Semi-arid Regions Of West Africa Research Articles

Present and Future of Heavy Rain Events in the Sahel and West Africa

Gridding precipitation datasets for climate information services in the semi-arid regions of West Africa has some advantages due to the limited spatial coverage of rain gauges, the limited accessibility to in situ gauge data, and the important progress in earth observation and climate modelling systems. Can accurate information on the occurrence of heavy precipitation in this area be provided using gridded datasets? Furthermore, what about the future of heavy rain events (HRE) under the shared socioeconomic pathways (SSP) of the Inter-Sectoral Impact Model Intercomparison Project (i.e., SSP126 and SSP370)? To address these questions, daily precipitation records from 17 datasets, including satellite estimates, interpolated rain gauge data, reanalysis, merged products, a regional climate model, and global circulation models, are examined and compared to quality-controlled in situ data from 69 rain gauges evenly distributed across West Africa’s semi-arid region. The results show a consensus increase in the occurrence of HRE, between observational and gridded data. All datasets showed three categories of HRE every season, but these categories had lower intensities and an overstated frequency of occurrence in gridded datasets compared to in situ rain gauge data. Eight out of 17 databases (~47%) show significant positive trends and only one showed a significant negative trend, indicating an increase in HRE for all categories in this region. The future evolution of HRE considered under the shared socioeconomic pathways SSP1-2.6 and SSP3-7.0, showed a trend toward the intensification of these events. In fact, the mean of the ensemble of the models showed significant changes toward higher values in the probability distribution function of the future HRE in West Africa, which may likely trigger more floods and landslides in the region. The use of gridded data sets can provide accurate information on the occurrence of heavy precipitation in the West African Sahel. However, it is important to consider the representation of heavy rain events in each data set when monitoring extreme precipitation, although in situ gauge records are preferred to define extreme rainfall locally.

Increasing Millet Planting Density with Appropriate Fertilizer to Enhance Productivity and System Resilience in Senegal

Climate forecasts show increased frequency and intensity of drought in the semi-arid regions of west Africa, which negatively impacts food and nutrition security. Developing and improving resilient cropping systems will require adequate varieties with improved agronomic practices. The purpose of the study was to evaluate grain and biomass production of newly released dual-purpose millet varieties under different fertilizer rates and planting densities across the millet-cropping regions of Senegal with different rainfall regimes (Bambey: 600 mm, Boulel: 700 mm, Nioro: 650 mm, and Sinthiou Malème: 800 mm). The experimental design was a split-split-plot with three replicates using one traditional variety (Souna 3) and four dual-purpose varieties (Thialack 2, SL28, SL 169, and SL423) as the main factor; two planting densities (E1: 12,500 seed hills ha−1 and E2: 25,000 seed hills ha−1) as second factor; and eight fertilizer combination as sub-sub-plots. Results showed that variety yield response differed with environments. Regardless of variety, increasing sowing density increased grain yields (1600 kg ha−1 for E2 vs. 1000 kg ha−1 for E1) and fodder yields (4200 kg ha−1 for E2 vs. 3100 kg ha−1 for E1). Fertilizer response differed between environments, but the application of 70N–10P–19K + 2.5 t ha−1 cow manure produced appreciable yields in all the environments. The dual-purpose varieties (SL 28, SL 169, and Thialack 2) sown at E2 produced the best grain and fodder yields. Soil water content was greater for all varieties (Thialack 2: 12.32%; Souna 3: 5.32%; SL28: 6.32%; and SL423: 9.23%) at higher planting density compared with normal density (Thialack 2: 9.25%; Souna 3: 3.21%; SL28: 5.43%; and SL423: 7.47%). The highest agronomic-use efficiency (AEg) of inorganic fertilizer applied was observed at 25,000 seed hill ha−1 and averaged 6.63 kg kg−1 at Boulel, 9.20 kg kg−1 at Sinthiou Malème, 4.67 kg kg−1 at Bambey, and 8.32 at Nioro kg kg−1. The AEg significantly varied among fertilizer combinations, with greatest AEg obtained with 70N–22.5P–22.5K (5.53 kg kg−1) at Boulel and with 95N–17P–27K (4.66 kg kg−1) at Bambey. This study provides crop-management options for millet-cropping systems in the semi-arid regions of west Africa for improving millet productivity while enhancing system resilience through better conservation and utilizing of soil water.

