Les changements d’occupation des sols dans la Béqaa Ouest (Liban) : le rôle des actions anthropiques

International audienceevolution of land tenure patterns reflects the footprint of anthropogenic activities and is rather a complex dynamic process that acts on natural resources. The agricultural region of the West Beqaa is characterized by favorable natural conditions for diversified agricultural production. Remote sensing shows the extent of changes in land use between 1962 and 2019. Diachronic analysis reveals a regression of the vegetation cover in favor of urban fabric in the plain. The interpretation of the results must take into consideration the local causes of this mutation by highlighting cultural and pastoral practices, economic factors, urban extension, Syrian migratory flows, and deforestation that weakens the environment through stripping away the superficial layers. The brightness index of the high-resolution Ikonos image was used to determine the severity degree of degradation. All this questions the agricultural future of the region, whose production is an essential contribution to the national market.L'évolution des modes d'occupation du sol porte l'empreinte des activités anthropiques et correspond à un processus dynamique assez complexe, qui agit sur les ressources naturelles. La région agricole de la Béqaa Ouest est caractérisée par des conditions naturelles favorables pour une production agricole diversifiée. La télédétection montre l'ampleur des changements des modes d'occupation du sol entre 1962 et 2019. L'analyse diachronique révèle une régression du couvert végétal au profit des tissus urbains dans la plaine. L'interprétation des résultats doit tenir compte des causes locales de cette mutation en mettant en évidence les pratiques culturales et pastorales, les facteurs économiques, l'extension urbaine, les flux migratoires syriens et le déboisement qui fragilise le milieu en provoquant le décapage des couches superficielles. L'indice de brillance de l'image Ikonos de haute résolution indique la sévérité de cette dégradation. Tout cela interroge l'avenir agricole de cette région dont les productions constituent un apport essentiel aux marchés nationaux

COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study

Background: The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods: International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results: ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P < 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation: This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men

Variation spatio-temporelle (1962-2018) du couvert forestier du haut massif du Mont-Liban : rôle du facteur anthropique

La forêt du haut massif du Mont-Liban, entre 1400 et 3086 mètres d'altitude, renferme la plus grande masse forestière de ce pays. Cependant, sous l'emprise des multiples besoins des riverains, le milieu forestier a été fragilisé et sa surface réduite. Les déboisements ont livré les versants fragiles à l'érosion hydrique. La combinaison des photos aériennes et des images satellitaires multi-dates permettent une analyse diachronique du paysage forestier ainsi qu'une description synthétique de l'organisation et de la répartition spatiale de ces formations végétales. L'interprétation des résultats, qui doit tenir compte de l'interaction entre l'Homme et son environnement, révèle une régression des surfaces forestières entre 1962 et 1984 et une progression sur les périodes 1984-2000 et 2000-2018.The forest of the hight Mount Lebanon massif, at altitudes between 1400 and 3086 meters, holds the largest forest extent in Lebanon. However, under the pressure of meeting local residents' needs, the forest gradually lost its density, causing the disappearance of this landscape. Deforestation has exposed fragile slopes to water erosion. The effects of deforestation have the direct impact of exposing fragile slopes to water erosion. The combination of aerial photographs and multi-date satellite images allows for a diachronic analysis of the forest landscape as well as a synthetic description of the organization and spatial distribution of these tree formations. Interpreting the results, that should account for the interaction between people and their environment, revealed a decline in the forest area between the years 1962-1984, while an increase is marked in the two periods 1984-2000 and 2000-2018

Variation spatio-temporelle (1962-2018) du couvert forestier du haut massif du Mont-Liban : rôle du facteur anthropique

