Search

Study region: Senegal river (SRB), Niger river (NRB), and Lake Chad basins (LCB). Study focus: We investigated the impacts of land use/land cover change (LULC) and climate variability on the water balance components from 1990 to 2020. We applied the Soil and Water Assessment Tool (SWAT) coupled with remote sensing retrievals of actual evapotranspiration (ETa) and surface soil moisture (SSM). To separate the impacts of the two aforementioned factors, two numerical experiments were designed: (i) climate variability effects by applying frozen LULC while changing the climate; (ii) LULC change impacts by applying frozen climate while changing LULC. New hydrological insights for the region: Overall, at the basin level, the results indicated that climate variability had the dominant role in increasing groundwater recharge, surface runoff, groundwater return flow and lateral flow in LCB and SRB. These increases triggered the recovery of lake area and higher water table in LCB and increased in SRB streamflow, while water scarcity increased in NRB. In contrast, the separate effect of LULC change, specifically natural vegetation expansion, increased actual ET and decreased the surface runoff, which could be a reason for lake area depletion in LCB and decreasing SRB and NRB streamflow. At the sub-basin level, LULC change, i.e. a gain in cropland and urban areas at the expense of forests in some sub-basins in NRB, led to a local increase in surface runoff. This implies a better redistribution of water in downstream and compensates the deficit in surface runoff caused by natural vegetation expansion in some other catchments. These changes, simultaneously with high intensity and long-duration precipitation, may increase the likelihood of inundation in some small catchments in the Niger river basin. These outcomes give useful hydrological insights into water and land management by emphasizing the crucial role of water recycling.

This reflection concerns the armed conflicts of the African Sahel and aims to historically analyze the role of Arab-Islamic colonization, Western colonization and the rivalries between the two. It is based on the hypothesis that the confrontation between jihadist and internal and external interventionists in the region constitutes a historical struggle motivated by humanitarian and non moral geoeconomic interests. Methodologically, a historical and comparative analysis is chosen to conclude that the main causes of conflicts should be located in the colonial maps and the historical rivalry between empires and not in ethnic, tribal and religious deferences or the borders created by Western colonization., Esta reflexão versa sobre os conflitos armados do Sahel africano e tem como objetivo analisar historicamente o papel da colonização árabe-islâmica, da colonização ocidental e das rivalidades entre os dois. Parte-se da hipótese de que o enfrentamento entre jihadistas e intervencionistas internos e externos na região constitui uma luta histórica motivada por interesses geoeconômicos não morais e humanitários. Metodologicamente, optou-se por uma análise histórica e comparativa para concluir que as principais causas dos conflitos devem ser situadas nos mapas coloniais e na rivalidade histórica entre impérios e não nas diferenças étnicas, tribais, religiosas e nas fronteiras criadas pela colonização ocidental.

Rangelands provide significant socioeconomic and environmental benefits to humans. However, climate variability and anthropogenic drivers can negatively impact rangeland productivity. The main goal of this study was to investigate structural and productivity changes in rangeland ecosystems in New Mexico (NM), in the southwestern United States of America during the 1984–2015 period. This goal was achieved by applying the time series segmented residual trend analysis (TSS-RESTREND) method, using datasets of the normalized difference vegetation index (NDVI) from the Global Inventory Modeling and Mapping Studies and precipitation from Parameter elevation Regressions on Independent Slopes Model (PRISM), and developing an assessment framework. The results indicated that about 17.6% and 12.8% of NM experienced a decrease and an increase in productivity, respectively. More than half of the state (55.6%) had insignificant change productivity, 10.8% was classified as indeterminant, and 3.2% was considered as agriculture. A decrease in productivity was observed in 2.2%, 4.5%, and 1.7% of NM’s grassland, shrubland, and ever green forest land cover classes, respectively. Significant decrease in productivity was observed in the northeastern and southeastern quadrants of NM while significant increase was observed in northwestern, southwestern, and a small portion of the southeastern quadrants. The timing of detected breakpoints coincided with some of NM’s drought events as indicated by the self-calibrated Palmar Drought Severity Index as their number increased since 2000s following a similar increase in drought severity. Some breakpoints were concurrent with some fire events. The combination of these two types of disturbances can partly explain the emergence of breakpoints with degradation in productivity. Using the breakpoint assessment framework developed in this study, the observed degradation based on the TSS-RESTREND showed only 55% agreement with the Rangeland Productivity Monitoring Service (RPMS) data. There was an agreement between the TSS-RESTREND and RPMS on the occurrence of significant degradation in productivity over the grasslands and shrublands within the Arizona/NM Tablelands and in the Chihuahua Desert ecoregions, respectively. This assessment of NM’s vegetation productivity is critical to support the decision-making process for rangeland management; address challenges related to the sustainability of forage supply and livestock production; conserve the biodiversity of rangelands ecosystems; and increase their resilience. Future analysis should consider the effects of rising temperatures and drought on rangeland degradation and productivity.

