1. What are drought and desertification?

A drought is a period of below-average precipitation in a given region, resulting in prolonged shortages in the water supply that can have a substantial impact on the ecosystem and agriculture of the affected region (Wikipedia).

Broadly speaking, desertification can result in an environmental crisis, producing conditions or landscapes close to those of a desert (Encyclopaedia of Environmental Sciences, 1999).

Drought and desertification have an impact on all aspects of life, showing the extent to which the environment and means of subsistence are interdependent. 

The risks inherent in drought and desertification can be summarised as follows: 

Risks pertaining to environment

Drought and desertification sometimes cause irreversible changes to biodiversity, the soil and vegetation. Such changes include the alteration of floristic composition, a reduction in biomass cover and diminished growth and reproduction capacities of vegetation. 

The most alarming consequences with respect to biodiversity affect: 

  • wildlife and domestic fauna, especially those kept in poor conditions;
  • flora – certain species are jeopardized;
  • certain waterways, which were formerly permanent but now flow only intermittently, undermining the biotopes of many species;
  • migratory birds, which are part of the World Heritage and which, particularly in the Sahel, encounter increasingly precarious residual wetland habitats.

Risks relating to soil impoverishment, vegetation and forests

The following consequences can be observed:

  • degradation caused by overuse of the soil to the point of exhaustion, aggravated by climate change at global level;
  • degradation caused by overgrazing, which destroys the vegetation cover needed to protect the ground from erosion;
Figure 2 – Combination effect of drought and overgrazing in the steppe zones

soil impoverishment caused by bad irrigation practices resulting in an increase in salinity, and poor draining of waterways that feed into big lakes.

  • deforestation, which destroys trees that protect the ground against water and wind erosion. Wood is also an independent source of energy for domestic use (lighting and cooking) in many arid areas.

Under extreme drought conditions, swarms of locusts can have catastrophic consequences for the environment and the economy of vulnerable countries.

Risks relating to the economy

Drought and desertification can directly result in a reduced yield or even loss of harvests. Consequently many populations (especially in rural areas) have difficulties in satisfying their requirements in terms of drinking water and in nourishing their families and cattle, since the price of agricultural produce increases under these conditions.

Research shows that rice yields decrease by 10% for any rise of 1°C in the night temperature. This has very serious consequences in countries where the economy relies largely on rice production.

Risks relating to poverty and mass migration 

Soil impoverishment is synonymous with famine and poverty. To find other means of subsistence, populations which live in areas threatened by desertification are obliged to move. Generally, they migrate towards urban areas which can better provide for their needs or they move abroad. Shifts in population are one of the principal consequences of desertification (http://remi.revues.org/document1654.html). According to the calculations made by the secretariat of the United Nations Convention to Combat Desertification (CCD), between 1997 and 2020, some 60 million people will have left the sub-Saharan desert zones of Africa to relocate to the Maghreb region or to Europe.

Risks relating to health

Drought and desertification (often a result of climate change) disturb the ecosystem and support the propagation of certain insects and diseases which are harmful for humans, plants and animals. According to research results, higher average temperatures increase fertility and growth rates among harmful insects. As a result, such insects, as well as diseases, take hold in a wider geographical zone and the frequency of epidemics increases.

  • Human health

Drought and desertification are generally accompanied by a qualitative and quantitative degradation of water resources, and can often lead to the development of epidemics (e.g. cholera, malaria).

Wind, especially during sandstorms, is also an important vector of ophthalmologic diseases (e.g. conjunctivitis) or respiratory problems.

In addition, cities are often ill-equipped to absorb the migratory flows coming from rural areas. Many cities have disastrous sanitary arrangements, a lack of infrastructure for cleaning waste water or processing liquid waste, and for managing waste more generally; in such cases, prevention schemes and medical facilities can prove largely insufficient.

  • Animal and vegetable health

Drought and desertification can cause the mass death of livestock through a lack of grass and the prevalence of new diseases. For example, in countries of the Sahel, in the hot summer period, cattle often die whilst giving birth and calves are born premature. Veterinary surgeons in these areas have linked new diseases to climate change. 

Alterations to wind patterns are likely to change the way in which insects, bacteria and mushrooms, all vectors of plant disease, are diffused. For example, a rise in winter temperatures would support the multiplication of bee moths and increase the damage they cause to rice cultivation systems. Studies reveal that the number of parasitoids — insects such as wasps or flies which lay their eggs on or in the bodies of other arthropods — diminishes in the event of irregular rainfall. However, these parasitoids are very useful in the biological fight against harmful pests in many tropical ecosystems.

The World Health Organization has established a clear link between the heavy rains which affected a large part of East Africa at the beginning of 2008 and the recurrence of malaria. Similarly, Dengue fever, a serious disease caused by a virus transmitted by mosquitoes, reached epidemic levels in the Caribbean.