The forest of the hight Mount Lebanon massif, at altitudes between 1400 and 3086 meters, holds the largest forest extent in Lebanon. However, under the pressure of meeting local residents' needs, the forest gradually lost its density, causing the disappearance of this landscape. Deforestation has exposed fragile slopes to water erosion. The effects of deforestation have the direct impact of exposing fragile slopes to water erosion. The combination of aerial photographs and multi-date satellite images allows for a diachronic analysis of the forest landscape as well as a synthetic description of the organization and spatial distribution of these tree formations. Interpreting the results, that should account for the interaction between people and their environment, revealed a decline in the forest area between the years 1962-1984, while an increase is marked in the two periods 1984-2000 and 2000-2018

Cartographie des conditions de l'érosion hydrique des sols au Mont-Liban : exemple de la région d'El Aaqoûra

International audienc

Modélisation de l’érosion hydrique à l’échelle du bassin versant du Mhaydssé. Békaa-Liban

Le Liban des hautes plaines subit une érosion hydrique qui tend à décaper ses sols et menacer ses activités agricoles. L’effet conjugué des actions anthropiques (conduites culturales, déboisement, surpâturage) et des facteurs naturels (agressivité climatique, versants abrupts, sol), fragilise le sol et menace les parcelles agricoles par le depôt des sédiments. Mhaydssé est un village concerné par le problème, représentatif des conditions naturelles et anthropiques du sud-est de la Békaa. L’étude utilise les SIG et l’équation universelle des pertes en terre (USLE). Pour remplacer l’intensité des précipitations, l’indice d’agressivité a été calculé à partir de l’équation de Renard et Freimund. Cinq types de sols ont été échantillonnés, pour lesquels la granulométrie a été analysée en cinq classes. La topographie (pente), le couvert végétal et les pratiques anti-érosives sont les autres facteurs qui ont été quantifiés. Sur les 1800 hectares du terrain d’étude, la perte moyenne en terre est de 46 t/ha/an. Cette valeur élevée est issue d’une grande hétérogénéité spatiale. Les versants dénudés subissent des taux supérieurs à 300 t/ha/an, tandis que le fond de la plaine n’est pratiquement pas touché. Les grandes différences spatiales sur de petites distances confirment le bienfondé d’une analyse précise de la texture des sols.The high plains of Lebanon are subject to water erosion which tends to strip its soils and threaten its agricultural activities. The combined effect of anthropogenic actions (cultural management, deforestation, overgrazing) and natural factors (climatic aggressiveness, steep slopes, soil), weakens the soil and threatens agricultural parcels by depositing sediments. Mhaydssé is a village concerned by this problem and its representative of the natural and anthropogenic conditions of the Békaa’s southeast. The study uses GIS and the Universal Earth Loss Equation (USLE). To replace the intensity of precipitation, the aggressiveness index was calculated from the equation of Renard and Freimund. Five soil types were sampled, for which the soil granulometry was analyzed in five classes. The topography (slope), the vegetation cover and the anti-erosion practices are the other factors that have been quantified. Of the 1800 hectares of the study area, the average loss of land is 46 t / ha / year. This high value comes from a high spatial heterogeneity. The barren slopes are subject to rates above 300 t /ha /yr, while the bottom of the plain is practically untouched. Large spatial differences over small distances confirm the thoroughness of an accurate analysis of soil texture

Modélisation et cartographie du risque érosif à Rachaya (Liban)

