West African Cities Research Articles

L'inégalité des chancessur le marché du travail urbain ouest-africain

Résumé Cette étude cherche à savoir si l’origine sociale des travailleurs détermine leurs opportunités sur le marché du travail, en comparant le degré d’inégalité des chances sur le marché du travail dans sept capitales ouest-africaines. Elle évalue ensuite pour chacune des villes si la situation professionnelle du père agit directement sur le positionnement sur le marché du travail ou si son effet est indirect, à travers l’éducation. Dans le premier cas, les politiques visant à égaliser les chances doivent agir directement sur le marché du travail, dans le second cas, elles doivent agir en amont, sur le système éducatif. Classification JEL : J24, J62, D63

Will they buy it? The potential for marketing organic vegetables in the food vending sector to strengthen vegetable safety: A choice experiment study in three West African cities

Considering the hazardous use of synthetic pesticides in vegetable production in urban West Africa, this research investigated the marketing potential of organic vegetables in the food vending sector of Cotonou (Benin), Accra (Ghana) and Ouagadougou (Burkina Faso). Certified organic production and marketing was examined as a potential strategy to improve chemical food safety. A stratified random sampling strategy was applied to study the preferences of food vendors (n=180) and consumers (n=360); vegetable use, risk perception, choice preferences and willingness-to-pay (WTP) for organic certification were specifically analyzed. The results showed that awareness of chemical contamination risks was generally low. Appearance of a product was central to vendor choice; consumers attributed similar utility to taste and organic certification. Consumer WTP was calculated to be a premium of 1.04 USD (per plate) if the food served contained only certified organic vegetables. In restaurants, this would mean an average premium of 19% for a meal. If certified organic vegetable production is to make a positive impact on food safety in urban West Africa, we suggest concentrating marketing efforts on the educated “elite” who frequent restaurants. However, considering that restaurant owners exhibited a lower preference for organic certification than lower class food vendors, the marketing situation is difficult. We therefore conclude that demand from the food vending sector alone will not institutionalize domestic certification mechanisms; this underlines the need for public commitment to facilitating such change.

A comparison between urban livestock production strategies in Burkina Faso, Mali and Nigeria in West Africa

We undertook a comparative analysis of (peri-)urban livestock production strategies across three West African cities. Using a semi-structured questionnaire, livestock-keeping households (HH) were interviewed in Kano/Nigeria (84 HH), Bobo Dioulasso/Burkina Faso (63 HH) and Sikasso/Mali (63 HH). Questions covered livestock species kept, herd sizes and structure, feeds used, manure management, livestock marketing and production constraints. Sheep and goats dominated (p < 0.001) in Kano (76 and 75 % of HH) compared to Bobo Dioulasso (48 and 40 %) and Sikasso (28 and 40 %), while cattle and poultry were more frequent (p < 0.001) in Bobo Dioulasso (82 and 69 % of HH) and Sikasso (65 and 79 %) than in Kano (29 and 20 %). Across cities, ruminant feeding relied on grazing and homestead supplementation with fresh grasses, crop residues, cereal brans and cottonseed cake; cereal grains and brans were major ingredients of poultry feeds. Cattle and sheep fetched highest prices in Kano, unit prices for goats and chicken were highest in Sikasso. Across cities there was little association of gardens and livestock, whereas field cropping and livestock were integrated. There was no relation between the education of the HH head and the adoption of improved management practices (p > 0.05), but the proportion of HH heads with a long-term experience in UPA activities was higher in Kano and in Bobo Dioulasso than in Sikasso (p < 0.001). We therefore postulate that the high illiteracy rate among (peri-)urban livestock keepers in West Africa does not threaten the acceptance of improved technologies and innovations supporting the sustainability of their livestock production.

