Desertification and land degradation: origins, processes and solutions

Table of Contents

1. Authors and acknowledgements
2. Introduction
   1. Aims
   2. Definitions and key concepts
   3. Synthesis of previous and ongoing projects
   4. Key issues and outline
3. Evolution of desertification in the Mediterranean
   1. Climatic fluctuation
   2. Human influence
4. Primary drivers of desertification
   1. Biophysical and socio-economic causes
   2. Pathways of desertification
   3. Driving forces in the Mediterranean
   4. Synthesis of causes for DESIRE hotspots
   5. Conclusions
5. Processes and consequences of desertification in the Mediterranean
   1. Socio-economic and political factors
   2. Biophysical processes
   3. Conclusions
6. Indicators: monitoring desertification
   1. History of monitoring
   2. Indicators
   3. Monitoring and mapping techniques
   4. Concluding remarks
7. Modelling desertification
   1. Definition of modelling
   2. Model types
   3. Biophysical modelling
   4. Socio-economic and participatory modelling
   5. Gaps and progression in modelling
8. Solutions
   1. Biophysical solutions
   2. Political and socio-economic solutions
9. References

History of monitoring

The first global attempt to quantify dryland degradation extent took place for the United Nations Conference on Desertification (UNCOD, 1977) in response to the Sahelian drought of the 1970s and (now discredited) research suggesting the southern limit of the Sahara was expanding by 5.5 km per year (Lamprey, 1975). The conference concluded that 3970 million hectares were desertified, an area four times the size of Europe (UNCOD, 1977). Despite the development of a provisional methodology for assessing and monitoring desertification by the FAO and UNEP in the 1980s, reliable data were still lacking at national and global scales and global assessments were still not based on systematic measurements. In 1984, with little new empirical evidence, UNEP revised their estimate to 3475 million hectares and in 1987 made the wild claim that because 27 million hectares were becoming desert each year, "in less than 200 years, at the current rate of desertification, there will not be a single hectare of fully productive land on earth" (UNEP, 1987). Figures of two-thirds to three-quarters of all drylands are still cited as being degraded (Diouf and Lambin, 2001; Eswaran et al., 2001). These assessments were challenged by a series of detailed remote sensing studies that showed the extent to which the location of desert margins can change in response to rainfall variability (Hellden, 1991; Tucker et al., 1991). This led some researchers to question the existence of dryland degradation (Warren and Agnew, 1988), suggesting it was an "institutional myth" (Thomas, 1993).

In response to this wide range of estimates, UNEP commissioned in 1987 a Global Assessment of Human-Induced Soil Degradation (GLASOD) from the International Soil Reference Centre (Oldeman et al., 1990). This indicated that 1016 to 1035 million hectares of drylands were degraded; less than a third of the area suggested by previous estimates. It was based on expert opinion, eliciting information about the type, extent, degree, rate and cause of soil degradation over the last 50 years from over 250 soil scientists and environmental experts in 21 regions of the world (Oldeman et al., 1990; UNEP, 1997). Despite being "the first scientifically systematic" assessment of land degradation, it has been criticised for various reasons, such as its subjectivity (e.g. Thomas et al., 1997). While claiming to assess trends over the last 50 years, few experts had personal experience of soil conditions in the 1940s, and there were few data available at this time for much of the world. The assessment does not take management goals or other contextual information into account. It does not involve local stakeholders who may have very different perspectives of land degradation. Related to this, it only provides information about one biophysical component of land degradation (the soil), ignoring other system components, notably ecological changes that are vital for semi-arid rangelands. Despite these problems and the fact that it is now fifteen years old, GLASOD is still cited in peer-reviewed literature (e.g. Conant and Paustian, 2002; Polyakov and Lal, 2004) and is still widely used by national and international policy-makers (ISRIC, 2003). It also forms the basis for the widely cited World Atlas of Desertification (UNEP, 1997).