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During April 2019 France experienced several frost events that caused extensive damage to almost all of its winegrowing regions. In Bourgogne-Franche-Comté the frost effects were very punctual and spatially diffused, the greatest damage being observed in the early bud breaking winegrowing sub-regions of Saône-et-Loire and the south of the Côte de Beaune. This study focuses on the multi-scalar analysis of the spring frost event underwent during the night between the 4th and 5th of April on a vineyard plot located in the Hautes Côtes de Beaune appellation. The analysis highlights the impact of local parameters (topography, surface discontinuity, etc.) on the spatio-temporal structuring of temperatures at a local scale. During the night temperatures drop to -3°C while the air relative humidity indicates a percentage close to full saturation. The weather is partially stable being under the influence of low-pressure conditions accompanied by a southwest atmospheric circulation., En avril 2019, la France a connu plusieurs épisodes de gel ayant occasionné des dégâts sur la quasi-totalité des régions vitivinicoles. En Bourgogne-Franche-Comté, les effets du gel ont revêtu un caractère très ponctuel, les plus forts dégâts étant observés dans les sous-régions viticoles très précoces de la Saône-et-Loire et du sud de la Côte de Beaune. Cette étude se focalise sur l’analyse multiscalaire de l’évènement gélif tardif survenu lors de la nuit du 4 et 5 avril sur une parcelle viticole localisée dans les Hautes Côtes de Beaune. L’analyse met en évidence l’impact des paramètres locaux (la topographie, les discontinuités de surface, etc.) sur la structuration spatio-temporelle des températures à l’échelle parcellaire. L’épisode de gel est caractérisé par des températures négatives, jusqu’à -3°C, accompagnées d’une très forte humidité relative de l’air (souvent 100%). Le temps est partiellement stable étant sur l’influence des conditions dépressionnaires marquées par une circulation atmosphérique en flux du sud-ouest.

Heat in Normandy, synoptic circulation patterns and climate change (1970-2019). This article focuses on the role and the evolution of the different kinds of synoptic circulation patterns in the occurrence of hot days in Normandy. Heat is here, very dependent on the presence of action centres over central Europe as well as, air flow coming from NE and E. Contemporary climate change expresses itself by a rise in thermal efficiency of all synoptic circulation patterns (more heat for the same flow). Lastly, the north of Cotentin stands out by being a real “cool island” during summer because of its peninsula position which imposes on any air mass, regardless of its origin, a cooling from its bottom., Cet article s’intéresse au rôle et à l’évolution des différents types de circulation atmosphérique dans l’occurrence des journées de chaleur en Normandie. La chaleur est ici très dépendante de la présence de centres d’action sur l’Europe centrale ainsi que, secondairement, des flux de NE et E. Le changement climatique contemporain se manifeste par une augmentation de l’efficience thermique de tous les types de circulation (plus de chaleur pour un même flux). Enfin, le nord du Cotentin se singularise par un véritable « îlot de fraicheur » en été en raison de son caractère de finisterre qui impose aux masses d’air un rafraîchissement par la base important quelles que soient leurs provenances.

