Drought and Desertification
Prepared by CRSTRA – The Centre for Scientific and Technical Research on Arid Regions, Biskra, Algeria & the Editorial Board.
Drought is the result of a deficiency in precipitation. It constitutes a major risk and can have a serious impact in a number of ways:
- climatic (e.g. an increase in temperature, sun or wind);
- hydrological (e.g. a decrease in surface overflow, the drying up of rivers, lakes and springs, groundwater drawdown);
- agronomical (e.g. drying out or loss of crops, including dry-land crops);
- geological (e.g. drying out of soil and an increase in salinity levels).
Roughly speaking, desertification can be considered as a severe case of drought (both in intensity and in duration) which leads to conditions generating landscapes similar to that of a desert. Desertification encompasses a wide range of effects which degrade the vegetation cover and soil, for example:
- raised vegetation cover (tropical forest) is degraded to savanna;
- savanna evolves to a steppe landscape;
- the climate becomes excessively dry.
In order for desertification to occur, two factors appear to be crucial:
- natural physical conditions which are susceptible to desertification;
- intensive human activity exceeding acceptable thresholds.
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;
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.
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.
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.
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.
Drought and desertification relating to soil:
- reduction in soil thickness;
- reduction in the organic matter of soil;
- reduction in the fertility of the soil;
- formation of a crust/compaction of soil;
- increase in the frequency/intensity of dust winds or in the formation and movements of dunes;
- reduction in the quantity and quality of surface and/or underground water;
- effects on rainfed agriculture which constitutes a large proportion of agriculture in some countries, for example in Africa (the Sahel and the Maghreb);
- irrigated agriculture is also affected: water restrictions can affect the irrigation of crops and domestic uses of water, such as watering gardens;
- increased drying up of sources and small watercourses;
- deterioration in ground reflectance (change in albedo).
Drought and desertification relating to biodiversity:
- reduction in plant cover;
- decrease in biogases;
- reduced levels of production;
- alterations to the distribution and prevalence of key species;
- deterioration in reproduction levels of key species.
- loss of forest and animal species (as the forest is increasingly used as a source of firewood).
Drought and desertification relating to animals (livestock):
- alterations to the distribution and prevalence of key species;
- change of composition of herds;
- decline in the reproduction of cattle.
Drought and desertification relating to socio-economic aspects:
- changes in the uses of soil and water;
- changes to the occupation patterns of a given territory (i.e. abandonment of villages);
- changes in the population (demography, migration, public health);
- loss of harvests and resulting difficulties (especially among rural populations) in satisfying the needs of both humans and livestock since prices of agricultural produce increase under the effects of drought;
- emergence of diseases;
- exacerbation of poverty, rural depopulation and mass migration;
- intensification of conflict between different groups or tribes, potential marginalisation, changes to dependence and wealth structures;
- appearance of locusts, which pose a threat for rural populations or across entire countries.
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).
Drought and desertification occur when:
- there is a climatic predisposition to drought, e.g. in certain arid and semi-arid areas worldwide;
- a high population density results in a greater need for resources;
- a region is dependent on agricultural activity for its economy, and is thus reliant on water and soil resources.
Desertification is accelerated by migratory movements and an exodus from rural areas, which has socioeconomic and political consequences and may aggravate tensions. This constant pressure in fact further degrades the environment.
The impact of this migration on natural resources is two-fold, affecting both the area of origin and the area of destination.
In the area of origin
People leave their area of origin because it has become degraded and unfruitful; these areas are often fragile, overexploited and prone to wind erosion. Moreover, the instability of techniques used to work the ground, poor levels of fertility, irrigation, etc. often do not allow for the generation of a surplus which could be reinvested to improve conditions. Indeed, the mass departure of men puts rural women in a difficult situation, as they must assume a new role for which they are often not prepared.
In the area of destination
The majority of immigrants arriving in destination areas practice intensive farming methods. Fallow periods are reduced, which in turn prevents fields from regenerating to full productive capacity. The arrival of migrants with other farming practices, such as the introduction of cotton production in Mali, has accelerated the pace of deforestation in this area. Other migrants practice intensive poaching in protected reserves, which leads to an imbalance of fauna in the locality.
Thus, poverty ultimately contributes to desertification which, in turn, generates more poverty.
In order to keep pace with global economic pressures, the ground in many regions has been overused and, generally, the most impoverished citizens are the worst affected.
In Mediterranean regions the worst affected zones can be subdivided as follows:
- hyper-arid zones where precipitation is less than 100 mm;
- arid zones where precipitation is between 100 mm and 350 mm;
- semi-arid zones where precipitation is between 350 and 600 mm;
- sub-humid zones, where precipitation is between 600 et 800 mm.
The zones particularly affected by drought represent approximately 5.1 billion ha (51 million km2), which is equivalent to 100 times the surface area of France.
The continent most affected by desertification and drought is Africa, with nearly 60% of its ground classified as either desert or arid. Several significant periods of famine have already been attested in the Sahel area, resulting in the migration of large parts of the population towards more habitable ground. Tens of millions of people who are victims of famine in sub-Saharan Africa will undoubtedly seek to move towards North Africa and Europe, increasing the migratory flux.
According to UNESCO and UNCCD, more than 110 countries have arid lands which are potentially threatened by desertification. These dry lands (whether arid, semi-arid or sub-humid), are found all across Africa, but also cover large parts of Asia, Latin America, Australia and the United States.
