Perspectives - Quel avenir pour les cuvettes oasiennes dans le Niger oriental ?

in Geo-Eco-Trop (2009), 33

The oasian interdunal depressions of eastern Niger are areas of life providing refuge to agro-pastoral activities in a generally hostile environment. The inter-university Targeted Program (ITP) funded by ... [more ▼]

The oasian interdunal depressions of eastern Niger are areas of life providing refuge to agro-pastoral activities in a generally hostile environment. The inter-university Targeted Program (ITP) funded by the Coopération Universitaire au Développement (CUD) called "Invasion of circular lowlands (cuvettes) of south-eastern Niger by aeolian deposits: processes, impacts and means of struggle" has studied the problem of silting of these refuge areas and proposed technical means, including physical and biological fixation of dunes that threaten the villages and interdunal depressions. Given the increasing human pressure and the present climate context that seems to move towards dryer conditions, environmental degradation of the study area should be investigated more broadly. Set up of strategies to allow people to adapt their conditions of life to an environment increasingly rough should also be considered. This paper presents some possible options for adaptation and examines the question of the very future of these interdunal depressions. [less ▲]

Evolution des caractéristiques pluviométriques dans l'est du Niger de 1940 à 2007

in Geo-Eco-Trop (2009), 33

Since the late 1960s, the Sahel of West Africa is affected by a dramatic drought. Based on long-term daily datasets in four synoptic stations, this article analyses recent trends in the Eastern Niger ... [more ▼]

Since the late 1960s, the Sahel of West Africa is affected by a dramatic drought. Based on long-term daily datasets in four synoptic stations, this article analyses recent trends in the Eastern Niger rainfall regime from 1940 to 2007. Results suggest that the Sahelian drought ended in the early 1990s. However, several rainfall indices still present strong significant downwards trends. We also show that the length of the rainy season has not been heavily impacted, except in its amplitude, which may suggest an increasing degree of vulnerability. [less ▲]

Effets de l'inoculation mycorhizienne du substrat sur la croissance et la résistance au stress hydrique de cinq espèces fixatrices de dunes : Acacia raddiana Savi ; Acacia nilotica (L.) Willd. Ex Del. var. adansonii ; Acacia senegal (L.) Willd ; Prosopis chilensis Stunz. et Bauhinia rufescens Lam..

in Geo-Eco-Trop (2009), 33

Effects of the addition of an indigenous mycorrhizal complex, coming from soils of Gouré and of Glomus intraradices in a non sterile culture substrate were assessed on five woody species, among which 3 ... [more ▼]

Effects of the addition of an indigenous mycorrhizal complex, coming from soils of Gouré and of Glomus intraradices in a non sterile culture substrate were assessed on five woody species, among which 3 acacias (A. nilotica, A. raddiana, A. senegal), Bauhinia rufescens and Prosopis chilensis, in a tree nursery and on a sand dune of Gouré. In the nursery, species underwent a water stress by interrupting the watering during six days. Foliar hydration has been determined in order to evaluate the respective effects of the mycorrhizal inoculation for water loss limitation. Mycorrhizal root colonization has been determined as well as plant height and total biomass. In a field experiment, inoculated and non inoculated species have been planted on a mechanically prefixed sand dune portion in order to evaluate the effects of mycorrhizal inoculations on growth in the field. Results in nursery showed that (i) the non sterile soil would contain some endogenous AMF (arbuscular mycorrhizal fungi) as infectious as those in soils with mycorrhizal additions; (ii) addition of Glomus intraradices would be efficient to stimulate total biomass and (iii) natural mycorhization would be as efficient as both mycorrhizal addition for growth stimulation and water loss limitation by transpiration. Results on site confirm the comparable effectiveness of the natural mycorhization and mycorrhizal additions. Although the addition of G. intraradices appears to be slightly superior by some aspects on some species, the observed effects do not justify preferring it, when compared to indigenous composite inoculum or to natural mycorhization in this zone. [less ▲]

Risques d'inondation dans la ville de Nouakchott (Mauritanie)

in Geo-Eco-Trop (2007), 31

After the drought and the desertification that affect strongly Mauritania during the years 70 and 80, the city of Nouakchott knew a spectacular demographic development. The city has widely expanded and ... [more ▼]

After the drought and the desertification that affect strongly Mauritania during the years 70 and 80, the city of Nouakchott knew a spectacular demographic development. The city has widely expanded and the newcomers constructed their houses in marginal zones without planning. Several districts have been installed either in areas of salty soils as sebkha, either in sandy zones. This work permitted to analyze the relation between rains and floods, to monitor the evolution of the urban growth of Nouakchott between 1978 and 2006 and its impact on the vulnerability of the population, to map the flood risk zones and to delimit the present unviable sectors if no planning measure would be taken. Was also studied the coastal area evolution and particularly coastline modification during the period 1978-2006, by using photographs and remote sensing. The results of the work constitute an excellent tool for helping the decisions makers. It's a reliable tool for the assessment and the management of the flood risks in Nouakchott. [less ▲]

Mesure des retombées au sol des aérosols désertiques durant l’hivernage 2005 à Mâle, Mauritanie méridionale.

in Geo-Eco-Trop (2005), 29

The Sahara and its margins largely contribute to the global injection of mineral dust into the northern hemisphere, about half of the yearly global mineral dust production. In this study, we have placed a ... [more ▼]

The Sahara and its margins largely contribute to the global injection of mineral dust into the northern hemisphere, about half of the yearly global mineral dust production. In this study, we have placed a pyramidal receptacle in Mâle (southern Mauritania) during the rainy season 2005 in order to measure daily Saharan dust deposition. The dust quantity collected totals 78.38 g/m2 during the 3 months experimented. Comparing our results to previous works achieved in the southern border of the Sahara shows that the levels of deposition in Mâle are extremely high. This could suggest a continuous environmental degradation resulting from always increasing human pressure. [less ▲]

Analyse des inondations en aval du barrage de Nangbeto sur le fleuve Mono (Togo et au Bénin).

in Geo-Eco-Trop (2005), 29

The analysis of risk of flood downstream from the hydroelectric dam of Nangbeto in the Mono River was about the survey of interannual variability of rainfall and rivers flows from 1955 to 1999, the ... [more ▼]

The analysis of risk of flood downstream from the hydroelectric dam of Nangbeto in the Mono River was about the survey of interannual variability of rainfall and rivers flows from 1955 to 1999, the population vulnerability, the hydrological modification and the impacts downstream in Togo and Benin from the dam constructed in 1987. The analysis of the mean annuel discharge has revealed no tendency, showing thus that the change of land use, the increase of waterproof areas and even the functioning of the hydroelectric dam have not modified in a significant manner the river's rate of flow. Apart from the return to the improvement in rainfull as far back as the end of years 80, the anthropic pressure and the demographic explosion have best explained the magnitude and frequency of flooding downstream from the hydroelectric dam of Nangbeto. The soil degradation, the deforestation of the floodplain, the increase in the number of human settlements in the river boundary increases the vulnerability of population faced with flooding. [less ▲]

Quelques spécimens exceptionnels de premières plantes terrestres découvertes au Brésil (Bassin du Paraná, Dévonien basal)

in Geo-Eco-Trop (2001), 25

Evolution du couvert vegetal dans la region de Kinshasa (1960-1987) selon une approche cartographique.

in Geo-Eco-Trop (1997), 21(1-4),