1,721,131 research outputs found
TEAL WCA: climate data platform for planning solar photovoltaic and wind energy resources in West and Central Africa
No full text<p>This data platform entitled '<strong>TEAL WCA: climate data platform for planning solar photovoltaic and wind energy resources in West and Central Africa' </strong>is a presentation of climate and energy resources data for two Sub-Saharan African regions. Climate change is now a fact and African countries are more vulnerable. To better prepare for mitigation and adaptation, projection information is needed. The challenge of climate model data output is that they are available at the global level and are associated with some biases. This makes studies at the country or sub-county level difficult especially impact study. This study aims to (i) downscale, (ii) bias-adjust, (iii) aggregate at country and sub-country levels, and (iv) estimate the wind power and solar power potential. Moreover, a database platform is built to make the prepared climate data and estimated energy potential dataset freely available for researchers, universities, and decision-makers in West and Central African countries. This manuscript presents the performance of the approach and the distribution of climate and energy variables. </p>
Multi-scale assessment of rainfall simulated by Regional Climate Models in Southeast France
No full textSur le bassin méditerranéen, les projections climatiques pour la fin du siècle indiquent un assèchement des étés accompagné d'une intensification des précipitations.Dans ce contexte, la caractérisation de la pluviométrie de la région est nécessaire pour appréhender son évolution future.Les modèles climatiques régionaux (RCM) sont des outils essentiels pour la compréhension du climat régional et pour la projection de son évolution.L'objectif de cette thèse est alors de caractériser et d'évaluer la pluie simulée par les RCM dans le sud-est de la France, typique des régions méditerranéennes côtières.La description de la pluie observée aux mêmes échelles que les RCM en est un préalable.La pluie observée et simulée est caractérisée en termes de valeurs et de structure spatiale et temporelle de l'occurrence et de l'intensité.Les liens entre ces caractéristiques et les processus physiques sous-jacents sont explorés grâce à une analyse par type de temps.Dans les modèles, le volume annuel total d'eau apporté par la pluie sur l'ensemble de la région d'étude est proche des valeurs observées.Ce volume n'est toutefois pas réparti également dans le temps et dans l'espace dans les observations et dans les simulations.Parmi les multiples caractéristiques de la pluie observée et simulée, cette étude souligne l'influence des forçages du relief et des processus liés au cycle diurne de l'énergie solaire à la fois sur le déclenchement et sur l'intensité des précipitations.Ainsi, la pluie se produit préférentiellement en fin d'après-midi, en lien avec le chauffage diurne de la surface.Cependant, dans les modèles, le maximum d'occurrence est plus précoce que dans les observations, ce qui suggère une réponse trop rapide du schéma de convection au cycle diurne des flux de surface, liée à l'absence de la phase de transition entre la convection peu profonde et la convection profonde dans la majorité des schémas.Par ailleurs, au sein du domaine d'étude, l'influence du relief sur les caractéristiques de la pluie est plus marquée pour les Cévennes que pour les Préalpes.Les RCM reproduisent cette influence du relief sur les caractéristiques de pluie.Toutefois, les contrastes entre plaines et reliefs sont plus accentués dans les modèles que dans les observations, notamment lorsque le forçage de grande échelle est faible et la convection dominante dans la région d'étude.L'accentuation du contraste entre plaine et montagne dans les modèles semble donc provenir d'une trop grande sensibilité des schémas de convection au relief qui favorise la convergence et l'instabilité de la masse d'air.Climate projections for the end of the century indicate drier summers and more intense precipitation in the Mediterranean.In this respect, the characterization of rainfall in the region is necessary to understand its future changes.Regional climate models (RCM) are essential tools to understand the regional climate and to project its future evolution.This thesis aims at characterizing and evaluating rainfall simulated by RCM in Southeast France, typical of the mediterranean coastal regions.The description of observed rainfall at the same scales as RCM is a prerequisite.Observed and simulated rainfall is described in terms of values and spatial and temporal structure of occurrence and intensity.Weather types are used to explore the relation between rainfall features and the underlying physical processes.In the RCM, the annual total volume of water precipitated over the study region is closed to the observed values.However, this total volume is not distributed the same in space and time in the RCM simulations and in the observations.Among the multiple facets of the rainfall climatology, this study highlights the influence of the relief and of the solar cycle both in the triggering and in the intensity of rain.Rain appears to occur preferentially in the late afternoon, in connection with the daytime heating of the surface.However, the maximum of rain occurrence simulated by the RCM is earlier than in the observations, suggesting a too quick response of the convection scheme to the diurnal cycle of surface fluxes, in relation to the absence of transition between shallow and deep convection in most schemes.Besides, within the study region, the orographic forcing appears to be quite different for the two ranges of the domain and is much more pronounced over the Cévennes.The RCM reproduce the influence of the topography on rainfall features.Yet, the contrast between plains and mountains is more pronounced in the models than in the observations, especially when the large-scale forcing is weak and the convection is prevailing in the study area.The contrast accentuation between plain and relief in the models seems to be due to a too high sensitivity of the convection schemes to the air mass convergence and instability favored by the relief
Comparative study of the 1982-1983 and 1997-1998 El Nino events over different types of vegetation in South America