Combining ability studies of grain Fe and Zn contents of pearl millet (Pennisetum glaucum L.) in West Africa.

Micronutrient malnutrition is a major challenge in Africa, where half a million children die each year because of lack of micronutrients in their food. Pearl millet is an important food and fodder crop for the people living in the Semi-Arid regions of West Africa. The present study was conducted to determine the stability, combining ability, and gene action conditions of the high level of Fe and Zn content in grain and selected agronomic traits. Hence, eight genotypes were selected based on the availability of grain Fe and Zn contents and crossed in a full diallel mating design. Progenies from an 8 × 8 diallel mating along with the parents were evaluated in an alpha lattice design with three replications in three locations for two years. The parental lines Jirani, LCIC 9702 and MORO, had positive significant general combining ability (GCA) effects for grain Fe concentration, while Jirani and MORO had positive significant GCA effects for grain Zn concentration. For the specific combining ability (SCA), among the 56 hybrids evaluated, only the hybrids LCIC 9702 × Jirani and MORO × ZANGO had positive significant SCA effects for grain Fe concentration across locations, and for grain Zn concentration, the hybrids Gamoji × MORO, LCIC 9702 × Jirani, and ICMV 167006 × Jirani had positive significant SCA effects. The reciprocal effects were significant for grain Zn concentration, grain yield, flowering time, plant height, test weight, and downy mildew incidence, suggesting that the choice of a female or male parent is critical in hybrid production. Grain Fe and Zn concentration, flowering time, plant height, panicle length, panicle girth, panicle compactness, and downy mildew incidence were found to be predominantly under additive gene action, while grain yield and test weight were predominantly under non-additive gene action. A highly positive correlation was found between grain Fe and Zn concentrations, which implies that improving grain Fe trait automatically improves the grain Zn content. The stability analysis revealed that the hybrid ICMV 167006 × Jirani was the most stable and high-yielding with a high level of grain Fe and Zn micronutrients.

Productivity of Soybean under Projected Climate Change in a Semi-Arid Region of West Africa: Sensitivity of Current Production System

The production of soybean is gaining more attention in West Africa. In light of projected changes in climate, there is a need to assess the potential impacts on yield productivity and variability among farmers. An evaluated GROPGRO module of the Decision Support System for Agro-technological Transfer (DSSAT) was used to simulate soybean productivity under both historical (1980–2009) and projected climate scenarios from multiple general circulation models (GCMs) under two representative concentration pathways (RCPs): 4.5 and 8.5. Agronomic data from 90 farms, as well as multiple soil profile data, were also used for the impact assessment. Climate change leads to a reduction (3% to 13.5% across GCMs and RCPs) in the productivity of soybean in Northern Ghana. However, elevated atmospheric carbon dioxide has the potential to offset the negative impact, resulting in increased (14.8% to 31.3% across GCMs and RCPs) productivity. The impact of climate change on yield varied widely amongst farms (with relative standard deviation (RSD) ranging between 17% and 35%) and across years (RSD of between 10% and 15%). Diversity in management practices, as well as differences in soils, explained the heterogeneity in impact among farms. Variability among farms was higher than that among years. The strategic management of cultural practices provides an option to enhance the resilience of soybean productivity among smallholders.

Effects of customized climate services on land and labor productivity in Burkina Faso and Ghana