OBJECTIVES Mode of subsistence is an important factor influencing dietary habits and the genetic structure of various populations through differential intensity of gene flow and selection pressures. Previous studies suggest that in Africa Taste 2 Receptor Member 16 (TAS2R16), which encodes the 7-transmembrane receptor protein for bitterness, might also be under positive selection pressure. METHODS However, since sampling coverage of populations was limited, we created a new TAS2R16 population dataset from across the African Sahel/Savannah belt representing various local populations of differing subsistence modes, linguistic affiliations, and geographic provenience. We sequenced the TAS2R16 exon gene and analyzed 2250 haplotypes among 19 populations. RESULTS We found no evidence for selection as a driving force of genetic variation at this locus; instead, we discovered a highly significant correlation between TAS2R16 genetic and geographical distances based on provenience of the sampled populations, strongly suggesting that genetic drift most likely prevailed over positive selection at this specific locus. We also found significant correlations with other independent loci, mainly in sedentary farmers. DISCUSSION Our results do not support the notion that the genetic diversity of TAS2R16 in Sahelian populations was shaped by selective pressures. This could result from several alternative and not mutually exclusive mechanisms, of which the possibility that, due to the pleiotropic nature of TAS2R16, selective pressures on other traits could counterbalance those acting on bitter taste perception, or that the change of diet in the Neolithic generally relaxed selective pressure on this gene.

OBJECTIVES Archeological evidence shows that first nomadic pastoralists came to the African Sahel from northeastern Sahara, where milking is reported by ~7.5 ka. A second wave of pastoralists arrived with the expansion of Arabic tribes in 7th-14th century CE. All Sahelian pastoralists depend on milk production but genetic diversity underlying their lactase persistence (LP) is poorly understood. MATERIALS AND METHODS We investigated SNP variants associated with LP in 1,241 individuals from 29 mostly pastoralist populations in the Sahel. Then, we analyzed six SNPs in the neighboring fragment (419 kb) in the Fulani and Tuareg with the -13910*T mutation, reconstructed haplotypes, and calculated expansion age and growth rate of this variant. RESULTS Our results reveal a geographic localization of two different LP variants in the Sahel: -13910*T west of Lake Chad (Fulani and Tuareg pastoralists) and -13915*G east of there (mostly Arabic-speaking pastoralists). We show that -13910*T has a more diversified haplotype background among the Fulani than among the Tuareg and that the age estimate for expansion of this variant among the Fulani (~8.5 ka) corresponds to introduction of cattle to the area. CONCLUSIONS This is the first study showing that the "Eurasian" LP allele -13910*T is widespread both in northern Europe and in the Sahel; however, it is limited to pastoralists in the Sahel. Since the Fulani haplotype with -13910*T is shared with contemporary Eurasians, its origin could be in a region encompassing the Near East and northeastern Africa in a population ancestral to both Saharan pastoralists and European farmers.