No full textThis work presents results which help to understand the behaviour of the Normalized Difference Vegetation Index (NDVI) anomalies over the South America continent during the two strongest El Nino events of the last century (1982-1983 and 1997-1998). The data used are parts of a long-term series (July 1981 to December 1999) of calibrated NDVI data derived from National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (NOAA AVHRR) datasets. Special emphasis has been given to the analysis of the response of the major Brazilian vegetation types. This paper introduces an approach that enhances NDVI anomalies relative to the long-term climatology of the region. We find a negative NDVI anomaly for most of the region during the 1982-1983 event, whereas for the 1997-1998 event positive NDVI anomalies were observed over most regions. Only the Nordeste region showed a similar vegetation response for both events. We identify three possible factors that may play a role in the different NDVI responses to the two El Nino events. Firstly, poor intercalibration of sensors may account for some, but not all of the differences. Secondly the response of the vegetation may depend upon the climate conditions prior to the El Nino events. Thirdly, the difference in the onset date and the duration of the mature phase of the two El Nino events, associated with very different Atlantic surface temperatures are shown to have dynamical consequences which may impact upon the vegetation.Pages: 4063-407
Less frequent and more intense rainfall along the coast of the Gulf of Guinea in West and Central Africa (1981-2014)
No full textSince the 1990s, rainfall has been reported to increase over the Gulf of Guinea. In light of the devastating floods that have occurred since then over the coastal areas of this region, this study aims to better characterize the recent trends in precipitation there. We used the Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) product, a new observational rainfall dataset that covers the period 1981-2014 at high resolution and daily time steps. During the first rainy season (April-June), we find that the lack of significant trend observed in mean precipitation hides a trend towards less frequent but more intense rainfall along the coast of the Gulf of Guinea, which is expected to increase the likelihood of flooding and droughts, and fits with the recent increase in devastating floods. Over the north however (between 7 degrees and 12.5 degrees N), rainfall has become more frequent and less intense, which is expected to decrease the likelihood of flooding and droughts. During the second rainy season (September-November), we find that the clear increase in mean precipitation observed between 5 degrees and 12.5 degrees N results from an increase in precipitation intensity and frequency, while over southern Cameroon, the decrease in mean precipitation hides a trend towards less frequent but more intense rainfall. In both seasons, the average duration of wet spells has greatly decreased along the coast, in favor of more numerous and more intense isolated wet days
West African Sahel has become wetter during the last 30 years, but dry spells are shorter and more frequent
No full textOver the twentieth century, Sahel rainfall has undergone extreme variations on a decadal timescale. This study investigated the recent precipitation changes in West African Sahel using a high-resolution Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) product over the period 1981-2014. We found that the recent increase in precipitation results principally from an increase in the number of wet days (+10 d compared to the normal) over the entire West African Sahel band, along with an increase in the precipitation intensity over the central part of the West African Sahel (+ 3 mm d(-1)). However, this overall increase in precipitation is associated with dry spells that are becoming more frequent but on average shorter over the entire West African Sahel band (on average by 30%), and with precipitation intensity that is decreasing (around 3 mm d(-1) during the study period) in the western part of the West African Sahel (Senegal). Such reorganization (i.e. weaker but more frequent precipitation) is expected to be beneficial for agriculture and society, reducing the likelihood of both flooding and droughts
Potential impacts of climate, land use and land cover changes on hydropower generation in West Africa: a review
No full textInternational audienceThis study aims to review the existing literature on the past and future effects of climate, land use, and land cover changes on hydropower generation in West Africa (WA), based on listings in the Scopus and Google Scholar databases. This review shows that several African hydropower plants have experienced repeated power disruptions over the last three decades due to climate change and variability but it is less documented how increasing land use and land cover changes around the major dams have impacted the hydrological system and the hydropower generation. In the future, the risks of hydropower in WA may not be equally distributed within a country or region. Despite uncertainties in precipitation and on impacts on streamflow and water level in major basins, climate change is likely to reduce the available water over the range of 10%-20% (15%-40%) for the RCP4.5 (RCP8.5) scenario by 2050, which may considerably affect the water demand across all sectors, including hydropower. However, in the Kainji dam (Niger River basin), models project an increase in rainfall favorable to hydropower production for both RCP4.5 and RCP8.5. In contrast, within the Black Volta sub-basin, the intensification of land use is predicted to favor runoff and, consequently, an increase in the generation of Bui hydropower in the near future, even though models predict a rainfall decrease. This increase in land use for agriculture to feed a growing population has other adverse effects that need to be assessed, namely sedimentation and siltation, which are harmful to hydropower plants. Finally, the combined impact of climate and land use changes on the efficiency of hydroelectric infrastructure in WA is not well documented, while sustainable planning and investments in the hydropower sector require consideration of the nexus between climate, land use changes, and water
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