Climate services favor adopting strategies to increase agricultural productivity, enhance sustainable development, and adapt to unavoidable climate variability and change. However, for climates services to be effective, they must be accessible and suitable to user needs. This study investigated the effects of customized climate services (CCS) on land and labor productivity. Portraying the case of CCS delivered in the districts of Bolgatanga (Northern Ghana), Dano and Ouahigouya (western and northern Burkina Faso) in West Africa, it used: i) historical panel data of daily rainfall, yields, agricultural input, and output prices; ii) cost statements of farm operations and iii) other survey data from beneficiaries of on-farm demonstrations (pilot sites). Different results were found across farmers on the demonstrator sites, with Dano and Bolgatanga recording the best land and labor productivity. Strong and positive effects were observed in Dano, where land productivity increased by 200% and labor productivity doubled despite consecutive pluviometric extremes such as heavy rain events and prolonged dry spells in the 2017 and 2018 cropping seasons. Further investigation showed that CCS was particularly favorable to land and labor productivity of farmers who were committed to the advisory given by the CCS providers. Therefore, as perishable goods, the success of CCS applications would require thorough co-production, delivery, and monitoring for their effectiveness in improving land and labor productivity for agriculture in semi-arid regions of West Africa.

Agromorphological Characterization Revealed Three Phenotypic Groups in a Region-Wide Germplasm of Fonio (Digitaria exilis (Kippist) Stapf) from West Africa

Fonio is an ancient orphan cereal, cultivated by resource-poor farmers in arid and semi-arid regions of West Africa, who conserved and used the cereal for nutrition and income generation. However, the extent and patterns of phenotypic variation within the fonio germplasm remain scarcely evaluated to inform breeding decisions. In this study, we used alpha lattice design to assess the phenotypic variability of 180 fonio accessions using 20 agro morphological descriptors, including both qualitative and quantitative traits at Bengou research station in 2018 and 2019. Descriptive statistics, combined analysis and multivariate analyses, including principal components analysis (PCA), hierarchical clustering, and multiple factor analysis (MFA) were performed. As results, we found significant differences among fonio accessions and among agro ecological zones of provenance for most of the quantitative traits. Furthermore, highly significant positive correlations were found between grain yield and other yield-related attributes such as harvest index and thousand seeds weight, whereas significant negative correlations were found between grain yield and flowering and maturity times. Clusters analysis revealed three phenotypic groups. Group 1 was characterized by early maturing fonio accessions with higher grain yield. Groups 2 and 3 were characterized by late maturing accessions with intermediate to moderate grain yield. The accessions from Group 1 are candidate for yield improvement and development of fonio lines with enhanced lodging resistance. Accessions from Group 2 and 3 can be improved for yield through marker-assisted selection of best thousand seed weight. This study highlights how traits are correlated within the major phenotypic groups of fonio in West Africa, and we discussed how these groups could be further exploited for improving traits of economic importance. Furthermore, this study exhibited agro morphological descriptors that discriminate fonio accessions and provide useful information for parental selection with economically important agronomic traits.

Sensitivity of Maize Yield in Smallholder Systems to Climate Scenarios in Semi-Arid Regions of West Africa: Accounting for Variability in Farm Management Practices

Climate change is estimated to exacerbate existing challenges faced by smallholder farmers in Sub-Sahara Africa. However, limited studies quantify the extent of variation in climate change impact under these systems at the local scale. The Decision Support System for Agro-technological Transfer (DSSAT) was used to quantify variation in climate change impacts on maize yield under current agricultural practices in semi-arid regions of Senegal (Nioro du Rip) and Ghana (Navrongo and Tamale). Multi-benchmark climate models (Mid-Century, 2040–2069 for two Representative Concentration Pathways, RCP4.5 and RCP8.5), and multiple soil and management information from agronomic surveys were used as input for DSSAT. The average impact of climate scenarios on grain yield among farms ranged between −9% and −39% across sites. Substantial variation in climate response exists across farms in the same farming zone with relative standard deviations from 8% to 117% at Nioro du Rip, 13% to 64% in Navrongo and 9% to 37% in Tamale across climate models. Variations in fertilizer application, planting dates and soil types explained the variation in the impact among farms. This study provides insight into the complexities of the impact of climate scenarios on maize yield and the need for better representation of heterogeneous farming systems for optimized outcomes in adaptation and resilience planning in smallholder systems.