Monitoring agricultural areas threatened by soil erosion often requires decimetre topographic information over areas of several square kilometres. Airborne lidar and remotely piloted aircraft system (RPAS) imagery have the ability to provide repeated decimetre-resolution and -accuracy digital elevation models (DEMs) covering these extents, which is unrealistic with ground surveys. However, various factors hamper the dissemination of these technologies in a wide range of situations, including local regulations for RPAS and the cost for airborne laser systems and medium-format RPAS imagery. The goal of this study is to investigate the ability of low-tech kite aerial photography to obtain DEMs with decimetre resolution and accuracy that permit 3-D descriptions of active gullying in cultivated areas of several square kilometres. To this end, we developed and assessed a two-step workflow. First, we used both heuristic experimental approaches in field and numerical simulations to determine the conditions that make a photogrammetric flight possible and effective over several square kilometres with a kite and a consumer-grade camera. Second, we mapped and characterised the entire gully system of a test catchment in 3-D. We showed numerically and experimentally that using a thin and light line for the kite is key for a complete 3-D coverage over several square kilometres. We thus obtained a decimetre-resolution DEM covering 3.18 km2 with a mean error and standard deviation of the error of +7 and 22 cm respectively, hence achieving decimetre accuracy. With this data set, we showed that high-resolution topographic data permit both the detection and characterisation of an entire gully system with a high level of detail and an overall accuracy of 74 % compared to an independent field survey. Kite aerial photography with simple but appropriate equipment is hence an alternative tool that has been proven to be valuable for surveying gullies with sub-metric details in a square-kilometre-scale catchment. This case study suggests that access to high-resolution topographic data on these scales can be given to the community, which may help facilitate a better understanding of gullying processes within a broader spectrum of conditions.

This study presents the evolution of droughts in Rennes since 1879 (observed data) up to 2100 (projected data). The methods used are the water balance with the choice of the index of the evaporation deficit and the types of annual climate (TCA) using the Köppen classification. The results show the strong inter-annual variability observed for more than a century with some extreme events (1906, 1921, 1976 or 2003) but without a clear trend. The projections of the Météo-France model show, on the other hand, a strong tendency of the deficit to increase during the 21st century as well as the increase of TCAs with hot and dry summers., Cette étude présente l'évolution des sécheresses à Rennes depuis 1879 (données observées) jusqu'à 2100 (données projetées). Les méthodes retenues sont le bilan hydrique avec le choix de l'indice du déficit d'évaporation et les types de climat annuel (TCA) utilisant la classification de Köppen. Les résultats montrent la forte variabilité interannuelle observée depuis plus d'un siècle avec des évènements historiques (1906, 1921, 1976 ou 2003) sans qu'une tendance très nette puisse être établie. Les projections du modèle Météo-France montrent, en revanche, une forte tendance à l'augmentation du déficit au cours du XXIe siècle et la recrudescence des TCA à étés chauds et secs.

17 pages; International audience; Mean diurnal rainfall regimes over Eastern Africa (also referred to as the Greater Horn of Africa) are studied based on 3-hourly data from the TRMM 3B42 data set, averaged over a 17-year period (1998–2014). The consistency with long-term mean raingauge data, available for partly independent periods, varies from good (Sudan, Ethiopia, Eritrea and Somalia) to very good (Kenya, Tanzania and Uganda). Over sea (Indian Ocean and Red Sea), the diurnal rainfall distribution is quite uniform; however, a morning peak dominates and there is evidence of offshore phase propagation south of the equator. Over land, both rainfall frequency and rainfall amounts show a dominant afternoon maximum (1500–1800 East African Time, i.e. GMT + 3). However, many inland regions show a delayed rainfall maximum (evening, night-time or morning). The evening to night-time maximum found over some land areas is associated with a phase propagation from areas showing an afternoon peak. This occurs west of high ground areas (Sudan and parts of the Great Lakes region) and in belts parallel to the seashores (Eritrea, northeastern Ethiopia, Somalia and eastern Kenya). The latter provide indirect evidence that sea breeze effects can be detected at unexpectedly great distances from the coast (up to 300–400 km) in parts of Eastern Africa. A remarkable ring of early afternoon (1500) maxima is found around most lakes, although some east–west asymmetries occur. Over the lakes, a morning or late night maximum is mostly found. It is generally inversely related to the distance to the shorelines for the larger lakes, but over the mid-size lakes it is replaced by or competes with a late afternoon to evening maximum.