Characterization of urban and peri-urban agroecosystems in three West African cities

Systems of urban and peri-urban agriculture (UPA) take many forms in terms of integration of different activities, production intensities and production orientations. The present study is aimed at a refined characterization of the diversity in terms of production orientation, resource endowments and production strategies of the different types of farm households involved in urban and peri-urban agriculture in three West African cities. A total of 318 UPA households were surveyed using a standardized semi-structured questionnaire in the West African cities Kano (Nigeria), Bobo Dioulasso (Burkina Faso) and Sikasso (Mali). Through categorical principal component analysis and two-step cluster analysis, six distinct household clusters were identified based on resource endowments and the degree of integration of vegetable, field crop and animal production. Three clusters appeared in all three cities; the remaining three were specific for one of the cities each and comprised (i) commercial gardening plus field crop–livestock (cGCL) keeping, (ii) commercial livestock plus subsistence field cropping (cLsC), (iii) commercial gardening plus semi-commercial field cropping (cGscC), (iv) commercial gardening plus semi-commercial livestock (cGscL) keeping, (v) commercial field cropping (cC) and (vi) commercial gardening (cG). Production constraints were similar across the cities, that is, high costs of inputs, water shortages and lack of fertilizers in the garden and field crop production systems, while feeding constraints and animal diseases were the main constraints in livestock production. UPA remains an important economic activity to livelihood strategy for urban and peri-urban farmers. Appropriate policies should be formulated that efficiently target the site-specific constraints for improving the quality and sustainability of UPA production systems.

Real time black carbon measurements in West and Central Africa urban sites

Abstract Real time measurements of Black Carbon (BC) in PM 2.5 aerosols were performed during AMMA and POLCA programs, between 2005 and 2010 in Cotonou (Benin), Dakar (Senegal), Bamako (Mali), and Yaounde (Cameroon). Indeed, BC was chosen as a metric because of its interest as an urban pollutant. The instrumented sites are representative of the traffic source. At Dakar, BC concentrations are high from November to April (13,000 ± 3500 ng m −3 ) and lower from May to September (8000 ± 3200 ng m −3 ). In dry season (November–April), high BC concentrations occurred as a result of northeasterly long-range transport of polluted air masses over West Africa, in addition to local emissions. However, during wet season (May–September) reduced traffic levels, school vacations and wet deposition processes contribute to lower BC concentration levels. Measured diurnal BC peak concentrations, at all sites, mainly occur during morning and evening rush-hour periods, indicating the paramount role of traffic. Highest values are observed between 5–9 a.m. and from 5 p.m. to 9 p.m. depending on the site, while lowest are occurred at night time and middle afternoon when activities of the population are reduced. BC source apportionment from absorption measurements also confirmed the relative importance of traffic (88%) versus biomass burning (12%). Also, BC measurements were functions of days of the week, with highest values occurring on Fridays and lowest ones on Sundays. Spatial variations associated to BC levels are very different from one site to another, revealing different types of sources with strong variations at the regional scale. It appears that mean BC concentrations in Dakar are lower by a factor of two, compared to those observed in Bamako, but remain higher than in some other West African sites (e.g. Cotonou, Yaounde). Overall, BC concentrations in our different sites are comparable to reported European and Asian megacity levels. Finally, using measured BC/PM 2.5 ratios, we have estimated PM 2.5 mass concentrations in Dakar from June 2008 to June 2009 to be 44.4 ± 14.3 μg m −3 , well above the WHO (2005) threshold of 10 μg m −3 . This paper clearly highlights high pollution levels in West African large cities, with potential important impacts on the health of the regional population.

Field-scale analysis of water and nutrient use efficiency for vegetable production in a West African urban agricultural system

Urban agriculture increasingly supplies food and non-food services to the rapidly growing West African cities. However, with its typically heavy use of fertilizers and uncontrolled use of water, it bears severe risks of soil and groundwater pollution. This study was carried out in Bobo Dioulasso (Burkina Faso, West Africa) at two commercial gardening sites. It aimed at performing a detailed characterization of farmer’s water and nutrient management strategies. Four vegetable crops were monitored (tomato, cabbage, carrot and lettuce). Water inputs (rainfall and irrigation), nutrient inputs (organic and mineral fertilizers and nutrients in irrigation water) and crop uptake were monitored over a 1–2-year period. In addition, pan lysimeters allowed monitoring drainage. Depending on the site, 3–8% of the input water was lost by drainage, i.e., as much as 293 mm/year at one of the sites. During the dry season, when the farmer has full control over the water supply, water application exceeded plant requirements by as much as 40%, which reveals inefficient water use. Up to 800 kg N ha−1, 140 kg P ha−1 and 500 kg K ha−1 were applied for a single crop cycle. With few exceptions, crops tended to be strongly over-fertilized, except for K at one of the two sites. Nutrient supply exceeded crop requirements by 109 to 2,012 kg N, 66 to 450 kg P and 0 to 393 kg K per year. These results, in combination with the large observed rates of drainage, are indicative of a high risk of nutrient leaching and groundwater contamination. The partial factor productivity of nutrients tended to be low. These results therefore suggested that there is scope to substantially reduce nutrient application rates in these systems without adverse effects on yields, which would be beneficial for groundwater resources and improve the economic returns.

