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L'objectif de ce chapitre est celui de caractériser le milieu physique, les ressources naturelles, les zones agro-écologiques et le peuplement afin de comparer les dynamiques en cours avec l'exposition aux catastrophes hydro-climatiques.

La région de Sédhiou dans la Moyenne Casamance au sud du Se´ne´gal bénéficie de conditions pédoclimatiques et hydro-agricoles favorables et d'une longue tradition rizicole, surtout dans les bas-fonds. Depuis les années 1970, l'Etat sénégalais, confronte´ a` des contraintes environnementales et sociales croissantes, a mis en oeuvre avec ses partenaires de l'aide au développement une politique de sauvegarde, re´habilitation et aménagement des vallées casamançaises, surtout destine´e a` juguler le phe´nome`ne de salinisation des terres rizicoles. La riziculture de bas-fond demeure dans ces vallées une activité agricole de subsistance : les pratiques traditionnelles des agriculteurs, notamment des femmes, visent a` minimiser les risques écoclimatiques plus qu'a` maximiser la production. Les interventions propose´es et poursuivies au cours des années se sont heurte´es a` diverses difficultés qui ont limite´ leurs effets et n'ont pas permis d'en assurer la pérennité. L'étude a permis de caractériser les zones des bas-fonds de la région et d'identifier les principales contraintes endogènes et exogènes d'ordre technique, environnemental et socio-économique, qui affectent durablement la production rizicole locale. Elle a aussi permis de comprendre que les actions de réhabilitation et d'aménagement des bas-fonds ont privilégie´ les effets a` court terme sans traiter les difficultés des agriculteurs a` long terme. Cette approche a permis de maintenir la fonctionnalité des aménagements pendant les années de gestion des projets, mais n'a pas garanti leur durabilité sur le long terme. Pour la relance de la riziculture de bas-fonds dans la région, ce travail propose pour l'avenir de promouvoir des actions de renforcement non seulement lie´es a` la protection et a` la sécurisation des aménagements hydroagricoles, mais également adapte´es et intégrées aux stratégies et aux objectifs des agriculteurs et, donc, capables d'assurer la durabilité des interventions. Une de´marche ope´rationnelle est propose´e comme outil d'étude et d'aide a` la réalisation des interventions.

In West Africa Early Warning Systems (EWSs) for food security have been widely recognized to have contributed in the last twenty years to better face famine emergencies. The improved understanding of the environmental and socio-economic dynamics of the region, a change in the causes for food insecurity and the evolution of Information and Communication Technologies (ICT) have favored the introduction of new approaches and the involvement of a network of stakeholders. In recent years the improvement of EWS has been concentrated in the adaptation and the transfer of existing tools rather than the development of the overall design of EWS in function of users needs, at the same time key scientific areas to be improved to provide major operational advancements needs to be better identified. This partially due to a difficulty of the research community to be in direct connection with operational processes and on the other side by an evident limit in following a demand driven approach due to the difficulties in modelling bio and social phenomena in a unique environment. In this context AMMA project had the ambitious objective of bridging the gap between state of the art research in the domains of geo-science and human related disciplines, and the operational EWS. The work carried out in AMMA, while improving the understanding of monsoon system, allowed to better orient research challenges in order to provide EWS with improved products effectively meeting the needs of end-users at different levels. In this work, advancements in providing appropriate information for the identification of agricultural risk zones by using short to long time forecasts are illustrated highlighting critical aspects still demanding scientific improvements.

The Keita Valley in Niger covers an area of about 4,800km(2) of plateaux with rocky slopes and valleys forming a complex system of watersheds moulded by strong winds and water erosion. The Keita Rural Development Project began in 1982. Its main objective was to reduce food insecurity in an arid region in danger of environmental collapse. The project proposed to increase rood security while combating desertification through the reduction of soil erosion and reforestation in this large area. More than 20 years of soil conservation and land reclamation interventions make Keita an open-air laboratory for the study of desertification dynamics and land reclamation activities. The availability of long series of environmental and socioeconomic data and information allows for ecosystem monitoring through indicators based both on field data and model output. This extraordinary Situation, almost unique in the Sahel, provides the opportunity not. only to model the behaviour of natural vegetation during the re-colonization of degraded lands but also to evaluate the impact on populations and production systems. Observing dynamics in the Keita Valley helps to extrapolate the potential evolution of environmental behaviour in arid and semi-arid ecosystems. Environmental monitoring in Keita has a dual target in planning support at national and local levels. The former supports the definition of national policies and actions plans to combat desertification and land reclamation while the latter, according to the decentralization process that Niger has initiated in natural resource management, sustains local authorities in territorial planning.