Sécheresse et désertification

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Sécheresse et désertification

Préparé par le CRSTRA – Centre de Recherche Scientifique et Technique sur les Régions Arides – Biskra, Algérie & the Editorial Board

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La sécheresse est un risque majeur qui tire son origine d’une insuffisance de précipitations, dont les répercussions sont de natures diverses :

  • climatiques (augmentation de la température, ensoleillement, vent, etc.) ;
  • hydrologiques (baisse du débordement de surface, assèchement des rivières et des lacs, assèchement des sources et abaissement des nappes phréatiques, etc.) ;
  • agronomiques (séchage ou pertes de récoltes, y compris les récoltes effectuées à sec, etc.) ;
  • géologiques (assèchement des sols et augmentation des niveaux de salinité, etc.).

En gros, la désertification correspond à un cas grave de sécheresse (à la fois en intensité et en durée) qui aboutit à des conditions engendrant des paysages similaires à ceux d’un désert. Cette situation engendre tout un éventail de conséquences qui dégradent la couverture végétale et le sol. Par exemple :

  • la couverture végétale cultivée (forêt tropicale) se détériore en savane ;
  • une savane évolue pour former un paysage de steppes ;
  • le climat devient excessivement sec.

Deux facteurs semblent être cruciaux pour que la désertification puisse se produire :

  • la susceptibilité des conditions physiques naturelles ;
  • une forte pression humaine dépassant le seuil acceptable.

La sécheresse est un état (normal ou momentané) du sol et/ou une situation dans laquelle la région doit faire face à une déficience dans son approvisionnement ordinaire en eau, sur une période suffisamment prolongée pour qu’on observe des impacts sur la flore naturelle ou cultivée (Wikipédia).

Dans un sens large, la désertification peut être le synonyme d’une crise environnementale qui peut être à l’origine de conditions ou de paysages similaires à ceux d’un désert (Encyclopaedia of Environ. Sciences, 1999).

La sécheresse et la désertification ont des effets sur tous les aspects de la vie, ce qui montre bien à quel point l’environnement et les moyens de subsistance sont interdépendants.

Les risques afférents à la sécheresse et à la désertification sont les suivants :

Les risques pour l’environnement

La sécheresse et la désertification font parfois peser des risques irréversibles sur la biodiversité en termes d’appauvrissement de la biodiversité, des sols et de la végétation. Ils entraînent une modification de la composition floristique, une réduction de la biomasse qui recouvre le sol et une diminution des capacités de croissance et de reproduction de la végétation.

Les conséquences les plus inquiétantes en matière de biodiversité concernent :

  • les animaux sauvages et domestiques, dont les conditions de gestion se détériorent ;
  • la flore, dont certaines espèces sont menacées ;
  • certains cours d’eau, dont le débit autrefois constant devient intermittent, qui perturbent le biotope de beaucoup d’espèces ;
  • des oiseaux migrateurs qui font partie du patrimoine mondial occupent des habitats de plus en plus précaires du Sahel, dans les zones humides résiduelles.

Les risques en termes d’appauvrissement des sols, pour la végétation et la forêt

  • Une dégradation liée à une surexploitation des sols jusqu’à l’épuisement, la surexploitation et la mauvaise utilisation des sols dans les régions arides, dues au changement climatique au niveau mondial ;
  • une dégradation liée au surpâturage, qui détruit la couverture végétale qui protège les sols de l’érosion ;
Figure 2 – Combination effect of drought and overgrazing in the steppe zones
  • un appauvrissement des sols découlant de pratiques préjudiciables en matière d’irrigation,  et impliquant une augmentation de la salinité et un assèchement des cours d’eau qui alimentent les grands lacs ;
  • une déforestation qui élimine les arbres qui protègent le sol de l’érosion hydrique et éolienne. De plus, dans de nombreuses régions arides, le bois est la seule source indépendante d’énergie (éclairage, cuisine).

Dans des conditions de sécheresse extrême, les invasions de sauterelles ont des conséquences catastrophiques sur l’environnement et l’économie des pays fragiles.

Les risques pour l’économie

La sécheresse et la désertification ont des conséquences directes sur la diminution et les pertes de récoltes et, du fait de l’augmentation des prix des produits agricoles qui en découle, les populations (notamment rurales) ont des difficultés à satisfaire leur demande d’eau potable et de denrées pour nourrir leurs familles et leurs troupeaux.

Des études ont montré que les récoltes de riz chutent de 10 % dès que la température nocturne augmente d’un degré Celsius. Or, la diminution des récoltes de riz a de graves conséquences dans les pays producteurs.

Les risques en termes de pauvreté et de migrations massives

L’appauvrissement des sols est synonyme de famine et de pauvreté. Pour trouver d’autres moyens de subsistance, les populations qui vivent dans des zones menacées par la désertification sont contraintes de se déplacer. Généralement, elles émigrent vers les zones urbaines pour y bénéficier de meilleures conditions de subsistance, ou quittent leur pays. Les mouvements de population sont l’une des principales conséquences de la désertification. http://remi.revues.org/document1654.html.
Entre 1997 et 2020, quelque 60 millions de personnes auront quitté les zones désertiques subsahariennes de l’Afrique pour gagner le Maghreb et l’Europe, selon la Convention des Nations Unies sur la lutte contre la désertification.

Les risques pour la santé

La sécheresse et la désertification (qui sont des conséquences du changement climatique) perturbent les écosystèmes et favorisent la propagation de certains insectes et maladies qui présentent un danger pour les humains, les plantes et les animaux. Selon les résultats d’études menées, des températures moyennes plus élevées sont susceptibles d’accroître les taux de fertilité et de croissance des insectes ravageurs ainsi que la fréquence des épidémies, et de permettre par ailleurs aux insectes et aux maladies de se propager sur d’autres espaces géographiques.

  • La santé des êtres humains

La sécheresse et la désertification (qui sont des conséquences du changement climatique) s’accompagnent généralement d’une dégradation qualitative et quantitative des ressources en eau et, bien souvent, du développement des épidémies (choléra, malaria, etc.).

Les vents, quand ils soulèvent des tempêtes de sable, sont aussi les vecteurs d’atteintes ophtalmologiques (conjonctivite) et de problèmes respiratoires.

Par ailleurs, alors que les mouvements migratoires dépeuplent les zones rurales, les villes se trouvent confrontées à des situations sanitaires désastreuses du fait du manque d’infrastructures pour le traitement des eaux usées et des effluents et pour la gestion des déchets. Dans ces conditions, les services médicaux et de prévention s’avèrent largement insuffisants.

  • La santé des animaux et des végétaux

La sécheresse et la désertification (qui sont des conséquences du changement climatique) déciment les troupeaux privés de pâture. Par exemple, dans les pays du Sahel (durant les chaudes journées d’été), il arrive que les vaches meurent lorsqu’elles mettent bas et, souvent, les veaux sont prématurés. Les chirurgiens vétérinaires de ces régions expliquent l’apparition de nouvelles maladies par les changements climatiques.

