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The catastrophic flash-flood event of 8â9 September 2002 in the Gard region, France: a first case study for the CĂ©vennesâVivarais Mediterranean Hydrometeorological Observatory
The CĂ©vennesâVivarais Mediterranean Hydrometeorological Observatory (OHM-CV) is a research initiative aimed at improving the understanding and modeling of the Mediterranean intense rain events that frequently result in devastating flash floods in southern France. A primary objective is to bring together the skills of meteorologists and hydrologists, modelers and instrumentalists, researchers and practitioners, to cope with these rather unpredictable events. In line with previously published flash-flood monographs, the present paper aims at documenting the 8â9 September 2002 catastrophic event, which resulted in 24 casualties and an economic damage evaluated at 1.2 billion euros (i.e., about 1 billion U.S. dollars) in the Gard region, France. A description of the synoptic meteorological situation is first given and shows that no particular precursor indicated the imminence of such an extreme event. Then, radar and rain gauge analyses are used to assess the magnitude of the rain event, which was particularly remarkable for its spatial extent with rain amounts greater than 200 mm in 24 h over 5500 km2. The maximum values of 600â700 mm observed locally are among the highest daily records in the region. The preliminary results of the postevent hydrological investigation show that the hydrologic response of the upstream watersheds of the Gard and Vidourle Rivers is consistent with the marked spaceâtime structure of the rain event. It is noteworthy that peak specific discharges were very high over most of the affected areas (5â10 m3 sâ1 kmâ2) and reached locally extraordinary values of more than 20 m3 sâ1 kmâ2. A preliminary analysis indicates contrasting hydrological behaviors that seem to be related to geomorphological factors, notably the influence of karst in part of the region. An overview of the ongoing meteorological and hydrological research projects devoted to this case study within the OHM-CV is finally presented
DĂ©veloppement d approches rĂ©gionales et multivariĂ©es pour la dĂ©tection de non stationnaritĂ©s d extrĂȘmes climatiques. Applications aux prĂ©cipitations du pourtour mĂ©diterranĂ©en français
ParallĂšlement au contexte du rĂ©chauffement climatique, la vulnĂ©rabilitĂ© face aux Ă©vĂ©nements hydrologiques extrĂȘmes est en constante augmentation, notamment en France. Si l'effet du changement climatique sur les tempĂ©ratures maximales est avĂ©rĂ©, son impact sur le rĂ©gime des pluies fortes n'est pas Ă©tabli, et l'on s'interroge, depuis quelques annĂ©es, sur la perception d'une recrudescence des Ă©vĂ©nements extrĂȘmes : urbanisation mal maĂźtrisĂ©e, surmĂ©diatisation ou changement climatique ? Dans ce contexte, l'objectif de cette thĂšse est double. PremiĂšrement, mettre au point des outils statistiques permettant l'Ă©tude rĂ©gionale de la stationnaritĂ© des extrĂȘmes climatiques. En effet, le changement climatique est un phĂ©nomĂšne Ă grande Ă©chelle qui devrait avoir un impact Ă l'Ă©chelle rĂ©gionale. DeuxiĂšmement, Ă©tudier la stationnaritĂ© des prĂ©cipitations mĂ©diterranĂ©ennes intenses. Deux approches sont ici proposĂ©es. La premiĂšre permet de mettre en Ă©vidence des changements locaux significatifs Ă l'Ă©chelle rĂ©gionale. La deuxiĂšme consiste Ă rechercher une tendance rĂ©gionale qui soit commune Ă l'ensemble des stations d'une mĂȘme zone. Cette deuxiĂšme mĂ©thode est basĂ©e sur l'utilisation de copules multivariĂ©es qui permettent de prendre en compte formellement la dĂ©pendance spatiale des donnĂ©es. L'estimation par maximum de vraisemblance est alors rĂ©alisĂ©e via les algorithmes gĂ©nĂ©tiques. Ainsi, 92 sĂ©ries de prĂ©cipitations du pourtour mĂ©diterranĂ©en français sont examinĂ©es. Une tendance Ă la hausse des maxima annuels est observĂ©e sur une bande mĂ©ridienne allant de l'AriĂšge Ă la CorrĂšze, mais Ă©galement dans le Massif Central, les CĂ©vennes et les montagnes du RoussillonAt the same time as the global warming context, the vulnerability in front of extreme hydrological events is in constant increase, notably in France. If the effect of the climate change on the maximal temperatures is turned out, its impact on the regime of strong rains is not established, and we wonder, for some