English

Pearl millet (Pennisetum glaucum L.) is an important staple food crop, especially in arid and semi-arid regions of West Africa. However, the genetic diversity of pearl millet in these regions is poorly understood, and yet it is useful in identification of landmarks for in situ germplasm conservation and breeding programs, particularly in establishment of heterotic groups. Therefore, the aim of this study was to assess the patterns of genetic diversity and relationships among 30 West African pearl millet accessions, using 21 microsatellite markers. Population structure and population genetic diversity were also assessed. Genotypic data was generated using the ABI Prism 3730 and alleles were called and sized using GeneMapper software version 3.7. Molecular data was analyzed using DARwin 4.0, PowerMarker 3.0 and Arlequin version 3.11. The average marker quality index was 0.29 while the total number of alleles detected was 171 with an average of 8 alleles per locus. The average polymorphic information content (PIC) was 0.64. The average Nei’s genetic diversity and heterozygosity were 0.533 and 0.433, respectively. Hierarchical partitioning of genetic variation by analysis of molecular variance (AMOVA) demonstrated that genetic differentiation was low but significant at p<0.003 with a fixation index (Fst) of 0.154. Of the total genetic diversity, 5.8, 9.5 and 84.6% were attributed to country differences, population differences within the countries and differences within populations, respectively. Cluster and principal coordinate analysis of the 30 populations revealed two distinct pearl millet accessions while the 49 individuals revealed four clusters, all on the basis of geographic origins and genotypes. This study demonstrates the utility of simple sequence repeats (SSR) markers in detecting polymorphism, estimating genetic diversity and assigning heterotic groups in a highly cross-pollinated species such as pearl millet.   Key words: Genetic variability, pearl millet, polymorphic information content, population structure, simple sequence repeats (SSR) markers.

Cooking to be Modern but Eating to be Healthy: The Role of Dawa-Dawa in Contemporary Ghanaian Foodways

Dawa-dawa, the Hausa name for the fermented paste made from the seeds of the African locust bean tree (Parkia biglobosa) is a widely used ingredient in soups in the semi-arid regions of West Africa. With a very distinctive odor and taste, the perceived palatability of dawa-dawa has decreased over the past few decades, a shift in taste that has occurred alongside the increased availability of industrially produced bouillon cubes marketed for soup preparation. Instead of dichotomizing dawa-dawa and bouillon cubes, the intent of this paper is to use dawa-dawa as a means to explore how global pressures complexly contribute to processes of dietary change in rural West Africa. In this context there are two distinguishable fronts of global capitalism—one that shapes norms of what it means to be a “modern” cook or eater and one that shapes preferred and healthy diets as inaccessible. The intersection of these two processes produces what I argue are eaters in rural Upper West Ghana who overtly disregard dawa-dawa for its sensual properties, but who simultaneously and in a more covert manner retain alliance to its nutritional contribution.

Visualizing relationships in interdisciplinary research with Geographic Information Systems: A case study utilizing food security research in Sahelian West Africa

Achieving food security in the semi-arid region of West Africa remains challenging, primarily due to a combination of harsh climate and low soil fertility. The University of Saskatchewan, in partnership with many international organizations, has been researching solutions to increase the profitability of smallholder farmers in the region. This joint partnership aims at improving soil fertility for smallholder farming in Benin, Burkina Faso, Mali, and Niger. Data have been collected in eight different research sites, and include rainwater harvesting, crop yields, and soil samples. The data have a timeframe ranging from one year to many years. Prior to the University of Saskatchewan’s commitment to the project, research data had only been utilized on a local scale, with relatively low success in sharing results and findings across national borders.With this project, collaboration occurred among multiple researchers from different countries and disciplines. A new technique used for collaboration was an interactive Geographic Information Systems (GIS) database. GIS has proven to be a powerful tool and platform for analysing and disseminating research data. This geospatial analysis laid the foundation for further research, resulting in a robust examination of soil and socioeconomic data from overseas.