Motorbike taxis in the "transport crisis" of West and Central African cities

Dans nombre de villes d’Afrique subsaharienne, un mode original de transport commercial de personnes, le moto-taxi, connaît un développement spectaculaire. L’objectif de cet article est d’analyser les conditions qui ont rendu possible l’émergence des motos-taxis comme l’un des principaux modes collectifs, et d’éclairer le rôle qu’ils tiennent dans la mobilité urbaine. L’essor des motos-taxis peut s’expliquer par le manque d’offre de transport public, par la disponibilité des facteurs de production, par le laxisme de la régulation publique en matière de transport urbain. Les résultats de deux enquêtes ménages mobilité menées en Afrique centrale (Douala) et de l’Ouest (Niamey) montrent que, là où ils sont utilisés, les motos-taxis peuvent contribuer à élargir l’accès à la mobilité motorisée et à satisfaire des besoins de mobilité non pris en compte par d’autres modes de transport collectif.

Analysis of landscape transformation processes in and around four West African cities over the last 50 years

Sub-Saharan Africa has experienced substantial urbanisation and land degradation processes over the past three decades. Using multi-source satellite imagery combined with geographical and demographic data, this study's aims were to analyse the extent of land cover changes (LCC) and identifying major landscape transformation processes (LTP) and their drivers for four West African cities in Mali, Burkina-Faso, Nigeria and Niger. A common classification scheme was used for a visual interpretation of Corona images from the 1960s and an automated classification of Landsat scenes from 1986, 2000/2001 and 2009. Based on a postclassification comparison LCC were summarized and related to the demographic trends of the past 50 years. Map changes were calculated from 1986 to 2009 to depict LTP (urbanisation, crop expansion, deforestation, and land abandonment) for the cities and their respective hinterlands. To investigate the effect of accessibility and infrastructural factors, LTP were related to the distance to roads, surface water and urban areas. From 1960 to 2009 a large-scale urban agglomeration was detected and the proportion of cultivated land in former natural woody savannas surrounding all four cities increased by 35%. The expansion of cropland during the past 30 years seemed to depend greatly on the availability of irrigation water in the semi-arid Sahelian cities (Kano and Niamey), whilst this was not a major driving factor for the cities of the Sudanian zone (Sikasso and Bobo-Dioulasso). Given the likely increase in water scarcity and land suitable for agriculture, ex ante land use planning and monitoring strategies will become increasingly important.

Seasonality of the dietary dimension of household food security in urban Burkina Faso

Food insecurity is affecting an increasing number of urban poor in the developing world. Yet seasonal characteristics of food intakes have rarely been studied in West African cities. The objective of the present study was to assess the seasonality of the dietary dimension of household food security in Ouagadougou (Burkina Faso). In 2007, two sets of data were collected during the lean and post-harvest seasons, respectively, on a representative sample of 1056 households. At each season, two non-consecutive 24 h recalls were performed at the household level. Food prices were also recorded. Household food security was assessed by the household's mean adequacy ratio (MAR) for energy and eleven micronutrients. Changes in the MAR according to the season were analysed by mixed multivariate linear regression. Results showed that intakes of energy and of ten micronutrients were significantly lower during the lean season than during the post-harvest season, leading to a lower MAR in the lean season (49·61 v. 53·57, P < 0·0001). This was related to less frequent consumption and consumption of smaller amounts of vegetables and of foods prepared at home. Food security relied heavily on food expenses (P < 0·0001) and on the price of meat/fish (P = 0·026). Households with economically dependent adults (P = 0·021) and larger households (P < 0·0001) were the most vulnerable, whereas education (P = 0·030), social network (P = 0·054) and urban origin other than Ouagadougou (P = 0·040) played a positive role in food security. To achieve food security in Ouagadougou, access to micronutrient-dense foods needs to be ensured in all seasons.

