Les travaux sur les brises de mer et de terre dans la région de la Corne de l'Afrique sont rares. À partir de données météorologiques horaires (2010-2021) et de l'imagerie satellitaire (NOAA-AVHRR) disponible pour la période 2014-2022, la présente étude apporte des informations originales sur les caractéristiques de ces brises dans l'agglomération de Djibouti. La vitesse moyenne des brises varie entre 2 et 8 m/s et leur direction dominante alterne de l'E (le jour) à l'O (la nuit). Leur fréquence oscille de 66 % en été à 93 % pendant la saison moins chaude. La baisse relative de la fréquence des brises en été s'explique par l'impact du vent synoptique, plus actif durant cette saison (jusqu'à 13 m/s en juin, puis 16 m/s en juillet et août). Le contraste thermique entre le continent et la mer étant plus fort pendant le jour, les brises diurnes (de mer) ont des vitesses plus élevées que celles nocturnes (de terre), qui ne dépassent pas 3 m/s.
Observations made in northern Gaspé since the early 1980s show that niveo-aeolian processes can play a very important role in the dynamic of scree slopes composed of small fragments. During blizzards, characterized by winds that can exceed 100 km/h, wind gusts can displace debris ranging in size from gravel to small pebbles. The sediments displaced by the wind originate from the summit rockwall and the scree slope itself when it is not entirely covered by snow. Depending on snow conditions, snow can play a role in two ways: 1/ when it is blown along with sediments, it produces mixed stratified deposits, whose mineral content consists mainly of silt and sand; 2/ when snow is covered by a layer of ice, it acts as a conveyor belt for particles the size of gravel and small pebbles that are blown onto the ice by wind gusts. Wind can thus contribute to the formation of long stratified basal concavities characterized by reverse grain sorting, with the concavity composed of finer debris than the scree slope. A significant portion of the sediments mobilized by the wind is blown into the adjacent forest. The intensity of niveo-aeolian processes varies considerably on a regional scale. They are highest near the coast, where annual sedimentation rates range from few millimeters to few centimeters, and decrease into the valleys. These dynamics are favored by windy climate, heavy snowfalls, frequent freeze-thaw cycles, and frequent rain-on-snow events. Given their rapidly changing weather conditions over relatively short periods of time, cold temperate and boreal maritime climates seem to be the most conducive to this types of dynamic.
This study analyses spatial changes and landscape fragmentation in western Burkina Faso between 1990 and 2022, using Landsat TM (1990 and 2007) and OLI (2022) satellite imagery. Supervised classifications, performed with the Random Forest algorithm, achieve high overall accuracies ranging from 90 % to 95 %, ensuring the robustness of the results. Land-use dynamics were assessed through annual and overall rates of change and transition matrices. Landscape structure was analysed using the total area, the number of patches and their mean size, complemented by the decision tree developed by J. BOGAERT et al. (2004). Local perceptions were collected on an indicative basis to support and better understand the observed land-use dynamics.The results reveal a continuous decline in dense vegetation formations, whose share of the landscape decreases from 37.7 % in 1990 to 11.7 % in 2022. Open vegetation formations also decline, from 51,0 % to 43.1 %. In contrast, agricultural areas experience a marked expansion, increasing from about 10 % to more than 43 % of the territory, with a clear acceleration after 2007.Structural analysis highlights a progressive dissection of open vegetation formations, characterised by an increase in the number of patches and a reduction in their mean size. Dense vegetation formations undergo severe fragmentation: the ratio of aeras 2022/1990 drops to 0.41, while the number of patches decreases from 1,379,763 to 595,433. Agricultural areas show simultaneous increases in total area and number of patches, reflecting their spatial diffusion and consolidation. These transformations, driven by agricultural expansion and increasing land pressure, indicate a rapid degradation of natural environments and underscore the urgency of sustainable management strategies aimed at preserving ecological continuity and limiting landscape fragmentation in western Burkina Faso.
