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The French critical zone initiative, called OZCAR (Observatoires de la Zone Critique-Application et Recherche or Critical Zone Observatories-Application and Research) is a National Research Infrastructure (RI). OZCAR-RI is a network of instrumented sites, bringing together 21 pre-existing research observatories monitoring different compartments of the zone situated between "the rock and the sky," the Earth's skin or critical zone (CZ), over the long term. These observatories are regionally based and have specific initial scientific questions, monitoring strategies, databases, and modeling activities. The diversity of OZCAR-RI observatories and sites is well representative of the heterogeneity of the CZ and of the scientific communities studying it. Despite this diversity, all OZCAR-RI sites share a main overarching mandate, which is to monitor, understand, and predict ("earthcast") the fluxes of water and matter of the Earth's near surface and how they will change in response to the "new climatic regime." The vision for OZCAR strategic development aims at designing an open infrastructure, building a national CZ community able to share a systemic representation of the CZ , and educating a new generation of scientists more apt to tackle the wicked problem of the Anthropocene. OZCAR articulates around: (i) a set of common scientific questions and cross-cutting scientific activities using the wealth of OZCAR-RI observatories, (ii) an ambitious instrumental development program, and (iii) a better interaction between data and models to integrate the different time and spatial scales. Internationally, OZCAR-RI aims at strengthening the CZ community by providing a model of organization for pre-existing observatories and by offering CZ instrumented sites. OZCAR is one of two French mirrors of the European Strategy Forum on Research Infrastructure (eLTER-ESFRI) project.

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International audienceThe objective of this study was to simulate the evolution of soil erosion in a semi-arid mountainouswatershed (225 km2, High Atlas Mountains, Morocco) under different scenarios of climate and land usechange to the end of 21st century. Erosion plots monitored over four years showed spatially contrastedresults. Most of the soils produced from 0.015 to 2.5 t/ha/y, whereas badlands produced350 t/ha/y The average sediment yield measured at the outlet during the same period wasapproximately 4 t/ha/y.The STREAM distributed erosion model was parameterized using these field measurements (infiltrationrates and runoff sediment concentrations). The results showed an overall agreement between themodelled and measured annual cumulative sediment yields.Simulations of the ARPEGE meteorological model were used for the 1960-1990 and 2070-2100 periods.The changes between these two periods were downscaled using three different methods,decreasing annual precipitations by 10-14%, although with more rainfall in summer and fall. Climatechange alone increased sediment yield by 4.7-10.1%. However, simulations showed that land usechanges might potentially induce much larger changes in erosion (up to 250%), approximately proportionalto the evolution of the extension of badlands

Recent efforts have been concentrated in the development of models to understand and predict the impact of environmental changes on hydrological cycle and water resources in arid and semi-arid regions. In this context, remote sensing data have been widely used to initialize, to force or to control the simulations of these models. However, for several reasons, including the difficulty in establishing relationships between observational and model variables, the potential offered by satellite data has not been fully used. As a matter of fact, a few hydrological studies that use remote sensing data emanating from different sources (sensors, platforms) have been performed. In this context, the SUDMED program has been designed in 2002 to address the issue of improving our understanding about the hydrological functioning of the Tensift basin which is a semi-arid basin situated in central Morocco. The first goal is model development and/or refinement, for investigating the hydrological responses to future scenario about climate change and human pressure. The second aim is the effective use of remote sensing observations in conjunction with process models, to provide operational prognostics for improving water resource management. The objective of this paper is to present the SUDMED program, its objectives and its thrust areas, and to provide an overview of the results obtained in the first phase of the program (2002)(2003)(2004)(2005)(2006). Finally, the lessons learned, future objectives and the unsolved issues are presented.

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