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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.

Ce document propose une analyse préliminaire des facteurs qui limitent la riziculture de bas-fond dans les vallées de la Région de Sédhiou pour identifier les mécanismes plus appropriés pour la gestion intégrée et durable des vallées rizicoles. Ce document est constitué de trois composants analysés : (i) socio-économique, (ii) agronomique, (iii) physique et environnementale. Dans le spécifique, ce document analyse deux cas d'étude, la vallée de Djimbana et la vallée de Samiron. Ces deux vallées ont été retenues comme site vitrine par le programme PAPSEN et elles représentent un premier cas d'étude pour affiner les outils qui pourront successivement être appliqués dans les autres vallées de la Région de Sédhiou. Cette analyse se base sur une méthodologie quali-quantitative qui a permis d'aborder les différents aspects et de collecter les informations contenues dans ce document. En particulier, les sources des données et des informations utilisées sont notées ci-dessous: ? les activités de démonstration, d'assistance technique et de suivi agronomique qui ont été réalisées pendant la saison 2014-2015 dans les deux vallées dans le cadre de la collaboration ISRA-CNR; ? des missions de collecte d'information sur le terrain (novembre-décembre 2014); ? les données météo fournies par la Direction Régional pour le Développement Rural ; ? les rencontres avec les institutions étatiques locales et les partenaires du programme PAPSEN; ? la revue bibliographique de la documentation fournie par ces institutions; ? une enquête sur un échantillon de 15 productrices1; ? des focus group réalisés dans 9 villages2 (janvier-février 2015). L'objectif de ce document est de créer une base de connaissances de référence sur laquelle définir les activités de recherche à entreprendre successivement, ainsi que mettre en place un système de suivi et d'évaluation des activités du programme.

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.

Over the past ten years, the horticultural production in Senegal has strongly increased, due to the productivity consolidation of some suitable areas (such as the coastal band of Niayes and the Senegal River Valley), and in relation to a progressive population growth concentrated in urban areas. Therefore the demand for domestic and subregional markets has raised together with an international commercial interest for off-season products. In fact, considering the main vegetable crops (e.g. onion, tomato, cabbage) the overall production has increased from 286,000 tons in 2001 to 640,000 tons during 2011, with an average annual growth rate of 7 %. In addition, the productive potential of traditional rain-fed crops such as groundnut, millet and sorghum has been dramatically affected by the global climate change, with wet seasons characterised by an increasingly uneven distribution of rainfall and a significantly higher intensity of rain events. In this changing environment, horticulture represents a real vector of economic growth, by the possibility to cultivate with the help of irrigation throughout the year, even in marginal areas. The "Programme d'Appui au Programme National d'Investissement dans l'Agriculture au S´en´egal (PAPSEN)", funded by the Italian Ministry of Foreign Affairs supports the diffusion of drip irrigated horticulture in the three Regions of Thies, Diourbel and Fatick. Within the programme, a research and development component aims to identify best performing species and varieties and improve crop management practices. The planned research activities foresee the implementation of a full-field experimental trial at the Centre National de Recherche Agronomiques (CNRA) of Bambey, in collaboration with the Institut S´en´egalais de Recherches Agricoles (ISRA). Experimental activities are focused on evaluating the performances of ten vegetable crops (onion, pepper and hot pepper, cabbage, melon, tomato, eggplant, lentil, carosello and barattiere) in three different seasons for the adaptation of crop production calendars to meet best market opportunities. At the same time, the effects of biochar on soil fertility and water holding capacity will be evaluated and an appropriate and simplified water balance model will be developed in order to optimise the use of water resources through a more efficient management of the irrigation practices

