Impact of Atlantic multidecadal variability on rainfall intensity distribution and timing of the West African monsoon

Previous studies agree on an impact of the Atlantic multidecadal variability (AMV) on the total seasonal rainfall amounts over the Sahel. However, whether and how the AMV affects the distribution of rainfall or the timing of the West African monsoon is not well known. Here we seek to explore these impacts by analyzing daily rainfall outputs from climate model simulations with an idealized AMV forcing imposed in the North Atlantic, which is representative of the observed one. The setup follows a protocol largely consistent with the one proposed by the Component C of the Decadal Climate Prediction Project (DCPP-C). We start by evaluating model's performance in simulating precipitation, showing that models underestimate it over the Sahel, where the mean intensity is consistently smaller than observations. Conversely, models overestimate precipitation over the Guinea coast, where too many rainy days are simulated. In addition, most models underestimate the average length of the rainy season over the Sahel; some are due to a monsoon onset that is too late and others due to a cessation that is too early. In response to a persistent positive AMV pattern, models show an enhancement in total summer rainfall over continental West Africa, including the Sahel. Under a positive AMV phase, the number of wet days and the intensity of daily rainfall events are also enhanced over the Sahel. The former explains most of the changes in seasonal rainfall in the northern fringe, while the latter is more relevant in the southern region, where higher rainfall anomalies occur. This dominance is connected to the changes in the number of days per type of event; the frequency of both moderate and heavy events increases over the Sahel's northern fringe. Conversely, over the southern limit, it is mostly the frequency of heavy events which is enhanced, thus affecting the mean rainfall intensity there. Extreme rainfall events are also enhanced over the whole Sahel in response to a positive phase of the AMV. Over the Sahel, models with stronger negative biases in rainfall amounts compared to observations show weaker changes in response to AMV, suggesting that systematic biases could affect the simulated responses. The monsoon onset over the Sahel shows no clear response to AMV, while the demise tends to be delayed, and the overall length of the monsoon season enhanced between 2 and 5 d with the positive AMV pattern. The effect of AMV on the seasonality of the monsoon is more consistent to the west of 10∘ W, with all models showing a statistically significant earlier onset, later demise, and enhanced monsoon season with the positive phase of the AMV. Our results suggest a potential for the decadal prediction of changes in the intraseasonal characteristics of rainfall over the Sahel, including the occurrence of extreme events.</p

Agroforesterie et services écosystémiques en zone tropicale

Respectueux de l’environnement et garantissant une sécurité alimentaire soutenue par la diversification des productions et des revenus qu’ils procurent, les systèmes agroforestiers apparaissent comme un modèle prometteur d’agriculture durable dans les pays du Sud les plus vulnérables aux changements globaux. Cependant, ces systèmes agroforestiers ne peuvent être optimisés qu’à condition de mieux comprendre et de mieux maîtriser les facteurs de leurs productions. L’ouvrage présente un ensemble de connaissances récentes sur les mécanismes biophysiques et socio-économiques qui sous-tendent le fonctionnement et la dynamique des systèmes agroforestiers. Il concerne, d’une part les systèmes agroforestiers à base de cultures pérennes, telles que cacaoyers et caféiers, de régions tropicales humides en Amérique du Sud, en Afrique de l’Est et du Centre, d’autre part les parcs arborés et arbustifs à base de cultures vivrières, principalement de céréales, de la région semi-aride subsaharienne d’Afrique de l’Ouest. Il synthétise les dernières avancées acquises grâce à plusieurs projets associant le Cirad, l’IRD et leurs partenaires du Sud qui ont été conduits entre 2012 et 2016 dans ces régions. L’ensemble de ces projets s’articulent autour des dynamiques des systèmes agroforestiers et des compromis entre les services de production et les autres services socio-écosystémiques que ces systèmes fournissent

Promotion de l’enseignement de la gymnastique a l’école élémentaire au Sénégal: Promotion of gymnastics teaching at elementary school in Senegal

Depuis l'antiquité grecque, l'éducation par les activités physiques trouve sa place dans l'éducation générale des jeunes. L’enseignement élémentaire au Sénégal vise à assurer à tous les enfants et particulièrement ceux en difficulté ou appartenant à des minorités ethniques la possibilité d’accéder à un enseignement obligatoire, gratuit, de qualité et de le suivre jusqu’à son terme. La gymnastique occupant une place importante dans le développement psychomoteur de l’enfant, son absence dans l’enseignement des activités physiques et sportives dans le cycle élémentaire ne s’explique pas. Ce fait nous a poussé à initier une recherche sur la problématique de l’intégration de l’enseignement de la gymnastique à l’école élémentaire au Sénégal. Notre problème de recherche porte sur les modalités et dispositions qu’il faudrait mettre en place pour que la gymnastique soit intégrée parmi les activités physiques et sportives qui sont enseignées à l’école élémentaire. Cette recherche s’inscrit dans le cadre d’une étude qualitative descriptive. Nous nous proposons de décrire les milieux de pratique de l’enseignement élémentaire ainsi que les parcours de formation des enseignants. Le programme d’enseignement des activités physiques et sportives et la perception de la gymnastique par les intervenants sont aussi explorés. Notre échantillon est composé de 85 enseignants issus des écoles élémentaires privées et publiques. Le questionnaire a été utilisé comme outil de collecte de données. ABSTRACTEducation through physical activity has since ancient Greece been part of the youth’s general education. Elementary education in Senegal aims to ensure that all children, particularly those in difficulty or belonging to ethnic minorities, have access to complete, compulsory and free quality education. Since gymnastics plays an important role in the child's psychomotor development, there is no explanation for its absence in the teaching of physical and sports activities in the elementary cycle. This fact prompted us to initiate research on the issue of the integration of gymnastics teaching into elementary school in Senegal. Our research problem concerns the modalities and provisions that should be put in place to ensure that gymnastics is integrated into physical and sports activities that are taught in elementary schools. This research is part of a descriptive qualitative study. We propose to describe the practice environments of elementary education as well as the teacher training specializations. The physical and sports activities teaching program, and the perception of gymnastics by the participants are also explored. Our sample consists of 85 teachers from private and public elementary schools. The questionnaire was used as a data collection tool