Crop-climate ensemble scenarios to improve risk assessment and resilience in the semi-arid regions of West Africa

Estimation of the response of rainfed crops to heat stress and water stress must ade- quately account for the uncertainty in climatic and non-climatic factors that affect impact assess- ments. The objective of this research was to narrow the range of values characterizing the limits within which estimates are expected to fall in the diagnostics of agroclimatic risks. Assessments were made by analyzing historical observations and evaluating the influence of heat stress and rainfall variability on crop water demand, biomass and grain yields of short-cycle cultivars of pearl millet and maize. We used a wide range of consistent and practical sets of crop model ensemble analyses (based on crop management practices such as plant density, fertilization levels, early/late sowing dates and soil types) and climate model ensembles from 2 climate change hypothesis (A1b and RCP8.5) over the West African Sudan-Sahel. Recent rainfall developments show that haz- ardous intra-seasonal rainfall distribution affects crop productivity, with increased frequency and intensity of daily rainfall, false start and early cessation of the rainy season and decreasing diurnal temperature range. In 2011�2050 perspectives, relative to the 1981�2010 baseline, a slight in - crease in temperature (i.e. +0.6 to +0.8°C) combined with a stationary to moderate decrease in precipitation leads to a 10 to 15% (8 to 15%) decrease in aboveground biomass production (grain yield). When the warming is moderate (i.e. +1.4 to 1.8°C), the decline in grain yield worsens (10 to 20%), despite a slight increase in rainfall projections. At these rates of loss in crop production, resilience can be reinforced. However, it will require that climate-smart crop management prac- tices be embedded in sub-seasonal and interannual monitoring and early warning systems.

PEARL MILLET PRODUCTION PRACTICES IN SEMI-ARID WEST AFRICA: A REVIEW

SUMMARYPearl millet (Pennisetum glaucumL.) is an important grain crop for millions of poor farmers and consumers in the semi-arid region of West Africa. During the past 40 years, much research on pearl millet production practices and adoption in this region has been conducted, but an attempt to summarize these results has not been previously completed and these research results are not readily available to many West African scientists. This review was completed to address this need and integrate knowledge, and at the same time identify research needs for the future and extension priorities for semi-arid West African agro-ecological zones. Research has shown that selection of improved varieties and cropping systems, appropriate cultural practices, and recommended integrated soil, nutrient, residue and pest management can greatly increase grain and stover yields of pearl millet. However, adoption by farmers has been minimal due to limited profitability, high risk and labour demand, limited input supply, market availability and appropriate public policy. This review has 196 articles included as in-text citations (Table 1) compared to 149 articles in the reference list, indicating that only one in four articles integrated two or more topics in the research. The obvious conclusion is that most of the past research has not addressed the ‘system’ but rather one or two management practices. In addition, most studies have interpreted responses in terms of yield without addressing other important considerations for farmer adoption. Recent conservation agriculture research moves closer to addressing the larger integrative types of research needed. Such research is complex and requires sustained funding for field and laboratory activities, but also for computer simulation modelling and economic assessment.

Combining Hydrology and Mosquito Population Models to Identify the Drivers of Rift Valley Fever Emergence in Semi-Arid Regions of West Africa

BackgroundRift Valley fever (RVF) is a vector-borne viral zoonosis of increasing global importance. RVF virus (RVFV) is transmitted either through exposure to infected animals or through bites from different species of infected mosquitoes, mainly of Aedes and Culex genera. These mosquitoes are very sensitive to environmental conditions, which may determine their presence, biology, and abundance. In East Africa, RVF outbreaks are known to be closely associated with heavy rainfall events, unlike in the semi-arid regions of West Africa where the drivers of RVF emergence remain poorly understood. The assumed importance of temporary ponds and rainfall temporal distribution therefore needs to be investigated.Methodology/Principal FindingsA hydrological model is combined with a mosquito population model to predict the abundance of the two main mosquito species (Aedes vexans and Culex poicilipes) involved in RVFV transmission in Senegal. The study area is an agropastoral zone located in the Ferlo Valley, characterized by a dense network of temporary water ponds which constitute mosquito breeding sites.The hydrological model uses daily rainfall as input to simulate variations of pond surface areas. The mosquito population model is mechanistic, considers both aquatic and adult stages and is driven by pond dynamics. Once validated using hydrological and entomological field data, the model was used to simulate the abundance dynamics of the two mosquito species over a 43-year period (1961–2003). We analysed the predicted dynamics of mosquito populations with regards to the years of main outbreaks. The results showed that the main RVF outbreaks occurred during years with simultaneous high abundances of both species.Conclusion/SignificanceOur study provides for the first time a mechanistic insight on RVFV transmission in West Africa. It highlights the complementary roles of Aedes vexans and Culex poicilipes mosquitoes in virus transmission, and recommends the identification of rainfall patterns favourable for RVFV amplification.

