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12 pages (3/4 p.); International audience; Weather and climate extremes such as droughts and floods have far reaching impacts in Kenya. They have had implications in a variety of sectors including agriculture, water resources, health, energy, and disaster management among others. Lake Victoria and its catchment support millions of people and any impact on its ability to support the livelihoods of the communities in this region is of major concern. Thus, the main objective of this study was to assess the potential future climatic changes on the Nzoia catchment in the Lake Victoria basin, and how they might affect streamflow. The Soil and Water Assessment Tool was used to investigate the impact of climatic change on streamflow of the study area. The model was set up using readily available spatial and temporal data, and calibrated against measured daily streamflow. Climate change scenarios were obtained from general circulation models. Results obtained showed increased amounts of annual rainfall for all the scenarios but with variations on a monthly basis. All - but one - global circulation models (GCMs) showed consistency in the monthly rainfall amounts. Rainfall was higher in the 2050s than in the 2020s. According to climate change scenarios, temperature will increase in this region, with the 2050s experiencing much higher increases than the 2020s with a monthly temperature change range of 0―1.7 °C. The range of change in mean annual rainfall of 2.4-23.2% corresponded to a change in streamflow of about 6-115%. The analysis revealed important rainfall-runoff linear relationships for certain months that could be extrapolated to estimate amounts of streamflow under various scenarios of change in rainfall. Streamflow response was not sensitive to changes in temperature. If all other variables, e.g. land cover, population growth etc., were held constant, a significant increase in streamflow may be expected in the coming decades as a consequence of increased rainfall amounts.

14 pages, 3 figures, 4 tables, Late in summer 2003, extensive mass mortality of at least 25 rocky benthic macro-invertebrate species (mainly gorgonians and sponges) was observed in the entire Northwestern (NW) Mediterranean region, affecting several thousand kilometers of coastline. We were able to characterize the mortality event by studying six areas covering the main regions of the NW Mediterranean basin. The degree of impact on each study area was quantified at 49 sites by estimating the proportion of colonies affected in populations of several gorgonian species compared with reference data obtained in years without mortality signs. According to these data, the western areas (Catalan coast and Balearic Islands) were the least affected, while the central areas (Provence coast and Corsica-Sardinia) showed a moderate impact. The northernmost and eastern areas (Gulf of Genoa and Gulf of Naples) displayed the highest impact, with almost 80% of gorgonian colonies affected. The heat wave of 2003 in Europe caused an anomalous warming of seawater, which reached the highest temperatures ever recorded in the studied regions, between 1 and 3 °C above the climatic values (mean and maximum). Because this exceptional warming was observed in the depth ranges most affected by the mortality, it seems likely that the 2003 anomalous temperature played a key role in the observed mortality event. A correlation analysis between temperature conditions and degree of impact seems to support this hypothesis. Under the present climate warming trend, new mass mortality events may occur in the near future, possibly driving a major biodiversity crisis in the Mediterranean Sea, This research was partly supported by the IFB Foundation (Institut Français de la Biodiversité), the environmental department of TOTAL-Fina-Elfgroup, an 'Action Concertée Iniciative' (ACI) program 'Jeunes chercheus 2003' (number JC5360) from French Research Ministry, research grants CTM2006-01463 and CGL2007-66757

Rain-causing mechanisms over Southern Africa (south of 15˚S) involve both tropical and temperate dynamics. Most studies focused on the synoptical timescale, while the intraseasonal (20-120 days) variability has more been neglected to date. This study aims at determining whether the dominant mode of intraseasonal variability in the Tropics, namely the Madden-Julian Oscillation (MJO), has a significant impact on Southern African rainfall and associated atmospheric dynamics. The examination of outgoing longwave radiation (OLR) over Southern Africa shows indeed significant intraseasonal fluctuations at the 30-60 day timescale, i.e. in the pe- riods that are typically reminiscent of the MJO. In order to confirm the implication of the latter, composite analyses are computed, based on the real-time MJO indices defined in Wheeler and Hendon (2004). Strong intraseasonal convective signals are particularly recorded over the region dur- ing its rainy season (November through March). Large-scale organized convective perturbations are seen to propagate eastwards, mainly between 10˚S and 20˚S, and then northwards, over the Rift Valley and the African Great Lakes. They finally reach the MJO-associated equatorial clusters over Tanzania, which complete their circuit towards the East over the Indian Ocean. The corresponding response of the rainfall field, obtained through the analysis of daily rain-gauge records in 7665 stations over Southern Africa, presents the alternation, over the intraseasonal cycle, of a dry and a humid phase, which are both significant. The influence of the MJO on the rainfall field is however not homogeneous spatially. While the southern part of the domain (Western Cape Province and surrounding countries) is very partially influenced, and more closely relates to the mid-latitude dynam- ics, the tropical parts of the domain (Northern Province of South Africa, Namibia, Botswana and Zimbabwe) logically show stronger dependency to the MJO forcing. Rainfall records exhibit there sharp periodicities in the 30-60 day timescale. Moisture flux anomalies, derived from the NCEP-DOE II reanalyses, reveal an in- traseasonal modulation of the mid-tropospheric easterly flow over the Congo basin at 700hPa; these fluctuations are coupled to northerly anomalies that extend from the tropical to the subtropical austral latitudes. They are hypothesized to convey mois- ture from the tropical air masses, and hence to favour wet conditions over the region. During the dry phase, southerly anomalies tend on the contrary to prevail, and are hypothesized to convey dryness from the mid-latitude air masses.

