OHMCV observatory

OHMCV observatory

Scientific context

The OHMCV observatory covers a large geographic area straddling the Vivarais and the Cévennes in the South-East of France, regions subject each year to strong climatic hazards characterized by intense meteorological events (Mediterranean events). The  studied territoryis characterized by strong topographic gradients:  (from sea level up to more than 1500 m), climatic (Mediterranean to mountainous), géological (granites, schist, marlstones and limestones) and land uses (peri-urban, scrublands, crops, forests…). To carry out these researches, 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 instrumented and are used as focal sites for the more detailed study of certain processes.


Starting year: 2000 (1981 for some sites)

Localisations: Cévennes, Vivarais, South of France

Keywords: Mediterranean climate, nested scales, flash floods, precipitation, erosion, hydrosedimentary transport, hydrochemistry

Database: https://ohmcv.osug.fr/-Donnees-et-Produits-44-

Web site:  https://ohmcv.osug.fr/

PIs: Brice BOUDEVILLAIN, Guillaume NORD, Philippe MARTIN

Scientific questions

The OHMCV aims to study extreme hydrometeorological 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 federates 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 provides stakeholders involved in flood risks prevention and spatial planning with pratical estimation tools based on the hydrological characteristics of the sites.

Sites and measured variables

In close collaboration with several operational services, the observatory develops different observation strategies including the long-term acquisition of hydrometeorological variables, but also hydrological and socio-economic feedback on extreme events, or the probabilistic characterization of rainfall and extreme flows by using historical archives. It develops and deploys innovative instrumentation such as rain drop granulometry.

The OHMCV monitors several small watersheds: the nested watersheds of Gazel (3.4 km²), Claduègne (44 km²), and Auzon (116 km²) in Vivarais; the watersheds of Tourgueille (14.5 km², schist), Valescure (3.9 km², gneiss), Avène (60 km², limestone) and Mont Lozère (14.5 km², granite). The monitoring concerns 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 completed by a social observation of mobilities and warning processes. The observatory also collects and valorizes operational data on rainfall (rain gauge and radar) and flows (45 stations).

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 (CNRM, ESPACE, HSM, IMFT, LaMP, LIG, IGE, PACTE, RiverLy). The operational services of Météo-France (DSO/CMR), Flood forecasting services (SPC), SCHAPI, EDF in Grenoble are also involved in the monitoring of 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 MediterraneanExperiment) of the meta-program MISTRALS MISTRALS (MediterraneanIntegratedSTudiesatRegional And Local Scales).