The summer monsoon inversion in the Arabian Sea is characterized by a large amount of low clouds and August as the peak season. Atmospheric stratification associated with the monsoon inversion has been considered a local system influenced by the advancement of the India–Pakistan monsoon. Empirical and numerical evidence from this study suggests that the Arabian Sea monsoon inversion is linked to a broader-scale monsoon evolution across the African Sahel, South Asia, and East Asia–Western North Pacific (WNP), rather than being a mere byproduct of the India–Pakistan monsoon progression. In August, the upper-tropospheric anticyclone in South Asia extends sideways corresponding with the enhanced precipitation in the subtropical WNP, equatorial Indian Ocean, and African Sahel while the middle part of this anticyclone weakens over the Arabian Sea. The increased heating in the adjacent monsoon systems creates a suppression effect on the Arabian Sea, suggesting an apparent competition among the Africa–Asia–WNP monsoon subsystems. The peak Sahel rainfall in August, together with enhanced heating in the equatorial Indian Ocean, produces a critical effect on strengthening the Arabian Sea thermal inversion. By contrast, the WNP monsoon onset which signifies the eastward expansion of the subtropical Asian monsoon heating might play a secondary or opposite role in the Arabian Sea monsoon inversion.

Motivated by an inconclusive debate over implications of resource scarcity for violent conflict, and common reliance on national data and linear models, we investigate the relationship between socio-ecological vulnerability and armed conflict in global drylands on a subnational level. Our study emanates from a global typology of smallholder farmers’ vulnerability to environmental and socioeconomic stresses in drylands. This typology is composed of eight typical value combinations of variables indicating environmental scarcities, resource overuse, and poverty-related factors in a widely subnational spatial resolution. We investigate the relationships between the spatial distribution of these combinations, or vulnerability profiles, and geocoded armed conflicts, and find that conflicts are heterogeneously distributed according to these profiles. Four profiles distributed across low- and middle-income countries comprise all drylands conflicts. Comparing models for conflict incidence using logit regression and ROC (Receiver Operator Characteristic) analysis based on (1) the set of all seven indicators as independent variables and (2) a single, only vulnerability profile- based variable proves that the non-linear typology-based variable is the better explanans for conflict incidence. Inspection of the profiles’ value combinations makes this understandable: A systematic explanation of conflict incidence and absence across all degrees of natural resource endowments is only reached through varying importance of poverty and resource overuse depending on the level of endowment. These are non-linear interactions between the explaining variables. Conflict does not generally increase with resource scarcity or overuse. Comparison with conflict case studies showed both good agreement with our results and promise in expanding the set of indicators. Based on our findings and supporting literature we argue that part of the debate over implications of resource scarcity for violent conflict in drylands may be resolved by acknowledging and accounting for non-linear processes.

BackgroundDietary changes associated to shifts in subsistence strategies during human evolution may have induced new selective pressures on phenotypes, as currently held for lactase persistence. Similar hypotheses exist for arylamine N-acetyltransferase 2 (NAT2) mediated acetylation capacity, a well-known pharmacogenetic trait with wide inter-individual variation explained by polymorphisms in theNAT2gene. The environmental causative factor (if any) driving its evolution is as yet unknown, but significant differences in prevalence of acetylation phenotypes are found between hunter-gatherer and food-producing populations, both in sub-Saharan Africa and worldwide, and between agriculturalists and pastoralists in Central Asia. These two subsistence strategies also prevail among sympatric populations of the African Sahel, but knowledge onNAT2variation among African pastoral nomads was up to now very scarce. Here we addressed the hypothesis of different selective pressures associated to the agriculturalist or pastoralist lifestyles having acted on the evolution ofNAT2by sequencing the gene in 287 individuals from five pastoralist and one agriculturalist Sahelian populations.ResultsWe show that the significantNAT2genetic structure of African populations is mainly due to frequency differences of three major haplotypes, two of which are categorized as decreased function alleles (NAT2*5BandNAT2*6A), particularly common in populations living in arid environments, and one fast allele (NAT2*12A), more frequently detected in populations living in tropical humid environments. This genetic structure does associate more strongly with a classification of populations according to ecoregions than to subsistence strategies, mainly because most Sahelian and East African populations display little to no genetic differentiation between them, although both regions hold nomadic or semi-nomadic pastoralist and sedentary agriculturalist communities. Furthermore, we found significantly higher predicted proportions of slow acetylators in pastoralists than in agriculturalists, but also among food-producing populations living in the Sahelian and dry savanna zones than in those living in humid environments, irrespective of their mode of subsistence.ConclusionOur results suggest a possible independent influence of both the dietary habits associated with subsistence modes and the chemical environment associated with climatic zones and biomes on the evolution ofNAT2diversity in sub-Saharan African populations.

