Lake drying and livelihood dynamics in Lake Chad: unravelling the mechanisms, contexts and responses

This article examines lake drying and livelihood dynamics in the context of multiple stressors through a case study of the ‘‘Small Lake Chad’’ in the Republic of Chad. Livelihoods research in regions experiencing persistent lake water fluctuations has largely focused on the wellbeing and security of lakeshore dwellers. Little is known about the mechanisms through which lake drying shapes livelihood drawbacks and opportunities, and whether locally evolved responses are enhancing livelihoods. Here we address these gaps using empirical, mixed-methods field research couched within the framework of livelihoods and human well-being contexts. The analysis demonstrates that limited opportunities outside agriculture, the influx of mixed ethnic migrants and the increasing spate of violence all enhance livelihood challenges. Livelihood opportunities centre on the renewal effects of seasonal flood pulses on lake waters and the learning opportunities triggered by past droughts. Although drying has spurred new adaptive behaviours predicated on seasonality, traditional predictive factors and the availability of assets, responses have remained largely reactive. The article points to where lake drying fits amongst changes in the wider socioeconomic landscape in which people live, and suggests that awareness of the particularities of the mechanisms that connect lake drying to livelihoods can offer insights into the ways local people might be assisted by governments and development actors

L'homme et le milieu végétal dans le bassin du lac Tchad = Man and vegetation in the lake Chad basin

Les défrichements de la majeure partie de la zone rurale du département de Maradi, au Niger, sont postérieurs à la colonisation mais le taux d'occupation agricole y est aujourd'hui proche de la saturation. La disparition quasi-complète des réserves foncières a contribué à faire évoluer les règles d'accès et d'usage de la terre ainsi que les systèmes techniques. L'analyse, menée dans le cas particulier d'un village, montre bien que la mise en culture ininterrompue des sols a façonné le couvert arboré, faisant régresser ou disparaître certaines espèces des champs les plus proches du village tandis que d'autres forment parc. Face à ce qui est perçu comme une péjoration de l'environnement, surtout depuis les sécheresses, les familles mettent en oeuvre des stratégies diverses montrant que les avantages et les handicaps sont souvent cumulatifs. (Résumé d'auteur

Biocultural diversity hypothesis : is it useful to understand the evolution of agrobiodiversity ? Snapshots from the Lake Chad Basin

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Groundwater recharge by Sahelian rivers-consequences for agricultural development : example from the lower Komadugu Yobe River (Eastern Niger, Lake Chad Basin)

In the Sahel region, temporary rivers and ponds constitute green spaces of welfare where sustainable development requires parsimonious management of water resources. The Komadugu Yobe valley in Eastern Niger is presented here as an example case of recent agricultural development based on irrigated pepper cropping. Piezometric maps indicate there that the river recharges the upper Quaternary aquifer. A simplified numerical model allows to quantify the exchanges between the river and the aquifer, based mainly on exploration geophysics data and three piezometric records, covering between 1 and 3 years of our 4 years modeling period. Recharge at the valley axis is modeled with a linear river coefficient constant for each hydrological year. The main findings are that: (i) during dry years, the river is disconnected from the aquifer and separated from it by a layer of unsaturated medium, (ii) however, this effect can be reversed, such as during the 2010-2011 wet year or after the Sahelian drought event of the 1980s and 1990s, (iii) the infiltration rate from the river amounts to 30-40 % of its total discharge and to at least four times the abstraction for pepper irrigation along its 150 km lower course at the Niger-Nigeria boundary, which implies that neither the aquifer recharge nor the river discharge is at risk due to the present agricultural development. Similar modeling near temporary river axes could provide some help in water resource management in the Sahel

Genetic diversity and gene flow among pearl millet crop/weed complex : a case study

Weedy plants with intermediate (domesticated x wild) phenotypes occur in most pearl millet Welds in West Africa, even in the absence of wild populations. They are usually found, in high numbers, both inside and outside of drills. Questions pertaining to the evolutionary dynamics of diversity within the pearl millet complex (domesticated-weedy-wild forms) were addressed in this study. The diversity of the different components of this complex sampled in two pearl millet Welds in two villages of southwestern Niger was assessed at both molecular (AFLP) and morphological levels. Results show that, in both Welds, weedy plants found outside of drills are morphologically distinct from weedy plants found inside drills, despite their close similarity at AFLP markers. The data suggest some introgression from the wild to the weedy population but nevertheless that the gene flow between the parapatric wild and domesticated populations is very low. This challenges the traditional view that regular hybridization between domesticated and wild pearl millets explains the abundance of these weedy plants despite farmers' seed selection. The level of genetic differentiation between Welds from the two villages was low when considering domesticated and weedy plants. This could be explained by high gene flow resulting from substantial seed exchanges between farmers. The fact that it is very difficult for farmers to keep their own selected seeds, and the consequent substantial seed exchanges between them, is probably the main factor accounting for the maintenance and dispersal of weedy pearl millets in the region, even in areas where no wild forms have been observed