Made available in DSpace on 2019-10-05T03:16:20Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-01-01 This article proposes to use the Koppen classification to define Annual Climate Types (ACT) for a set of 208 stations, representative of the climatic diversity of Brazil. The average monthly temperature and precipitation data for the period 1961-2015 allow to establish the frequency of ACTs for each station. The statistical and cartographic treatment of this information makes it possible to define the limits of the climates of Brazil: here we apply the concepts of strong nuclei, defined as the regions where the ACT are systematically or mostly the same, and transition areas, i.e. regions where there is a great diversity of ACT. This approach allows us to propose a detailed study of the transitions between the tropical climates types (mainly Aw, Am and Af) and those of the south, subtropical and temperate (Cwa and Cfa in particular) and discuss these climatic limits. Univ Rennes 2, CNRS, UMR 6554, LETG Rennes COSTEL, Rennes, France Univ Estadual Paulista UNESP, Presidente Prudente, Brazil Univ Estadual Paulista UNESP, Presidente Prudente, Brazil

Monitoring agricultural areas threatened by soil erosion often requires decimetre topographic information over areas of several square kilometres. Airborne lidar and remotely piloted aircraft system (RPAS) imagery have the ability to provide repeated decimetre-resolution and accuracy digital elevation models (DEMs) covering these extents, which is unrealistic with ground surveys. However, various factors hamper the dissemination of these technologies in a wide range of situations, including local regulations for RPAS and the cost for airborne laser systems and medium-format RPAS imagery. The goal of this study is to investigate the ability of low-tech kite aerial photography to obtain DEMs with decimetre resolution and accuracy that permit 3-D descriptions of active gullying in cultivated areas of several square kilometres. To this end, we developed and assessed a two-step workflow. First, we used both heuristic experimental approaches in field and numerical simulations to determine the conditions that make a photogrammetric flight possible and effective over several square kilometres with a kite and a consumer-grade camera. Second, we mapped and characterised the entire gully system of a test catchment in 3-D. We showed numerically and experimentally that using a thin and light line for the kite is key for a complete 3-D coverage over several square kilometres. We thus obtained a decimetre-resolution DEM covering 3.18 km(2) with a mean error and standard deviation of the error of +7 and 22 cm respectively, hence achieving decimetre accuracy. With this data set, we showed that high-resolution topographic data permit both the detection and characterisation of an entire gully system with a high level of detail and an overall accuracy of 74 % compared to an independent field survey. Kite aerial photography with simple but appropriate equipment is hence an alternative tool that has been proven to be valuable for surveying gullies with sub-metric details in a square-kilometre-scale catchment. This case study suggests that access to high-resolution topographic data on these scales can be given to the community, which may help facilitate a better understanding of gullying processes within a broader spectrum of conditions.

In Tunisian semi-arid areas, human pressure, torrential rains and low vegetation cover are the essential factors of gully erosion. In these areas, gullies naturally exhibit complex morphologies. Hence they are difficult to measure. This type of erosion, in its most severe form, threatens cultivated lands by the extension of badlands as well as water resources by water reservoir sedimentation. For a long time, the objective of most gully erosion studies was the morphological characterization of the gullies in order to properly understand erosion processes. Gradually, the technological advancement in sensors and platforms for aerial image acquisition made it possible to achieve more detailed mapping of gullies. During the last decade, low altitude aerial platforms have experienced the strongest development in acquiring high-resolution aerial photographs and generating associated digital elevation models (DEMs), in particular with the rise of structure from motion algorithms use in geosciences. Such DEMs meet the need for mapping at the sub-meter scale as well as the capability of studying the gullies in three dimensions. In previous studies, a DEM and the corresponding orthophotography were produced at very high resolution (6.2 cm for the DEM, 3.1 cm for the orthophotography). The 3D reconstruction was performed from overlapping images taken from a consumer grade camera hung down a kite. Such experiments, producing unusual aerial datasets, are poorly reviewed in the literature. Therefore, the objective of this paper is to assess the accuracy of such DEMs obtained from overlapping aerial photographs taken from kite platforms.