The impact of human management, in particular livestock grazing, on the vegetation cover of the Sahel is still debated. In a range of studies, satellite images have been used to analyze the development of the Sahelian vegetation cover over time. These studies did not reveal any significant degradation of the Sahel in the last two decades. In this paper, we examine the ecological assumptions underlying the use of satellite imagery to analyze degradation of the Sahel. Specifically, we analyze the variability of the rain-use efficiency (RUE), which is often used as an indicator for the state of the vegetation cover. We detect a fundamental flaw in the way RUE has been handled in most remote sensing studies; they ignored the relation between annual rainfall variation and RUE. Because of the upward trend in annual rainfall that occurred during the 1980s and 1990s, this leads to a bias in the interpretation of the satellite images. In this paper, we show the importance of the variability in RUE for the analysis of remote sensing imagery of semiarid rangelands. Our analysis also shows that it is likely that there has been anthropogenic degradation of the Sahelian vegetation cover in the last two decades. This has important consequences for the debate on the impacts of grazing on semiarid rangelands. Furthermore, the occurrence of anthropogenic degradation is relevant to explain the magnitude of 20th century Sahelian droughts. The analyses also indicate that the population of the Sahel may be more vulnerable for droughts than currently assumed

Vegetation forms a main component of the terrestrial biosphere and plays a crucial role in land-cover and climate-related studies. Activity of vegetation systems is commonly quantified using remotely sensed vegetation indices (VI). Extensive reports on temporal trends over the past decades in time series of such indices can be found in literature. However, little remains known about the processes underlying these changes at large spatial scales. In this study, we aimed at quantifying the spatial relationship between changes in potential climatic growth constraints (i.e. temperature, precipitation and incident solar radiation) and changes in vegetation activity (1982-2008). We demonstrate an additive spatial model with 0.5° resolution, consisting of a regression component representing climate-associated effects and a spatially correlated field representing the combined influence of other factors, including land-use change. Little over 50% of the spatial variance could be attributed to changes in climatologies; conspicuously, many greening trends and browning hotspots in Argentina and Australia. The nonassociated model component may contain large-scale human interventions, feedback mechanisms or natural effects, which were not captured by the climatologies. Browning hotspots in this component were especially found in subequatorial Africa. On the scale of land-cover types, strongest relationships between climatologies and vegetation activity were found in forests, including indications for browning under warming conditions (analogous to the divergence issue discussed in dendroclimatology). © 2013 Blackwell Publishing Ltd.

Traditional pastoralists survive in few places in the world. They can still be encountered in the African Sahel, where annual alternations of dry and wet seasons force them to continual mobility. Little is known about the genetic structure of these populations. We present here the population distribution of 312 hypervariable segment I mitochondrial DNA (mtDNA) and 364 Y-short tandem repeat haplotypes in both farmer and pastoralist groups from the Lake Chad Basin and the West African Sahel. We show that the majority of pastoral populations (represented in the African Sahel by the Fulani nomads) fail to show significant departure from neutrality for mtDNA as evidenced by Fu's Fs statistics and exhibit lower levels of intrapopulation diversity measures for mtDNA when contrasted with farmers. These differences were not observed for the Y chromosome. Furthermore, analyses of molecular variance and population distributions of the mtDNA haplotypes show more heterogeneity in the sedentary groups than in the pastoralists. On the other hand, pastoralists retain a signature of a wide phylogenetic distance contributing to their male gene pool, whereas in at least some of the farmer populations, a founder effect and/or drift might have led to the presence of a single major lineage. Interestingly, these observations are in contrast with those recorded in Central Asia, where similar comparisons of farmer and pastoral groups have recently been carried out. We can conclude that in Africa, there have been no substantial mating exchanges between the Fulani pastoralists coming to the Lake Chad Basin from the West African Sahel and their farmer neighbors. At the same time, we suggest that the emergence of pastoralism might be an earlier and/or a demographically more important event than the introduction of sedentary agriculture, at least in this part of Africa. The project was supported by the Grant Agency of the Czech Republic (Grant no. 206/08/1587), the Portuguese Fundação para a Ciência e a Tecnologia (project—PTDC/ANT/66275/2006; post-doc grant—SFRH/BPD/64233/2009), and the Italian Ministry of University (MIUR-PRIN2007). Instituto de Patologia e Imunologia Molecular da Universidade do Porto is an Associate Laboratory of the Portuguese Ministry of Science, Technology and Higher Education and is partially supported by FCT, the Portuguese Foundation for Science and Technology.