International audienceExtended abstract.Soil erosion is a phenomenon that undermines the natural environment and the agricultural activities in the Bekaa Valley (Lebanon) and on the surrounding foothills. In the absence of some data, that the situation in Lebanon during recent decades has caused, it may be relevant to change or adapt some of the classical equations about soil loss. This research is done on an area located near the village of Rachaya, extending over 130 km2. The study area lies between latitudes 33o30’30’’ and 33o38’30’’ North and longitudes 35o49’30’’ and 35o59’30’’ East (plate 1). It comprises two types of geomorphic-dynamic units: the plain and the slopes of the western chain culminating at 1750 m. The median elevation is between 1350 and 1400 m, according to the hypsometric curve (plate 2), and the mean slope has an order of 9 degrees. The Mediterranean environment, the aggressiveness of the climate, the relief and geology (plate 3), the slopes locally rather strong, the deforestation and the extent of crops form a context favorable to erosion.The methodology (plate 4) is based on a modeling adapting the Wischmeier and Smith Universal Soil Loss Equation, USLE, (A = R * K * C * P* LS) (Wischmeier & Smith (1960, 1978) whereby the factors entered into the model are: rainfall erosivity (R), soil erodibility (K), soil cover (C), cultural practices (P), slope value and slope length (LS) (plate 4). This model uses the contributions of geographical information systems and satellite images (Ikonos, Landsat). -The R factor (plate 5) is calculated based on the formula elaborated by Renard & Freimund, (1994). -The K factor (plate 6) depends on soil texture, structure and organic material. The calculation of this factor relies on the formula of Wischmeier et Smith (1978). Soil samples were taken from the site to show the soil granulometric characteristics of the study area (table 1).-The C factor (plate 7) is determined based on tables established by Wischmeier & Smith (1978). It depends on the vegetation height, the recovery rate and the bibliographic knowledge of the Mediterranean region (Sadiki et al., 2009, El Garouani et al., 2008) (table 2).-With respect to the P factor, two codes were identified, one for the agriculture terraces and the other for areas of anti-erosion practices. -For the purpose of this study, the adopted model for the LS factor (plate 8) combines only the length and the inclination of the slope.The results (plate 9) show the role of the steeper slopes and of the less protective vegetation cover. On a third of the surface of the study area, soil loss is between 400 and 1800 t/ha/year and on one fifth of the surface between 50 to 400 t/ha/year. On the ledges, losses decrease to values between 50 and 5 t/ha/year (plate 9). However, only 6 % of the study area shows significant soil losses. Soil cover is generally the most discriminant factor. It strengthens soil resistance by breaking the kinetic energy of raindrops and by intercepting some of the precipitations. It is true that the Rachaya area has been affected by a strong degradation of the vegetation cover, so that the C factor varies between 0.7 and 1 for 77% of the study area (plate 7). Anti-erosion practices are not widespread and subsist only on a few hectares of agricultural terraces. These conditions reveal the insufficiency of protection against the aggressiveness and that is why the R factor may exceed 1600 (plate 5). Several parameters are decisive to explain the soil erodibility: the infiltration capacity, the retention texture and the tearing susceptibility. Most of the soil in Rachaya is fragile and prone to erosion. The force of the relief, especially where there are steep slopes and topographical irregularities, greatly helps erosion; Rachaya high values of LS in some places, contributed largely to the erosive risk (plate 8). The validation of our results was made on the one hand on fieldwork and the other hand using the spectral response of the eroded areas, based on the gloss value processed from the Ikonos satellite image with high spatial resolution of 1 m. The gloss index dissociates vegetated areas from bare mineral areas: it authorizes to assess the surface condition of soils in the study area. This index, which is generated from the red and near infrared channels, characterizes the albedo and allows the diagnosis of soil degradation from color changes reflecting changes in the soil. The soil spectral signature depends on the organic matter content, on the moisture content and on the mineralogical composition. These variables have a major impact on the color and brightness of soil. The erosion mechanism, which strips the surface layer, makes the soil clearer because of the destruction of organic matter. At the opposite, the soil moisture, the presence of organic matter or an increase of the vegetation cover give a dark color to the soil. Finally the overall accuracy of our validated results is approximately 80 %. Due to the importance of the erosion phenomenon which has been quantified, it seems necessary to increase the stabilization of the slopes and to implement protective farming techniquesL’érosion des sols fragilise le milieu rural de la plaine de la Békaa et ses bordures. La méthodologie utilisée repose sur une modélisation adaptant l’équation universelle des pertes en sol (USLE) de Wischmeier et Smith, en utilisant les systèmes d’informations géographiques et des images satellitaires. Les facteurs entrés sont : l’érosivité de la pluie, l’érodibilité du sol, la couverture du sol, les pratiques culturales, la déclivité et la longueur de la pente. Sur un tiers de la surface, les pertes en terre sont comprises entre 400 et 1800 t/ha/an, sur un cinquième entre 50 et 400 t/ha/an. Sur les replats, elles tombent entre 50 et 5 t/ha/an. 6% de la surface présentent des pertes négligeables. La validation de ces résultats est faite sur le terrain et en utilisant la réponse spectrale, grâce à l’indice de brillance de l’image Ikonos de haute résolution spatiale. Devant l’importance du phénomène, il semble nécessaire de conseiller des techniques agricoles protectrices