The island of Santiago has many naturalized species, among which some of them are invasive. This is especially the case of Acacia holosericea, a shrub originated from Australia and introduced in the 1980s to stabilize soils and erosion. This shrub has now spread widely in the environment. It also colonizes agricultural lands, thus causing additional work for farmers who must remove it from crops. Using high-resolution multispectral drone imagery, we extracted the Normalized Difference Vegetation Index (NDVI) for Acacia holosericea (n = 421). For comparison, we carried out the same operation for Prosopis juliflora (n = 267), an exotic tree widely planted for reforestation on the island. NDVI values provide indirect information on photosynthesis activity and plant growth. In this paper, we tested whether some simple physical parameters (elevation, slope steepness, and exposure) could influence the NDVI values of Acacia holosericea. Our statistical results show that, for this species, 5 to 10 % of the NDVI variance are related to elevation and slope steepness, respectively. Acacia holosericea presents a better NDVI on sloping areas located around 495 m altitude, which correspond to the upper part of the mesophilic zone, also called subhumid zone. This zone can therefore be viewed as a preferential physical environment for this acacia. Thus, our results lead us to predict an important extension of Acacia holosericea on the mesophilic zone in the future.
The study focuses on the cases of Sabria and Aouinet Rajeh. These villages are typical examples of sites highly exposed to the risk of sand encroachment. They are characterised by a fragile ecosystem, restrictive climatic conditions and irrational exploitation of the environment. A diachronic and comparative approach was adopted. It aims to map the evolution of aeolian accumulation forms between 1990 and 2022 and to study the dynamics of sand encroachment. Observations show that Aouinet Rajeh is in a very advanced state of degradation, reaching a stage of irreversibility. This has led to its total abandonment, with only ruins remaining as evidence of its former existence. In Sabria, sand encroachment is becoming increasingly widespread, posing a major threat to the oasis and infrastructure.
Despite its exponential population growth and accelerated urbanization process, which is far from benefiting urban vegetation, the commune of Ziguinchor still has Adansonia digitata on its surface. This spontaneous species adapts to the urban environment by maintaining itself in a dynamic environment. The present research is a contribution to a better understanding of the baobab's potential and the various factors militating for its conservation in the commune of Ziguinchor. Baobabs taller than 3 m were geo-referenced using a GPS. The results reveal 514 trees, including 324 productive stands, spread over 27 of the 28 districts in the study area. Surveys were also carried out with different socio-economic actors: chiefs of concessions including baobabs, traditional practitioners, Water and Forestry Department and plant product processing companies. Conservation factors for this majestic tree were highlighted. Some are internal to the species (resilience traits) and others anthropic (interventions by stakeholders). These factors together contribute to the conservation of this species.
The article examines the growth of woody vegetation in the agglomeration of Touba-Mbacke, which is marked by a very strong demographic and economic dynamism. It is studied by remote sensing between 1973 (period of rainfall deficit) and 2024. The results show a strong spatial spread of the urban core built ex nihilo after the inauguration of the Great Mosque of Touba (1963) to the city of Mbacke. The less-expected result is that vegetation has increased in size within the agglomeration, thus forming a "green island" in this Sahelian part of Senegal. Indeed, the contrast is clear between the progression of woody vegetation scattered in the recent urban fabric and the decline of plant cover in the nearby rural area. At a finer scale, urban vegetation is the result of individual initiative (trees for yards and front-line buildings) rather than public action (plantings for alignment and public gardens). Finally, the article looks at the many services that woody vegetation provides to populations.
