Monitoring Land Degradation

Previous and existing approaches to assessing and monitoring land degradation have not been effective because the system for collecting and disseminating information and adoption of sustainable land use and management practices have been weak in the dryland regions that represent many poor countries. Some countries have databases on the biophysical aspects of land and land resource use and degradation and on various aspects of society and the economy. However, these data are usually not comparable in terms of scale, are often not compatible, and certainly are not integrated and interlinked enough to facilitate decision-making and policy-making. Information about land degradation is rarely standardized or integrated into local planning and management processes. At the international level, this information is not comparable and has insufficient resolution for defining and implementing regional and national action plans (RAPs, NAPs) for international conventions such as the United Nations Conference on Environment and Development (UNCED) held in Rio de Janeiro, Brazil, in 1992.

The earliest assessment of land degradation was biophysical in nature and was derived at the farm level using the universal soil loss equation (Wischmeier, 1976). Early attempts to assess land degradation on larger scales, such as at river basin and bioregional scales, using a combination of remote sensing and ground-based techniques, encountered difficulties mainly due to lack of financial resources and technical limitations. In 1979, the Food and Agriculture Organization (FAO) of the United Nations developed a methodology for assessing soil degradation with detailed criteria for each type of biophysical degradation. Subsequently, FAO conducted a Global Assessment of Progress on Desertification in 1984 and 1992. The global estimate of land degradation or desertification ranged from 2001 million ha in 1984 to 3475 million ha in 1992 (i.e., 13-23% of the earth's surface; FAO, 1979, 1995).

Global Assessment

In 1987 the United Nations Environment Programme (UNEP) requested an expert panel to produce, in the shortest time possible, a scientifically credible method to assess soil degradation at the global scale. The first Global Assessment of Soil Degradation (GLASOD) in the early 1990s provided a systematic qualitative assessment of the extent and severity of land degradation, and its results formed the basis for the World Atlas of Desertification at a scale of 1:10 million (UNEP, 1992, 1997). This map is based on input from more than 250 soil scientists in the 21 regions dividing the world. This expert assessment method used a mapping base, a set of semiquantitative definitions for soil degradation, case studies, and a team of national and international experts.

GLASOD is criticized today as inaccurate, subjective, and not appropriate for assessing soil degradation at the country level. Most of the indicators used in the GLASOD were biophysical and not socioeconomic and therefore did not include the institutional and policy driving forces of land degradation. Despite these drawbacks, GLASOD remains the only global database on the status of human-induced soil degradation, and no other data set comes as close to defining the extent of desertification at the global scale (UNEP, 1997). In another approach, Dregne et al. (1991) used results of vegetation degradation estimates for comparison with soil degradation.

Assessment of South and Southeast Asia

In response to requests for more detailed information on soil degradation, in 1993 the Asia Network on Problem Soils (www.isric.nl) recommended preparation of a soil degradation assessment for South and Southeast Asia (ASSOD) at a scale of 1:5 million. The methodology of this assessment reflects comments from the peer review of GLASOD. As a result, ASSOD has a more objective cartographic base and uses the internationally endorsed World Soils and Terrain Digital Database (SOTER) to delineate mapping units (Oldeman, 1988; see also www.isric.nl). Like GLASOD, ASSOD focuses on displacement of soil material by water or wind and in situ deterioration of soil by physical, chemical, and biological processes. ASSOD, however, places more emphasis on trends of degradation and the effects of degradation on productivity.

Although an improvement over GLASOD, ASSOD is not without prob lems. The assessment of the degree, extent, and past rate of soil degradation is still based on expert opinion, and the scale (1:5 million) is still not adequate to guide national soil improvement policies.

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