Gender and ethnic earnings gaps in seven West African cities

In this paper, we measure, compare and analyse gender and ethnic earnings gaps in seven West African capitals using data from an original series of urban household surveys. Our results show that gender earnings gaps are large in all the cities in our sample with significant variations across cities. Cities with large gender earnings gaps are also where gender education gaps are wider and where the female labour market participation is highest. Decomposition of the gender gaps shows that differences in characteristics explain around 40% of the raw gender gap on average, but this varies somewhat across cities. The results of the full decomposition of the gender earnings gaps suggest that differences in sector allocation contribute, on average, to one third of gender earnings gaps. Gender gaps are very wide in the informal sector and differences in micro-firm characteristics also account for differences in self-employment earnings. In contrast to the large gender earnings gaps measured in the seven cities, majority ethnic groups do not appear to be in a systematically advantageous position on the urban labour markets in our sample of cities, and observed gaps are small compared with gender gaps. Looking at more detailed levels of ethnic disaggregation, ethnic earnings differentials are found to be systematically smaller than gender differentials. Moreover, none of the minority “favoured” groups seem to have any relation to the ethnicity of the Head of State at the time of the survey. Holding productive characteristics constant, some unexplained differences persist however.

Cross-Location Analysis of the Impact of Household Socioeconomic Status on Participation in Urban and Peri-Urban Agriculture in West Africa

This study explores the relation between household socioeconomic status (SES) and participation in urban and periurban agriculture (UPA) in three West African cities. We used a structured questionnaire to survey 700 randomly selected households: 250 in Kano, Nigeria, 250 in Bobo Dioulasso, Burkina Faso, and 200 in Sikasso, Mali. Multiple correspondence analysis was applied on household asset variables to create an index of assets which was used as a proxy for household SES. The results showed no significant differences in households’ rate of participation in UPA across socioeconomic groups. Participation in UPA was rather significantly (P < 0.001) and positively related to household size. Interestingly, the analysis revealed that field crop cultivation and gardening were more common among households in the low and medium SES groups while those in the high SES group were more likely to keep livestock.

Tropospheric ozone production related to West African city emissions during the 2006 wet season AMMA campaign

Abstract. During African Monsoon Multidisciplinary Analyses (AMMA) airborne measurements of ozone, CO and nitrogen oxides (NOx) were collected by French and German Falcon aircraft near three cities in West Africa (Cotonou, Niamey and Ouagadougou). They have been analysed to identify the good conditions to observe ozone plumes related to city emissions during the monsoon season. Results show that an O3 increase of 40–50 ppbv above the summer average concentration took place during two specific events: one near Cotonou on the coast of the Gulf of Guinea, and the other near Niamey in the Sahel region. In both cases a high level of NOx (3–5 ppbv) is related to the ozone production. Air mass transport simulations with FLEXPART and a tracer simulation with the BOLAM mesoscale model shows that Southern Hemisphere biomass burning emissions are always at higher altitude (&gt;3 km) compared to the city emissions. In Niamey and Ouagadougou, the daily variability of ozone and CO correlates with the FLEXPART analysis showing the role of air mass stagnation near the city for 1–2 days and advection of emissions from the vegetated areas. Absence of ozone enhancements for high CO values can be explained by the occurrence of deep convection near the city. In the Sahel region, convection must be accounted for to understand the small number of observed ozone plumes but also to explain the high level of NOx in the 3–5 ppbv range, due to increasing soil emissions after rainfall. To verify that daily ozone production can reach 20 ppbv day−1 for the NOx and CO conditions encountered near West African cities, a simulation of the CiTTyCAT Lagrangian model was conducted using the observed average chemical composition reported by other aircraft during AMMA. Such ozone production is possible for NOx levels up to 5 ppb showing that West African cities are potentially significant sources of tropospheric ozone.