The current climate crisis has pre-eminently become a planetary challenge to be met, leading the scientific community to question the contribution of plant ecosystems to this phenomenon through, among other things, studies of their carbon potential and monitoring of their evolution. With this in mind, the aim of this study was to diagnose the effect of land-use change on carbon stock flows in woody vegetation units in the Djilor district. To this end, a non-destructive approach based on allometric equations was adopted to estimate carbon stocks in each of these units from inventory data. Inventory data were collected randomly on square plots of varying sizes depending on the unit (10 by 10 m for mangroves, 20 by 20 m for savannah formations, 40 by 40 m for cultivated areas). The evolution of these units and their carbon stock was carried out using Landsat satellite images over the period from 1985 to 2017. The results revealed the carbon stocks of the different woody plant formations (5.2 tC.ha-1 for shrub savannah, 7.5 tC.ha-1 for cultivated areas, 10.2 tC.ha-1 for gallery forest, 11.7 tC.ha-1 for shrub to tree savannah, 22.7 tC.ha-1 for tree savannah and 25.3 tC.ha-1 for mangrove). Land-use changes over the 32-year period considered indicate a regressive dynamic for all spontaneous woody plant units, with degradation and deforestation outweighing conservation and restoration. The resulting reduction in carbon stock corresponds to an average annual global CO2 emission of around 11,5 kt. This study therefore shows the impact of land use changes on the carbon stocks of woody plant formations, and can serve as a basis of information for their monitoring and management.
In its June 2023 report, the French Ministry of Higher Education and Research requires postsecondary training programs, starting in 2025 at the latest, to "train in the ecological transition for sustainable development". This article presents the thematic progression of the Environmental Geography curriculum at the University of Limoges. The starting point is the Climate Fresk, which has been developed in depth to show the importance of transition for societies. Thus, throughout the undergraduate program, the themes taught concern societies in relation to their environment, their demography and their economy; societies in relation to climate change, risks and their vulnerability. This progression, which clarifies the processes, interactions and implications of the ecological crisis on populations, reveals the urgency of concrete measures and actions. These challenges inevitably involve the commitment of students and educators, through workshops geared towards the conception of new futures and the creation of a "Chair of Excellence". It would enable us to set up a low-carbon dynamic at the local level. The role of the University is thus crucial in guiding society towards a new world.
The study focuses on the cases of Sabria and Aouinet Rajeh. These villages are typical examples of sites highly exposed to the risk of sand encroachment. They are characterised by a fragile ecosystem, restrictive climatic conditions and irrational exploitation of the environment. A diachronic and comparative approach was adopted. It aims to map the evolution of aeolian accumulation forms between 1990 and 2022 and to study the dynamics of sand encroachment. Observations show that Aouinet Rajeh is in a very advanced state of degradation, reaching a stage of irreversibility. This has led to its total abandonment, with only ruins remaining as evidence of its former existence. In Sabria, sand encroachment is becoming increasingly widespread, posing a major threat to the oasis and infrastructure.Translated with DeepL.com (free version) and Google traduction.
The island of Santiago has many naturalized species, among which some of them are invasive. This is especially the case of Acacia holosericea, a shrub originated from Australia and introduced in the 1980s to stabilize soils and erosion. This shrub has now spread widely in the environment. It also colonizes agricultural lands, thus causing additional work for farmers who must remove it from crops. Using high-resolution multispectral drone imagery, we extracted the Normalized Difference Vegetation Index (NDVI) for Acacia holosericea (n = 421). For comparison, we carried out the same operation for Prosopis juliflora (n = 267), an exotic tree widely planted for reforestation on the island. NDVI values provide indirect information on photosynthesis activity and plant growth. In this paper, we tested whether some simple physical parameters (elevation, slope steepness, and exposure) could influence the NDVI values of Acacia holosericea. Our statistical results show that, for this species, 5 to 10 % of the NDVI variance are related to elevation and slope, respectively. Acacia holosericea presents a better NDVI on sloping areas located around 495 m altitude, which correspond to the upper part of the mesophilic zone, also called subhumid zone. This zone can therefore be viewed as a preferential physical environment for this acacia. Thus, our results lead us to predict an important extension of Acacia holosericea on the mesophilic zone in the future.