Modeling has emerged as a key technology in analysis of social–ecological systems. However, the tendency for modeling to focus on the mechanistic materiality of biophysical systems obscures the diversity of performative social behaviors and normative cultural positions of actors within the modeled system. The fact that changes in the biophysical system can be culturally constructed in different ways means that the perception and pursuit of adaptive pathways can be highly variable. Furthermore, the adoption of biophysically resilient livelihoods can occur under conditions that are subjectively experienced as the radical transformation of cultural systems. The objectives of this work are to: (1) highlight the importance of understanding the place of culture within social–ecological systems, (2) explore the tensions between empirical and normative positions in the analysis of social–ecological resilience, and (3) suggest how empirical modeling of social–ecological systems can synergistically interact with normative aspects of livelihoods and lifeways.

Modeling has emerged as a key technology in analysis of social–ecological systems. However, the tendency for modeling to focus on the mechanistic materiality of biophysical systems obscures the diversity of performative social behaviors and normative cultural positions of actors within the modeled system. The fact that changes in the biophysical system can be culturally constructed in different ways means that the perception and pursuit of adaptive pathways can be highly variable. Furthermore, the adoption of biophysically resilient livelihoods can occur under conditions that are subjectively experienced as the radical transformation of cultural systems. The objectives of this work are to: (1) highlight the importance of understanding the place of culture within social–ecological systems, (2) explore the tensions between empirical and normative positions in the analysis of social–ecological resilience, and (3) suggest how empirical modeling of social–ecological systems can synergistically interact with normative aspects of livelihoods and lifeways.

In semi-arid south-western Niger, external fertilizer inputs are a complement of livestock-mediated nutrient transfers for maintaining soil fertility. This paper discusses scenarios of intensification for different farm household types in an area representative of the wetter parts of semi-arid Sahel. Twenty-five-year projections suggest that soil fertility may not always or irreversibly deteriorate under intensification, and that nitrogen is the main external input required. Owning animals allows some households to achieve food security and maintain soil fertility by capturing and mobilizing soil nutrients. Intensification will bring various benefits to livelihoods, but these will be unevenly distributed. The results of this paper should caution scientists and policy-makers against the often heard warning of inevitable losses in soil fertility in the Sahel associated with intensive technologies, and against extrapolating conclusions attained at specific locations or social groups. Endogenous coping strategies based on using local inputs can also be effective and should be explored in addition to a continued attention for the need for more targeted uses of external inputs.

The impact of human management, in particular livestock grazing, on the vegetation cover of the Sahel is still debated. In a range of studies, satellite images have been used to analyze the development of the Sahelian vegetation cover over time. These studies did not reveal any significant degradation of the Sahel in the last two decades. In this paper, we examine the ecological assumptions underlying the use of satellite imagery to analyze degradation of the Sahel. Specifically, we analyze the variability of the rain-use efficiency (RUE), which is often used as an indicator for the state of the vegetation cover. We detect a fundamental flaw in the way RUE has been handled in most remote sensing studies; they ignored the relation between annual rainfall variation and RUE. Because of the upward trend in annual rainfall that occurred during the 1980s and 1990s, this leads to a bias in the interpretation of the satellite images. In this paper, we show the importance of the variability in RUE for the analysis of remote sensing imagery of semiarid rangelands. Our analysis also shows that it is likely that there has been anthropogenic degradation of the Sahelian vegetation cover in the last two decades. This has important consequences for the debate on the impacts of grazing on semiarid rangelands. Furthermore, the occurrence of anthropogenic degradation is relevant to explain the magnitude of 20th century Sahelian droughts. The analyses also indicate that the population of the Sahel may be more vulnerable for droughts than currently assumed

