Back to Environment > Desertification Review
The spread of desertification can be difficult to access from the ground. When investigators monitor large regions, information must be gathered from thousands – if not tens of thousands – of locations. The teams must also return periodically to each site to detect changes over time. This ongoing surveying would typically require many years due to the variability of weather conditions and human activity. Gathering the long-term manpower for such work could be dismaying – and its costs formidable.
Today, students of desertification can take advantage of the scanning services of tens of detectors on artificial satellites that provide high-resolution readings of visible and other forms of electromagnetic radiation reflected off the earth. These devices repeatedly cross all points of the globe, including those inaccessible to humans. The data collected is constantly recorded via tracking stations, enabling researchers to view past as well as present conditions in an area under study. Thus the progress of different desertification events can be followed in detail over wide areas.
Researchers at the Remote Sensing Laboratory (RSL) of the Jacob Blaustein Institutes for Desert Research, Ben-Gurion University, are using satellite data in explicating the extent, intensity and rate of change of desertification phenomena around the world. Their work, carried out in the Blaustein Institutes’ Department of Solar Energy and Environmental Physics, advances scientific theories, methodologies, and computer image processing, as well as the development of geographic information systems for managing earth resources. Their goal is the development of low-cost management approaches and predictive techniques over expanses of settled and unsettled drylands.
Some projects carried out by the RSL have clarified, among other things, the degradation of rangelands in Mongolia, the effect of drought on forests in Israel’s Negev desert, the impact of salt dust on the Aral Sea basin agriculture, and vegetation degradation in the Egyptian Sinai desert.
Vegetation degradation in Sinai
High-resolution satellite images clearly delineate the borderline between Israel’s Negev and Egypt’s Sinai desert. The Israel side is much darker. This anomaly derives from desertification in the Sinai caused by destruction of biological soil crusts by human and animal trampling of the soil. Absence of crusts and the resultant wind-engendered movement of sand dunes and soil make the land less habitable for plant growth.
Salinization and water logging
Salt buildup in soil and underground aquifers is a major cause of land degradation, particularly in irrigated areas. However, salts have no distinguishing features in satellite measurements of soil. By developing sophisticated indirect methods, involving satellite determinations of vegetation status, changes over the year, and thermal data manipulation, RSL investigators were able to detect and map different degrees of soil salinization in the Dashguz oasis in Turkmenistan.
Drought
Long periods of abnormally dry weather can upset a region’s ecological, agricultural, or hydrological balance. Collection of remote sensing datathat determine plant health, namely, the normalized difference vegetation index(NDVI), was carried out in the Yatir pine forest in the northern Negev. The study showed that in 2000, after five consecutive years of drought, the forest exhibited a clear deterioration of plant health. Moreover, areas that suffered most could be distinguished from these that better withstood reduced rainfall.
Grazing gradient around watering points in Kazakhstan
Remote sensing is extremely useful in monitoring desertification around watering holes that can be caused by overgrazing. With the collapse of the Soviet Union, basic socio-economic changes took place in the newly independent former Soviet Republic of Kazakhstan. RSL studies demonstrated recovery of the vegetation cover near watering holes due to the drastic decline in grazing livestock populations. At the same time, resources on the Ust-Urt Plateau were being developed as a source of gas and oil, with the building of large-scale plants. The operation of heavy-duty equipment, vehicles and pollution damaged the soil surface, which was clearly seen in satellite detection of reduced natural vegetation.
Plant invasion due to overgrazing in Mongolia
Construction of the north-south cross-Mongolian railroad in the 1960s provided a unique opportunity to monitor the effects of grazing on vegetation populations. To prevent the entry of animals, the tracks were fenced off, in some instances leaving as much as 4 km. wide protected areas. Image processing of remotely sensed data showed a buildup of unpalatable, toxic plant species in the intensively grazed rangeland when compared with the protected areas. Avoidance of these plants by animals enabled them to survive and propagate, further decimating the needed forage in the steppe biome of Mongolia.
Hydrology and water resources
In arid areas, water supplies are often dependent on aquifers that store the meager precipitation penetrating through the soil over many years. Depletion of these supplies due to climatic changes or intensive pumping is a major cause of desertification and the migration of indigenous populations. Although space-borne imagery detects only surface phenomena, researchers have found ways of exploiting satellite data to indirectly detect the presence of groundwater. The RSL team at BGU has used the unexpected appearance of vegetation to identify points at which groundwater seeps out due to underlying geological formation. Such studies were carried out at the Amatzia Fault in the northern Negev and at the edges of alluvial fans of the Turfan Depression in China.
Salty dust storms around the Aral Sea (Kazakhstan and Uzbekistan)
Windblown salt dust is a major intensifier of land degradation associated with desertification. For example, water diversion carried out by Soviet planners since the 60s has led to a shrinking of the Aral Sea to less than half its size. The exposed salty lakebed is then subject to wind storms, which disperse salt particles over great distances. Aside from the respiratory problems resulting from this particulate air pollution, the saline soil has severely reduced crop yields, causing widespread nutritional deficits. These storms can be easily followed by remote sensing and their severity evaluated.
Previous section Next section
