Global Assessment of Human-induced Soil Degradation (GLASOD)

The Global Assessment of Soil Degradation (GLASOD) is a first attempt to prepare a world map on the status of human-induced soil degradation. The study was conducted by ISRIC between 1988 and 1991 and led to a global paper map  at scale of 1:10 million. The status of soil degradation was mapped by defining physiographic units, themselves based on expert judgment, in which type, degree, extent, rate and main causes of degradation were characterized. The assessment was undertaken through a network of regional correlators - institutes and individual experts –who were requested to prepare draft regional soil degradation maps on supplied topographic base maps following general guidelines and in consultation with national soil experts in their region. Over 250 soil and environmental scientists have cooperated  with these regional correlators in the course of the project.

Twelve types of soil degradation were recognized: (i) two related to water erosion (loss of topsoil, and mass movements); (ii) three related to wind erosion (loss of topsoil, terrain deformation, and overblowing).; (iii) four related to chemical deterioration (loss of nutrients and/or organic matter, salinization, acidification, and pollution), and (iv) three related to physical deterioration (surface and subsoil compaction, waterlogging, and subsidence of organic soils). The map also shows areas without human-induced soil degradation and wastelands without appreciable vegetative cover or agricultural potential.

To map the degree of soil degradation four levels were recognized: light, moderate, strong, infrequent.

The relative extent of each soil degradation type was estimated using five classes, from infrequent (up to 5% of the unit affected) to dominant (more than 50% of the unit affected). The severity of soil degradation was indicated by a combination of the degree and relative extent.

Five causal factors for soil degradation were recognized: (i) deforestation and removal of the natural vegetation, (ii) overgrazing, (iii) agricultural activities, (iv) overexploitation of vegetation for domestic use, and (v) (bio)industrial activities.

The GLASOD map was primarily intended as a guide to global policy-makers to pinpoint regions of immediate concern, not as a highly accurate technical product to be used at national or sub-national level. For the latter purpose tools such as LADA and GLADA are more suitable.