Estimation expédiée du risque érosif dans l’amont du bassin versant du Nahr el Kalb

La dégradation du sol par l’érosion hydrique est un phénomène naturel qui peut être amplifié par les actions anthropiques. Les conséquences de ce phénomène sont néfastes et peuvent nuire aux caractères intrinsèques du sol, et entraîner sa disparition dans certains cas. Pour cartographier l’aléa érosion dans l’amont du bassin versant du Nahr el Kalb, nous avons adopté une approche hiérarchique, nommée MESALES, qui combine les paramètres pondérés de l’érosion (occupation du sol, pente, érodibilité du sol et climat) dans un Système d’information géographique (SIG). Afin de tenir compte des spécificités du milieu, l’érodibilité des sols a été calculée à partir de l’équation de Wischmeier et Smith (1960 ; 1978). Le bilan de ce travail montre le rôle prépondérant du couvert végétal. 67 % du périmètre d’étude subit une forte et très forte érosion, il s’agit essentiellement des secteurs ayant un couvert végétal dégradé ou en étant dépourvus. La précision globale du modèle et l’indice Kappa qui en sont ressortis sont estimés respectivement à 84 % et 80%.Soil degradation by water erosion is a natural phenomenon that can be amplified by anthropogenic actions. The consequences of this phenomenon are harmful and can harm the intrinsic characteristics of the soil, and lead to its disappearance in certain cases. For mapping the erosion hazard upstream of Nahr el Kalb watershed, we have adopted a hierarchical approach, called MESALES, that combines the weighted parameters of erosion (land use, slope, soil erodibility and climate) using GIS. The soil erodibility was calculated from the equation of Wischmeier et Smith (1960; 1978) to take account of the specific environmental features. The results of this work show the predominant role of plant cover. 67% of the study area is undergoing strong and very strong erosion, mainly in sectors of either degraded plant cover or no plant cover. The overall accuracy of the model and the Kappa index resulting from it are estimated at 84% and 80% respectively

L’érosion hydrique à l’échelle de Kfar Qouq (Liban)

International audienceLes caractères semi-arides de la plaine de la Békaa, le climat méditerranéen qui se particularise par une période sèche suivie d'une autre pluvieuse et les pratiques culturales participent à placer au centre des inquiétudes l'impact de l'érosion hydrique sur le paysage géographique de la région de Kfar Quouq. L'insuffisance des données météorologiques, pose un problème pour la recherche scientifique, notamment pour l'application des équations classiques en pertes de sol. Afin de surmonter cette difficulté, un certain nombre de stratégies permettent de contourner les obstacles rencontrés. Cette démarche permet d'estimer les pertes en sol sur un secteur avoisinant les 20km² où le risque érosif est fort et assez mal pris en compte actuellement. Quel est l'intérêt géographique du travail de recherche à une si grande échelle cartographique? L'équation universelle des pertes en terre (USLE) est-elle applicable ici et quelles sont ses difficultés d'utilisation dans le cadre d'un croisement avec un SIG? Pour tenter d'apporter des réponses plus précises, l'emploi de l'équation a nécessité, d'une part un travail préliminaire de reconstitution de l'intensité des précipitations, d'autre part un ensemble d'analyses d'échantillons de sols récoltés sur le terrain. La méthodologie développée, met en évidence son originalité par rapport aux démarches existantes. L'estimation des pertes en terre sera exposée sous forme de résultats spatialisés, avant d'être discutée