La modification du régime des vents est susceptible de changer la répartition des insectes, mais aussi des bactéries et des champignons qui sont des vecteurs de maladies pour les plantes. La hausse des températures hivernales favorise la multiplication des pyrales qui perforent les tiges du riz, par exemple. Des études révèlent que le nombre de parasites et d’insectes, comme les guêpes et les mouches, qui pondent leurs œufs sur/à l’intérieur des chenilles diminue en cas de pluies irrégulières. Or, ces parasites sont très utiles dans la lutte biologique contre les ravageurs de beaucoup de cultures tropicales.

L’Organisation mondiale de la santé a établi un lien clair entre les fortes pluies qui ont affecté la majeure partie de l’Afrique de l’Est au début 2008 et la recrudescence de la malaria. La dengue par exemple, une maladie grave provoquée par un virus transmis par les moustiques, a atteint des niveaux de contagion catastrophiques dans les Caraïbes.

On observe l’apparition du mildiou dans certaines régions où l’on cultive la pomme de terre, une maladie qui tend à se répandre dans des conditions humides plus chaudes.

Les risques pour la sécurité alimentaire

La sécheresse et la désertification (qui sont des conséquences du changement climatique) sont indubitablement des menaces pour la sécurité alimentaire des 9 milliards d’individus que la terre devra nourrir au milieu du 21e siècle. Il faudrait pour cela tripler la capacité de production alimentaire d’ici 2050. Néanmoins, paradoxalement, les surfaces arables diminuent. Il est prévu que les pays développés verront leurs surfaces arables passer de 0,65 à 0,4 ha par personne entre 1990 et 2010.

Les risques liés au changement climatique (puits de carbone)

La sécheresse et la désertification conduisent à un appauvrissement du sol. Par conséquent, elles réduisent l’aptitude du sol à faire office de « puit de carbone » et, inversement, augmentent sa capacité à être une « source de carbone ».

Le sol et les écosystèmes terrestres jouent un rôle fondamental en tant que puits de carbone : ils collectent et stockent le carbone. Il a ainsi été estimé que les sols retiennent 2,3 Gt (gigatonnes) de carbone par an, ce qui représente plus d’un tiers du carbone émis par la combustion des combustibles fossiles qui sont à l’origine du changement climatique. Le stock total de carbone contenu dans les écosystèmes terrestres avoisine les 2 500 Gt, dont 2 000 Gt se trouvent dans le sol.

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.

Ceux qui affectent les sols :

  • réduction de l’humidité des sols ;
  • diminution de la présence de matières organiques dans les sols ;
  • diminution de la fertilité des sols ;
  • formation d’une croûte / compactage des sols ;
  • apparition / croissance de la fréquence / intensité des vents de poussière / de la formation et des mouvements des dunes ;
  • réduction de la quantité et de la qualité des eaux de surface et/ou souterraines ;
  • incidences sur l’agriculture pluviale qui occupe une surface importante dans certains pays de l’Afrique (Sahel et Maghreb) ;
  • incidences sur l’agriculture ; les restrictions en eau peuvent avoir des effets sur l’irrigation des cultures, l’utilisation domestique de l’eau, notamment l’arrosage des jardins ou l’hygiène industrielle, le tourisme, etc. ;
  • augmentation du nombre de sources et de petits cours d’eau qui s’assèchent ;
  • détérioration de la réflexion relative de l’énergie solaire par les sols (modification de l’albédo).

Ceux qui affectent la biodiversité :

  • réduction de la couverture végétale ;
  • diminution la biomasse aérienne ;
  • diminution de la production ;
  • modification de la répartition et de la fréquence des espèces clés ;
  • dégradation de la reproduction des espèces clés ;
  • augmentation de la fréquence et de l’ampleur des incendies (disparition de forêts et d’espèces animales).

Ceux qui affectent les animaux (élevage) :

  • modification de la répartition et de la fréquence des espèces clés ;
  • modification de la composition des troupeaux ;
  • déclin de la production bovine.

Ceux qui affectent les aspects socioéconomiques :

  • changement des modes d’utilisation des sols et de l’eau ;
  • changement des modes d’occupation des territoires (par exemple, abandon des villages) ;
  • modification de la population (démographie, migration, santé publique) ;
  • baisse/pertes de récolte : les populations, notamment rurales, ont des difficultés à satisfaire leurs besoins et ceux de leurs troupeaux compte tenu de l’augmentation du prix des produits agricoles sous l’effet de la sécheresse ;
  • apparition de maladies ;
  • exacerbation du phénomène de pauvreté et de dépeuplement rural, voire migration des populations ;
  • intensification des conflits entre groupes et tribus, marginalisation, changements liés à une dépendance accrue à l’argent, etc. ;
  • apparition de sauterelles, avec les dommages qu’elles causent à la population rurale voire à tout le pays.

Above all, we have to distinguish between drought and aridity. Indeed, the last one, is a constant climatic phenomenon to which the human was adapted. Nevertheless, the drought is a brutal and irregular reduction of water (Dauphiné, 2003).

Indeed, arid regions populations had developed, by the time, indigenous knowledge allowing them boosting spaces in desert environment (oasis).
The drought, starts like a climatic event in its initial phase, extends gradually to all the fields where water forwards. Thus, it is fundamental to distinguish various types of drought:

  • Meteorological (lack of precipitations),
  • Agricultural ( when the conditions are not able to support agriculture and breeding),
  • Hydrological (lack of water in brooks and aquifers),
  • Socio-Economic (when the insufficiency of water starts to affect people and their lives),
  • The forest drought (refers to the situations where the moisture of the soil and the water reserves become insufficient to satisfy the needs for the trees, the herbaceous plants and forest fauna).
Figure 5: Arid Oued in semi- Arid Region (Algeria)

La sécheresse et la désertification se produisent à cause de :

  •  la prédisposition climatique de certaines régions arides et semi-arides dans le monde ;
  •  l’importance des populations vivant dans ces régions et qui ont de plus en plus de besoins ;
  •  l’économie de ces régions, fondée sur l’activité agricole, dépend des ressources en eau et en sols.

Ce qui provoque une pression de plus en plus forte et par conséquent une accélération du processus de dégradation de l’environnement, dont la désertification :

  •  migration et exode, avec des conséquences conflictuelles sur les plans politiques et socio-économiques.

Les incidences de cette migration sur les ressources naturelles sont doubles : sur les zones de départ et sur les zones d’accueil.