La commune de Ziguinchor, malgré sa croissance démographique exponentielle et son processus d'urbanisation accéléré qui est loin d'être à l'avantage de la végétation urbaine, garde dans sa surface Adansonia digitata. Cette espèce spontanée s'adapte au milieu urbain en se maintenant dans un environnement dynamique. La présente recherche est une contribution à une meilleure connaissance du potentiel du baobab et des différents facteurs qui militent pour sa conservation dans la commune de Ziguinchor. Les baobabs de plus de 3 m de hauteur ont été localisés au moyen d'un GPS. Les résultats révèlent 514 individus, dont 324 sont productifs, répartis dans 27 des 28 quartiers de la zone d'étude. Par ailleurs, des enquêtes ont été menées auprès de différents acteurs socio-économiques, les chefs des concessions abritant des baobabs, des tradithérapeutes, le Service des Eaux et Forêt et les entreprises de transformation des produits végétaux. Les facteurs de conservation de cet arbre majestueux ont ainsi été mis en évidence. Les uns sont internes à l'espèce (caractères de résilience), les autres anthropiques (interventions des acteurs). Ces facteurs participent de concert à la conservation de cette espèce.
L'article examine la progression de la végétation ligneuse dans l'agglomération de Touba-Mbacké, qui est marquée par un très fort dynamisme démographique et économique. Elle est étudiée par télédétection entre 1973 (période de déficit pluviométrique) et 2024. Les résultats mettent en évidence un fort étalement spatial du noyau urbain, né ex nihilo après l'inauguration de la Grande Mosquée de Touba (1963), jusqu'à la ville de Mbacké. Résultat moins attendu, la place de la végétation s'est accrue au sein de l'agglomération, formant ainsi un "îlot vert" dans cette partie sahélienne du Sénégal. En effet, le contraste est net entre la progression de la végétation ligneuse éparpillée dans le tissu urbain récent et la régression du couvert végétal dans l'espace rural proche. À l'échelle plus fine, la végétation urbaine résulte d'initiatives individuelles (arbres de cour et de façade) plus que de l'action publique (plantations d'alignement et jardins publics). Enfin, l'article s'intéresse aux nombreux services que la végétation ligneuse rend aux populations.
Le mil (Pennisetum glaucum) et le sorgho (Sorghum bicolor) sont les principales céréales sèches cultivées en agriculture pluviale au Nord-Est du Sénégal. Mais, confrontées à des contraintes comme la baisse des précipitations, l'augmentation des températures, la fréquence des pauses sèches, leur production tend à baisser. L'article examine les contraintes climatiques et autres chocs subis par la culture pluviale des variétés de mil Souna 3, ICTP 8203, GB 8735, Gawane et Chakti ainsi que de celles de sorgho CE 180-33, Payenne et Golobé, qui sont les principales variétés homologuées et actuellement cultivées dans le Nord-Est du Sénégal. À partir des données collectées à Podor, Matam et Linguère, l'article analyse l'adaptation de différentes variétés de mil et de sorgho aux conditions climatiques et à leur évolution au fil du temps. Les résultats montrent un déficit des précipitations depuis le début des années 1970, qui se conjugue à de plus fortes contraintes thermiques. L'analyse des écarts entre le cumul pluviométrique et l'évapotranspiration maximale des variétés aux différents stades de croissance révèle des déficits hydriques constants pour le mil Souna 3 et le sorgho CE 180-33. En revanche, le mil Chakti présente des bilans hydriques positifs dans plus de 80 % des années à l'est et à l'ouest du secteur d'étude, et dans 47 % des cas au nord. Seules les variétés Chakti et ICTP 8203 sont adaptées aux conditions climatiques des parties est et ouest, avec une probabilité d'adéquation supérieure à 80 % sur les périodes 1931-1969 et 1999-2020. En revanche, aucune des variétés n'est adaptée aux conditions climatiques du nord. Outre ces contraintes climatiques, les agriculteurs enquêtés incriminent la divagation des animaux, les attaques d'oiseaux ravageurs et les infestations parasitaires pour expliquer la baisse des productions agricoles. Il est donc primordial de développer des stratégies complémentaires, incluant une plus large diffusion de variétés mieux adaptées aux conditions climatiques actuelles, comme le Chakti et l'ICTP 8203, et le renforcement des dispositifs de protection des cultures, notamment par la lutte biologique et la gestion intégrée des ravageurs.