Ponencia presentada en: IV Congreso de la Asociación Española de Climatología "El Clima entre el Mar y la Montaña", celebrado en Santander del 2 al 5 de noviembre de 2004. [ES]Se ha analizado el efecto de la topografía sobre la circulación de la brisa marina en el área vitivinícola de South Western Cape en Suráfrica. Se han llevado a cabo simulaciones numéricas utilizando el Regional Atmospheric Modelling System (RAMS) para una típica situación meteorológica estival. Los resultados muestran los efectos climáticos a muy pequeña escala de la compleja topografía del sector cuando la brisa marina penetra hacia el interior: la rugosidad, brisas de vertiente, la humedad superficial y las diferencias de temperatura. [EN]The effect of the topography on the sea breeze circulation was studied in the South Western Cape wine growing area of South Africa. Numerical simulations were performed using the Regional Atmospheric Modelling System (RAMS) for a typical summer meteorological situation. The results showed the smallscale climatic effects of the complex topography of the area when the sea breeze penetrated inland: roughness effect, up-slope breezes, surface humidity and temperature differences.

Ponencia presentada en: III Congreso de la Asociación Española de Climatología “El agua y el clima”, celebrado en Palma de Mallorca del 16 al 19 de junio de 2002. [ES]Se ha calculado el coeficiente de correlación de la r de Pearson entre el índice NAO y la precipitación de diciembre (1961-90) en 70 observatorios repartidos por las dos vertientes del Pirineo oriental (Francia, Andorra y España). Los resultados muestran una clara relación entre la distribución de las isolíneas y el relieve, sobre todo en aquellos sectores con barreras orográficas destacables y valles bien orientados a los flujos de suroeste. [EN]In this work, the Pearsons “r” values were calculated for the corrrelation between NAO index and December precipitation (1961-90) in 70 weather stations in the two sides of the eastern Pyrenees (France, Andorra and Spain). The results show an intimate relationship between isopleth distribution and relief, specially in the high orographic barriers and valleys well oriented to southwest flows.

Nous nous proposons dans cette communication de décrire la démarche et les principaux résultats qui ont été obtenus dans le cadre du projet CLIMASTER, pour contribuer au débat sur l’état actuel des connaissances sur le changement climatique (CC) dans le Grand Ouest. Vis-à-vis du climat, nous avons développé des analyses originales portant essentiellement sur différentes longues chroniques climatiques du passé dans le Grand Ouest, pour voir l’évolution déjà en cours du CC. Ces analyses ont porté sur des données « classiques » (températures, précipitations) montrant ainsi qu’environ un degré de température a été « gagné » en moyenne sur les cinquante dernières années. Sur les précipitations, on note des tendances saisonnières opposées avec une augmentation des précipitations l’hiver et une diminution l’été, surtout au nord du grand Ouest. Les analyses ont porté également sur les types de circulations atmosphériques, durant la période disponible (1850-2009) et également sur les types de temps (1971/2010). Vis-à-vis des ressources naturelles (eau, sol), il n’existe pas dans le Grand Ouest de chroniques longues de données passées permettant de capter une évolution sur le long terme. La vulnérabilité de la ressource en eau à la variabilité climatique annuelle, du fait de l’absence de ressources exogènes et de nappes d’importance, doit être soulignée. L’ensemble de ces travaux conduisent à donner à la variabilité locale des propriétés du sol un rôle clé dans l’évaluation de la vulnérabilité des ressources en eau et en sol. L’impact direct du CC sur les écosystèmes d’eau douce – dernier point abordé -, montre aujourd’hui un impact peu mesurable, car masqué par des pressions anthropique plus importantes (agriculture, modification du lit etc..) qui nécessitent une approche intégrant l’effet du bassin versant et pas simplement l’hydrosystème. Vis-à-vis de l’agriculture, des travaux originaux sur les jours agronomiquement disponibles ont été réalisés. Les tendances actuelles et passées des systèmes de culture et de production ont été aussi abordées à partir des chroniques spatiales d’occupation du sol sur des données de télédétection (capteur MODIS qui constitue un outil novateur), sur une décennie. Vis-à-vis des acteurs régionaux et de leur capacité à prendre en compte l’impact du CC, il s’est agi de caractériser le regard, la sensibilisation et la capacité à agir des acteurs agricoles face au CC, à partir d’enquêtes, de séminaires d’échange et de réflexions prospectives au sein de groupes d’agriculteurs. En contre point des enquêtes avec les acteurs de l’eau ont été également réalisées. En conclusion, l’ensemble des travaux de CLIMASTER, les méthodes choisies, le corpus de connaissances élaboré sont là pour «donner à penser» le changement climatique dans le Grand Ouest plus que pour pronostiquer un avenir incertain.