Dans les zones de départ
Les zones quittées par les populations sont laissées dans un état de dégradation, d’improductivité et de fragilité à l’érosion éolienne causé par la surexploitation. De plus, la précarité des techniques de travail du sol, de fertilisation et d’irrigation ne permet pas de produire un surplus qui pourrait être réinvesti dans leur amélioration. De fait, le départ des hommes laisse les femmes des zones rurales dans une situation compliquée dans laquelle elles vont devoir assumer un nouveau rôle auquel elles n’ont pas été préparées.

Dans les zones d’accueil
Dans la pratique, les migrants optent en majorité pour des systèmes de production intensive. Ainsi, ils contribuent à la réduction du temps de jachère, ce qui freine la régénération de la capacité productive des champs. On observe de ce fait une augmentation des troupeaux dans une seule région. L’introduction par les migrants d’autres cultures, par exemple celle du coton au Mali, tend à accélérer le rythme de la déforestation des zones concernées. D’autres migrants pratiquent un braconnage intensif, responsable de déséquilibres, dans les réserves protégées.

Au final, la pauvreté engendre la désertification qui, à son tour, engendre davantage de pauvreté.

Du fait de la pression économique mondiale, les populations pratiquent une surexploitation des sols et, généralement, les populations les plus démunies sont les plus affectées.

Dans les régions méditerranéennes, les zones les plus concernées se répartissent entre :

  • les zones hyper arides, où les précipitations sont inférieures à 100 mm ;
  • les zones arides, où les précipitations sont comprises entre 100 mm et 350 mm;
  • les zones semi-arides, où les précipitations sont comprises entre 350 et 600 mm;
  • les zones subhumides, où les précipitations sont comprises entre 600 et 800 mm ; ces zones sont particulièrement affectées par la sécheresse, et notamment environ 5,1 milliards ha (51 millions de km2), ce qui équivaut à la surface de France x 100.

Le continent plus particulièrement touché par la désertification et la sécheresse est l’Afrique, presque 60 % de ses sols étant soit désertiques, soit arides. Déjà, un certain nombre de grandes famines ont touché la région du Sahel et déclenché des migrations de population vers des terres plus hospitalières. 10 millions de personnes victimes de la famine dans l’Afrique subsaharienne devraient venir grossir les flux migratoires en direction de l’Afrique du Nord et de l’Europe.

Selon l’Unesco et l’UNCCD, plus de 110 pays possèdent des terres arides, potentiellement en danger de désertification. Ces terres sèches (arides, semi-arides et subhumides), si elles sont réparties dans toute l’Afrique, couvrent aussi de grandes zones d’Asie, d’Amérique latine, d’Australie et des États-Unis.

L’Afrique (le vieux continent oublié)

Les deux tiers du continent africain sont constitués de déserts ou de terres arides. L’Afrique possède le plus vaste territoire de terres arables arides, dont près de trois quarts souffrent déjà de dégradation, à divers degrés. En Afrique, les sécheresses sont à la fois graves et fréquentes. Pour assurer leur subsistance, beaucoup de pays africains sont contraints de puiser abondamment dans leurs ressources naturelles. La désertification du continent a de graves conséquences en termes de pauvreté et de sécurité alimentaire.

  • Niger
In this country, where climate conditions, explosive growth of the population, for lack of arable lands (insufficient to ensure a harvest or breed cattle), help increasing the vulnerability of this country towards food insecurity, more than three million people were jeopardized by the famine in 2005.
Much of them are confronted with forced exiles towards more fertile zones, in the South, towards the Benign and in the North towards Algeria and Libya and even Europe through fortune boats. This means not improbable that an important exodus of immigrant populations, like the natives of Niger or Burkinabe, is directed towards the Beninese territory where the conditions of life are less difficult. This will without any doubt cause tensions between migrants and autochthones. More over, This process is already locally started (Pierre OZER, 2005).
  • The region of the Sahel
West Africa undergoes a drought without precedent. This persistent drought resulted in an increased desertification of the region: impoverishment of the soil in the surface and depth of the Chad Lake, modification of the flow of certain watercourses and the level of the groundwater. This desertification has dramatic consequences for the 44 million inhabitants of the Sahel: reduction in drinkable water resources, lower agricultural outputs, losses of livestock and famines (in particular for the periods 1968-1973 and 1980-1984). The drought of the Sahel is the one which sensitized the international opinion with 600000 deaths between 1972 and so much between 1984-1985 (Matari, 2007).
  • Countries of the Maghreb
The Maghreb, with a lesser intensity, was not saved from this risk. Indeed, multiannual droughts continued during these last decades and had an indisputable impact on the steppe ecosystems, in this particular case, the most vulnerable ecosystems to the desertification but also in particular on cereal and fodder agricultural productions.
  • Asia
Asia presents 1.7 billion hectares of arid lands, semi-arid lands and arid sub-wetlands located between the Mediterranean coast and the Pacific shores. The degraded areas include deserts expanding in China, in India, in Iran, in Mongolia and in Pakistan, sand encroachment in Syria, mountainous slopes deeply eroded in Nepal, and medium mountains deforested and overgrazing in Popular Democratic Republic of Laos. In terms of many people affected by desertification and drought, Asia is the most seriously affected continent.
In terms of number of persons affected by the desertification and the droughts, Asia is the most seriously affected continent.
  • Latin America and the Caribbean
Deserts and arid lands cover approximately a quarter of Latin America and the Caribbean, rather known regions for their ombrophil forests. Poverty and pressures exerted on the available lands resources cause degradation of the grounds in these arid areas.
  • Europe

At the moment, 17 % of the European population is affected by the problem of water lack. However, in the absence of new measures, the situation of  » severe hydric stress  » could increase more.

The drought is pertaining to the natural conditions, such as the pluviometric deficit. During the last thirty years, these episodes considerably increased in number and in intensity in the Union. The cost of the damages caused in the European economy during this period was estimated at an amount included between 85 and 100 billions €.

In 2003, one of the greatest droughts affected more than 100 million persons and near a third of the territory of the EU, involving a damage evaluated to 8,7 billions €. As a rough guide, in the U.E. 1303: knew the most important aridity of the millennium: the Rhine could be crossed on foot.
The droughts of the years: 1540, 1719, 1874, on 1906, 1911, 1912, on 1921, 1945, 1947, on 1949, 1953, 1957, on 1964 are very revealing of the continent vulnerability.

For recent period, the droughts of 1976, 1988 1989, 1990, 1991, on 1992 and 2003 had important impacts on the ecosystems and the cultures
Europe, as well as on the health (abnormally high death rate linked to the scorching heat, the number of deaths being from 15000 deaths to France (vulnerable persons)).

Also, Spain is confronted with a water shortage stressed by the drought (MARGAT, on 1990).
Besides, forest fires know an outbreak in particular in the Mediterranean Basin. Portugal was a victim since 2001: 800 000ha missing persons. It’s the same for Greece, Spain and the South of France.

