LAND

Processes on the Earth's land surfaces have important links to climate and atmospheric composition that are currently absent or inadequately represented in models of the Earth system. These links involve exchanges of energy and moisture, radioactive trace gases like carbon dioxide and methane, and chemically active species such as methane, nitric oxide, and non-methane hydrocarbons that soils, plants, and biomass burning release. These exchanges depend on properties of the underlying soils and overlying vegetation and on land management practices. NASA's Earth Observing System will provide data on land use and land cover change, vegetation patterns, desertification, deforestation, and occurrence of fires. With these data and data on precipitation, soil moisture, and radiation budgets, the key hydrological and vegetative processes can be understood in a global context.


Land Cover, Use, and Change



Deforestation

Deforestation affects the soil and local climate by reducing the evaporative cooling that takes place from plant life. As a result, temperatures rise. In addition, the loss of vegetation leads to increases in soil erosion and rainfall runoff and drastically affects the biodiversity of the ecological system.

The photo at the left was taken from the space shuttle on September 7, 1985, showing waters of the Mahajamba Bay on Madagascar Island. This sedimentation, seen flowing to the left into the bay, is a result of extreme erosion due to deforestation.

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Tropical Deforestation and Habitat Degradation

The Amazon Basin is the largest continuous region of tropical forest in the world, containing nearly 31 percent of the world total. Tropical deforestation has a major impact on the carbon cycle and has profound implications for biological diversity. Deforestation increases atmospheric carbon dioxide and other trace gasses, possibly affecting climate. While occupying less than 7 percent of the terrestrial surface, tropical forests provide homes to half or more of all plant and animal species. As a result, an additional adverse effect of tropical deforestation is massive extinction of species including large numbers of vascular plant species.

This Landsat Thematic Mapper color composite image of southern Rondonia state, Brazil, illustrates areas of deforestation. Among other effects, deforestation increases atmospheric carbon dioxide and other trace gases, possibly affecting climate.

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This illustration shows where biological diversity was adversely affected in the Brazilian Amazon Basin in 1988 by deforestation, isolation of forest, and the 1-kilometer edge effect from adjacent areas of deforestation. Reds represent the areas that were affected the most.

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The above graphic shows tropical deforestation, forest isolation by deforestation, and the area of forest affected by a 1-kilometer edge effect from adjacent areas of deforestation in the Brazilian Amazon. The area of the forest was 4,092,831 square kilometers before deforestation.

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Biomas Burning

Deforestation can affect both regional and global climate. One consequence of biomass burning is the release of tiny smoke particles that diffuse into the atmosphere, traveling long distances before settling back to the surface. These particles, called aerosols, can change the amounts of solar radiation reaching the Earth's surface and also return radiation from the Earth back to the surface. This combination of effects can change global temperatures. The smoke particles also can serve to increase the number of droplets in clouds, thereby changing the way that clouds reflect or transmit radiation coming from the Sun and from the Earth's surface.

It has been estimated that the net effect of smoke particles from fires is to cause some slight cooling at the Earth's surface. Additionally, gas emissions from biomass burnings add to the amount of greenhouse gases in the atmosphere, which can affect global climate.

According to satellite-based estimates, about 5.6 percent of the Brazilian Amazon Basin had been deforested by the end of 1988.

The Earth Science Enterprise's future plans include using data from such instruments as the Enhanced Thematic Mapper Plus (ETM+), currently in flight on Landsat 7 and the Moderate-resolution Imaging Spectroradiometer (MODIS) as well as the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER - provided by Japan) and currently in flight on the Terra satellite.

The photograph at right shows a section of the Rio Sao Francisco in northeast Brazil and the small town of Bom Jesus da Lapa. Because of the size of the rectangular agricultural field patterns, this area is probably a plantation and the crop is likely sugarcane. Numerous smoke plumes are visible in the photograph, possibly indicating that more land is being prepared for agriculture. It should be noted that this particular area is included in the general northeast region of Brazil that is subject to extensive periods of drought.

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Example: Tropcial Deforesation

These two Landsat Multi Spectral Scanner (MSS) images at left are of the state of Rondonia Brazil. Rondonia experienced a rapid growth in population during the period of 1975 through 1986 due to immigration from surrounding states. Settlers typically colonized the region adjacent to the main highway to take advantage of the cheap land offered by the government for agricultural development. Areas where forest lands were converted to agricultural uses are easily identifiable as a fishbone pattern radiating from the spine of the highway in the 1986 image.