La crise climatique actuelle est devenue de manière prééminente un défi planétaire à relever, ce qui entraîne la communauté scientifique vers des interrogations sur la contribution des écosystèmes végétaux à ce phénomène à travers, entre autres, des études sur leur potentialité en stockage de carbone et des suivis sur leur évolution. C'est dans cette optique que cette étude s'est fixée pour objectif d'effectuer un diagnostic de l'effet des changements d'affectation des terres sur les stocks de carbone des unités de peuplement végétal ligneux dans l'arrondissement de Djilor. Pour ce faire, une approche non destructive, basée sur des équations allométriques, a été adoptée pour estimer le stock de carbone de chacune de ces unités à partir de données d'inventaire. Ces dernières ont été recueillies de manière aléatoire sur des placettes carrées de taille variable en fonction des unités (10 sur 10 m pour la mangrove, 20 sur 20 m pour les formations de savane, 40 sur 40 m pour les espaces cultivés). L'évolution de ces unités et de leur stock de carbone a été évaluée à l'aide d'images satellitaires Landsat sur la période allant de 1985 à 2017. Les résultats ont révélé les stocks de carbone des différentes formations végétales ligneuses (5,2 tC/ha pour la savane arbustive, 7,5 tC/ha pour les terrains en culture pluviale, 10,2 tC/ha pour la forêt galerie, 11,7 tC/ha pour la savane arbustive à arborée, 22,7 tC/ha pour la savane arborée et 25,3 tC/ha pour la mangrove). Les changements d'affectation des terres indiquent, sur la période de 32 ans considérée, une dynamique régressive des unités végétales ligneuses spontanées, leur dégradation et leur déforestation l'emportant sur leur conservation et leur restauration. La diminution du stock de carbone qui en résulte, entraîne une émission globale annuelle moyenne de l'ordre 11,5 kt de CO2. Cette étude témoigne donc de l'impact des changements d'occupation du sol sur les stocks de carbone des formations végétales ligneuses et peut servir de base à leur suivi et leur gestion.
Millet (Pennisetum glaucum) and sorghum (Sorghum bicolor) are the main rainfed cereals grown in North-Eastern Senegal. However, faced with constraints such as falling rainfall, rising temperatures and frequent dry spells, their production is tending to decline. This article examines the climatic constraints and other shocks suffered by rainfed millet varieties Souna 3, ICTP 8203, GB 8735, Gawane and Chakti, as well as those as sorghum CE 180-33, Payenne and Golob & eacute;, which are the main varieties released and currently grown in north-eastern Senegal. Based on data collected in Podor, Matam and Lingu & egrave;re, the article analyses the adaptation of different millet and sorghum varieties to climatic condition and their evolution over time The results show a rainfall deficit since the early 1970s, combined by greater thermal constraints. Analysis of the differences between cumulative rainfall and maximum evapotranspiration for varieties at different growth stages reveals constant water deficits for Souna 3 millet and CE 180-33 sorghum. In contrast, Chakti millet shows positive water balances in over 80% of years in the east and west of the study area, and in 47% of cases in the north. Only Chakti and ICTP 8203 are adapted to the climatic conditions of the eastern and western zones, with a probability of suitability of over 80% for the periods 1931-1969 and 1999-2020. However, none of the varieties is adapted to the climatic conditions in the north. In addition to these climatic constraints, the interviewed farmers attribute the decline in agricultural production to livestock straying, attacks by bird pests and parasitic infestations. exacerbate agricultural losses. It is therefore essential to develop complementary strategies including wider dissemination of varieties better adapted to current climatic conditions, such as Chakti and ICTP 8203, and the strengthening of crop protection systems, notably through biological control and integrated pest management.