Exploring the diversity of urban and peri-urban agricultural systems in Sudano-Sahelian West Africa: An attempt towards a regional typology

Developing appropriate and innovative technologies and policies to respond to the challenges that urban and peri-urban agriculture (UPA) faces in West Africa requires a better understanding of the existing production systems. Although there is an increasing recognition of the importance of UPA in the region, its extent, forms and related practices may vary across countries and cities because of different socio-economic conditions and urbanization patterns. A systematic classification of the regional UPA systems is lacking but is necessary to allow for meaningful comparisons between cities and avoid misleading generalizations. The purpose of this study was to develop a typology of UPA households across three selected West African cities. Survey data from 318 UPA households (Kano: 99, Bobo Dioulasso: 111, Sikasso: 108) were submitted to principal components analysis for categorical variables (CATPCA). Next, the Two-Step cluster method was used to classify the households using object scores obtained from the CATPCA. Diversification of farm activities, farm resource endowment and production orientation were the major discriminating variables. In each city, four distinct UPA systems were identified, of which three were common to Kano, Bobo Dioulasso and Sikasso: commercial gardening plus field crops and livestock (59%, 18%, and 37%), commercial livestock plus subsistence field cropping (14%, 41%, and 7%), and commercial gardening plus semi-commercial field cropping (14%, 28%, and 30%). The fourth group was different at each location and was characterized as follows: commercial gardening plus semi-commercial livestock in Kano (13%), commercial field cropping in Bobo Dioulasso (13%) and commercial gardening in Sikasso (26%).

Economic Benefit to Gardeners and Retailers from Cultivating and Marketing Vegetables in Niamey, Niger

Little is known about the effects of season and marketplace on the return obtained by urban gardeners and retailers in West African cities from the cultivation and sale of amaranth, cabbage, lettuce and tomato. To fill this knowledge gap, measurements of yields and weekly price interviews were conducted in Niamey, Niger, during the rainy season (August–October) and the cool dry season (November–January) of 2007–08. Using gross margin (GM) analysis, net profits (NP) and returns (R) on investments were calculated. During the rainy season, farm-gate prices of tomato averaged 660 FCFA kg−1fresh matter, compared with 450 FCFA kg−1fresh matter (p &lt; 0.05) in the cool dry season, while prices of amaranth, lettuce and cabbage were more stable across seasons (100 FCFA = 0.15 Euro). The estimated GM (FCFA per hectare and season) and R (FCFA per FCFA invested) were 5.83m (R = 12.78) for amaranth, 10.09m (R = 18.98) for cabbage, 5.90m (R = 12.21) for lettuce and 6.40m (R = 16.58) for tomato during the cool dry season, compared with 4.71m (R = 8.44, amaranth), 9.50m (R = 13.48, cabbage), 6.52m (R = 7.08, lettuce) and 15.17m (R = 23.46, tomato) in the rainy season. Inputs in terms of labour, fertilizers and seeds strongly affected returns. Cabbage and tomato market prices (per kg FM) averaged 804 FCFA and 832 FCFA in the rainy season, compared with 410 FCFA (p &lt; 0.05) and 574 FCFA (p &lt; 0.05) in the cool dry season. For amaranth and lettuce, the NP of market retailers depended only on marketplace, whereas the NP of cabbage and tomato strongly depended on season and marketplace. Reducing mineral fertilizer use would lower production costs and thus increase gardeners' profits; at the same time, it would reduce environmental hazards ensuing from urban vegetable production in Niamey

Mineral‐nitrogen and phosphorus leaching from vegetable gardens in Niamey, Niger

AbstractUrban and periurban agriculture (UPA) contributes significantly to meeting increasing food demand of rapidly growing urban populations in West African cities. The often intensive high‐input vegetable production within UPA results in large positive nutrient balances, being presumably linked to strong nutrient leaching which needs quantification. This study aimed at estimating leaching losses of mineral N and P in three representative urban gardens of Niamey, Niger, using ion‐exchange‐resin cartridges installed below the crop rooting zone at 0.6 m soil depth. In 2007, a year with below‐average annual rainfall (425 mm as compared to 542 mm), mean leaching of mineral N amounted to 5.9 and 7.3 kg N ha–1 for two gardens with &gt; 80% sand fraction and only 2.2 kg N ha–1 for a garden with 40% silt and clay. Apparent annual P leaching was 0.7 kg P ha–1 in all three gardens. Additional multiannual studies are necessary to assess the effect of inter‐ and intraannual variation in precipitation on nutrient leaching in intensive UPA vegetable production of semiarid West Africa.