Food security in East Africa region essentially depends on the stability of rain-fed crops farming, which renders its society vulnerable to climatic fluctuations. These ones in Africa are most widely and directly related to rainfall. In this study, the relation between recent spatial rainfall variability and vegetation dynamics has been investigated for East Africa territories. Satellite raster products SPOT-4 Vegetation 1 km resolution (Saint, 1995) and RFE (rainfall estimates) from Famine Early Warning Systems Network (FEWS NET) are used. The survey is carried out at administrative level scale using 10-day summaries extracted from raster data for each spatial area unit thanks to specific polygonal layers. Time series covers two different periods: 1996-2009 for rainfall estimates and 1999-2009 for NDVI. The first step of the analysis has been to build for each administrative unit a coherent set of data, along the time series, suitable to be processed with state-of-art statistical tools. The analysis is based on the assumption that every structural break in vegetation dynamics could be caused by two alternative/complementary causes, namely: (i) modifications in crop farming systems (adaptation strategy) related to eventual break-shift in rainfall regime and/or (ii) other socio-economic factors. BFAST (Verbesselt et al, 2010) R package are employed to lead a comprehensive breakpoint analysis on 10-day RFE (spatial mean and standard deviation) and 10-day NDVI ones (spatial mean, mode and standard deviation). The cross-viewing of the years where significant breaks have occurred, throughout opportune GIS layering, provides an explorative interpretation of spatial climate/vegetation dynamics in the whole area. Moreover, the spatial and temporal pattern of ecosystem dynamics in response to climatic variability has been investigated using wavelet coherency by SOWAS R package (Maraun, 2007). The wavelet coherency (WCOH) is a normalized time and scale resolved measure for the relationship between two time series (Maraun and Kurths, 2004). This kind of multi-scale temporal investigation provides an explanation of break detected in time series, confirming or not their climatic linkage; results of the analysis are shown. Finally, in order to support the dissemination and sharing of information, interactive vegetation maps have been implemented with Google Earth mash-up. The maturity of Web-based GIS enables the generation of thematic maps dynamically and efficiently, with a thin/thick client or hybrid architectures. This could be a great support for the understanding environmental phenomena.

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.

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.

Late in the ,,70s, as a consequence of recurrent droughts occurred in West and East Africa, the famine struck millions of people imposing to national authorities and to the international community to coordinate efforts and to develop Early Warning Systems to limit the dramatic impact on the affected population. Between 1980 and 2007 the EWS concepts evolved passing from a stand-alone famine oriented analysis tool to a component either of a comprehensive food security information system or of a disaster prevention system. To early detect areas where drought could affect crop production and food security the "ZAR - Zones at Risk" agrometeorological software, based on Meteosat Second Generation rainfall estimation and Global Forecast System rainfall forecast images, has been developed. ZAR is presently exploited by the National Meteorological Services in various Sahelian countries and by Agrhymet Regional Center for regional assessments. The integration of ZAR impact maps (crop onset, soil water availability, crop conditions and phenological phases in a settled time) with the surveys data has improved National Meteorological Services capability in predicting and identifying areas where drought conditions would jeopardize crop production and consequentially quantify the population involved. The ZAR products are validated with the ground data collected in several agricultural campaigns. The analysis of the cropping season 2009 and the impact of localized droughts in terms of area and groups at risk for food security are presented. In particular, the dimension of crop production reduction and its geographical areas distribution over the Sahel have been assessed with the identification of the most vulnerable productions systems.

Nel Sahel, a fronte del progressivo degrado delle risorse forestali dovuto al fenomeno dei cambiamenti climatici e alla crescente pressione antropica, sono stati realizzati negli ultimi 30 anni importanti interventi di rimboschimento. La quantificazione della biomassa legnosa è il sistema più opportuno per valutarne l'efficacia. In questo lavoro viene proposto un approccio a basso impatto ambientale per stime correnti di biomassa. Sono stati sviluppati e analizzati modelli allometrici in piantagioni di Acacia spp. nella valle di Keita, in Niger e si è valutata la possibilità di utilizzare un modello generalizzato per le specie dominati: Acacia seyal Del., A. raddiana Savi (syn. A. tortilis Hayne), A. nilotica (Guill. et Perrott.). Le funzioni sono state costruite adottando come variabili esplicative il diametro a 0,80 m e l'altezza totale delle piante modello. L'analisi della regressione è stata realizzata con il metodo dei minimi quadrati ordinari dopo aver eseguito la trasformazione logaritmica delle osservazioni. In seguito è stata confrontata l'efficacia perequativa del modello multi-specifico con quella dei modelli specie-specifici. L'analisi dell'entità degli scostamenti tra valori osservati e attesi ha mostrato un'ottima capacità interpretativa in entrambi gli approcci (R2>0,98, P

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.