Scientific context
The Mediterranean Hydrometerological Observatory Cévennes-Vivarais (OHMCV) is composed of four sets of instrumented sites characteristic of these regions subject to intense weather events (Mediterranean events).
The studied territory is characterized by strong gradients: topographic (from sea level up to more than 1,500 m), climatic (Mediterranean to mountainous), geological (basalts, granites, schist, marlstones and limestones) and land uses (peri-urban, scrublands, crops, forests, livestock farming…).
To carry out this research, the OHMCV observatory develops observations at different spatial and temporal scales and complements them with those of the State’s operational services. Some nested watersheds are particularly intensly instrumented and are used as focal sites for the more detailed study of processes .
Summary
Starting year: 2000 (1981 for some sites)
Location: Cévennes, Vivarais, South of France
Keywords: Mediterranean climat, nested scales, flash floods, precipitation, erosion, hydrosedimentary transport, hydrochemistry
Database:
https://ohmcv.osug.fr/-Donnees-et-Produits-44-
Web site:
https://ohmcv.osug.fr/
Scientific questions
The OHMCV aims to study extreme hydro-meteorological phenomena (intense rainfall, flash floods) in the Mediterranean mid-mountain region in a context of climate change and increased anthropogenic pressure.
To this end, the observatory combines the skills of researchers from various disciplines (meteorology, hydrology, geophysics, geography, applied mathematics, socio-economics, etc.) to better understand and predict the genesis of Mediterranean events related to climate change, and to understand the factors conditioning socio-economic vulnerability. OHMCV makes available stakeholders involved in flood risk prevention and spatial planning with practical estimation tools based on the hydrological characteristics of the sites.
Sites and measured variables
The observatory is developing various observation strategies, including the long-term acquisition of hydro-meteorological physico-cheminal and hydro-sedimentary variables, as well as hydrological and socio-economic feedback on events. It develops and deploys innovative instrumentation, notably on rainfall granulometry and hydro-sedimentary monitoring.
A better understanding of the predominant processes of flood generation, erosion and water and sediment transfer in these regions requires a multi-scale observation approach ranging from the small basin (fine scale, 1 km2) to the meso-scale basin (about 100 km2) aiming at characterizing the physical properties of the environments, to determine the initial conditions before events generating transfers and to quantify, with their uncertainties, atmospheric precipitation, contributions to flood flows as well as transported materials (suspended solids and dissolved) during the events.
The OHMCV is piloting the detailed monitoring of several small watersheds within 4 instrumented sites: «Olivier de Serres» basins (116 km2, on basalt and marlstone, 2 sub-basins) in Vivarais, basins of Valescure (3,9 km2 on gneiss and granite, 6 sub- basins), of Galeizon (61 km2 on black mica) on black micaschists) and Mont Lozère (14.5 km2 on granite, 5 sub-basins) in the Cevennes. The monitored variables include rainfall, soil moisture, water levels and river flows, sediment monitoring, as well as a characterization of the physical properties of the basins by geophysical and geochemical techniques. This physical observation is complemented by a social observation of mobilities and warning devices. The observatory also collects and valorizes operational data on rainfall (rain gauge and radar) and discharge.
Partners and further information
The OHMCV is managed by the Institut des Géosciences de l’Environnement (IGE, CNRS/Grenoble INP/IRD/UGA) in Grenoble in collaboration with several research units (ESPACE, CREER, HSM, RiverLy, PACTE, CERMOSEM, «Eau et Environnement») and research organizations (CNRS, INRAE, IMT Mines Alès Universities of Grenoble Alpes, Montpellier, Avignon, Aix-Marseille, Côte d’Azur and Gustave Eiffel). The operational services of Météo-France, Flood forecasting services (SPC), SCHAPI and EDF in Grenoble are also involved in the observatory. The OHMCV is labeled Service National d’Observation (SNO) by the INSU of CNRS since 2006 and is coordinated by OSUG.
Over the period 2008-2020, it has strongly contributed to the research program HyMeX (Hydrological Cycle in the Mediterranean Experiment) of the meta-program MISTRALS MISTRALS (Mediterranean Integrated STudies at Regional And Local Scales).