Desertification: mapping constraints and challenges.

Mapping desertification has proven to be a challenging task. Difficulties derive from its ambiguous definition and the comprehensive integration of various biophysical and socioeconomic indicators that need to be considered in the evaluation process. In the early 1990s, assessments and mapping were based primarily on expert opinions that introduced uncertainties and obvious shortcomings. Later on, with the development of the remote sensing technology and the advancement of the geographic information systems, global mapping became common place. Results showed that temporal and spatial scales are crucial components of the mapping and assessment process, but great difficulties arose comparing maps that were developed using different methodologies. Global maps could depict only general trends in desertification caused by human-induced land-use changes or climatic variations but proved to be of limited value at local level. On the other side, local studies have problems of extrapolation. This necessitates the performance of mapping at various scales, but only after a methodological approach has been developed that accounts for all the components of the desertification process, allowing upscaling from global to local level and vice versa. Desertification mapping is under way by the new World Atlas of Desertification (WAD) 3rd edition to be published. The WAD places particular importance to case studies that document local realities affected by desertification as well as mitigation actions. Finally, concerned efforts must be made to develop and implement sustainable land-use planning and land management techniques that arrest and reverse the negative consequences of desertification.