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Toulouse, France

Tramblay Y.,Montpellier University | Bouvier C.,Montpellier University | Ayral P.-A.,Ecole des Mines dAles | Marchandise A.,SCHAPI
Natural Hazards and Earth System Science

A good knowledge of rainfall is essential for hydrological operational purposes such as flood forecasting. The objective of this paper was to analyze, on a relatively large sample of flood events, how rainfall-runoff modeling using an event-based model can be sensitive to the use of spatial rainfall compared to mean areal rainfall over the watershed. This comparison was based not only on the model's efficiency in reproducing the flood events but also through the estimation of the initial conditions by the model, using different rainfall inputs. The initial conditions of soil moisture are indeed a key factor for flood modeling in the Mediterranean region. In order to provide a soil moisture index that could be related to the initial condition of the model, the soil moisture output of the Safran-Isba-Modcou (SIM) model developed by Météo-France was used. This study was done in the Gardon catchment (545 km 2) in South France, using uniform or spatial rainfall data derived from rain gauge and radar for 16 flood events. The event-based model considered combines the SCS runoff production model and the Lag and Route routing model. Results show that spatial rainfall increases the efficiency of the model. The advantage of using spatial rainfall is marked for some of the largest flood events. In addition, the relationship between the model's initial condition and the external predictor of soil moisture provided by the SIM model is better when using spatial rainfall, in particular when using spatial radar data with R 2 values increasing from 0.61 to 0.72. © Author(s) 2011. Source

Desprats J.-F.,Bureau de Recherches Geologiques et Minieres | Cerdan O.,Bureau de Recherches Geologiques et Minieres | King C.,Bureau de Recherches Geologiques et Minieres | Marchandise A.,SCHAPI
Houille Blanche

Soil permeability is an important input parameter of several physical hydrological model used by Flooding Forecast Services: On the Gardon d'Anduze catchment selected by SCHAPI as experimental catchment for flash floods, permeability measurements were done between 2002 and 2007 by the French Geological Survey. A statistical analysis allowed to calculate the permeability of each unit combining information on soil and land use and so to propose a permeability map for the catchment. This map was validated using the runoff model STREAM.With this model, correlation between simulated and observed discharges (0.83) is satisfactory when using distributed soil permeability for Gardon d'Anduze catchment or Mialet and Saumane sub catchment. Correlation significantly decreases (0.66) when using STREAM with an homogeneous averaged permeability value of 30 mm/hour for the catchment. This showed clearly the importance of distributed soil permeability for runoff modelling with a hortonian model a Mediterranean catchment. © 2010 Société Hydrotechnique de France. Source

Habert J.,DREAL Champagne Ardenne | Habert J.,European Center for Research and Advanced Training in Scientific Computation | Ricci S.,European Center for Research and Advanced Training in Scientific Computation | Le Pape E.,SCHAPI | And 5 more authors.
Journal of Hydrology

This paper presents a data-driven hydrodynamic simulator based on the 1-D hydraulic solver dedicated to flood forecasting with lead time of an hour up to 24. h. The goal of the study is to reduce uncertainties in the hydraulic model and thus provide more reliable simulations and forecasts in real time for operational use by the national hydrometeorological flood forecasting center in France. Previous studies have shown that sequential assimilation of water level or discharge data allows to adjust the inflows to the hydraulic network resulting in a significant improvement of the discharge while leaving the water level state imperfect. Two strategies are proposed here to improve the water level-discharge relation in the model. At first, a modeling strategy consists in improving the description of the river bed geometry using topographic and bathymetric measurements. Secondly, an inverse modeling strategy proposes to locally correct friction coefficients in the river bed and the flood plain through the assimilation of in situ water level measurements. This approach is based on an Extended Kalman filter algorithm that sequentially assimilates data to infer the upstream and lateral inflows at first and then the friction coefficients. It provides a time varying correction of the hydrological boundary conditions and hydraulic parameters.The merits of both strategies are demonstrated on the Marne catchment in France for eight validation flood events and the January 2004 flood event is used as an illustrative example throughout the paper. The Nash-Sutcliffe criterion for water level is improved from 0.135 to 0.832 for a 12-h forecast lead time with the data assimilation strategy. These developments have been implemented at the SAMA SPC (local flood forecasting service in the Haute-Marne French department) and used for operational forecast since 2013. They were shown to provide an efficient tool for evaluating flood risk and to improve the flood early warning system. Complementary with the deterministic forecast of the hydraulic state, the estimation of an uncertainty range is given relying on off-line and on-line diagnosis. The possibilities to further extend the control vector while limiting the computational cost and equifinality problem are finally discussed. © 2015 Elsevier B.V. Source