Meteorological and marine conditions leading to coastal flooding along the French coast of the eastern English channel. Coastal flooding due to storm is the result of a combination of factors : a low air pressure, a strong wind with a direction perpendicular to the coast at the time of spring high tide (the average coefficient of spring tide is about 95). Characterization of coastal floods leading to damages has received attention and many studies have been carried out along the coast of the oriental English Channel. Thanks to our inventory of coastal flooding events from 1949 to 2010, the identification of the meteorological parameters such as the north-west pressure gradient or the passage of an atmospheric cold front during the storm has been possible. This identification leads to a better warning of numerous coastal flooding events. However, some of them cannot be explained by these parameters. To understand them, it is necessary to integrate another factor : the meteorological and marine conditions before coastal flooding. For a few days or weeks before a coastal flooding event, the beach can adapt to stronger hydro-dynamic conditions. This adaptation can be a lowering of the beach profile. Lowering can lead to flood and damages. The aim of the study is to improve prediction/ warning of these events that can end in major damages on these coastal areas., L’inondation par la mer due aux tempêtes («submersion de tempête » ) est le résultat d’une conjonction de facteurs : une faible pression atmosphérique, un fort vent d’afflux (ces deux facteurs peuvent déterminer une surcote ou «onde de tempête » ) au moment d’une pleine mer de vive-eau. Le littoral français de la Manche orientale a fait l’objet de travaux sur la caractérisation des submersions de tempête génératrices de dommages. A partir d’un inventaire des submersions de tempête entre 1949 et 2010, l’identification de paramètres météorologiques tels que le gradient de pression de nord-ouest et le passage du front froid permet de mieux appréhender la genèse de la majorité des submersions. Cependant, quelques cas ne peuvent être expliqués par ces seuls paramètres. Pour les comprendre, il est nécessaire d’intégrer un autre facteur à savoir les conditions météo-marines préalables à l’inondation par la mer. En effet, durant quelques jours à quelques semaines avant l’inondation, la plage peut s’adapter à des conditions hydro-dynamiques un peu plus fortes en subissant un abaissement de son profil. Cet abaissement peut favoriser les franchissements et les dommages associés. La finalité de ce travail est de participer à l’amélioration du système d’alerte des inondations par la mer du secteur d’étude., Letortu Pauline, Costa Stéphane, Cantat Olivier, Planchon Olivier. Conditions météo-marines responsables des inondations par la mer en Manche orientale française. In: Evénements extrêmes fluviaux et maritimes. Leurs variabilités spatiales et chronologiques dans l'ouest de l’Europe. 34èmes journées de l’hydraulique Paris, 1 et 2 février 2012. 2012.