A further problem is the appearance of mildew in certain potato-growing regions, a disease which spreads in hot and wet conditions. 

Risks relating to food security

Drought and desertification pose a serious threat for the food security of the 9 billion individuals who will have to be fed by the middle of the 21st century. Current food production capacities would have to triple by 2050 in order to ensure access to healthy food. Yet arable areas are in decline. It is estimated that arable areas in developing countries diminished from 0.65 to 0.4 hectares per person between 1990 and 2010.

Risks relating to climate changes (carbon sinks)

Drought and desertification lead to soil impoverishment and consequently reduce the aptitude of the ground to act as a carbon sink. Instead, drought can increase its potential as a source of carbon.

Soil and land ecosystems are an essential source of carbon sinks as they collect and store carbon. It has been estimated that soil captures 2.3 gt (gigatons) of carbon per annum, which represents more than one third of all carbon emitted by the combustion of fossil fuels, one of the major origins of climate change. The total carbon stock contained in the earth’s ecosystems amounts to around 2,500 gt of carbon, including 2,000 gt stored in the ground. 

The drought is a major natural risk linked to long-term climatic abnormalities.
It appears by a drying out of the soil in other words a decline of its hydric potential resulting from an important pluviometric deficit (Lefèvre and Schneider, 2003).

If desert regions are subjected to quasi-permanent drought because of the presence of the subtropical high pressures. The zone of Sahel (Mauritania, Senegal, Niger, Chad and Côte d’Ivoire), undergo a rarefaction of rains more and more marked since 1968 to this day.
Certainly, the successive years of drought are interrupted by a return to normal (year 1 to 2) from time to time but the hydric deficit persists with peaks (73/77/82…).

Indeed, the measures made in the experimental fields of Senegal and Mauritania indicate that since 1968, isohyets 300/400 mm are uncalled-for from 100 to 200 km southward in the space of 15 years (from75 to 90) and no year was superfluous (Sircoulon, on 1992).

In the sector of the pluvial farming in Senegal, we record a clear production decrease of groundnut due to the useful shortening of the duration of rainy season and to the more and more frequent appearance of arid periods during the culture.

Although, in Sahel, the drought is at the origin of famine, of conflicts, of exodus and mortality (200 000 died only for the year 1973 when the drought reached its peak.)

The Mediterranean countries also know droughts of several months on the south bank (4 months in Tunis and Algiers, 7 months in Alexandria) and in a lesser degree the North shore (2 months in Barcelona and 3 months in Istanbul) with the exception of the South of Spain (Drain, 2006) already confronted with the water shortage (Margat, 1990).

Multiannual aridity also occurs in Mediterranean region. Besides, the fall of the agricultural productions (especially cereal), the droughts of the period 1990-1999 are also at the origin of the decay of the cedar of the ATLAS in Algeria and in Morocco. (Halitim, 2006).

In Europe, also the decay of the forest domains is also relatively important following the successive episodes of droughts between 1947 and 1976. In France, the drought from 1989 till 1992 engendered an drying out of streams (11000km), a reduction of the agricultural productions (especially those of May) and an increase of the frequency of the fires of bit in Southern zone especially (Lefèvre and Schneider, 2003).
According to the same authors, the aridity can lead disorders at the level of the constructions further to dehydrations of underground clays.

Nevertheless, the difference of rainfall between the North and the South of Sahara is very strong, because in Mediterranean region except the summer aridity, we find the rest of the year of more or less important rains (350 in 750m). Despite very different pluviometric regime, we can hold some criteria common to these arid climates:

  • The global incapacity of the precipitation in view of the potential evaporation.
  • A marked interannual irregularity
  • The momentary excesses of water even in Sahelian region (SIRCOULON, 1992)

What constitutes a major constraint for the biological rise and a threat for the agriculture whose the socioeconomic impact is roughly more striking in the regions of the world where the followed of the populations is strictly connected to a food-producing agriculture and\or to a practice of the breeding as in Sahel.

The drought is also a factor of degradation of natural resources such as the vegetation, pastoral courses and soils, thus, accentuating the process of desertification. in fact, both of the drought and the desertification are very dependant phenomena. Therefore, the Convention to Combating Desertification encouraged countries of the world to begin to fight at the same time the desertification and the effects of the drought (OSS).

From the ecological point of view, desertification is defined as being the conjunction of two phenomena: the occurrence of the prolonged droughts and the excessive pressure of the man and his animals on unstable fragile ecosystems or little cancelling. (Le HOUEROU, 1979/1987).
In the broad sense, desertification can mean environmental crisis which produces conditions or nearby landscapes of those of a desert (Encyclopedia of Environ-Sciences, 1999).