Response of exotic sorghum (Sorghum bicolor [L.] Moench) cultivars to planting date under natural infestation of Striga hermonthica (Del) Benth. in the Sudan savanna zone of northeast Nigeria

Sorghum (Sorghum bicolor [L.] Moench) is one of the most important cereal crops grown in the dry savannas and semi-arid regions of West Africa under rain-fed conditions. Although total sorghum production in Nigeria has increased over the years, the average grain yield on farmers' fields has remained low. A two-year trial was conducted to evaluate the effect of planting dates on three exotic sorghum cultivars (P9402, P9405, and PSL985061) and an improved local cultivar (KSV 8) under natural infestation with Striga hermonthica in northeast Nigeria. At Nzuda, the highest yield was obtained when planting was carried out on 19 July 2006 and on 5 July 2007. The decline in yield in 2007 as planting dates increased was largely due to early cessation of rain, which affected grain yield. At Sabon-Gari, KSV 8 and P9402 produced comparable grain yields that were higher than the yields of other cultivars at all planting dates. Grain yields of KSV 8 and P9402 were greater for 5 July than for the other planting dates and decreased significantly as the planting date was delayed, probably due to long maturity period. The highest grain yields were obtained from P9405 and PSL985061 when planted on 12 July and 19 July, respectively. KSV 8 had the highest number of emerged Striga plants at both locations. The number of emerged Striga plants under KSV 8 was 4.0–5.1 times higher at Nzuda and 2.4–2.6 times higher at Sabon-Gari than the number on the exotic cultivars at those locations. Among the exotic cultivars, differences in the number of emerged Striga plants were not significant. Farmers in the zone would maximize sorghum yield if improved cultivars are planted at the appropriate dates in Striga infested fields.

An integrated approach to hydro-geological lineament mapping of a semi-arid region of West Africa using Radarsat-1 and GIS

In the 21st century, water resource management will be a major socioeconomic issue and an essential component of progress in semi-arid regions. The Soudano-Sahelian region of Africa suffers from a chronic lack of reliable hydro-geological maps for local water resource managers. To provide better tools for groundwater exploration, this paper focuses on hydro-geological lineament mapping using remote sensing data. The objectives were (1) evaluate the potential of multi-angular and multi-temporal Radarsat-1 images for extracting lineaments in semi-arid regions and (2) provide map of potential hydro-geological lineaments. No significant relationship was found between lineament yield and incidence angle of Radarsat-1 images, while lineament spatial distribution was in good agreement with the land use and geology of the study area. The high scores observed for NNE–SSW and NNW–SSE orientations match the results of local lineament studies of the region. Radarsat-1 image acquired on May 01, 2001 offers the greatest potential, due to the reduced effect of vegetation during this region's dry season. Potential hydro-geological lineaments were mapped using the weighting of well location, presence of green vegetation during the dry season, preferential lineament orientations and presence of cross-points. The mapping revealed five classes (Very low, Low, Moderate, High and Very high) of potential hydro-geological lineaments with high and very high potential poorly represented. Results also reveal that most wells are far enough from lineaments or cross-points and hence the inefficiency of existing drilling programs.

La lutte contre l'insécurité alimentaire au Sahel: permanence des questionnements et évolution des approches*

Food security is potentially uncertain and unstable throughout the rural semi-arid regions of West Africa often affected by repetitive and severe phenomenon. It is, however, still difficult to determine where and how the insecurity will next appear and which categories of population will be most exposed and vulnerable to it. At present, politicians, humanitarians and technical experts base their decisions mainly on immediate and apparent indicators in spite of the analysis of complex nature-society interactions. For the same reason, public and private interventions in the non-food crisis context are often technically and ideologically oriented rather than locally and specifically based. Since the colonial era, there has been little change in the way to tackle rural and urban food poverty and vulnerability: agricultural intensification, food shortage, food purchasing, food aid. Moreover, combined strategies aimed at reducing food insecurity prove inefficient at eradicating it as real and long term food policies no longer exist in the weak, poor and fragile States of western Africa after two decades of hotly debated economic and political adjustment. This article emphasizes the conceptual and methodological approaches currently used to investigate food insecurity for the future of the Sahel.

