World Day to Combat Desertification and Drought
Dryland areas are experiencing significant alterations in soil characteristics, climate patterns, and vegetation composition, which are often irreversible and commonly referred to as ‘desertification’. This term refers to a shift towards conditions similar to a desert, often resulting in the loss of ecosystem services and rural livelihoods. The term ‘desertification’ was first coined in 1927 by the French zoologist and explorer Louis Lavauden to describe the decline in land productivity in Tunisia. This term was once again used in 1949 by the forester Andre Aubreville to describe the rise in soil erosion following deforestation in West Africa. More recently this term has been used by the American agronomist and dryland scientist, Harold Dregne (1977), and the UN Convention to Combat Desertification (1994) to denote a set of processes contributing to the deterioration of arid and semiarid landscapes as a result of land use and climate change. Nevertheless, the concept of land deterioration (or ‘degradation’) can be highly subjective and ambiguous. Transition to ‘desert-like’ conditions is also an ill-defined and inherently ambiguous process because deserts exist in different forms and shapes, depending on whether they are classified based on annual precipitation, vegetation cover, landforms, or suitability for agriculture, animal husbandry and other economic activities that allow humans to thrive. Moreover, while desertification is typically associated with a loss of dryland productivity, it has also been related to shifts in plant community composition that lead to soil losses and a decline in economic productivity despite an overall increase in ecosystem productivity or biodiversity. Due to this ambiguity, it is challenging to accurately determine the extent and distribution of areas impacted by desertification. The most common method involves analyzing changes in vegetation cover and greenness using satellite remote sensing, although the interpretation of these maps can be challenging. The processes underlying the transition to ‘desert-like’ conditions can be of different nature, both natural and anthropogenic. Many of the deserts that exist today formed millions of years ago and expanded and contracted in the course of the Earth’s history. ‘Desertification’, typically refers to ongoing changes associated with human action (such as climate warming and land use change). Such changes are often irreversible – at least at the timescales of human generations – partly because they are sustained by positive biophysical or socio-environmental feedback mechanisms. Biophysical feedbacks can involve the ability of vegetation loss to (a) enhance land degradation (for instance, soil erosion or salt accumulation), which further reduces vegetation cover, (b) reduce in precipitation (for instance, as a result of changes in surface brightness or the impact of dust emissions on cloud microphysics) and the consequent further reduction in vegetation cover, (c) changes in plant community composition such as woody plant encroachment or exotic grass invasions, which may alter fire regime, microclimate or other environmental conditions in positive feedbacks that lead to an overall loss in the economic productivity of the land.
Socio-environmental feedbacks are often associated with indirect drivers such as changes in economic conditions, demographic factors, technology, markets demands, norms and institutions (such as land tenure) that lead to changes in land use such as the expansion or intensification of crop production, livestock ranching, or wood extraction, with the undesired effect of enhancing land degradation and consequently leading to the relocation of the same economic activities to the surrounding areas. The construction of infrastructure can also favor the intensified use of land. This is typically observed after drilling wells and boreholes, which lead to increased grazing pressure in the surrounding areas, a process that can trigger desertification feedback as observed in many regions of the world after the widespread adoption of diesel pumps in the second half of the 20th century.
Overall desertification has direct and indirect linkages to environmental change, rural livelihoods and poverty, with ramifications to food insecurity and environmental migration. Desertification prevention, reversal, mitigation and adaptation are needed to sustain or improve living standards in dryland areas across the developing world
Thomas J. Graff Professor of Natural Resources in the Department of Environmental Science, Policy, and Management at the University of California, Berkeley