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Vanishing Old Growth in the Pacific Northwest

Recent deforestation is most often associated with activities in the tropical rainforests of South America, but it can be seen as a serious problem in temperate zones of the Earth as well.

Clear-cutting "old growth" evergreen trees in the national forests of the U.S. Pacific Northwest is causing a high degree of habitat fragmentation. Logging of these ancient forests has destroyed the continuity of the forests; large portions have been cut into small segments by roads. This fragmentation tends to destroy the habitats required by many species of animals.

The image on the left shows a portion of Mount Hood National Forest in western Oregon. Dark-red areas represent old growth; light-red areas represent regrowth; and pink areas are places where young saplings have appeared. Blue areas indicate lack of vegetation due to logging.

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These, and other forests, are important not only for their role in maintaining biological diversity but also because of their role in global climate. They are a significant factor in taking carbon dioxide, the primary anthropogenic greenhouse gas, out of the atmosphere. Increased deforestation could lead to a greater build-up of greenhouse gases in the atmosphere, with consequent global warming.

This image, constructed using Landsat data, highlights the deforestation caused by logging in the Olympic Peninsula in the state of Washington. The small yellow "dots" represent regions logged between 1973 and 1982. Red areas represent regions logged between 1982 and 1988.

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Desertification

Desertification is a complex land degradation process involving man, land, and climate. It comes in two forms: man-induced degradation of the land and natural expansion of the desert. Desertification reduces both resilience and productive potential of the land to an extent that cannot be readily reversed by removing the cause.

Changes of the land surface over large areas can influence or alter climate. Vegetation, soil moisture and albedo influence circulation of the atmosphere, rainfall and temperature.

The Landsat Multi Spectral Scanner (MSS) image at the right is of modern-day Cairo, Egypt which lies adjacent to the Nile River and its delta. The delta is shown in maroon, the city (in the red circle) is gray and the surrounding desert is tan.

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Desertification and Global Climate

Desertification has effects on both our immediate habitat and on global climate. As you can see from this computer enhanced image, desert sands are the bright surfaces that strongly reflect solar radiation (seen mainly in upper Africa). An increase in the area of these bright surfaces would result in more solar energy reflected back to space and less absorbed at the surface. This would tend to dry the area even further, continuing the process of desertification.

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Expansion/Contraction of Deserts

The overall 10-year trend is an expansion of the Sahara Desert. Scientists look for signs of land degradation, or desertification. In the short-term, satellite information about vegetation and desertification allows scientists to warn governments and policy makers of possible impending famine.

This comparison shows that the Sahara Desert contracted between 1984 and 1990, but this does not necessarily mean that the Sahara is getting smaller over the long term. Between 1980 and 1984, the desert grew steadily larger. For this four-year period, the southern boundary of the Sahara creeped southward as much as 240 kilometers.

Data from such instruments as the Moderate-Resolution Imaging Spectroradiometer (MODIS), currently in flight on the Terra satellite (and scheduled for the Aqua mission) and the Enhanced Thematic Mapper Plus (ETM+), currently in flight on Landsat 7, will provide such information routinely and globally.

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Coastal Change

The coastal zone, which represents the interface and interaction between the land and the sea, is one of the most dynamic areas on Earth. Change is occuring on all timescales, from seconds to days to centuries. The waves and resulting currents act as agents of sediment transport and coastal modification.

These sequential vertical aerial photographs of the Big and Little Blackwater Rivers on the eastern shore of Maryland indicate progressive marsh loss as interior ponds coalesce.

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Example: The Aral Sea

Large bodies of water have a moderating influence on local climate. They are also extremely important to local ecological conditions, helping to determine which life forms can thrive (or survive) in a particular area. The Aral Sea was once one of the Earth's largest bodies of land-locked water. Since 1960, the sea has lost more than 60 percent of its volume. The associated drop in sea level has lowered the surrounding water table. The cause of the depletion of the Aral Sea is the rerouting of two large rivers for the irrigation of cotton fields. The two rivers were major sources of fresh water to the Aral Sea.

Reduced water flow, coupled with evaporation, has had three primary effects: first, the remaining water has become extremely salinized; second, the moderating effect of the Aral Sea on local climate has diminished, resulting in hotter summers, colder winters, and a decreased growing season; third, over 20,000 square kilometers of land that were once submerged now are exposed. Dust storms raise up massive amounts of salt from the exposed sea bed and move it hundreds of kilometers away, depositing on surrounding land and reducing crop production.

If this process continues at the same rate, the Aral Sea will cease to exist by the year 2020. The two images are from the Landsat Multi Spectral Scanner (MSS).

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