 

La sécheresse et la désertification ont des effets sur tous les aspects de la vie, ce qui montre bien à quel point l’environnement et les moyens de subsistance sont interdépendants. Les conséquences sont de divers ordres :

  • Les conséquences sur le plan humain

La désertification et la sécheresse exacerbent la pauvreté et, ce faisant, l’instabilité politique. Elles contribuent de manière importante à la rareté de l’eau, induisant des déplacements internes de population, des migrations et des ruptures sociales. Elles peuvent être une cause majeure d’instabilité sociale, de tensions, voire de conflits armés entre pays voisins. Il apparaît de plus en plus clairement qu’il existe souvent une relation étroite entre les troubles et les conflits sociaux, d’une part, et les problèmes environnementaux comme la désertification, d’autre part.

Plus de 500 000 Subsahariens sont actuellement massés sur les côtes de la Mauritanie dans l’espoir d’atteindre les Iles Canaries ; et ce n’est que le début parce que, selon les Nations Unies, presque 60 millions de personnes quitteront la région subsaharienne et les régions affectées par la désertification pour rejoindre l’Afrique du Nord et l’Europe d’ici 2020.

  • Les conséquences socioéconomiques

La dégradation des terres résultant de la sécheresse, de la désertification et des changements climatiques affecte une part importante des terres arables de la planète et a des conséquences directes sur le niveau de vie des populations et le développement économique des pays. Elle implique des pertes économiques pour les fermiers, elle perturbe les marchés alimentaires locaux et régionaux et elle est une source d’instabilité politique et sociale.

L’appauvrissement des sols dû aux effets de la sécheresse et de la désertification entraîne pauvreté et érosion socio-culturelle. Il y a un relâchement des structures traditionnelles et leur transformation sous les effets de l’économie de marché (BEDRANI, BESSAOUD, 2006).

Les premières évaluations effectuées sur les conséquences de la sécheresse en France, par exemple, avancent le chiffre d’un milliard d’euros de dommages pour l’agriculture et 1,6 milliards d’euros pour les dommages causés par les incendies. Il reste à évaluer l’impact de ces événements sur le patrimoine culturel et la nature (Communiqué de presse, première évaluation des conséquences de la sécheresse, rapport du Conseil des ministres français).

En Afrique du Nord, par exemple, le coût annuel de la désertification se situe entre 0,4 % et 1,36 % du PIB, pour respectivement le Maroc et l’Algérie. Dans les pays subsahariens, il se situe entre 1 % et 10 % du PIB agricole. Globalement, ces coûts sont sous-estimés dans la mesure où ils ne tiennent compte que des coûts directs de la désertification (uniquement les pertes agricoles).

Au niveau socio-économique, la désertification réduit considérablement les ressources économiques. Selon les nouvelles études de la Banque mondiale, la perte des ressources naturelles d’un pays du Sahel correspond à 20 % de son produit intérieur brut (PIB) annuel. On estime qu’à l’échelle mondiale, les déficits des zones immédiatement touchées par la désertification s’élèvent à 42 milliards de dollars par an environ. Les coûts économiques et les coûts sociaux indirects induits en dehors des zones touchées, y compris par la recrudescence des « réfugiés écologiques » et la baisse de la production alimentaire nationale, pourraient être beaucoup plus élevés.

  • Les conséquences sur l’environnement

Étant donné que les zones à la périphérie des déserts sont soumises à un processus de désertification de plus en plus fort, la végétation a disparu sur des centaines de millions d’hectares et de nouvelles terres (fines couches) ont été transportées par les vents. Ces couches fines réduites en poussières ont très fortement augmenté depuis les années 80.

Chaque année, le Sahara injecte près d’un milliard de tonnes de poussières dans l’atmosphère. Plus de 100 millions de tonnes de ces poussières prennent la direction de l’Europe. Elles constituent de véritables problèmes de santé publique dans le sud de l’Europe, comme en Espagne, car l’importante concentration de ces particules fines dégrade la qualité de l’air qui est respiré.

  • Le patrimoine culturel

Les communautés vivant dans les déserts ou aux environs vivent en parfaite harmonie avec la nature en maintenant des traditions et un savoir communs. Ces traditions sont mises en danger par les pressions économiques et une augmentation des problèmes environnementaux dus à la sécheresse, à la désertification et au changement climatique.

De toute évidence, si ces communautés sont obligées d’abandonner leur culture pour survivre ou d’adopter un nouveau mode de vie, un patrimoine mondial d’une valeur inestimable sera perdu.

Un bon exemple est celui de l’écosystème des oasis (ou agriculture des oasis), considéré comme faisant partie du patrimoine culturel dans tout le Maghreb : il doit faire face à de multiples problèmes environnementaux qui menacent sa subsistance.

La menace la plus importante est le sable (stade extrême de la désertification), qui menace les zones urbaines, les terres agricoles et les plantations de palmiers (près de 60 %) ainsi que les canaux d’irrigation (30 km) et les routes (10 km).

Figure 6 – Sand dune of village at Sahara

Consequences on health (Human, animal and vegetal)

Drought and desertification (climate changes impacts) disturb the ecosystem and support the propagation of certain harmful insects and diseases of humans, plants and animals. According to the research results, higher average temperatures will increase the fertility rate and of growth of the devastating insects and the frequency of epidemics, and will allow insects, diseases and adventitious to gain new geographical surfaces.

Human health

Drought and desertification (climate changes impacts) are generally accompanied by a qualitative and quantitative degradation of water resources, and often of the development of epidemics (cholera, malaria etc).

Winds are also, at the time of the sandstorms, vector of ophthalmologic diseases (conjunctivitis).
In addition, as migratory movements empty rural areas, cities fill under often disastrous sanitary arrangements, for lack of infrastructures of cleansing of waste water, of liquid waste processing, management of waste; in these cases the prevention and the medical departments will be largely insufficient.

Drought and desertification (climate changes impacts) disturb the ecosystem and support the propagation of certain harmful insects and diseases of humans, plants and animals. According to the research results, higher average temperatures will increase the fertility rate and of growth of the devastating insects and the frequency of epidemics, and will allow insects, diseases and adventitious to gain new geographical surfaces…

Animal and vegetable health

Drought and desertification (climate changes impacts) cause the decimation of herds for lack of grass. New diseases appear. For example, in countries of the Sahel (for periods of hot summer days), cows generally die at the time when they put low, often calves are premature. The veterinary surgeons as of these areas bound these new diseases to climate change.

The modification of the mode of winds is likely to change the diffusion of insects as well as bacteria and mushrooms vectors of plants diseases. The rise in the winter temperatures will support the multiplication of bee moths drilling machines in the rice systems for example.
Studies reveal that the number of parasitoids – insects such as wasps and flies which lay their eggs on /or inside the caterpillars – falls in the event of irregular rains. However, these parasitoids are very useful in the biological fight against ravagers of many tropical cultures.

