In many parts of the world the quality of land is decreasing, thereby limiting its capacity to provide the manifold goods and services humanity depends on for existence. It is estimated that the health and livelihoods of an estimated 1.5 billion people are currently threatened through the negative impacts of land degradation.
Alarmed by the Sahelian drought in the early 1970‖s, the global community made first attempts to determine and map the extent of land degradation in the world’s drylands. Until today, several more efforts have been made to assess state and trends in global land and soils. Over time, the scope widened from drylands to total terrestrial land, and definitions of land degradation moved from production-based aspects to the evaluation of ecosystem goods and services, and the inclusion of economic and socio-cultural dimensions.
Main assessment methods applied were expert opinion (through questionnaires), modelling, and remote sensing (through satellite imagery). The results varied substantially, depending on the conceptual framework used, total area analysed, parameters chosen for analysis, and methodologies applied. Uncertainties aside, most experts agree that at this point in time some 20-25% of terrestrial surface area are affected by land degradation.
It is somewhat sobering that it has so far not been possible to conciliate expert-based knowledge (“bottom-up”) with remote sensing information (“top-down”). Both approaches have their strengths and weaknesses, and would ideally need to be combined for an ultimate global assessment. Since 1990 there has been no more truly global, land based assessment, which is in stark contrast to the demand for such data.
Hopes are growing that the Sustainable Development Goals (SDGs) in general, and the target of Land Degradation Neutrality (LDN) in particular, will soon generate sufficient momentum for a universally agreed conceptual framework, and an up-to-date analysis of global land degradation. This could be the beginning of a global monitoring effort to better understand trends of soil degradation and improvement over time.
Land degradation is a global issue with local solutions. Therefore, a concerted global effort on the post-2015 development agenda should also include the many promising SLM technologies and approaches that are already applied. This would help empower the global community to learn from each other, and contribute to building resilience at local, national, and regional levels.
This document portrays the major land and soil degradation assessments of the past and critically evaluates their results. Another section is devoted to the various methodologies that can be applied, including their strengths and weaknesses. It finally explores promising potential corner stones of future assessments, with particular reference to the SDG target of Land Degradation Neutrality.
Despite the numerous challenges involved, the document is making the case for global assessments of land and soil quality. And it suggests that besides an agreed conceptual framework it is awareness, respect for complexity and diversity, an ecosystem approach and last but not least adequate funding that will make future endeavors a success.