Bresson E.,Meteo - France | Ducrocq V.,Meteo - France | Nuissier O.,Meteo - France | Ricard D.,Meteo - France | de Saint-Aubin C.,SCHAPI
Quarterly Journal of the Royal Meteorological Society

Northwestern Mediterranean coastal regions are frequently affected by torrential rainfall associated with quasi-stationary mesoscale convective systems (MCSs). The present work examines how the characteristics of a conditionally unstable flow impinging on the coastal complex terrain of the Northwestern Mediterranean can affect the location and intensity of quasi-stationary MCSs. The study is based on idealized simulations, but including the major ingredients of Northwestern Mediterranean heavy precipitation events: a moist conditionally unstable marine flow of about 100 km width facing the true terrain, composed of the Massif Central surrounded by the Alps and the Pyrenees. We find that MCSs are located upstream of the mountain range with a slow flow, whereas with a rapid flow the heaviest precipitation is over the Massif Central slopes. In a similar way, when the lateral environment is drier the heaviest precipitation is located upstream whereas a humid environment favours precipitation over the slopes. The dominant lifting mechanism is strongly related to the location of the system: (1) direct orographic triggering for systems over mountain slopes and (2) cold-pool triggering for upstream systems. In addition, the neighbouring mountains interplay through deflection of the flow and induced low-level convergence favoured by slow or dry lateral environments and through cold-pool blocking within valleys. © 2012 Royal Meteorological Society. Source

Within the Thematic User Commissioning for the VHR Pléiades valorization, imagery was tasked in emergency following disaster events or user-exercise at the request of French Ministries (Ministry of the Environment, Ministry of Finance). These activities were also aimed at familiarizing French institutional users with the use of space technologies within crisis event management. One long term objective would be to set up a national capacity for these users, outside of the International Charter 'Space and Major Disasters' and Copernicus scope which did not support all the needs of the French Ministries. In March and May 2013, in coordination with CNES, SERTIT, SCHAPI, IGN and CEREMA, some Pléiades data have been tasked and processed in rush mode for the case of the Agly, Yonne and Marne 2013 flood events. In June 2013, two new rapid mapping actions have been carried out by CNES and SERTIT. The first one, liaising with the SCHAPI and the Rhin Sarre Flood Forecast Service (DREAL Alsace) for the Sarre river flooding, and the second one in coordination with the French State reinsurance company (Caisse Centrale de Réassurance) over the Gave de Pau floods. Finally, in February 2013, the exercise "SEISME 13" was performed at the request of the crisis center of the Ministry of the Environment (SG/SDSIE/CMVOA). Regarding user's needs, the objectives concerned water surface detection, dyke breaks, affected built features. In the case of rapid floods as Agly and Gave de Pau events, images analysis also included the recognition of residual flood water surfaces, mud deposits and current flows. In addition, the Agly case mapping got the benefits to flood mapping that can be derived from a Pléiades stereoscopic pair. For "SEISME 13" Exercise, the value added products took into account the specific needs expressed by the Ministries of the Environment, Transport and Health (damages to infrastructure, network, and building). Source

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