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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.