The World Health Organization established a clear bond between the strong rains which have affected the major part of the East Africa at the beginning of 2008 and the recrudescence of malaria. Dengue for example, grave disease caused by a virus transmitted by the mosquitoes, reached catastrophic epidemic levels in the Caribbean.
Appearance of mildew in certain areas of potato growing, a disease which is spread under the hotter and wet conditions.

Consequences on soil and biodiversity:

On soil

  • Reduction of soils thickness;
  • Reduction in the organic matter of soils;
  • Reduction in the fertility of the soils;
  • Formation of a crust/soils compaction;
  • Appearance/growth of the frequency/intensity of winds of dust/formation and movements of dunes;
  • Saltiness/alkalization;
  • Reduction in quantity and quality of surface and/or underground water ;
  • Effects on the pluvial agriculture which occupies an important surface of countries for example Africa (the Sahel and the Maghreb);
  • Irrigated agriculture is also affected; water restrictions can be pertaining to irrigation of crops, the domestic uses of water, such as gardens watering or industrial sampling, tourist etc;
  • Increase in the sources arid up and the small watercourses;

Deterioration of the relative reflectance of grounds (change of the albedo).

Figure -7-: Map of the geography of water dominant problems in the world (MARGAT, 1990)

On biodiversity

  • Reduction in the cover;
  • Decrease of air biomass;
  • Decrease of production;
  • Modification of distribution and frequency of key species;
  • Deterioration of the reproduction of key species.
  • Firewood is more current and more important (loss of forest and animal species);

On animal (breeding)

  • Modification of distribution and frequency of key species.
  • Change of composition of herds.
  • Decline of the production of cattle.
  • the productivity of the cattle.

Global consequences on the human stabilization

Drought and desertification are unquestionable threats for the food security of the 9 billion individuals who will have to be nourished in the middle of the 21st century. Their healthy food would be likely to triple production capacities food from here 2050. Nevertheless, paradoxically, arable surfaces decline. It is provided that the developed countries will have seen passing their arable surfaces from 0.65 to 0.4 hectares through anybody between 1990 and 2010.

Then, desertification and drought exacerbate poverty and thus political instability. It contributes in an important way to the scarcity of water, with interior displacements of populations, the migrations and social ruptures. That can be a major cause of social instability, tensions between bordering countries, even of armed conflicts. It appears more and more clearly that there is often a close relationship between disorders and social conflicts, on the one hand, and environmental problems, like desertification, on the other hand.

Socio-economic consequences

The impact is essentially on:

  • The agricultural systems (falls of returns, the quality is affected…)
  • Declines of agricultural income: this situation is more marked at the level of countries on agricultural economic base.

The lands degradation of consequence of drought, desertification and change of climate, affects a significant share of arable lands of the planet and has a direct impact on the standard of living of populations and the economic development of countries. It involves economic losses for farmers, it disturbs the local and regional food markets and it is source of a social and political instability.

The soil impoverishment by the effect of drought and desertification is carrying poverty and socio-cultural erosion. It is a relaxation of traditional structures and their transformation under effects of the market economy (BEDRANI, BESSAOUD, 2006).

The first assessments carried out on consequences of drought in France for example, advance the figure of a billion Euros of damage for agriculture and 1.6 billion Euros for the damage caused by fires. It still remains to evaluate the impact of these events on cultural heritage and naturalness.
(Press release, first assessment of drought consequences, reported by the French Council of Ministers).

In North Africa, for instance the annual costs of desertification included are between 1.36% from the PIB (Algeria) and 0.4% (Morocco). In the sub-Saharan countries, they range between 1 and 10 % of the agricultural PIB. These costs are under-estimated altogether. They take into account, indeed, only the direct costs of desertification (only agricultural losses).

On the socio-economic level, desertification reduces economic resources considerably. According to a new research of the World Bank, the loss of natural resources of a country of the Sahel corresponds to 20% of its annual (PIB) gross domestic product. It is estimated that on a worldwide scale, the shortfall of zones immediately affected by desertification amounts to 42 billion dollars per annum approximately. Economic costs and social indirect undergone apart from the Affected areas, including the surge of “ecological refugees” and the national food production loss, could be definitely higher.

The infringement of the systems of production leads to an indisputable poverty, where from a threat of famine. To escape it, men, women and children make appeal to the exodus towards lands more favorable to the life.

The case most illustrating is of that of the migrants en masse from the desert regions of Sahel towards Spain.

It is worth noting that the FAO plans before 2020, a migratory flow about 60 million persons of the desert regions of sub-Saharan Africa towards North Africa and Europe with all that it leads to socioeconomic pressure and thus, political on the territories of reception.

Since zones died desert are subject to the processes more and more accelerated by desertification, the vegetation disappeared on hundreds of million hectares, of new grounds (fine cover) were taken by the wind. By the effect of the wind erosion more and more increased in the weather.
More than 100 million tons of these dusts take the path of Europe in the indisputable consequences both for the health and the environment generally.
Perpetually for a better living environment in development of indigenous knowledge.

Drought and desertification cause sometimes irreversible risks on biodiversity, on the soil and vegetation impoverishment. They involve a modification of floristic composition, a reduction in the covering of the produced biomass and capacities of growth and reproduction of vegetation.

The most alarming consequences with respect to biodiversity appear on:

  • The wildlife and domestic fauna, whose management conditions are bad;
  • Flora, where certain species are jeopardized;
  • Certain waterways, formerly permanent and which became intermittent and upsetting biotopes of many species;
  • Migratory birds which constitute a world heritage and which find in the Sahel of the increasingly precarious habitats in residual wetlands.
  • Degradation pertaining to an overexploitation of grounds until exhaustion, the overexploitation and the bad use of grounds in arid regions caused a change of climate at the global level which is accelerated by climate changes.
  • Degradation pertaining to the overgrazing destroying the vegetable cover which protects grounds against erosion

 

Figure-8– Combination effect of drought and overgrazing in the steppe zones

The soil impoverishment pertaining to the bad practices as regards irrigation involve an increase in salinity, and drain sometimes the waterways that feed the big lakes.

  • The deforestation destroys trees which protect the ground against hydrous and wind erosion. Wood is the domestic independent source of energy (lighting, cooking) in many rural areas.

Risks of grasshoppers invasions in the catastrophic consequences on environment and agricultural economics.

Where a risk can activate another one.

The communities which live in deserts or in neighborhoods live in perfect harmony with nature and maintain traditions and single knowledge, these receipts are jeopardized by economic pressures and increasing environmental problems due to drought, desertification and climate change.

