The desert and desertification
The formation of arid areas results from the combination of different phenomena, which in turn enter a more and more extensive interactive mechanism.
On a world scale, the big processes, the thermal factors and the general atmospheric circulation and the geographical components on a local scale act and reciprocally integrate each other in specific areas as the sum of many elementary conditions.
The overall system work as a big amplification mechanism within which the micro factors can also spread and produce lasting effects with a series of consequences over a long period.
The desert regenerates itself and once small areas of degradation have started they spread and extend by accumulation.
Thus, one can understand that the theory of the advance of the desert has often been used to explain the causes of desertification differ from each other.
The latter has assumed the look of a real calamity in the Sahel regions in the southern Sahara.
The disastrous effects it produces on the soil may be ascribed to different causes : wind erosion creates vaste bare areas and the accumulation of dunes; water erosion gives rise to sterile sand and mud concretions or limestone crusts; the strong evaporation contributes to the salination and alkalization because of a high concentration of salts in the waters, insufficient drainage and a water shortage.
Therefore, the spread od physical or chemical-physical degradation is driven by biological or physical mechanisms, which reduce the plant cover and the original bio-productivity of the soil and make the environment impossible to use.
In the Sahel these processes start in a climatic area that receives more than 200mm of precipitation for year and also in a deeper strip in the south where the rains may reach 800mm for year, i.e. areas that cannot be properly defined as a desert.
It is estimated that in these countries one million hectares of tropical forests are destroyed and 100,000 hectares of soil are irremediably covered every year with the advance of the sands produced by wind erosion.
c changes in recent years.
Therefore, non-natural factors trigger an environmental mechanism of degradation which must therefore be ascribed to a single factor : human intervention.
In Africa, altogether more than one billion hectares have been damaged by this phenomenon.
Millions of people have been forced to emigrate elsewhere.
In Mali and in Burkina Faso one sixth of the inhabitants have been forced to abandon their villages.
In Senegal two fifths of the population of the upper valley of the homonymous river have been forced to emigrate.
Mauritania is disappearing under the sands.
Here, the population established in the capital,Nouakchott, has increased from 9 to 41 per cent in twenty years, while the nomadic groups have fallen from 73 to 7 per cent.
All this is apart from the cyclical climatic fluctuations and from the climatic changes in recent years.
The demographic growth, the abandoning of archaic techniques and social habits even though they were in harmony with the environmental potentialities, as well as the imposition of new crops according to the requirements coming from the world market and the dissemination of the monoculture are only some of the causes of a state of degradation.
Above all, the settlement of people gathered in small areas according to the necessity of the modern economies gives rise to a large energy demand which is satisfied with a massive devastation of the arboreal and forest heritage.
The wounds inflicted on the woods trigger processes of continual and substantial collapse of the biological variety, quality and productivity.
Animals and plants are decreasing and the number of species is falling so much that they have no potential to provide a genetic answer to the altered circumstances and for that reason they are irremediably destined to disappear.
The soil becomes sterile and its physical and chemical features are altered, so it is impossible for the soil to retain water.
The triggering of both the processes of wind and water erosion and the mechanisms of sand accumulation is a consequence of this situation.
The misuse and the overexploitation of the resources are the main causes of desertification which in the United Nations Convention is so defined : ”deterioration of the lands in the arid, semiarid and semi humid dry areas due to different factors including climate changes and human activity”.
This process starts right around the main centres of human activity and irremediably spreads over the whole territory.
It is incorrect, therefore, to speak of the advance of the desert.
There is a precise environmental model that occurs in a specific climatic context with its own laws, biological activities and an appropriate human use, whereas desertification produces an environment in full decay and totally devoid of ecological balance.
In these circumstances as in the other ones originated by human intervention such as climate change, the difference lies in a specific variable : time.
The antural establishment of the desert has followed the very long geologic times enabling the species to follow the changes with a process of transformation and evolution and therefore allowing the creation of environments that in spite of the harsh climate are rich in adaptations and in the biodiversity of the species.