Quantifying Health Improvements from Water Quantity Enhancement: An Engineering Perspective Applied to Rainwater Harvesting in West Africa

Knowledge of potential benefits resulting from technological interventions informs decision making and planning of water, sanitation, and hygiene programs. The public health field has built a body of literature showing health benefits from improvements in water quality. However, the connection between improvements in water quantity and health is not well documented. Understanding the connection between technological interventions and water use provides insight into this problem. We present a model predicting reductions in diarrhea disease burden when the water demands from hygiene and sanitation improvements are met by domestic rainwater harvesting (DRWH). The model is applied in a case study of 37 West African cities. For all cities, with a total population of over 10 million, we estimate that DRWH with 400 L storage capacity could result in a 9% reduction in disability-affected life years (DALYs). If DRWH is combined with point of use (POU) treatment, this potential impact is nearly doubled, to a 16% reduction in DALYs. Seasonal variability of diarrheal incidence may have a small to moderate effect on the effectiveness of DRWH, depending on the storage volume used. Similar predictions could be made for other interventions that improve water quantity in other locations where disease burden from diarrhea is known.

Vertical distribution of heavy metals in wastewater-irrigated vegetable garden soils of three West African cities

Application of untreated wastewater to irrigate urban vegetable gardens is raising serious concern about possible health risks associated with the consumption of these vegetables particularly with regard to the concentrations of heavy metals (HM) in their edible portions. The soil concentrations of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn), were investigated in seven vegetable gardens from the three West African cities of Kano (Nigeria), Bobo Dioulasso (Burkina Faso) and Sikasso (Mali). Also determined were input–output balances of Cd and Zn from five vegetable gardens under 30 years of wastewater irrigation in Kano. In these gardens Cd (2.3–4.8 mg kg−1) and Zn (13–285 mg kg−1) concentrations throughout the profile attained unsafe levels. The concentrations of Cu (0.8–18 mg kg−1), Cr (1.8–72 mg kg−1), Ni (0–17 mg kg−1) and Pb (0.6–46 mg kg−1) were below the safety thresholds for arable soils. Overall, concentrations of Zn, Cd, Pb and Ni were higher in Kano than in Bobo-Dioulasso and Sikasso. Input–output analyses in Kano indicated that irrigation wastewater contributed annually 400–3,700 g Cd ha−1 and 7,200–22,300 g Zn ha−1, fertilizer 30–2,100 g Cd ha−1 50–17,600 g Zn ha−1, harmattan dust 0.02–0.4 g Cd ha−1 and 40–200 g Zn ha−1 while 300–500 g Cd ha−1 and 2,700–4,700 g Zn ha−1 came from rainwater inputs. Input–output calculations subtracting the amounts of HM taken out in vegetable biomass and that lost to leaching from total inputs yielded an annual net positive balance of 700–4,160 g Cd ha−1 and 9,350–39,700 g Zn ha−1. If such balances remain unchanged for another 10–20 years vegetables raised in these garden fields are likely to be unsuitable for human consumption.