[1] North Atlantic variability in general, and the North Atlantic Oscillation (NAO) in particular, is a long-studied, very important but still not well-understood problem in climatology. The recent trend to a higher wintertime NAO index was accompanied by an additional increase in the Azores High not coupled to changes in the Icelandic Low, as shown by a self-organizing maps (SOMs) analysis of monthly mean DJF mean sea level pressure data from 1957 to 2002. SOMs are a nonlinear tool to optimally extract a user-specified number of patterns or icons from an input data set and to uniquely relate any input data field to an icon, allowing analyses of occurrence frequencies and transitions complementary to principal component analysis (PCA). SOMs analysis of ERA-40 data finds a North Atlantic monopole roughly colocated with the mean position of the Azores High, as well as the well-known NAO dipole involving the Icelandic Low and the subtropical high. Little trend is shown in December, but the Azores High increased along with the NAO in January and February over the study interval, with implications for storminess in northwestern Europe. In short, our SOM-based analyses of winter MSLP have both confirmed prior knowledge and expanded it through the relative ease of use and power with nonlinear systems of the SOM-based approach to climatological analysis.

The question of spatial generalisation of results obtained in different stations of study and measurement of gully erosion on marls in French Southern Alps is, in this paper, approached through the presentation of five master's degree works. Editing a GIS (Geographic Information System) a regional scale is purposed and the practical details in the implementation of this GIS are reviewed. The information «layers» are chosen from the examination of the context, which is the more or less important activity of gully erosion. This context was studied in some areas, notably the «Val de la Méouge» (Southern Baronnies). The interest of some information «layers» like lithological diversity of marls, structural data, quaternary slopes formas, difference in altitude between the summits of gully and the basic level of the local hydrographie net is underlined. The formalization of the information about climate and vegetation asks some specific problems. Actually, climate is only known through a limited numerous of measuring posts. However, dynamic climatology ensures a better understanding of the changes in rainfall regime ; then a better spatialization of these changes, which modulate the aggressiveness of the mountainous submediterranean climate of Southern Alps, is allowed. As for vegetation, it plays a protecting role only at the scale of elementary gullies. The usefulness of a specific GIS about changes in vegetal landscapes is also underlined., La question de la généralisation spatiale des résultats obtenus dans les stations d'étude et de mesure de l'érosion par ravinement dans les secteurs marneux des Alpes du Sud est abordée à travers la présentation de cinq mémoires de maîtrise. L'établissement d'un système d'information géographique (SIG) couvrant l'ensemble régional est proposé et les modalités de mise en oeuvre de ce SIG sont examinées. Les couches d'information qu'il conviendrait d'y entrer sont précisées par l'examen du contexte qui préside à la plus ou moins grande activité de l'érosion ravinante, contexte qui a été étudié sur quelques sites, notamment dans le Val de la Méouge (Baronnies méridionales). L'intérêt de faire entrer en ligne de compte des informations comme la diversité lithologique des marnes, les données structurales, les formes de versants façonnées au Quaternaire, le dénivelé entre les tètes de ravine et le niveau de base du réseau hydrographique local est souligné. La formalisation de l'information concernant le climat et la végétation pose des problèmes spécifiques. Le climat n'est en effet connu qu'à travers un nombre limité de postes de mesure. Le recours à la climatologie dynamique permet cependant de mieux comprendre et donc de mieux spatialiser les changements intervenant dans le régime des précipitations, changements qui modulent l'agressivité du climat montagnard subméditerranéen des Alpes du Sud. Le couvert végétal joue, quant à lui, un rôle protecteur qui ne se précise bien que lorsque l'on descend à l'échelle de la ravine élémentaire ; le piégeage des sédiments derrière les écrans végétaux se révèle particulièrement efficace lorsque ces écrans sont situés dans la partie aval des roubines. Il apparaît par ailleurs nécessaire de concevoir un SIG spécifique sur la dynamique des paysages végétaux, à l'échelle de temps de plusieurs décennies., Lecompte Michel, Alexandre Frédéric, Bertherlot Mickaël, Casagrande Axelle, Cohen Mariane, Garlatti Florence, Genin Alain. Eléments pour une géographie du ravinement dans les secteurs marneux des Alpes du sud (France). In: Travaux de l'Institut Géographique de Reims, vol. 31-32, n°123-124, 2005. Erosion, végétation, aménagement, pollutions. pp. 27-58.

The dynamical phytoclimatology : a different approach of nature of climate. — Spatial climatic variations are the expression of circulation of the atmosphere and are described by vegetation. A climatic study of moroccan Moyen Atlas exhibits these relationships. The ordering of vegetal species reveals the location of climatic limits and allows to measure its intensity using the theory of probability and information system. To talk of " dynamical phytoclimatology " is justified because climatic transition that can be located through vegetation change can be interpreted as limits of influence of circulation of the atmosphere., Les variations spatiales du climat sont l'expression des mouvements de l'atmosphère et sont intégrées par la végétation. Une étude climatologique du Moyen Atlas marocain confirme ces relations. L'agencement des espèces végétales permet de préciser la localisation des limites climatiques et de mesurer leur intensité relative, grâce au calcul des probabilités et à la théorie de l'information. L'expression « phytoclimatologie dynamique » se justifie par le fait que les transitions climatiques, localisables par les accélérations du renouvellement de la flore, peuvent être interprétées comme des limites d'influence de circulations atmosphériques., Lecompte MichelLecompte Michel. La phytoclimatologie dynamique : une approche différente de la nature du climat. In: L'Espace géographique, tome 17, n°2, 1988. Milieux d'Afrique - Histoires de vie, espaces de vie - Analyses de l'espace. pp. 109-121.