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Welcome to the web site of the FloodScale project

Multi-scale hydrometeorological observation and modelling for flash floods understanding and simulation

The FloodScale project is a contribution to the HyMeX (Hydrological Cycle in the Mediterranean Experiment) international program. Its general objective is to improve the understanding and simulation of the hydrological processes leading to flash floods, which are one of the most destructive natural hazards, especially in the Mediterranean region. The spatial and temporal variability of rainfall, landscape characteristics and soil humidity are recognised as important influential factors in flash flood generation. However, their quantification and the role of their variabilities at the various scales remain open questions. Understanding flash floods is particularly challenging since it requires observations at very small space and time scales (1 km2, 5min), as well as over large areas. As an illustration, the September 2002 flash flood event in the Gard was localised on an area of about 5000 km2, but half of the casualties occurred in catchments smaller than 20 km2. Flash floods are very difficult to observe using operational rain gauge and discharge networks. Weather radar data proved to be particularly valuable for characterizing the spatial and temporal variability of rainfall, although the radar signal interpretation is more difficult in complex terrain and/or over urbanized areas, which are the most prone to such events. Gauging flash-flooding rivers with classical techniques also remains a challenge due to practical and security reasons.

FloodScale builds on the concepts of Hydrometeorological Observatory (HO) promoted in France since 2002 with the Cévennes-Vivarais Mediterranean Hydrometeorological Observatory (OHM-CV) , the ideas being i) to perform long-lasting and detailed hydrometeorological observation in a well-instrumented flash-flood prone region (the Cévennes-Vivarais region), including both operational and research observation systems, and ii) to perform post-event surveys following the most extreme events wherever they occur in the Mediterranean, in order to document both the physical processes and societal factors associated with such events. To progress in flash flood modelling two fundamental questions in hydrology need to be addressed (i) the change of scale problem or how to transfer knowledge acquired at a given scale to another scale; (ii) the prediction in ungauged basin (PUB) problem, in order to assess the risk at every point over a given region.

FloodScale will address these questions using a combined multi-scale observation and modelling effort, relying on nested-catchments instrumentation covering the following scales: (i) the hillslope scale, where process understanding on runoff generation and concentration can be tackled; (ii) the small to medium catchment scale (1-100 km2) where the impact of network structure, rainfall, landscape, initial soil moisture variability can be quantified; (iii) the larger scale (100-1000 km2) where the river transfer and flooding processes become important. The potential of innovative observations (enhanced weather radar and disdrometer networks, gauging of river using remote sensing techniques, dense limnimeter networks, very high resolution remote sensing data, lidar Digital Elevation Models…) at various scales, complementing traditional measurements will be assessed within the project. FloodScale will also favour the combination of various measurements on the same hillslopes/catchments (soil moisture, infiltration tests, geophysics, geochemistry, geomorphological and vegetation surveys, river gauging..) in order to enhance our potential for understanding the active processes during and between floods.


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