Les subsahariens en Chine : solidarité inter migrants face à une politique migratoire chinoise complexe : étude des cas des Africains de Guangzhou (Chine) dans ETHOS

International audienc

Les subsahariens en Chine : solidarité inter migrants face à une politique migratoire chinoise complexe : étude des cas des Africains de Guangzhou (Chine) dans ETHOS

International audienc

Potential contribution of climate conditions on COVID-19 pandemic transmission over West and North African countries

COVID-19, caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), is a very contagious disease that has killed many people worldwide. According to data from the World Health Organization (WHO), the spread of the disease appears to be slower in Africa. Although several studies have been published on the relationship between meteorological parameters and COVID-19 transmission, the effects of climate conditions on COVID-19 remain largely unexplored and without consensus. However, the transmission of COVID-19 and sensitivity to climate conditions are also not fully understood in Africa. Here, using available epidemiological data over 275 days (i.e., from 1 March to 30 November 2020) taken from the European Center for Disease Prevention and Control of the European Union database and daily data of surface air temperature specific humidity and water vapor from the National Center for Environmental Prediction (NCEP), this paper investigates the potential contribution of climate conditions on COVID-19 transmission over 16 selected countries throughout three climatic regions of Africa (i.e., Sahel, Maghreb, and Gulf of Guinea). The results highlight statistically significant inverse correlations between COVID-19 cases and temperature over the Maghreb and the Gulf of Guinea regions. In contrast, positive correlations are found over the Sahel area, especially in the central part, including Niger and Mali. Correlations with specific humidity and water vapor parameters display significant and positive values over the Sahelian and the Gulf of Guinea countries and negative values over the Maghreb countries. Then, the COVID-19 pandemic transmission is influenced differently across the three climatic regions: (i) cold and dry environmental conditions over the Maghreb; (ii) warm and humid conditions over the Sahel; and (iii) cold and humid conditions over the Gulf of Guinea. In addition, for all three climatic regions, even though the climate impact has been found to be significant, its effect appears to display a secondary role based on the explanatory power variance compared to non-climatic factors assumed to be dominated by socio-economic factors and early strong public health measures

An efficient strategy for 3D numerical simulation of friction stir welding process of pure copper plates

International audienceCopper and its alloys have a wide spectrum of engineering applications such as heat exchangers, hot water tanks or nuclear pressure vessels. Most of these structures are obtained by welding. Unfortunately, the use of conventional arc welding process is affected by several factors such as the thermal conductivity of the alloy being welded, the shielding gas, the joint design, the welding position, and the surface condition and its cleanliness. Friction stir welding process could be an interesting alternative as it can be performed without melting the material, it involves a non-consumable tool, and provides good mechanical properties. To understand in depth both the physical and the thermal mechanisms involved in this process, numerical modelling is essential. The aim of this paper is to propose an efficient simulation strategy based on the coupled Eulerian Lagrangian finite element method. The mass scaling procedure, which is used to decrease the computation time will be presented, as well as its effect on the temperature field distribution and on the down force. This model will then be used for a parametric study in order to improve the friction welding process's parameters. Published under licence by IOP Publishing Lt

International conference ICAWA 2016 : extended book of abstract : the AWA project : ecosystem approach to the management of fisheries and the marine environment in West African waters

The Joint International Laboratory ECLAIRS set up an oceanographic and meteorological buoy, dedicated to monitoring and analysis of the short and long-term changes in climate, atmosphere and marine environment within the Senegal coastal upwelling. The buoy "MELAX" was deployed early 2015 in the heart of the Senegalese upwelling by 30 m-depth at (14,20'N, 17,14'W). Data collected are, for the atmosphere, surface wind, solar radiation, humidity and rain, and for the ocean, temperatures, salinity, and currents (from the surface to the bottom) and oxygen. We present the first year and a half of observations, in particular the relationship between wind, sea surface temperatures, and hydrology. Satellite and model data are used to provide a larger-scale context to the local monitoring