ABSTRACT
Desertification is a global phenomenon which afflicts drylands in more than 100 countries, of which about sixty with substantial areas of drylands are the most critically affected. The first part of this chapter gives a broad overview of where desertification occurs and the relative significance in each region of the four major direct causes: overcultivation, overgrazing, poor irrigation and deforestation. Numerous detailed examples of each cause were given in Chapter 2. The second part summarizes the most recent estimates of the actual extent and rate of increase of desertification (made in 1983 and 1984), but also shows how inaccurate these estimates are. Few large-scale measurements have been made, desertification is still quite loosely defined, and we are much too reliant on the subjective assessments of experts for these estimates. The shortage of reliable data on the extent of desertification, and on its social and economic impact, leads to scepticism among the scientific community about the reality and relevance of the phenomenon, and is a major obstacle to securing the political and financial support of governments and international agencies for programmes which could bring it under control. Improving the monitoring of desertification is therefore of the utmost importance. Consequently, the final part of the chapter discusses possible ways to do this by means of remote-sensing techniques, and the concomitant need for measurable "indica-- tors" which will allow the degree of desertification in an area to be estimated with far more accuracy than in the past.