Though, it is obvious, that if men are obliged to give up their culture to survive or adopt a new mode of life, a world patrimony of a priceless value will be lost.
The alive example is the one of the oasis ecosystem where the oasis agriculture which is considered as a cultural heritage in Algeria, even in all the Maghreb knows environmental requirements linked mainly to the blocking with sand which compromises in the long term the durability of these ecological entities of human but ingenious conception (ancestral knowledge in: water management, the ground, the local bio-resources and the built).

In these areas, the most important threat is the silting up (extreme stage of the desertification). He threatens, the towns, Ksours, farmlands, palm groves, roads….

Figure 9: Sand dune of a village in Sahara

So, we attend a threat of preservation of the natural, historical and cultural sites such as: ksour, of a big patrimonial wealth, is also threatened by the blocking with sand, Saoura, Gourara, Touat and Tidikelt in the southwest of Algeria. Ksar de Taghit is considered as a famous historic and tourist site of rupestral engravings).

Their conception allows to emphasize indigenous knowledge, exploited could establish an experience to ease and better manage the impacts of the global warming.

Recapitulation on the process drought / desertification and climate changes:

Having reviewed, all the triggering factors and partial consequences which ensue from it we cannot omit to make the synthesis of the various interactions amplifying the impacts of the risks object of the BE SAFE NET, through the plan illustrating the enchainment and the interdependence of the risks in the deeply moving consequences of the systems of production and socioeconomic organization. As an example, the droughts which raged in 1972/73 in Sahel forced the breeders to settle and the farmers to reduce their food-producing plots of land. The consequences were heavy and amounted to 200 000 deaths for only year of 1973.

Le comportement humain peut en effet influer sur les conséquences de la sécheresse et de la désertification (conséquence du changement climatique) par diverses mesures de nature scientifique, technique, sociale et politique.

Mesures scientifiques et techniques :

  • accroissement des ressources en eau, en particulier grâce à une meilleure gestion des stocks (techniques d’irrigation qui évitent le gaspillage et la salinité des sols) ;
  • plantation de végétation (arbres, barrages verts);
  • stabilisation des dunes par une végétation adaptée et d’autres moyens respectueux de l’environnement;
  • maîtrise de l’irrigation, drainage;
  • identification et développement de cultures adaptées au stress hydrique et salin;
  • mise en place de réseaux d’observation des écosystèmes vulnérables et des périmètres irrigués : développement de systèmes d’alerte précoce;
  • augmentation de la capacité des sols à retenir l’eau pour permettre le développement de l’agriculture (amendement organique).
Figure 10: Green Dam (isohyètes 300 / 200mm / Algeria)
Figure 11: refforestation in semi-arid region

Mesures sociales :

  • mise à profit du « savoir indigène » des communautés locales (par exemple, gestion des oasis du Sahara) ;
  • éducation des populations pour favoriser chez ces dernières une prise de conscience et un changement des attitudes et des comportements ;
  • formation technique des populations;
  • aide alimentaire, offre de ressources de substitution (par exemple, gaz au lieu du bois).

Mesures politiques :

  • adoption de mesures législatives, par exemple lois de protection;
  • développement de politiques et stratégies nationales d’intervention (lutte contre l’érosion, production de biomasse et reforestation, contrôle et valorisation des ressources en eau, réorganisation des activités pastorales, modernisation de la production, diversification et développement de nouvelles activités);
  • développement de programmes internationaux, en particulier pour la surveillance de la désertification et le partage d’expériences et de bonnes pratiques.

Despite human awareness of these risks, the means made available to halt, manage or limit desertification have so far not been proportional to the scale of these risks. Whilst the notion of sustainable development has only recently emerged as a profitable model, there are other models of development that have long been adopted by traditional societies and which were always sustainable: consider the example of oases discussed above.

It is clear that the extent of people’s willingness to adapt their practices influences the causes of drought and desertification. Good practices include the conservation of biodiversity; the protection of land which is already arid; appropriate use of land likely to maintain high levels of fertility so as to spare more fragile areas; rational and economic usage of surface and subterranean water supplies; mastery of better irrigation and drainage systems.

Steps can also be taken to protect forests from fires and deforestation and to protect pasture zones. This can have a positive influence on the regeneration of the undergrowth and can protect these zones from wind erosion (winds storms and dune movements) and hydric erosion (loss of fertile ground cover).

In steppe regions, the conservation of pasture lands against over-grazing or any kind of degradation is one of the key actions taken by the populations which live there. This action must also be respected at policy level and by governments and administrations.

There are, on the one hand, traditional methods of predicting risks pertaining to drought or desertification (indigenous knowledge and local experience, e.g. of sandstorms) and, on the other hand, those based on scientific research (measurements and modelling).

Some research has included data modelling of the atmosphere, while other research has studied cycles of drought, or tried to identify which physical factors can be used to make predictions (starting from solar activity or anomalies in the surface temperature of oceans and comparing them with past climatic cycles). 

In order to do so, it is first of all necessary to collect measurements and data on precipitation, the flow of waterways, and water levels, in various climatological and hydrometric stations in all countries prone to these risks. With the help of these data, it is possible to carry out statistical analyses to determine the average conditions over a long period of time, to identify the possible beginning of a drought and the seriousness of a drought that has already set in. Mechanisms to reduce the harshness of the drought can then be put in place. 
Besides the physical indicators, there are also mechanisms which take measurements using bioindicators. 

The difficulty lies in predicting the onset date, the duration and the intensity of the periods of drought or desertification. Desertification is closely related to drought and in fact the onset of one often provokes the other.

It is easier to prevent the factors leading to drought and desertification than it is to treat the symptoms. Early warning systems which can forecast drought and sandstorms (causes of desertification) make it possible to implement plans in preparation for these in a timely manner. In the case of drought, there are several strategies or measures that could be implemented on farms, notably concerning replacement crops, soil and water protection systems and water recovery techniques. These measures could increase the resistance of soils to drought and would allow production to meet the levels needed; they would lead to a reduction in the number of ecological refugees and cases of drought would no longer be such an emergency. With regard to sandstorms (a cause of desertification), devices and means of protection could be placed at the public’s disposal (e.g. telephones or refuges) in order to help them protect themselves from the dangers of sandstorms.

Intervention devices for redirecting assistance are also necessary in preparation for periods of great shortage or even famine.

To surmount the risks linked to drought and desertification, good management of potential crises would include assigning to the most competent department the task of establishing an inter-sectoral unit to manage risks.

NB: when locating intervention units during storms or the very hot season, the parameter outstrip must be taken into account to allow for the greatest efficiency during emergency operations.

The best way of minimising the risk of drought and desertification is to refer to the traditional or indigenous knowledge of the local populations in arid regions.

Traditional or indigenous knowledge

Local populations have a wealth of traditional knowledge about their environment and tend to use indigenous methods that are well adapted to local conditions. It is vital that such practices are applied, protected and improved at the national and regional levels. In many cases, they prove to be more sustainable than the short-term solutions, which only tackle drought and desertification (see Figure 12).