On the contrary the processes of desertification and the climate changes triggered by human intervention are rapid.
The biological and physical structure of the planet has not had time to adapt to them, resulting in desolation and decay.
Thus, it may be asserted that even the desert can undergo a process of desertification.
Precisely in the environments with a more critical and difficult balance, characterized by a strong interaction between the processes, each intervention from the smallest to the most macroscopic one may produce lasting devastating effects.
In the Sahara the traces left by the vehicles during the Second World War are still evident on the characteristic microvegetation of the soil that forty years later has still not recovered.
In the Sahel the environment reacted to the roughness of the seasonal differences and to cyclical climatic alterations by properly diversifying and varying each situation.
Because of the overexploitation due to human action, which intensifies its destructive activity against the species and the residual varieties just when the resources are becoming rarefied, any capability of recovery disappears even when the favourable conditions have been re-established.
This mechanism is operating today all over the world and consequently 30% of the lands have been estimated as undergoing a risk of decay.
In the Amazon, the process of deforestation exposes the soils to the climate’s violence.
The waters take away the thin layer of fertile soil which is no longer able to be reproduced.
The plants do not grow again and in time the rain itself fails.
The result is a desert where there was previously a pluvial forest.
The deepest forms of desertification affect over one hundred countries, menacing the survival of more than one billion people.
24 billion tons of topsoil disappear each year all over the world.
The world loss in the last two decades was equivalent to the total arable land in the United States.
The situation in particularly dramatic in the arid zones where about 70% of the areas corresponding to a quarter of the total earth’s area are threatened.
However, this problem is largely present also in the temperate areas.
In the United States the proportion of the arid zones undergoing desertification in the highest in the world and reaches 74%.
In Asia, desertification has spread over 1.4 billion hectares and the worst threatened lands are in the area of the former soviet bloc.
In Italy, according to European Union estimates 27% of the territory is exposed to a high risk of erosion.
The regions of Apulia, Basilicata, Calabria, Sicily and Sardinia show an already advanced process of desertification.
On the basis of the evaluation of the United Nations Programme for the Environment, desertification costs the world 42 billion dollars for year ( 9 in Africa alone).
More than 135 million people risk losing their lands in a very short time.
Desertification concerns both the agricultural contexts and the urbanized areas.
In the agricultural environment the process manifests itself through the following phenomena : water erosion; loss of fertility of the soil; salination of the soil; destruction of the humus; disappearance of the plant cover; exhaustion of the aquifers and drought; dacay of the slopes and landslides.
The urban areas contribute both directly and indirectly to the process of desertification.
Directly, the massive urbanization may be considered in itself as a form of desertification due to the spread of concrete over large natural surfaces; but also indirectly through the absorpition from the soil of the natural resources and their destruction in the areas with a high demographic concentration.
A close relationship between urbanization and desertification may be found both in the non-industrialised countries and in the most developed ones.
In the first case, the process of decay is triggered and extends starting right from the areas undergoing a modern and accelerated urbanization which by their necessity impoverish the surrounding territory.
In the advanced economies, and in particular in Italy, whose territory is strongly characterised by human settlement, the spread of the process of desertification is directly linked to the crisis of the historic city centres which replaces the traditional arrangement of the landscape made out of building systems that have a strong natural component and low consumption of resources with a model based on massive building operations that waste energy and pollute the environment.
The exodus of the population from the ancient centers and the consequent disappearance of the local systems that were able to properly manage the landscape are the result of the urbanization of new areas.
Thus, a process of physical and social desertification begins.
The impoverishment of the human resources corresponds to the architectural decay and to the erosion of the mountain, hilltop and slope systems.
Emigration, the loss of identity and of values are the socio-cultural aspects of desertification.
The extreme situations of the Sahara and the Sahel are the test-bed and the alarm signal of a peril involving everyone: desertification caused by man’s negative interaction with the environment is today a menace in any climate and in every region.