Lesser than 12 Percent of Area. (After Central...
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