Saharan Dust Pollution: Implications for the Sahal?

To the Editor: The main source of atmospheric mineral dust is the Sahara desert, which produces about half of the yearly global mineral dust.1 About 12% of the Saharan dust moves northwards to Europe, 28% westwards to the Americas, and 60% southwards to the Gulf of Guinea.1 Saharan dust storms can lead to particulate matter (PM) levels that exceed internationally recommended levels.1–3 Recently, special attention has been paid to the mineral PM air pollution of dust storms, which may be a serious health threat. We took a systematic review of the literature to find relevant studies on the effects of Saharan dust on air quality or human health. We searched the ISI web of knowledge database using “PM10,” “PM2.5” or “health” AND “dust storm,” “sand storm,” “African dust,” “Saharan dust,” or “dust events” without restrictions. The search extended from January 1999 to December 2008. We selected 97 articles of which 72 studied PM air pollution in Europe, 13 in the Americas, 7 in the Near East and Asia, and 4 considered international data. Only one specifically addressed air pollution in the Sahal. Four focused on human health effects—2 in the Mediterranean and 2 in the Caribbean. Recent work has shown that windblown Saharan dust causes daily mortality to increase by 8.4% per 10 μg/m−3 increase in PM10–2.5 in Barcelona, Spain. However, the increase in average PM concentration during Saharan and dust days was modest: from 14.9 to 16.4 μg/m−3 PM10–2.5, and from 38.9 to 46.3μg/m−3 PM10.4 These findings are consistent with results from a 10-year time-series analysis of morbidity in Cyprus. All-cause admissions were 4.8% higher on Saharan dust storm days and cardiovascular admission were 10.4 higher.5 On the Caribbean island of Trinidad, Saharan dust clouds have been associated with increased pediatric asthma accident and emergency admissions,6 although these results have been challenged.3 Despite this large body of information far from the source, information about health effects of dust storms in the Sahel is remarkably scarce. In 41 villages across Niger, a survey assessed farmers’ views about the relative importance of constraints to agricultural production. Surprisingly, health problems related to dust storms were of more concern than crop damage or loss of topsoil. Eighty percent of villagers (n = 892) reported severe health symptoms during the Harmattan season, when people are exposed to high dust concentration.7 In Nouakchott, Mauritania, mineral dust accounts for an estimated 137 daily exceedances of the 50 μg/m−3 PM10 EU limit value per year. The annual mean PM10 is 108 μg/m−3.3 An appeal for more studies about health effects of desert dust in Europe appeared recently in this journal,8 with concern that the toxicity from coarse mineral particles may be underestimated. However, most of the desert dust is deposited near its source1; the mass concentration of PM affecting air quality several thousand kilometers away is relatively modest. What are the effects of the much larger PM concentrations near the Sahara? How sensitive are Sahelian people to large amounts of coarse mineral dust? What are the health effects of exposure to several consecutive days of high dust concentration? No systematic particulate air pollution data are available for the Sahel, and the potentially-affected countries do not have good-quality public health data to adequately support such studies. More research on this topic is sorely needed in arid and semiarid regions of West Africa, where air pollution studies are currently as scarce as rainfall. Florence de Longueville Sabine Henry Department of Geography, University of Namur, Namur, Belgium, [email protected] Pierre Ozer Environmental Sciences and Management Department, University of Liège, Liege, Belgium

Early growth performance and water use of planted West African provenances of Vitellaria paradoxa C.F. Gaertn (karité) in Gonsé, Burkina Faso