A new inventory for two-wheel vehicle emissions in West Africa for 2002

Rather surprisingly, urban atmospheric particulate levels in West Africa compare with measured concentrations in Europe and Asia megacities (Liousse, C., Galy-Lacaux, C., Assamoi, E.-M., Ndiaye, A., Diop, B., Cachier, H., Doumbia, T., Gueye, P., Yoboue, V., Lacaux, J.-P., Guinot, B., Guillaume, B., Rosset, R., Castera, P., Gardrat, E., Zouiten, C., Jambert, C., Diouf, A., Koita, O., Baeza, A., Annesi-Maesano, I., Didier, A., Audry, S., Konare, A., 2009. Integrated Focus on West African Cities (Cotonou, Bamako, Dakar, Ouagadougou, Abidjan, Niamey): Emissions, Air Quality and Health Impacts of Gases and Aerosols. Third International AMMA Conference on Predictability of the West African Moosoon Weather, Climate and Impacts. Ouagadougou, Burkina Faso. July 20–24). This pollution mainly derives from road traffic emissions with, in some capitals (e.g. Cotonou), the strong contribution of two-wheel vehicles. Two key questions arise: are presently available emission inventories (e.g. Junker, C., Liousse, C., 2008. A global emission inventory of carbonaceous aerosol from historic records of fossil fuel and biofuel consumption for the period 1860–1997. Atmospheric Chemistry Physics, 8, 1–13; Bond, T.C., Streets, D.G., Yarber, K.F., Nelson, S.M., Woo, J.H., Klimont, Z., 2004. A technology-based global inventory of black and organic carbon emissions from combustion. Journal of Geophysical Research, 1009, D14203, DOI:10.1029/2003JD003697) able to account for these emissions? And, if not, how can we remedy this? The aim of this paper is to develop a methodology to estimate emissions produced by two-wheel vehicles in West Africa for 2002 in a context where reliable information is hardly available. Fuel consumption ratios between two-wheel engines (in this work) and all vehicles issued from UN database ( http://data.un.org/Data.aspx?d=EDATA&f=cmID%3aMO%3btrID%3a1221) are as high as 169%, 264% and 628%, for Burkina Faso, Mali and Chad respectively, indicating that this global database does not properly account for regional specificities. Moreover, emission factors for black carbon (BC) and primary organic carbon (OCp) have been measured for two-stroke engines in Benin (Guinot, B., Liousse, C., Cachier, H., Guillaume, B., et al. New emission factor estimates for biofuels and mobile sources. Atmospheric Environment, in press.), giving significantly higher values than in Europe. This is particularly true for OCp, and consequently the calculated emissions for two-stroke engines are also significantly larger than total road traffic previously estimated in global inventories ( Junker and Liousse (2008) with United Nations database for 2002; Bond et al., 2004). The ensuing discussion illustrates the importance of two-stroke engines in the West Africa transport sector and the strong need for inventory updating.

Nitrogen and carbon losses from dung storage in urban gardens of Niamey, Niger

Intensive vegetable production in urban and peri-urban agriculture (UPA) of West African cities is characterized by high nutrient inputs. However, little is known about nitrogen (N) and carbon (C) losses in these systems, in particular during the storage of manure, the main organic fertilizer in these systems. We therefore aimed at quantifying gaseous emissions of ammonia (NH3), nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) as well as leaching losses of C, N, phosphorus (P) and potassium (K) from animal manure stored in vegetable gardens of Niamey, Niger. During a first 3.5-month experiment in the hot dry season, cumulative gaseous N losses, measured with a closed-chamber system, were with 0.11 g kg−1 manure DM highest (P < 0.05) in the uncovered control treatment accounting for 1.8% of total manure N. Nitrogen losses decreased by 72% under plastic sheet roofing and by 50% under roofing + ground rock phosphate (RP) application at 333 g kg−1 manure DM. Carbon losses from manure amounted to 73 g kg−1 DM in the control and to 92 g kg−1 DM and 68 g kg−1 DM under roofing and under roofing + RP, respectively. In a second 3.5-month experiment conducted in the rainy season, C losses from the control were 164 g kg−1 manure DM and reduced to 77 and 65% of the control by roofing and roofing + RP, respectively. Leaching losses during the rainy season were only observed for the unroofed control and averaged 2.1 g C, 0.05 g N, 0.07 g P and 1.8 g K kg−1 manure DM.

Education and earnings in urban West Africa

Using a series of comparable labor force surveys in urban West Africa, we estimate the private returns to education among representative samples of workers in seven economic capitals (Abidjan, Bamako, Cotonou, Dakar, Lome, Niamey and Ouagadougou). The data allow us to provide a unique cross-country comparison using rigorously the same variables and methodology for each country. We tackle the issues of endogenous sector allocation (public, formal private and informal sectors) and endogeneity of the education variable in the earnings functions. We find that the returns to schooling are most often enhanced once an endogenous education variable is accounted for. This effect holds particularly true in the informal sector. In most West African cities of our sample, the public sector gives more value to education, followed by the formal private sector and then the informal sector. We also shed light on convex returns to education in all the cities and sectors, including in informal activity. More generally, a major contribution of this paper is to provide evidence of significant effects of education on individual earnings in the informal sectors of the West African cities, even at high levels of schooling.