OMERE is part of the study of global changes affecting Mediterranean hydro-agrosystems. It focuses on a hydrological context that is intermediate between arid and temperate environments and subject to a wide range of hydrological processes ranging from intense droughts to extreme floods, and on a social and human context that is currently undergoing considerable changes (intensification of agricultural production in favourable areas, abandonment of land that cannot be intensified, increase in catchment areas, hydro-agricultural or conservation developments) linked in particular to a rapid increase in population density. The various climate change scenarios developed by the IGCC predict major rainfall changes at these latitudes: a decrease in winter rainfall, an increase in stormy rainfall and extreme rainfall. In this context, the observatory is based on the acquisition of climatic, hydrological, sediment and solute flow records over the past two decades in two elementary Mediterranean catchment areas that are differentiated in terms of soils, hydro-agricultural developments, farming practices and their evolutionary dynamics: Roujan (France, mainly cultivated with vines) and Kamech (Tunisia, mixed farming). The observatory aims to i) understand the impact of agricultural activities on mass flows in elementary Mediterranean catchment areas: The observatory aims to i) understand the impact of agricultural activities on mass flows in elementary Mediterranean catchment areas: hydrological regimes and balances, allocation of water resources, erosion dynamics, changes in water quality; ii) assess the intensities and speeds of quantitative and qualitative changes in water and soil resources as a function of changes in land use; iii) support the development of approaches for modelling flows in cultivated areas; iv) provide scientific bases, references and diagnostic tools for agri-environmental engineering of cultivated landscapes OMERE is co-managed by four French and Tunisian laboratories (HSM, INAT, INRGREF, LISAH). It is part of several networks, including the OZCAR research infrastructure (https://www.ozcar-ri.org/), and is a stakeholder in the CRITEX project "National park of innovative equipment for the spatial and temporal study of the Critical Zone of Watersheds" selected by the Ministry in the framework of the 2nd wave of the call for projects "Investissement d'Avenir Equipements d'excellence".

The evaluation of soil moisture in different areas of the Roujan catchment area is carried out by measuring the moisture content of fresh soil samples.

These data correspond to a non-systematic monitoring of dissolved, particulate or total organic carbon contents in water (rain, surface overflow, underground water) in the Roujan catchment area.

Water sampling in rain, runoff and undergroundwater are performed on the fields and send to a specialized laboratory to quantify major elements contents (Ca, Mg, Na, K, SO4, PO4, HCO3, NO3) ( FILTRATION ???. PH ??? ? EC, ???)

Pesticide contents are determined on the suspended matter extracted by filtration (0,7µm) in runoff water. Contents allow quantification of particula transport of pesticides and allow too compare it to solute transport.

Isotope analysis of groundwater, rainfall and surface water in the Roujan watershed area. Samples of rainfall accumulated over a day or an event as well as instantaneous samples of runoff and groundwater are sent to a specialized laboratory to determine their oxygen 18 and deuterium contents.

The physico-chemical parameters measured in the Kamech basin and accessible via the data portal concern the electrical conductivity of the water.