Le climat futur des régions méditerranéennes françaises : quelles tendances ? -

La forte sensibilité climatique de la région méditerranéenne, notamment celle des espaces forestiers, nécessite une meilleure prise en compte des projections climatiques pour le siècle à venir. Pour ce faire, l'information climatique mise à disposition doit être à haute résolution spatiale. D'une part pour prendre en compte de manière plus réaliste que les simulations globales, les contraintes et processus physiques d'échelle fine. Et, d'autre part, pour permettre à certaines communautés d'alimenter des modèles d'impacts par des variables atmosphériques scalairement cohérentes. Les méthodes de régionalisation statistiques et dynamiques sont les deux grandes approches méthodologiques permettant de produire une information climatique régionalisée, allant de 50 à 8 km de résolution horizontale en fonction de la méthode et de la région prise en compte. Les résultats de ces méthodes obtenues par la communauté climatique française mettent en évidence pour la fin de siècle une augmentation (diminution) des températures (précipitations) en été. En hiver une incertitude persiste sur l'amplitude du réchauffement, alors qu'aucune tendance sur les précipitations ne se dégage

A multi-model climate response over tropical Africa at +2 °C

The impact of a +2 °C global warming on temperature and precipitation over tropical Africa is examined, based on an ensemble of 12 regional climate model scenario simulations. These 12 scenarios are re-phased so that they all correspond to the same global warming of 2 °C with respect to pre-industrial conditions. The continental temperature increase is above the global average. If heat waves are defined with the same temperature threshold in the reference climate and in the scenario, their frequency increases by a factor of 10. When the temperature threshold is adapted to future conditions, there is still a slight increase in frequency. The average precipitation does not show a significant response, due to model-to-model spread. However two compensating phenomena occur, which are robust among the models: (a) the number of rain days decreases whereas the precipitation intensity increases, and (b) the rain season occurs later during the year with less precipitation in early summer and more precipitation in late summer. Simulated daily temperature and precipitation data are combined in two impact models, one for the hydrology of the Nile and Niger basins, one for the food security of the different countries. They show that the main feature of the climate change is not a continuous trend signal, but an alternation of dry and wet decadal to multidecadal episodes

The sub-seasonal to seasonal prediction (S2S) project database

A database containing sub-seasonal to seasonal forecasts from 11 operational centres is available to the research community and will help advance our understanding of the sub-seasonal to seasonal time range. Demands are growing rapidly in the operational prediction and applications communities for forecasts that fill the gap between medium-range weather and long-range or seasonal forecasts. Based on the potential for improved forecast skill at the sub-seasonal to seasonal time range, a sub-seasonal prediction (S2S) research project has been established by the World Weather Research Program/World Climate Research Program. A main deliverable of this project is the establishment of an extensive database, containing sub-seasonal (up to 60 days) forecasts, 3-weeks behind real-time, and reforecasts from 11 operational centers, modelled in part on the THORPEX Interactive Grand Global Ensemble (TIGGE) database for medium range forecasts (up to 15 days). The S2S database, available to the research community since May 2015, represents an important tool to advance our understanding of the sub-seasonal to seasonal time range that has been considered for a long time as a “desert of predictability”. In particular, this database will help identify common successes and shortcomings in the model simulation and prediction of sources of sub-seasonal to seasonal predictability. For instance, a preliminary study suggests that the S2S models underestimate significantly the amplitude of the Madden Julian Oscillation (MJO) teleconnections over the Euro-Atlantic sector. The S2S database represents also an important tool for case studies of extreme events. For instance, a multi-model combination of S2S models displays higher probability of a landfall over Vanuatu islands 2 to 3 weeks before tropical cyclone Pam devastated the islands in March 2015

Sanctissimi in Christo Patris et Domini Nostri Benedicti XIII ... Constitutio de Regularium, Monachorum & Mendicantium, Episcopali munere insignium vestibus & Clericali corona, deque iisdem & ceteris cujuscunque regularis instituti eodem munere abdicatis

A 111/078(10

Development of a European Multi-Model Ensemble System for Seasonal to Inter-Annual Prediction (DEMETER)

A multi-model ensemble-based system for seasonal-to-interannual prediction has been developed in a joint European project known as DEMETER (Development of a European Multimodel Ensemble Prediction System for Seasonal to Interannual Prediction). The DEMETER system comprises seven global atmosphere–ocean coupled models, each running from an ensemble of initial conditions. Comprehensive hindcast evaluation demonstrates the enhanced reliability and skill of the multimodel ensemble over a more conventional single-model ensemble approach. In addition, innovative examples of the application of seasonal ensemble forecasts in malaria and crop yield prediction are discussed. The strategy followed in DEMETER deals with important problems such as communication across disciplines, downscaling of climate simulations, and use of probabilistic forecast information in the applications sector, illustrating the economic value of seasonal-to-interannual prediction for society as a whole

De la prévision à longue échéance à la prévision saisonnière : Des modèles numériques pour prédire le temps au-delà du prévisible

Titre traduit en anglais : From long-range to seasonal forecast : Numerical models to predict weather beyond what can be foreseen. Résumé traduit en anglais : This paper presents historical aspects of long-range numerical prediction from the 1970s when medium range weather forecast, from 3 to 10 days, was gaining ground in America and in Europe with the founding of ECMWF. Atmosphere and later coupled ocean-atmosphere models have been used to predict the mean of meteorological parameters for the forthcoming month, then the mean forthcoming season. The question of probabilistic formulation of the prediction was raised rather early. In the mid-1990s, thanks to ECMWF initiatives and with financial support from the European Commission, Europe became a leader and new projects such as Demeter or Eurosip were lanched. This paper summarizes the author's memorandum for his « Mémoire d'habilitation à diriger des recherches » diploma (Déqué, 2006) and follows the same thread, namely the models that have successively been used: Sisyphe, Emeraude, Arpege. An overview of future prospects finishes this paperInternational audienceCet article présente un historique de la prévision numérique à longue échéance, depuis les années 1970 qui ont correspondu à la montée en puissance de la prévision opérationnelle à moyenne échéance, de 3 à 10 jours, aux État-Unis et en Europe, avec la création du CEPMMT. Les modèles d'atmosphère, puis les modèles couplés océan-atmosphère ont été utilisés pour prédire la moyenne des paramètres météorologiques du mois à venir, puis de la saison à venir. Assez vite, s'est posée la question de mettre les prévisions sous forme probabiliste. Au milieu des années 1990, grâce à l'impulsion du CEPMMT et au soutien financier de la Commission européenne, l'Europe prend une position dominante et de grands projets comme Demeter et Eurosip sont lancés. Cet article reprend le contenu du Mémoire d'habilitation à diriger des recherches de l'auteur (Déqué, 2006) et en suit le même fil directeur, à savoir les modèles successifs de Météo-France qui ont été utilisés : Sisyphe, Émeraude et Arpège. Un tour d'horizon des perspectives futures termine cet article