We appoint by desertification, the ecological consequences of an aridification of the climate (Ramade, 2002).
In the sense of the United Nations convention, desertification is the degradation of land in arid and arid sub-humid areas. It occurs when soils are fragile, the vegetable cover is reduced and the particularly harsh climate ( 07-06-94 ).

There are more than 130 definitions of the word desertification in the literature according to Mainguet 1998.

The desertification knew numerous definitions which were the object of intellectual controversies. Beyond the political compromises, a consensual definition of the process was proposed by the Convention on the fight against the

Desertification: ” the desertification is the degradation of land in arid and arid sub-humid areas due to various factors: including climatic variations and human activities “. The desertification thus concerns a process of degradation of lands linked to natural factors aggravated by the action of the man.

Indeed in arid regions, when the degradation of grounds accelerates ceaselessly, reducing the reserves of the productive grounds, it creates an environment similar to that of the deserts: we speak then about desertification. The desertification does not content with destroying the base of the productive resources, it also provokes the loss of the genetic resources, and it increases the atmospheric dust, disrupts the process of natural recycling of waters and disrupts the economy of a country pulling movements of populations. It is synonymic of loss of biological and economic productivity of arable, pastures and woody lands.

In view of the various examined definitions, the climate countered as a determining factor.

What is the climate determining?

The process of desertification appears, generally in the bioclimatic floors characterized by a pluviometer from 100 to 400 mm / year.

Besides, the irregularity and the level of precipitations, the strong temperatures, the drying winds loaded with particles of sand and the intensity of the ETP are so many factors deteriorating especially when the human activities are transplanted there.

The figure 3 illustrates the action combined by the natural and anthropological factors involved in the process of desertification.
The climate has diverse, direct and indirect incidences on ecosystems:
On water resources (weakness of the rainfall, the irregularity);

  • Frequency and continuation of arid period;
  • Aridity of streams and brooks;

On the type of vegetation, its distribution and its density
On grounds by reducing their rate of organic matter and their power of keeping back to water with increase of the risk of Salinization
In other words, by acting on these essential parameters, the climate shapes the ecosystems.
The anthropological action is also important. It falls on behind the step in the climatic action by amplifying the process.

How is the process of desertification made?
The desertification is distinguished from risks with shock effect (devastating floods, earthquakes, forest fires) by the involved mechanisms, by the mode of expression and by its spatiotemporal evolution.

Figure 3: Desertification Process (Lakhdari, 2009)

Two factors seem essential so that the desertification occurs:

  • Conditions of natural physical weakness (physical and biological);
  • A strong human pressure exceeding the acceptable threshold.

As the vegetation declines grounds are subjected more and more to the degradation hazards (erosion, Salinization,) being able to lay bare the source rock.

When the vegetation disappears, the desertification accelerates leaving cleaned grounds where the hydrous and wind erosion causes important damages.

If this phenomenon occurred in an insidious and slow way even in the geologic scale, nowadays, the conjugation of several factors (natural and anthropological) seems to look to it a speed of perceptible acceleration and a faster extension.

For illustration:
In Sudan, the desert encroachment is from 90 to 100 km between 1956 and 1975;
In the Chad, the plant cover setting degraded of 32 % between 1954 and 1974;
In Tunisia, on a sample of 20 000 ha, 7500 ha are become depopulated or 347 % between 1965 and 1974. (The HOUEROU, 1979)
In Algeria, on a sample of 13 000ha, 500 000ha of the steppe become totally depopulated or 41 % (KARA 2000) with an effect more marked at the level of the steppe West where we also note a considerable regression of let us tax climatic (white Artemisia and Alfa), during these last years (SALAMANI and HIRCHE, 2007; AYDOND, on 2009)
In Spain, 31 % of lands would be threatened with desertification. The degradation of the socioeconomic conditions is in the heart of the problems of desertification:
destruction of the bases of production, social system in danger, impoverishment of the populations …
The scale of drought and desertification differs according to the zones of impact in the world: the phenomenon affects more than a country and more than a continent and tends to increase these last decades. Meadows of the third party of the appeared lands is threatened.
So, the vulnerable zones represented in figure 4 are situated in arid zones and semi arid in particular in the suburb of the climatic deserts.

Figure 4: Desertification Vulnerability (Sources :FAO)

The process seems to reach continents of which we thought formerly under cover such as Europe in particular in its south bank: the current situation of the South of Spain is worrisome (Figure 6).

The scale of desertification at the world level:
Meadows the third party (1/3) of the appeared lands is threatened
1 billion persons are concerned
A reduction of the farmlands of: 2/3 for Africa, 1/3 for Asia and 1/5 for the Latin America and the Caribbean (Caribbean islands) [Source: the UNO, the FAO and the UNESCO]
24 billion tons of fertile soils disappear every year.