Ponencia presentada en: I Congreso de la Asociación Española de Climatología “La climatología española en los albores del siglo XXI”, celebrado en Barcelona del 1 al 3 de diciembre de 1999. [ES]En la línea litoral de Cataluña domina un régimen pluviométrico mediterráneo marítimo, con su máximo otoñal y su mínimo estival. Pero las costas orientadas al Sureste se diferencian de las orientadas al Este, donde la topografía favorece matices locales. El régimen marítimo sufre una fuerte variabilidad interanual sobre el litoral. El régimen medio no se observa más que algunos años. A veces, incluso, pueden presentarse lluvias intensas en primavera y verano. [EN]In Catalonia, the Mediterranean and maritime precipitation regime, with an autumn maximum and a summer minimum, is prevailing on the continental fringe. The coast faces southeast is distinguished from the coast faces east, where the topography explains local differences. The coastal regimes are subjected to high interannual variations. The mean regime is shown only for a few years. Heavy rainfall is occasionally observed in spring and summer.

http://www.mercator.ufc.br/index.php/mercator/article/view/536; Brittany, as many French territories, experiences sometimes drought issues which can vary in intensity and duration. The aim of this study is to determine the impacts of droughts on soil water resources since the early XIXth century. Thus, a soil water balance suited to regional scales was used and applied to different cities of Brittany and surroundings such as Rennes, Plougonvelin and Nantes. The evaporation deficiency obtained at a monthly scale revealed droughts intensity and inter-annual variability. At a yearly scale a positive tendency of the deficiency was noticed. At a monthly scale the inter-annual variability was clearly shown and revealed a 4-year period rhythm with soils lacking of water for one summer month. Finally, we used the NDVI calculated from SPOT-Vegetation images for monitoring the spatial extent of drought in Brittany. For 2003 (the last great drought observed in western France), we found a good relationship between the NDVI and the evapotranspiration but bidirectional reflectance effects, angular values and compositing's procedures may also have a great impact on observed values of NDVI.; A Bretanha, como a maior parte de outras regiões francesas, sofre ocasionalmente com secas de duração e intensidade variaveis. O objetivo deste estudo é de analisar o impacto das secas sobre os recursos hídricos e sua evolução à partir do século XIX. Foi utilisado um modelo de balanço hídrico adaptado para escala regional para diversas estações na Bretanha (Rennes, Plougonvelin, Nantes, etc.). A deficiência da evaporação calculada em escala temporal mensal destaca a variabilidade espaço-temporal da seca. Em escala temporal anual, é observada uma leve intensificação que resulta essencialmente do aumento do déficit no mês de agosto, no fim do verão. A utilisação dos dados do índice de vegetação (NDVI) derivados das imagens SPOT-Vegetation permete estabelecer a extensão horizontal deste fenômeno. Análises para o ano de 2003 (ano da última grande seca na França Ocidental) mostraram uma boa relação entre o NDVI e a evapotranspiração, entretanto os efeitos bidirecionais, os angulos de visada, bem como os algoritmos utilisados podem afetar significativamente os valores do NDVI.

The aim of this study is to show the relations between the water balance calculated in Rennes (Brittany, western France) and the weather patterns. Homogeneized data series of temperature, precipitation and sunshine duration recorded at the weather station of Rennes for the 1880-2004 period were obtained in order to calculate the evapotranspiration according the Turc's formula at a monthly time-scale, and to show the interannual variability of the water balance. The atmospheric circulation patterns were identified using the Hess-Brezowsky classification. The results show that 47% of all circulation types were anticyclonic situations, including 71% of cyclonic situations in 1921. The proportion of anticyclonic situations was 49% in summer, including 10 years with a proportion ofabove 70%. Significant but small correlations were shown between water deficits and frequency of anticyclonic situations (year: 0.51; summer: 0.59; spring: 0.46; autumn: 0.44)., Cette étude vise à montrer la relation entre les données du bilan de l'eau à Rennes (Bretagne, France de l'ouest) et les types de situations atmosphériques observées sur la région. On utilise pour cela dans un premier temps les données homogénéisées de températures, précipitations et insolation disponibles pour la station de Rennes de 1880 à 2004 : le calcul de l'ETP Turc au pas de temps mensuel permet de montrer la variabilité interannuelle du bilan de l'eau. Les types de circulations atmosphériques ont été définis en utilisant la méthode de classification des types de circulations de Hess et Brezowsky. Les types anticycloniques représentent 47% des situations météorologiques avec un record de 71% en 1921. En été les types anticycloniques représentent 49% des situations en moyenne avec 10 années où la fréquence a dépassé 70%. Au total les corrélations entre les déficits annuels et la fréquence des situations anticycloniques sont significatives mais modestes : elles atteignent 0,51 pour l'année, 0,59 pour l'été, 0,46 pour le printemps et seulement 0,44 pour l'automne.