Dans son rapport de juin 2023, le Ministère de l'Enseignement Supérieur et de la Recherche donne l'obligation aux formations post-bac, à partir de 2025 au plus tard, de "former à la transition écologique pour un développement soutenable". Cet article présente la progression thématique de la maquette de géographie environnementale de l'Université de Limoges. Le point de départ est la Fresque du climat qui est approfondie pour montrer l'importance des enjeux de la transition pour les sociétés. Ainsi, de la L1 à la L3, les thématiques enseignées concernent les sociétés face à leur milieu, leur démographie et leur économie ; les sociétés face aux changements climatiques, aux risques et leur vulnérabilité. Cette progression qui permet de préciser les processus, les interactions et les implications de la crise écologique sur les populations, révèle l'urgence de mesures et actions concrètes. Celles-ci passent inévitablement par l'engagement des étudiants et des enseignants par le biais d'ateliers permettant d'imaginer de nouveaux futurs et d'une chaire d'excellence pour mettre en place, à l'échelle locale, une dynamique bas-carbone. Le rôle de l'Université est ainsi crucial pour guider la société vers un nouveau monde.
In Bizerte, a coastal agglomeration in the far north of Tunisia, the right-angled shape of the coastline and the contrasting topography as well as the varied land use influence the local aerology. In order to analyze the different situations during which thermal breezes were recorded, we used data over the period 1990-2022 from the weather station at Sidi Ahmed aerodrome and those from the DAVIS station that we managed in the summer of 2020. Mobile measurements were also carried out in August 2021 and August 2022. Lastly, remote sensing data were used: land cover, surface temperature, Sky View Factor (FVC) maps. The land-sea thermal contrasts give rise to the sea breezes and the land breezes. The latter are split by the breezes that flow on the slopes of jebel Ennadhour. The sea breezes are more frequent in summer, a season during which they are observed for two thirds of the days. They blow at an average speed of 6 m.s(-1) from the north and east because of the shape of the coastline. These sea breezes are often preceded by a breeze blowing from the Lake of Bizerte to the south. The land breezes have speeds not exceeding 3 m.s(-1). Their trajectory, influenced by the topography, runs along low plains and valleys. In the city, the urban morphology and the disposition towards the coast impact both the orientation and the speed of the breezes. For ways parallel to the direction of the sea breezes, when they are wide and shallow, average wind speeds oscillate between 3 m.s(-1) (at the start of afternoon) and 4 m.s(-1) (at the end of afternoon). The more deeply and less wide ways of the same orientation show higher average speeds, which rise from 4 to 7 m.s-1 between the beginning and the end of the afternoon.
The study focuses on the temporal evolution of meteorological drought in a semi-arid agricultural territory located in the heart of the Beqaa plain in Lebanon. To define this climatic hazard, the Standardized Precipitation Index (SPI), recommended by the World Meteorological Organization, was used. This index, based on rainfall data alone, was calculated at three scales (12, 6 and 3 months), over a period going from September 1933 to August 2020. The results provided by the annual data (SPI-12) and data for the six months from October to March (SPI-6) show that the study area has experienced more frequent droughts since 1956-57, with successive dry years spanning 6, 7 and even 9 years. On a seasonal scale, winter (December-February), by far the wettest season, also shows a decrease in rainfall and an increase in dry droughts since 1956-57. On the other hand, autumn and spring data are characterised by the presence of two breaks, the first (1962-63 for spring and 1963-64 for autumn) resulting in an increase in rainfall and the second (198485 for spring and 1996-97 for autumn) in a decrease. The frequency of droughts has been particularly high since the second break. Despite their large number, droughts have remained of limited intensity. Even in 2013-14, the driest year in the series, only the October-March half-year was extremely dry (SPI of-2.03). On all time scales, light droughts (SPI <-1.0) were by far the majority. Translated with DeepL.com (free version)
