Removal of wood - in developing countries, people use wood for cooking. As the population in desert areas increases, there is a greater need for fuel wood. When the land is cleared of trees, the roots of the trees no longer hold the soil together so it is more vulnerable to soil erosion. Overgrazing - an increasing population results in larger desert areas being farmed.
Sheep, cattle and goats are overgrazing the vegetation. June Sahel Rainfall Index. Joint Institute for the Study of the Atmosphere and Ocean. Accessed January 1, Nicholson, S. Nicholson, S. Land Surface Processes and Sahel Climate. Reviews of Geophysics, 38 1 , Olson, D. Dinerstein, E. Wikramanayake, N. Burgess, G. Powell, E. Underwood, J. Itoua, H.
Strand, J. Morrison, C. Loucks, T. Allnutt, T. Ricketts, Y. Kura, J. Lamoreux, W. Wettengel, P. Hedao, and K. BioScience 51, Prince, S. While these various causal factors have been identified, the actual process of desertification remains poorly understood. For instance, it is difficult to pinpoint when drought, which is driven by temporary changes in atmospheric circulation patterns, may become a long-term, permanent condition. Some meteorologists and soil scientists measure the impacts and length of a drought to determine if it is an example of desertification.
Droughts can persist for months or years, but eventually subside; lands undergoing desertification never recover past productivity.
In the United States, for example, 65 percent of the country was affected by drought in the s, but the Great Basin eventually recovered, and modern occurrences of drought usually affect no more than 10 percent of the land. They can also play havoc with infrastructure, reducing the effectiveness of solar panels and wind turbines by covering them in dust, and causing disruption to roads, railways and airports. Adding dust and sand into the atmosphere is also one of the ways that desertification itself can affect the climate, says Kimutai.
Dust particles in the atmosphere can scatter incoming radiation from the sun, reducing warming locally at the surface, but increasing it in the air above. They can also affect the formation and lifetimes of clouds, potentially making rainfall less likely and thus reducing moisture in an already dry area.
Soils are a very important store of carbon. This process also makes nutrients in the soil available for plants to use as they grow. Soil erosion in Kenya. And typically, respiration declines with decreasing soil moisture to a point where microbial activity effectively stops. While this reduces the CO2 the microbes release, it also inhibits plant growth, which means the vegetation is taking up less CO2 from the atmosphere through photosynthesis.
Overall, dry soils are more likely to be net emitters of CO2. So as soils become more arid, they will tend to be less able to sequester carbon from the atmosphere, and thus will contribute to climate change. Other forms of degradation also generally release CO2 into the atmosphere, such as deforestation , overgrazing — by stripping the land of vegetation — and wildfires. But coming up with a robust global estimate for desertification is not straightforward, explains Kimutai:.
The multiplicity and complexity of the processes of desertification make its quantification even more difficult. Studies have used different methods based on different definitions. And identifying desertification is made harder because it tends to emerge relatively slowly, adds Michaelides:. By the time it is detected, it may be hard to halt or reverse. Status of desertification in arid regions of the world.
Taken from Dregne, H. The GLASOD project was itself based on expert judgement, with more than soil and environmental scientists contributing to regional assessments that fed into its global map, which it published in It categorised the degradation into chemical red shading , wind yellow , physical purple or water blue.
Shading indicates type of degradation: chemical red , wind yellow , physical purple and water blue , with darker shading showing higher levels of degradation. Source: Oldeman, L. As the report puts it:. A single global map of land degradation cannot satisfy all views or needs.
The parts of the world with the most potential issues shown by orange and red shading — such as India, Pakistan, Zimbabwe and Mexico — are thus identified as particularly at risk from degradation. Shading indicates the number of coincident risks. The areas with the fewest are shown in blue, which then increase through green, yellow, orange and the most in red.
Credit: Publication Office of the European Union. As desertification cannot be characterised by a single metric, it is also tricky to make projections for how rates of degradation could change in the future. In addition, there are numerous socio-economic drivers that will contribute. For example, the number of people directly affected by desertification is likely to increase purely because of population growth.
The impact of climate change on aridity is also complicated. A warmer climate is generally more able to evaporate moisture from the land surface — potentially increasing dryness in combination with hotter temperatures.
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