SRef-ID : 1607-7962/gra/EGU2008-A-02797; International audience; Wildfire may lead to long-term soil carbon gain or loss, depending on the ability of the system to conserve chemically stable black carbon (BC). Rainfall events can lead to erosion of this organic matter form deposited on the soil surface. The objective of this study was to quantify horizontal as well as vertical BC transport during a rainfall simulation experiment with sandy soil in northern Senegal. The conceptual approach consisted of artificial burning of harvested residues, which were subsequently exposed to two different rainfall regimes: with and without occurrence of splash. After the rainfall simulation experiment, we quantified the total amount of carbon added to the soil and chemically recalcitrant black carbon (BC) (1) exported from the plots, (2) infiltated into the soil and (3) remaining on the soil surface. Transport processes affected around 40-60 % of the total carbon and BC added. Our results showed that 30 % of the total carbon added by the fire was exported from the site, whereas another 15 % were vertically transported into the soil. BC, which represented about 40 % of the total carbon added, was transported in higher proportions compared to total C (horizontally as well as vertically) when the splash erosion was allowed to occurr. The preferential export of BC was strongly dependent on the rainfall regime: when splash erosion was suppressed, BC export was greatly reduced, whereas BC infiltration increased compared to rainfall with splash occurring.We conclude that water erosion of BC during rainfall events after wildfire is an important factor determining the fate of potentially stable carbon in the ecosystem.

Wildfire may lead to long-term soil carbon gain or loss, depending on the ability of the system to conserve chemically stable black carbon (BC). Rainfall events can lead to erosion of this organic matter form deposited on the soil surface. The objective of this study was to quantify horizontal as well as vertical BC transport during a rainfall simulation experiment with sandy soil in northern Senegal. The conceptual approach consisted of artificial burning of harvested residues, which were subsequently exposed to two different rainfall regimes: with and without occurrence of splash. After the rainfall simulation experiment, we quantified the total amount of carbon added to the soil and chemically recalcitrant black carbon (BC) (1) exported from the plots, (2) infiltated into the soil and (3) remaining on the soil surface. Transport processes affected around 40-60 % of the total carbon and BC added. Our results showed that 30 % of the total carbon added by the fire was exported from the site, whereas another 15 % were vertically transported into the soil. BC, which represented about 40 % of the total carbon added, was transported in higher proportions compared to total C (horizontally as well as vertically) when the splash erosion was allowed to occurr. The preferential export of BC was strongly dependent on the rainfall regime: when splash erosion was suppressed, BC export was greatly reduced, whereas BC infiltration increased compared to rainfall with splash occurring.We conclude that water erosion of BC during rainfall events after wildfire is an important factor determining the fate of potentially stable carbon in the ecosystem.