In the African Sahel the history of which is marked by recurring food crises, agriculture and food gathering have remained until recent years complementary activities. In the Soninke country, in particular, food gathering is a regular, socially organized practice, which provides complementary food in periods of plenty and food substitutes during times of crisis. When there is no famine it plays an important part in nutritional balance. This formerly servile work has progressively concerned all social groups since the end of the 19th century, being in that way part of a more global evolution of Soninke society. At present, however, there is a decrease in food gathering, which varies according to the region and is related to the degradation of the vegetation cover and changes in the way of life. In the high Senegal valley it is due, in particular, to the monetization of the economy with the increase in migration of the labour force, and the transformation of the production system with the creation of irrigated perimeters. This trend may well have been strengthened by the lack of interest given to this activity in the fields of research and development. Food gathering practices depend on the knowledge of the vegetation and on different harvesting and preparation techniques. Food gathering plays as much a part in the management of the environment as agriculture or breeding stock, fishing or hunting. These practices are also strongly imbued with social and symbolic meaning, as the oral statements and the food gathering songs show. As a means of subsistence and a sign of poverty during times of famine, it can be either considered praiseworthy or as something to be denied. When a crisis occurs not only is survival in jeopardy but also social identity. This ambiguous perception of food gathering is the backcloth to its present depreciation and its decline. Without losing sight of the ambivalence of this practice in the Soninke society - and in other African societies - the consequences of its decrease from the point of view of knowledge and preservation of the environment can be questioned. The decline of food gathering also reinforces the present trend for uniform agricultural systems and increases their vulnerability to different forms of ecological and economic risks. Before the disappearance of these skills with their related practices should not these same skills be taken into consideration and reassessed, and if so, how?, En Afrique sahélienne, marquée dans son histoire par des crises alimentaires récurrentes, l'agriculture et la cueillette ont été des activités complémentaires jusqu'à ces dernières années. En pays soninké, en particulier, la cueillette est une pratique régulière et socialement organisée, qui procure des aliments de complément en période d'abondance et des nourritures de substitution en période de crise. En l'absence de famine, elle joue un rôle important dans l'équilibre nutritionnel. Cet ancien travail servile a progressivement concerné tous les groupes sociaux depuis la fin du XIXème siècle, participant ainsi d'une évolution plus générale de la société soninkée. Actuellement, cependant, on constate un recul de la cueillette, plus ou moins marqué selon les régions, recul qui est lié à la dégradation du couvert végétal et au changement des modes de vie. Cela est dû notamment dans la haute vallée du Sénégal, à la monétarisation de l'économie, avec l'essor des migrations de travail, et à la transformation du système de production, avec la création de périmètres irrigués. Cette tendance a sans doute été renforcée par le manque d'intérêt pour la cueillette dans les milieux de la recherche et du développement. Cette activité repose sur la connaissance de la végétation et sur différentes techniques de récolte et de préparation. Elle joue un rôle dans la gestion de l'environnement, au même titre que l'agriculture, l'élevage, la pêche ou la chasse. Cette pratique a aussi une dimension sociale et symbolique, comme le montrent les témoignages et les chants de cueillette. En tant que moyen de subsistance et signe de pauvreté, la cueillette peut être à la fois un objet d'éloge et de dénégation. En temps de crise, en effet, non seulement la survie est menacée mais aussi l'identité sociale. Cette perception ambigüe de la cueillette constitue l'arrière plan de sa dévalorisation et de son déclin actuels. Sans perdre de vue l'ambivalence de la cueillette en milieu soninké - comme ailleurs en Afrique -, on peut s'interroger sur les conséquences de son recul au niveau de la connaissance et de la protection de l'environnement. Le déclin de la cueillette va dans le sens de l'uniformisation des systèmes agricoles, tout en augmentant leur vulnérabilité aux risques écologiques et économiques. Avant que ne disparaissent ces savoir-faire et les différentes pratiques qui leur sont liées, ne faudrait-il pas les prendre en considération et les réévaluer ? Si oui, selon quelles modalités ?