Figure 12: Oases in sand dune environment (Souf, Algeria)

Several arid regions offer good examples of how to live harmoniously with the environment. Nomadic lifestyles are particularly well adapted to the special conditions of arid lands; notably by moving from one water source to another and by never staying on the same land. These pastoral populations only have a small impact on the environment as long as their routes are chosen in a responsible manner.

In Algeria, the many policies aimed at fighting desertification have been diversified; since the 1970s, the authorities have undertaken actions such as the “Green Dam” (see Figure 13), the implementation of pastoral cooperatives, the enactment of a Pastoral Code, the introduction of land value stake programmes (DGF2, 2004), usage of surface water and the introduction of renewable energies.

Figure 13: Localization of the green dam in Algeria

Other actions can limit the consequences of the drought and desertification as for example:

  • Regeneration and fertilization of soils

To fertilize the soil, it is worth preparing compost, which will become humus and regenerate the soil with its organic matter.

  • Economy of water

Mitigation of drought passes by a better management of water, a good economy and a collective management of the resource (more sparing systems of irrigation).
In period of drought, it is necessary to treat on a hierarchical basis uses of water, to limit them, even to prohibit some of them to privilege others of them.

  • Fight the wind effects

This action is more effective by associating the mechanical fight with the biological fight by building barriers and by stabilizing the progress of sand dunes with local plants besides device mechanics. This way of operating takes into account experiences indigenous knowledge premises which proved their efficiency especially at the level of the blackheads of the main highways of Sahara.

 

Refforestation

Practice culturale adapted

Elaborate sustainable agricultural practices and Adapt cultural plans
Most of the experts agree to say that a combination of global and local strategies can make a lot to help the producers to hold out. The agriculture of preservation, which minimizes the work of the ground, can improve the use of the water, the detention of the carbon and the capacity, to support climatic stress. The producers will have to modify their farming calendar and the plants which they cultivate. For example, the sorghum can better suit than the corn in the drier conditions planned in certain zones of Africa. In South Africa, the farmers already take into account the new distribution of rains and delay the sowing of corn.
Other option, it is worth thinking of using agricultural practices as the direct sowing, which consists in sowing directly in the ground of the seeds of perennials supporting the drought.

Livestock (breeding)

  • The use of improved local breeds are better suited to the climate and its variations that imported breeds. Example: During a recent drought, farmers in Uganda who had kept their Ankole cattle were able to drive to distant water, while those who were replaced by imported breeds lost everything.
  • Where are scarce pastures and forage crops as possible, it is also advisable to keep animals in the lairage to reduce their pressure on the environment.
  • Efforts are underway to recover forage and other foods and make them more digestible for ruminants.
  • Similarly, we look forwards to improve the management of waste (manure and slurry) to reduce methane emissions, notably through more efficient conversion into biogas.
  • Combating desertification is also through a less intensive pasture practice (rotation term) which requires a good knowledge of livestock production and rangeland fodder balances (production / consomation).

In the event of drought or desertification, public authorities should implement primary measures to preserve key resources, notably water (awareness raising among the largest water consumers, informing citizens of the situation, initial restrictions on water usage). If the situation worsens, more restrictive measures can then be taken.

Awareness raising, education and training are steps that can be taken at the first sign of risks pertaining to drought and desertification. 
Awareness of risks and safeguarding of the environment can be developed through several concrete measures taken at the local level (city, district and region). There are several ways of disseminating information:

  • communication with citizens;
  • organisation of conferences, sharing of knowledge, projection of videos, literature, exhibitions, television and radio broadcasts, etc..

Education and preventative training on the subject of drought and desertification can, as a complement to the education provided by families, state education and other societal actors, help to build a true culture of understanding the risks of drought and desertification.
In these cases, the national education system has a role to play in better informing the public about the issue of desertification and drought, in particular by including ecological and environmental education in the curriculum of primary and secondary schools, notably covering the following aspects: knowing one’s environment; understanding the vulnerability of the environment; understanding existing interactions between humans and the environment and the risks that human activities can entail; learning good practices for emergency situations; raising awareness among children and pupils about the need to be pay attention to one’s own behaviour; and how to encourage appropriate, responsible, and interdependent behaviours in others.

What can encourage local and national representatives to implement citizen safety plans in cases of risk?

Through the development of a risk culture, a pilot educational experiment on the risks of climate change in arid regions has been conducted by the Centre for Scientific and Technical Research on Arid Regions CRSTRA in Biskra, Algeria, in collaboration with the Green Club of the local secondary school. The book developed as part of this project with contributions from the children involved has been translated into three languages with a direct link to the Be Safe Net website.
To inculcate attitudes in the population that can mitigate these threats, the competent services (agriculture, forestry, civil protection, public safety, etc.) provide climate information, which constitutes an important resource to combat the negative effects of drought and desertification. Limited access to information is a constant obstacle to ensuring that appropriate measures are taken and that citizens and decision-makers can adapt their behaviour accordingly.

Citizens from rural areas and the general public must be encouraged to follow the weather forecast on television or on the radio in order to better manage their activities (farming activities, travel plans, etc.).

It is necessary to enhance early warning systems for drought and desertification (for instance, the occurrence of sandstorms), with news announcements by the competent authorities in the countries concerned, so that appropriate measures can be taken where there is a risk of damage to roads or other infrastructure (schools, hospitals, etc.).

Capacity building

Drought, desertification and other impacts of climate change do not take account of national borders. There is therefore a need for joint answers to these problems at the regional level. Regional co-operation has an enormous potential in developing regional programmes for the common management of water resources and in fighting against the propagation of diseases caused by climate change and sandstorms. The efforts required to implement adaptation measures and minimise risks are so extensive that no country alone can carry the burden. Regional co-operation can also increase coherence. These threats (such as Acrididae) know no borders, and water table exploitation as well as technical installations and management in the case of cross-border rivers require supranational and regional approaches.

Human resources must be reinforced by developing networks which will allow the various institutions to share information on adaptation research, measures for combating drought and desertification and the findings of local and regional desertification observatories.

Agricultural support programmes must be put in place to allow grazing ground to lie fallow, and special aids must be foreseen for the transportation of animal feed. Programmes must also ensure the payment of national insurance contributions, the advance payment of agricultural and farming subsidies or the use of cereal reserves supplied by donors (European Union and others) to supplement animal feed. 

Other sectors suffer from a lack of water, such as tourism (the reduced flow of certain waterways restricts their use for leisure or sports activities) and energy (as nuclear power plants need water to function). This situation has, for example, pushed EDF to reduce the output of its nuclear power plants.