Africa (the old forgotten continent)
Two thirds of the African continent is desert or arid land. Africa comprises a vast area of arid arable lands, of which close to the three quarters already suffer from degradation, to various extents. In Africa, droughts are both serious and frequent. In order to ensure their subsistence, many African countries are obliged to draw abundantly on their natural resources. Desertification of the continent thus has serious consequences in terms of poverty and food safety.
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
- Countries of the Maghreb
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
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.
Drought and desertification have an impact on all aspects of life, which shows the extent to which the environment and means of subsistence are interdependent. There are several different types of consequences of drought and desertification, which fall into several categories:
Desertification and drought exacerbate poverty and therefore political instability. In addition to being an important factor contributing o the scarcity of water, drought and desertification lead to the interior displacement or migration of populations, and to social ruptures. This can be a major cause of social instability, resulting in tensions between bordering countries, and even in armed conflict. It is becoming increasingly evident that there is often a close relationship between social conflicts and environmental problems, such as desertification.
More than 500,000 sub-Saharan Africans are currently gathered on the coast of Mauritania in the hope of being able to reach the Canary Islands. Yet this is only the tip of the iceberg since, according to the United Nations, nearly sixty million people will have left the sub-Saharan arid regions for North Africa and Europe by 2020 as a result of desertification.
Go to 5.1 for more information on human consequences
Degradation of land as a consequence of drought, desertification and climate change affects a significant share of the planet’s arable lands and has a direct impact on standards of living and the economic development of countries. It entails economic losses for farmers, disturbs local and regional food markets and is a source of a social and political instability.
Soil impoverishment caused by drought and desertification perpetuates poverty and socio-cultural breakdown. It can be seen as a relaxation or transformation of traditional structures due to the effects of the market economy (BEDRANI, BESSAOUD, 2006).
The first evaluations carried out on the consequences of drought in France, for example, suggest a figure of one billion euros worth of damage caused to agriculture and another 1.6 billion euros for the damage caused by fires. The impact of these events on cultural heritage and nature remains to be assessed. (Press release, first assessment of drought consequences, reported by the French Council of Ministers).
In North Africa, the annual costs of desertification vary from 1.36% of GDP (Algeria) to 0.4% of GDP (Morocco). In the sub-Saharan countries, they range between 1 and 10% of the agricultural GDP. However, these costs are certainly under-estimated as they only take into account the direct costs of desertification (i.e. only agricultural losses) and not secondary costs.
On a socio-economic level, desertification considerably reduces economic resources. According to recent research by the World Bank, the loss of natural resources of a country in the Sahel corresponds to 20% of its annual GDP. It is estimated that, on a worldwide scale, the shortfall of the zones directly affected by desertification amounts to approximately 42 billion dollars per annum. Economic costs and indirect social costs outside the affected regions, including the surge of “ecological refugees” and a loss in national food production levels, are almost certainly higher.
Go to 5.2 for more information on socio-economic consequences
Since arid zones are prone to desertification, vegetation in these areas has diminished from millions of hectares to just hundreds of hectares, and the fine upper layers of the soil are carried away by the wind. This fine layer, reduced to dust, has drastically increased since the 1980s.
Each year, the Sahara injects nearly a billion tonnes of dust into the atmosphere. More than 100 million tonnes of this dust is carried towards Europe. Dust constitutes a real problem for public health in southern Europe, for example in Spain, because a high concentration of these fine particles degrades the quality of the air that we breathe.
Go to 5.3 for more information on environmental consequences
Many communities that live in deserts or in arid neighbourhoods live in perfect harmony with nature, thanks to their unique knowledge and the upholding of traditions. This harmony is jeopardized by increasing economic pressures and environmental problems due to drought, desertification and climate change.
Yet it is clear that if any community is forced to give up its culture or adopt a new mode of life in order to survive, an invaluable example of world heritage will be lost.
A striking example is that of oasis agriculture, which is considered as cultural heritage in Algeria and across the Maghreb region. Oasis agriculture is facing a multiplicity of environmental threats to its balance and even to its existence.
In these environments the greatest threat is siltation (an extreme stage of desertification). This threatens up to 60% of all urban areas, agricultural land and palm plantations, around 30 km of irrigation canals and 10 km of road.
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.
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:
- 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;
- 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)
- 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.
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
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….
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.
Human behaviour can influence the impact of drought and desertification (brought about by climate change) through a variety of scientific, technical, social and political solutions.
Scientific and technical solutions:
- increase in water resources and in improved stock management (irrigation techniques that avoid water waste and salinisation of the ground;
- planting vegetation (trees, Green Dam);
- stabilisation of dunes through adapted vegetation and other environment-friendly devices;
- application of irrigation and drainage techniques;
- identification and development of crops that are well-adapted to hydric and salt stress;
- establishing observation networks for monitoring vulnerable ecosystems and irrigated perimeters; development of early-warning systems.
- improvements to the ground’s capacity to retain water to allow the development of agriculture (organic amendment).
- drawing on the “indigenous knowledge” of local communities (e.g. the management of Saharan oases);
- educational programmes to raise awareness about desertification and to change attitudes and behaviours;
- technical training of populations;
- food aids, substitution of materials used for supplies and resources (e.g. gas instead of wood).
- egislative measures: protective laws;
- development of national policies and strategies of intervention (anti-erosive measures, biomass production, forestation, control and enhancement of water resources, reorganisation of pastoral activities, modernisation of production processes, diversification and development of new activities).
- development of international programmes, particularly for monitoring desertification and to exchange experiences and good practices.
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).
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.
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.
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.
- 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.).
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.
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.
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
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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