A reassessment of the status and trends of desertification was called for as part of a general assessment of progress in the implementation of the United Nations Plan of Action to Combat Desertification, seven years after the UN Conference on Desertification (UNCOD) in 1977. Because of the inadequate data existing at the country or state level, the basic generalization has been set at a wider regional scale.

The new assessment has confirmed the global scale of the problem of desertification as presented to UNCOD, and has increased the area and populations considered to be at risk through its recognition of the threat of desertification in the sub-humid tropics. The threatened area of 4,500 million ha constitutes 35% of the land surface of the Earth, with almost 20% (850 millions) of the world's total human population. Estimates indicate that, of this area, 75% is already moderately desertified, and 30% is severely or very severely desertified.

The rural population affected by severe desertification totals some 280 millions, or 470 millions if the urban component is included, with, respectively, 135 millions and 190 millions severely affected. These are significantly larger than the figures presented to UNCOD—mainly through the inclusion of additional sub-humid land in this assessment, but partly through national population increases and growth in the extent of severely desertified land.

Both in terms of areas and population affected, the so-called developing regions are shown to be those worst-hit by desertification; and within these, the tropical semiarid and sub-humid lands tend to be the most ‘critical’ areas.