When the risk of drought is high, all citizens must show good environmental citizenship by adopting the attitudes and good practices summarised in the sections above on prevention and precaution, which recommend a series of actions in order to prevent the serious consequences of such disasters in future. This can be assisted by implementing monitoring measures, safeguarding ecosystems and the environment, and stepping up environmental education, information campaigns and impact studies.

It must be borne in mind that successfully managing the environmental impact of drought and desertification depends on all segments of society: the state, citizens, economic actors, teachers, researchers and so on. Everyone should take responsibility and must be involved at their own level.

Moreover, in order to be effective, environmental management must be carried out in partnership with all segments of society, namely government ministries, local government, professional bodies, international partners and citizens.

Finally, the state must play a role in defining rules and laws on the environment and in ensuring their enforcement, following up on their implementation, guaranteeing the preservation and promotion of the environment, and ensuring a long-term and sustainable overview of any changes in areas at risk.

International dimension of environmental questions

Beyond national borders, in an era of globalisation, the international dimension of environmental questions calls for action. The persistence and scope of drought, desertification and other effects of climate change are challenges for all countries and must bring them together on a global scale.

This is why countries affected by these disasters are resolutely committed to international co-operation and have ratified about thirty conventions relating to the environment. The most important are the United Nations Convention to Combat Desertification, the Convention on Biological Diversity, the Convention on Climate Change, the Convention on International Trade in Endangered Species of Wild Fauna and Flora, the Convention on Wetlands, the Montreal Protocol on Substances that Deplete the Ozone Layer and the Stockholm Convention on Persistent Organic Pollutants (see http://www.un.org/events/rio92/agenda21/action12.htm).

The effectiveness of these treaties depends on their application by all parties. Desertification is a complex phenomenon since it combines several biophysical and socioeconomic factors which interact over time.
Experience shows that human intervention can have positive or negative effects on drought and desertification via agricultural production methods, urban planning and the use of natural resources. In order to counter desertification, all of these interdependent factors must be taken into consideration through a strategy founded on scientific tools and research programmes aimed at tackling the problems encountered on the ground.

Knowledge of drought and desertification (impacts of climate change) has greatly increased over the last few years, as space-time synoptic images produced by various satellites since the 1990s have enabled specialists to draw up reports on the progression of drought and desertification, locating and delimiting the affected areas by producing a series of thematic maps. It is therefore essential to systematically collect data and make observations about natural resources and their uses so as to better understand the processes of soil impoverishment, drought and desertification and to evaluate their effects. These data are also necessary in order to quickly alert decision makers to the problem. This will help them to evaluate the benefits of local ecosystems in a realistic way and allow them to establish appropriate development and conservation policies. Creating risk awareness maps and updating them regularly can also increase investment in improved land planning and development and justify investments in sustainable means of subsistence.

Go to 12.1 More information on remote sensing applied to drought and desertification mapping

Go to 12.2 References

Remote sensing: a tool for monitoring.

Several researches were launched in this objective of monitoring, follow-up and cartography of drought, desertification and climatic changes impact in countries affected by these plagues.

Figure -15- Wind lane Map and the risk of silting in West region of Biskra CRSTRA (Algeria)

Example:

Research carried out in the Algerian steppe, the Tunisian South (Menzel Habib) in sub-Saharan countries (Niger) and on the desert fringe of the Nile clearly proved the feasibility of the follow-up of desertification by satellite. Time to confront resultants with the reality of the ground and necessity of the spacial imaging

Reports:

Indicators of the drought and desertification state (color and composition of soils, roughness, deposit rates of vegetation) and of its evolution, could be obtained since space by remote sensing. Maps can be elaborated from these indices whose crossings in a GIS give the state of environment to a T time.

Expander cards of mobile sands and the biomass degradation were established by remote sensing by image processing and of indices such as the vegetation index, color and brightness of surfaces recorded by images are calculated.

The remote sensing techniques, combined with a very good knowledge of soil, allow detecting the evolution of degradation of arid regions but also their restoration.

Considering these risks exceed the limits of countries even continents, programs such as the Cameleo program (). The IRD led, in collaboration with the Egeo unit of Institute of space applications of the Joint Research Center and with the support of the European Union, This research, which associates Algeria, Egypt, Morocco and Tunisia, and is based on the Roselt network; aim at defining a complete method of follow-up of desertification in the south of the Mediterranean.
It is in particular a question of obtaining, on field and by satellite remote sensing, data usable for management of the arid environment and similar from a country to another. This in order to identify, at a local scale, zones where soils and vegetation are degraded, are stable or to be improved, and to understand relations between these changes and their use by the man.

In Algeria, map of sensibility in the desertification was elaborated in 1995 by the FGD and the ALSA. It is perpetually actualisable.Therefor,the Center of Scientific and Technical Reasearch on Arid Regions (CRSTRA),elaborated vulnerability maps on desertification and silting through ecological entities.
Besides, the OSS, the HAD and the partners of the Magreb (ALGERIA TUNISIA MOROCCO) work at the implementation of the early alarm system through the Life SMAS project, this alert focuses on the production and the distribution of indicators of vulnerability of naturalresources, compared to the climatic and anthropological press to which they are subjected. The elaboration of indicators has to use all the available approaches, climatic satellital embellish with images, in the compilations of the meteorological, dated, the biophysics and socioeconomic. The indicators of premature alert of the drought will feed also information flow systems of the national and sub-regional action plans to combat desertification, established in accordance with principles of the Convention of the United Nations to Combat Desertification.

To evaluate the progression of these insidious phenomena (drought, desertification and climate changes impacts), the remote sensing helps collecting data on vast surfaces with regular intervals. By comparing data images between dates, it is probable to find out the evolution of drought and desertification.

Maps can be established such as the albedo (R0), the vegetation index (NDVI) and the temperature of surface Ts recorded thanks satellite measurements of sensor MODIS of TERRA or VEGETATION of SPOT or by sensors AVHRR of NOAA these satellites which provide images to weak space resolution and allow carrying out a regular follow-up at very weak cost of natural resources.

These images have a broad observation field (about entire country) and a daily temporal resolution, very useful for a regular follow-up, mainly the vegetation.

Furthermore, to make a note of the use of images with average resolution such as Land sat, (30m of resolution space) Alsat (32m), SPOT (20m) and images with high resolution such as IKONOS (1m) Quicbird (1m).

For characterization and cartography of the hydric state, the soil quality and state of degradation of a surface. One of the key ideas is the combination of these parameters resulting by image processing two to two (R0 – Ts; NDVI – Ts and R0 – NDVI).

The quoted images may be provided by manufacturers of these satellites as they may be ordered by representatives of these structures in several countries. Each image includes its price (see site SPOTIMAGE). Concerning the factorial maps, grounds, of the ground occupation, drought, desertification; May be that they are public and setting on line on Internet as it is the case of several countries, are requested from the manufacturer.

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