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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RESUMEParmi les aquireres régionaux importants de tres ?rande extension au Maroc, celui du Haouz qui s'étend sur une superficie de 6.000 km , circule au niveau du remplissage mioplioquatemaire issue du démantelement de la chaíne Atlasique. Ce demier présente un facies constitué de galets, graviers, argiles, mames et calcaires, dont la puissance atteint les 100 metres. Cet aquifere joue un role tres important dans l'alimentation en eau potable des habitants de la plaine du Haouz d'une population de plus de 4 millions d'habitants, en sus d'un complément al'irrigation de 80.000 ha.Le climat aride de type continental, qui y regne se caractérise par des amplitudes thermiques assez importantes entre 1'hiver et l'été. La pluviométrie présente une moyenne de 250 mm par ano La piézométrie de la zone étudiée est caractérisée par un écoulement général du sud vers le nord ouest en direction de l'oued Tensift, également principal colIecteur des eaux de surface de la région.Une traduit un régime atlantique des précipitations, sans évaporation, ce qui implique que la recharge se fait rapidement, probablement atravers les formations miocenes gréseuses largement fissurées al'affleurement de l'aquirere mio-plioquatemaire.Un gradient altitudinal moyen de -0,26 %0 par 100 metres est déterminé pour la plaine du Haouz, tres proche des autres valeurs trouvées pour d'autres régions au Maroc, confirmant la validité régionale de celui-ci.Les variations des teneurs en oxygene-8 peuvent etre interprétées en termes de diffé-rence d'altitude entre les altitudes de recharge et d'émergence.Mots c1és: Aquifere mio-plioquaternaire, isotopie, gradient altitudinal, Haouz de Marrakech. ABSTRACTThe study area «Haouz plain» is Located at the center of Morocco, it extend on a surface of 2800 km 2 , limited by the Jbilet hilIs in the North, the High-Atlas range in the South, R' dat wadi in the East and the Essaouira-Chichaoua plateau in the West. The area climate is semi-arid, characterized by low precipitations varying between 160 mm/year and 250mm/year and important variation in temperature between the winter and the summer with respectively 5°C and 45°C. Its hydrographic network is represented by the Tensift system which receives alI the affluents of central and Westem Haouz. These affluents are characterized by weak flows with important seasonal variations.The Haouz plain is a sedimentary basin, being along the northem edge of the high atlas, it presents a geologic succession going from the primary to the recent Quatemary. The mio-plioquatemary formations, stemming from the dismantling of the atlasic chain, refuge an important and generalized water table on alI the plain. This water table shows very variable hydrodynamic characteristics, reflecting the complexity of the deep structures of the plain, 1986) and also the lithological variability of the mio-plioquatemary formations. The Haouz plain includes also the deep reservoirs of the Jurassic, Cretaceous and Eocene which finish sorne meters at the north of the Atlas, thus having a very limited ex...

L’objectif de ce travail est d’étudier les risques de ruissellement et d’érosion dans le bassin versant du Rhéraya (Haut-Atlas du Maroc) au moyen d’un irrigateur manuel à rampe sur 1 m2. Nous recherchons des indicateurs faciles à déterminer directement sur le terrain (états de surface du sol) ou à partir des tests en laboratoire (stabilité des agrégats, texture, matière organique), qui soient bien corrélés avec l’infiltrabilité et la turbidité issues des tests d’infiltrométrie. Pour les différents sols affleurant dans le bassin, les résultats ont mis en évidence une grande variabilité de l’infiltrabilité (de 1 à 70 mm.h‑1) et de turbidité des eaux de ruissellement (de 1,5 à 325 g.L‑1). La turbidité a pu être mesurée correctement grâce à la mise au point d’un nouveau dispositif de collecte des eaux de ruissellement de l’irrigateur. Bien que l’infiltrabilité et le ruissellement soient la résultante d’interactions entre toutes les caractéristiques physiques du sol, certaines apparaissent dominantes dans notre contexte. Nous montrons ainsi que l’infiltrabilité est déterminée principalement par la texture et l’ouverture de la surface du sol et que la turbidité est due essentiellement à la surface de sol nu exposée au ruissellement. Ces indicateurs cartographiables offrent la possibilité d’une spatialisation des risques d’érosion au niveau du bassin versant.The objective of this study was to investigate the risks of runoff and erosion of soils in the Rheraya catchment (High Atlas, Morocco) using infiltrometer tests on 1 m2 plots. We were looking for indicators that are easily obtained directly from field observations (ground surface features) or by laboratory tests (aggregate stability, soil texture and organic matter), and are well correlated with infiltrability and turbidity measurements from the infiltrometer tests. For the various soils present in the study area, the results show a large variability of infiltrability values (from 1 to 70 mm·h-1) and turbidity (from 1.5 to 325 g·L-1). The turbidity was correctly measured thanks to the development of a new runoff collector that doesn’t disturb the soil. Although runoff and erosion are the result of interactions among many parameters, some of these appear to be dominant in our case. The measurements show that the infiltrability was correlated mainly with texture and soil surface opening, whereas turbidity was related to the surface of bare soil that was exposed to runoff. These indicators may be used to determine the spatialization of potential erosion in the Rheraya catchment