International audience

This paper presents the limit as a notion applied to coastal morpho-climatic objects out. From a spatial point of view, the notion of limit has a legal pertinence : it allows to define the (French) Domaine Public Maritime. However, the space and time variability of a limit results in a spatial gradient more than into a physical line. The theoretical requirements of the limit do not match its physical position. On a macro-tidal beach, the hydrological reference level is 1) exactly calculable, 2) never observed, neither as a stabilization of the sea level, nor as the geometrical centre of the beach cross section. On the other hand, the coastal climate, particularly on a coastal fringe with dunes (in South Africa) is more different from the climate of the close inland area than from the climate of the open sea. These examples show that the notion of limit, in this scientific context, is not a satisfactory concept. The coastal morpho-climatic feature can be analysed without putting it forward. An example is developed in New Zealand on a coastal area which responds to the tsunamis and to the periods of relaxations., Le travail présente la notion de limite appliquée à des objets morpho-climatiques littoraux. D'un point de vue spatial, la notion de limite a une pertinence juridique (elle sert à définir le Domaine Public Maritime) mais il est délicat de lui trouver une existence concrète sur le terrain, tant elle est mobile et prend le plus souvent la forme d'un gradient. Son caractère de non discontinuité est accentué par le fait que ses caractéristiques théoriques ne coïncident pas avec sa position physique. On peut prouver, sur une plage macro-tidale, que le niveau hydrologique de référence est 1) parfaitement calculable, 2) jamais observé, ni par le stationnement de l'eau, ni par le centre géométrique du profil de plage. On peut également prouver que le climat littoral, particulièrement sur une côte à dunes (en Afrique du Sud), différencie plus le littoral de l'intérieur immédiat que de la mer ouverte. Ces exemples montrent que la notion de limite, dans ce type de contexte scientifique, n'est pas un concept satisfaisant. On peut très bien analyser le fonctionnement morpho-climatique d'un littoral sans l'invoquer. Un exemple est développé en Nouvelle Zélande sur un littoral répondant et aux tsunamis et aux périodes de relaxations., Regnauld Hervé, Planchon Olivier. La notion de limite et les objets morpho-climatiques littoraux: un enjeu théorique?. In: L'information géographique, volume 67, n°1, 2003. pp. 60-74.

L'étude porte sur les relations contrastées, en Afrique de l'Ouest, lors du croisement des cartes de densité de population et de dégradation des sols. Une relation forte entre dégradation et population est ainsi mise en évidence, particulièrement dans le cas de l'érosion hydrique. Un modèle d'évolution est proposé sur la base de cette relation. Il est appliqué à une projection à 30 ans. Selon ce modèle, la superficie des terres dégradées en Afrique de l'Ouest progresserait de 13% en 30 ans, soit une superficie égale à celle du Sénégal. Parmi elles, les superficies cultivables gravement dégradées progresseraient de 16%, soit une superficie supérieure à celle du Togo. L'analyse suggère qu'une relation aussi directe entre croissance démographique et dégradation des sols est directement liée au fait que les conditions nécessaires à l'innovation dans le monde rural ouest africain ne peuvent être réunies aujourd'hui qu'en quelques cas très particuliers. (Résumé d'auteur)

La dégradation des sols est mise en cause dès 1906 pour expliquer la baisse progressive de la productivité agricole au Sénégal. Depuis, de nombreuses études sont faites sur les formes de dégradation telles que l'érosion hydrique. Des recherches en stations expérimentales ont fait état d'une forte dégradation des sols par les eaux de pluies consécutive à une baisse de la fertilité et des rendements. Ces conséquences ne sont toutefois pas évaluées directement mais elles relèvent encore aujourd'hui essentiellement de conjectures. Les pertes en terre causées par l'érosion éolienne restent quant à elles mal connues. Depuis les années 70, plusieurs évolutions concomitantes défavorables à une bonne productivité des sols ont provoqué une rapide évolution des expertises en matière de dégradation des sols. Ces expertises ont pu représenter les conséquences du phénomène, notamment l'érosion hydrique, mais aucune prévision n'est possible en raison de sa complexité. La croissance rapide de la population sénégalaise (2.9%) est tenue pour principal responsable du rythme accéléré de dégradation des sols. Cependant, les études sur cette relation laissent en suspens autant de questions que de réponses effectivement fournies, surtout les aspects concernant les changements dans les modes d'utilisation et d'occupation des sols. La connaissance des phénomènes érosifs nécessite l'élaboration de méthodes qui restent entièrement du domaine de la recherche. (Résumé d'auteur)