years, about the perception of an increasing number of extreme events: badly mastered urbanization, excessive media coverage or climate change? In this context, the objective of this thesis is double. In the first place, to define statistical tools allowing the regional study of the stationnarity of climatic extremes. Indeed, the climate change is a large-scale phenomenon which should have an impact at the regional scale. Secondly, to study the stationnarity of the intense Mediterranean precipitations. Two approaches are proposed here. The first one allows to detect significant local changes at the regional scale. The second consists in looking for a regional tendency which is common to all the stations of a same zone. This second method is based on the use of multivariate copula which allow to take formally into account the spatial dependence of the data. The estimation by maximum likelihood method is then realized via the genetic algorithms. So, 92 precipitation series of the French Mediterranean region are examined. An increase of annual maxima is observed on a meridian band going from the AriĂšge to the CorrĂšze, and also in the Massif Central, Cevennes and the mountains of RoussillonMONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF
Retour dâexpĂ©rience sur la crue des 6 et 7 octobre 2014 Ă Montpelllier, Grabels (HĂ©rault, France) : caractĂ©ristiques hydro-mĂ©tĂ©orologiques et contexte historique de lâĂ©pisode.
International audienc
Influence de la dynamique du manteau neigeux et des stocks en sub-surface sur la disponibilité en eau de surface en Himalaya
International audienc
Application du modĂšle hydro-nival HDSM sur deux petits bassins versants himalayens (NĂ©pal)
International audienc
Spatial daily rainfall descriptors to reproduce sub-daily dynamics in the analog method for temporal disaggregation
International audienc
Extreme Rainfall Analysis at Ungauged Sites in the South of France : Comparison of Three Approaches
International audienc
Conceptual rainfall-runoff model with a two-parameter, infinite characteristic time transfer function
International audienceA two-parameter transfer function with an infinite characteristic time is proposed for conceptual rainfall-runoff models. The large time behaviour of the unit response is an inverse power function of time. The infinite characteristic time allows long term memory effects to be accounted for. Such effects are observed in mountainous and karst catchments. The governing equation of the model is a fractional differential equation in the limit of long times. Although linear, the proposed transfer function yields discharge signals that can usually be obtained only using non-linear models. The model is applied successfully to two catchments, the Dud Koshi mountainous catchment in the Himalayas and the Durzon karst catchment in France. It compares favourably to the linear, non-linear single reservoir models and to the GR4J model. With a single reservoir and a single transfer function, the model is capable of reproducing hysteretic behaviours identied as typical of long term memory effects. Computational efficiency is enhanced by approximating the infinite characteristic time transfer function with a sum of simpler, exponential transfer functions. This amounts to partitioning the reservoir into several linear subreservoirs, the output discharges of which are easy to compute. An efficient partitioning strategy is presented to facilitate the practical implementation of the model
LâĂ©vĂ©nement pluvieux des 8-9 septembre 2002 dans le Gard : estimation des prĂ©cipitations par radars et pluviomĂštres
Cette communication fait partie dâune sĂ©rie de contributions, prĂ©sentĂ©es lors du Colloque de la SociĂ©tĂ© Hydrotechnique de France « Crues MĂ©diterranĂ©ennes » de juin 2004, rendant compte des Ă©tudes menĂ©es par la communautĂ© scientifique rassemblĂ©e autour de lâObservatoire HydromĂ©tĂ©orologique MĂ©diterranĂ©en CĂ©vennes-Vivarais (OHM-CV) sur lâĂ©vĂ©nement catastrophique des 8-9 septembre 2002 dans le Gard. On sâintĂ©resse particuliĂšrement dans ce qui suit Ă lâestimation des prĂ©cipitations. On prĂ©sente tout dâabord le systĂšme dâobservation et les donnĂ©es utilisĂ©es, puis lâon dĂ©crit les mĂ©thodes dâestimation dĂ©veloppĂ©es dans le contexte des retours dâexpĂ©rience hydrologique. On analyse dans une derniĂšre partie lâampleur et la structure spatio-temporelle de lâĂ©vĂ©nement