A participatory selection trial of five provenances from Burkina Faso (3), Mali (1) and Senegal (1) was established in Burkina Faso in 1997 with the aim of addressing issues of the long juvenile phase and the large variability in annual fruit yields of Vitellaria paradoxa C.F. Gaertn in West Africa. The objectives of the present study were to evaluate survival rate and the growth performance of the five provenances, characterize the wetting profile under which the trees of these provenances are growing and quantify the variation in their seasonal transpiration. The design was a randomized complete block design (RCBD) with single tree as the experimental unit which was replicated 70 times. The results showed a mean survival rate of 50% for all provenances. Passore (Burkina Faso), Djonon-Karaba (Mali) and Botou-Fada (Burkina Faso) provenances showed the highest height and collar diameter whereas the provenance of Gonse (Burkina Faso) performed poorly. Djonon-Karaba provenance displayed the highest water use (2.70 l day−1 tree−1 in 2004 and 2.85 l day−1 tree−1 in 2005). Soil water content under Passore provenance was the lowest (9.38%) whereas its content under Gonse provenance (11%) was the highest with no clear pattern according to the distance from tree trunk. Samecouta and Djonon-Karaba provenances showed the highest transpiration values per sapwood unit area in 2004 (0.079 l cm−2 day−1) and in 2005 (0.069 l m−2 day−1), respectively. Based on growth performance and water use, it can be recommended at this early stage the selection of Djonon-Karaba and Passore provenances as the most suitable for semi-arid regions of West Africa. However, there is a need for further data to model the long term effects of these provenances on soil water balance and their fruit production before reliable recommendations can be made to farmers.

Trees to control weeds in pearl millet

This study shows that growing trees represents a sustainable and efficient alternative to control weeds in millet. A survey was conducted on farmers’ fields in September 1998 at the end of the rainy season in Maiduguri in the semi-arid zone of Nigeria to assess the potential of the Faidherbia albida tree for the control of the Striga hermonthica weed in millet. A random survey was carried out in four locations on the farmers’ fields. The results show that F. albida trees could completely control S. hermonthica weeds occuring in millet under the tree canopy. Indeed, no single Striga emergence was observed under all trees surveyed, while the adjacent crops outside the tree canopies were seriously infested with S. hermonthica, causing reduction in plant growth of 76.5%, panicle length of 23.8% and millet panicle yield of 171.3%. Furthermore, plant performance under the tree canopies was very high, as plant height was increased by 80.0%, stem diameter by up to 15.9%, panicle length by 34.4% and panicle yield by 298.6% as compared with the Striga-infested plants outside the tree canopy. Plants within the 6–15 m area away from the tree trunk performed better than the 0–5 m area. The implication of these results in relation to Striga control in the semi-arid region of West Africa is discussed.

Energy partitioning over the West African savanna: Multi-year evaporation and surface conductance measurements in Eastern Burkina Faso

Seasonal variability of the energy partitioning was analyzed with a combination of eddy fluxes of sensible and latent heat and weather data on intensely farmed land in the savanna area of Eastern Burkina Faso, West Africa. The analysis covers two rainy seasons (May-October 2003 and 2004), one dry season (December-April 2004), one dry to wet transition period (May-June 2004) and two wet to dry transition periods (October-November 2003 and 2004). This is the first long-term flux measurement reported upon for this part of the world. The inter-annual partitioning of the available energy between the latent heat (actual evaporation) and sensible heat flux shows a conservative relationship between a decrease in annual rainfall (33%) and the sum of the increase in sensible heat flux (20%) and decrease in latent heat flux (10%). The latent heat flux was the main consumer of the available energy during the rainy season (71%), while sensible heat flux was dominant during the dry season (77%). In terms of the rainy season water balance, 1229 mm of rainfall was observed in 2003, of which 351 mm evaporated, while 825 mm of rainfall was observed in 2004, of which 268 mm evaporated. During the dry season, the latent heat flux was strongly coupled to the atmosphere, with the decoupling coefficient (?) ranging from 0.18 to 0.4. These low values were due to low soil moisture availability and high vapor pressure deficit (VPD > 4 kPa). During the rainy season, the latent heat flux was decoupled from the atmosphere (0.6 ? ? <0.9). Following this pattern of coupling and decoupling, a new formulation of actual evaporation and surface conductance was proposed. The results are thought to be relevant inputs for eco-hydrological models in the semi-arid region of West Africa.