Desertification is a serious global problem, affecting one-sixth of the world’s population. One-quarter of the total land area in the world and 70% of all the drylands are seriously affected by adverse impact of the desertification. And 47.2% of the earth’s land surface is dryland.
A total of 5.1 billion ha are made up of arid, semi-arid and dry sub-humid areas; a part of which is vulnerable and subject to degradation. These lands are the habitat and the source of livelihood for about one-fifth of the world’s population, experiencing pressures on environment caused by human mismanagement.
“Desertification” is not only a global environmental problem but is also a serious threat to the socio-economic fabric all-over. Environmentally, it contributes to climate change, water, air and soil pollution, deforestation and soil loss.
Some of the glaring aftermath effects of the environmental degradation are: less of global biological diversity, loss of biomass and bio-productivity, exhaustion of humus reserve, disrupting normal global bio-geochemical turnover, and reduction on the global carbon-dioxide sink.
More importantly, desertification contributes to climatic changes by increasing potential and decreasing actual evapo-transpiration rate, changing ground-surfaceenergy budget and adjoining air temperature, and adding dust and carbon-dioxide to atmosphere.
Socio-economically, desertification constitutes the main cause of loss of productive land resources, thereby contributing to spread of poverty and hunger, economic instability and political unrest. It prevents achievement of sustainable development in affected regions and countries and directly threatens health and nutrition status of the populations.
What is desertification
Desertification is land degradation in arid, semi-arid and dry sub-humid areas resulting from adverse human impact.
Desertification may basically be considered a process of environmental change either naturally induced or human-made, through which an arid, semi-arid and dry sub-humid landscape suffers degradation and may become more desert-like. The mechanisms of desertification has physical, chemical and biogenetic aspects, but the consequences affect both the environment and the human society.
The four desertification processes that have an extensive impact on the biological productivity of the land are: degradation of vegetative cover, soil erosion, salinization and waterlogging and soil compaction.
Vegetative cover serves as the direct or indirect source of human food and as the protection against soil erosion. The potential for damage to plants is greatest in the drier parts of the arid regions. The destruction of vegetation in the drier areas is more difficult to reverse.
Water erosion is the dominant type of erosion responsible for changing land surface. Erosion may be geologic (natural) or accelerated (due to man’s activities). In desertification, the concern is with accelerated erosion, which can be controlled by altering man’s activities. Wind erosion, likewise, may also be accelerated due to man’s activities.
The moving sand dunes can be stabilized by revegetating them. Dune encroachment can be construed as the special case of desertification. Severity of water erosion is determined by estimating or measuring soil loss. In wind erosion, the amount of deposition indicates the loss.
Salinization and waterlogging of irrigated cropland go together; the latter leading to former. Application of saline irrigation water to slowly permeable soil can lead to salinity. Salinization poses greater threat to crop production than waterlogging.
Soil compaction assumes greater importance in dry arid areas. These soils are low in organic matter and are dry to a considerable depth. The pressure of tillage machinery, the pounding of livestock hoofs, and dispersion and packing effects of rain drops striking soil can cause soil compaction. Surface-soil compaction is called soil crusting, which is widespread on grazing lands and on the cultivated lands.
Effects of desertification
Adverse impacts of desertification are varied and immense and can be viewed under two major heads-environmental and socio-economic impacts.
‘Desertification‘ causes irreversible damage to environment, food and livelihood security, loss of biodiversity and a perceptible decline in the quality of life; ultimately leading to poverty. In short, impacts of desertification could be stated as follows.
- (i) Loss of ecological stability,
- (ii) loss of biodiversity,
- (iii) reduction in carbon-sink capacity and its effect on climate,
- (iv) floods, drought and related losses,
- (v) damages to watershed,
- (vi) soil erosion,
- (vii) silting up of reservoirs,
- (viii) desertification and drought, and
- (ix) changes in hydrological regime.
Social and economic impacts:
- (i) employment and
- (ii) food and livelihood security.
There are some other more important impacts of desertification such as vegetative cover, losses in productivity as the result of soil erosion and inefficient water management, overabstraction of groundwater and decline in quality of life.
Impacts on depletion of vegetative cover: There has been a gradual change of ecosystem through loss or replacement of one species with another.
In many parts of Rajasthan there has been a gradual change in natural vegetation found in the region and its plant density. For example, in sandy areas of less than 200 mm annual rainfall zone, the grass species such as Lasiurus sindicus and Eleusine compressa are being slowly replaced with the concomitant decline in basal cover and plant density.
Desertification indicators can serve two useful purposes:
(i) estimating how much land degradation has occurred in the past, and
(ii) what effect the current management practices are having on the ecosystem.
Range scientists were the first to look for indicators of range conditions and trends. Soil Conservation Service (SCS) has evolved a classification system, based on the response of plants to grazing. Plant ecologists have found the concept of climax vegetation useful in analyzing plant succession.
In rainfed crop-lands, soil erosion is the number one desertification problem. Indicators of desertification should, therefore, indicate changes in soil characteristics over time. Periodic measurements of the amount of removal and deposition of soil indicate amount of land degradation that has occurred in the past.
Repeated measurements will also show the trends of degradation. The FAO has identified additional soil characteristics for evaluation of soil degradation.
Regardless of the challenges involved, desertification control and restoration of degraded lands is a win-win strategy. It needs to be done.
Before taking up desertification control on any dryland or area, it is necessary to assess and monitor the type and the severity of the land degradation.
The causes of land degradation are also to be ascertained. Based on degradation, the selection and application of appropriate actions, will have to be taken. Whatever steps or actions are taken to combat desertification, they should aim at achieving sustainable development of the area, which can be possible with the management and conservation of the resource-base, the land, so as to meet the present and future needs of the people habitating that area or zone.
Soils, climate and land slopes are variables, and that must be known to develop appropriate control measures.