OMERE (Observatoire Méditerrannéen de l’Environnement Rural et de l’Eau) is co-driven by UMR LISAH (INRA, IRD, Montpellier SupAgro), Hydrosciences Montpellier (CNRS, IRD, Univ. Montpellier), INAT (Tunisia) and INRGREF (Tunisia). It is composed of two instrumented headwater catchments, Kamech in Tunisia and Roujan in in France .
Among the global changes affecting cultivated and natural hydrosystems, changes related to anthropogenic actions can be considerable both on the regime and on the quality of water resources. The scientific community is strongly questioned on this subject by society, in particular to predict and control the hydrological impacts in the medium and long term of anthropogenic actions.
The answer to this question involves the implementation of research programs on the determination of hydrosystem response processes and response times to anthropogenic forcings, the development of hydrosystem evolution indicators, the development of generic models of hydrosystems to simulate the influence of anthropogenic actions. For this purpose, the joint acquisition in the medium and long term of structured observations on flow regimes, on physical and chemical erosion of soils and on the evolution of the surface and grounwater quality, and on the spatio-temporal evolution of the drivers of hydrosystems subject to anthropogenic actions (land use, hydro-agricultural development, agricultural and water use practices, water abstraction) is crucial.
Indeed, observations over short periods (less than a few years) certainly make it possible to study certain mechanisms, but do not make it possible to distinguish between the long-term evolutions linked to human activities and the short-term evolutions induced notably by climate fluctuations. In addition, they do not include a sufficient range of hydrosystem operating conditions to develop and evaluate generic models and decadal evolution indicators of the impact of anthropogenic actions.
Within this context, this observatory OMERE focuses on the cultivated Mediterranean hydrosystems, whose study has several strong interests. It is an intermediate hydrological context between arid and temperate environments, which is therefore subject to a wide range of hydrological processes, ranging from intense drought events to extreme floods. Moreover, it is a social and human context, where human actions are millennial and widespread, and which is currently undergoing considerable changes (intensification of agricultural production in favorable soils, land abandonment in non-intensifiable soils, increase in catchments, hydro-agricultural development or environmental conservation) related notably to a rapid increase in population density.
The exploitation of the observations proposed by this ORE is in line with four main scientific objectives addressed by the laboratories participating in the ORE:
To analyze the impact of land use and environmental management on the hydrological regimes and budgets of Mediterranean basins
To evaluate the dynamics and respective intensities of the soil degradation due to water erosion phenomena in relation with the anthropisation of the environment
To analyze the medium and long-term evolution mechanisms of water quality in response to a change in polluting pressure by organic xenobiotics used in agriculture.
To develop a generic hydrological distributed modeling structure for cultivated areas that allows the simulation of the impacts of land use and management scenarios on water and soil resources.
Roujan site is a 0,9 km2 catchment located in Hérault (France) monitored since 1992. Main cultivation is vineyards. The site is deeply shaped by anthropic activities (ditch network, terraced slopes). Climate is Mediterranean sub-humid with long dry season. Average annual rainfall and PET (Penman) are 630 mm and 1100 mm respectively.
The Kamech catchment is a 2,65 km2 catchment located north of Cape Bon, in Nabeul CRDA, between the sub-humid and semi-arid Mediterranean climates. It is monitored since 1994. Land use is characterized by a cultivation rate close to 75% with, in the order of importance: cereals, legumes and irrigated market gardening. Extensive cattle breeding completes the agricultural system. average inter-annual rainfall and PET (Penman) are about 600 mm and 1300 mm respectively. The outlet of the basin is occupied by a hilly reservoir (with an initial storage capacity of 140 000 m3) built in 1994.
The monitoring system on the two catchments are very similar and includes a monthly recording of the anthropogenic activities (typically land use and agricultural practices), a weather station, a flux tower for monitoring actual evapotranspiration, a network of rain gauges, pluviographs, piezometers, soil moisture profiles measurements, and a system of river discharge, suspended material and pesticides concentration measurements at different locations inside the catchments. In addition, the are recorded every two months.
All the data of OMERE are processed, qualified and stored into an information system (http://www.obs-omere.org).