Le changement climatique et les migrations humaines constituent deux problématiques majeures de notre époque. Et, partant du constat d’une connaissance fragmentée entre maximalistes et minimalistes, qui s’est traduite par une capacité limitée de la recherche scientifique à prendre en compte les interactions complexes entre le climat et les migrations humaines, cette thèse propose, à travers une approche renouvelée (celle de la vulnérabilité du système socio-écologique), une meilleure compréhension et explication des relations climat- migrations. Elle cherche à répondre à deux objectifs. D’une part, produire des connaissances nouvelles en nous appropriant de façon sélective et ordonnée les apports empiriques produits par les approches précédentes. Et, d’autre part, par une analyse instrumentée des interactions mises en évidence, générer des informations chiffrées pertinentes permettant un ciblage plus efficace des politiques. Cette thèse insiste en premier lieu sur une certaine difficulté à mettre en évidence une relation robuste entre changement climatique et migrations à l’échelle Sahélienne. Contrairement aux idées reçues sur l’image type du « migrant/réfugié climatique » sahélien véhiculée par les médias et reprise, sans un recul critique, dans la littérature grise et certaines études scientifiques, la région, souvent vue et analysée comme une entité relativement homogène, présente de fortes hétérogénéités spatiales physico-climatiques, outre celles socio-économiques. Et, ces dernières ne permettent pas une compréhension des migrations, une des expressions des transformations sociétales. Il convient de repenser la problématique sur des échelles plus homogènes (Sénégal des zones agro-écologiques et régions administratives)Nos résultats montrent un effet climatique accélérateur/amplificateur des migrations interrégionales sous-jacent aux conditions de vie des populations. Généralement, le climat ne suffit pas, à lui seul, à « produire » des migrations. Il transite par les variables socio-économiques (vulnérabilité initiale). Ce qui nous a amené à retenir l’appellation de «migrants éco-climatiques ». Ainsi, les politiques devraient aller à la fois vers : (i) des questions de développement en réduisant des vulnérabilités socio-économiques (pauvreté et inégalités) en agissant sur l’environnement d’action et les acteurs respectivement de manière cohérente et extensive ; mais, également, (ii) des questions d’économie du climat par la réduction de la vulnérabilité physico-climatique à travers des politiques d’atténuation et d’adaptation du milieu et des populations face au changement climatique. / Climate change and human migration are two major issues of our time. Starting from the observation of a dichotomous knowledge between maximalists and minimalists, which results in a limited capacity of scientific research to take into account the dynamic and complex interactions between climate and human migrations, this thesis proposes a better understanding and explanation of the climate-migration relations through a renewed and integrative approach (the vulnerability of the socio-ecological system). It aims to fulfill two objectives. On the one hand, to produce new knowledges those take into accounts socio-ecological interactions and feedbacks at different spatial and temporal scales and, on the other hand, to propose a quantified instrumentation of these social-ecological interactions and feedback. This contribution could serve as a starting point for a decision-making tool to evolve towards more targeted and effective policies.This thesis emphasizes a certain difficulty in highlighting a robust relationship between climate change and migration in the Sahel region. This latter, often seen as a relatively homogeneous entity, presents complex socio-economic and physical-climatic spatial heterogeneities that do not allow a stronger understanding of migratory movements which are in change since the 1970s. For this purpose, a reduced complexity model, based both on a partitioning of the study area (Senegal) and a partitioning of data (agro-ecological zones and regions of Senegal), is mobilized as a framework for the analysis of social-ecological migrations in terms of vulnerability induced by climate change. Thus, the innovative heuristic framework built (knowledge model with a sequencing of variables) has made it possible to instrument the climate-migration relationships within Senegal.Our results show an accelerating/amplifying climatic effect of interregional migrations underlying the living conditions of populations. In general, climate alone is not sufficient to "produce" migration. The climatic effects channel through the socio-economic variables (initial vulnerability). Under these results, we retained in fine the name of "eco-climatic migrants". Thus, policies relating to eco-climatic migration in this western part of the Sahel should move towards both: (i) development issues by reducing socio-economic vulnerabilities (poverty and inequality) by acting on the environment and the populations consistently and extensively respectively; and (ii) climate economics issues by reducing the physical-climatic vulnerability through appropriate mitigating and adapting policies to face climate change.

Este trabalho objetiva contribuir para o desenvolvimento de metodologia de análises de vulnerabilidade ecológica de bacias hidrográficas, com foco nos ecossistemas de água doce. Partiu-se de uma base metodológica proposta pela Rede WWF e de sua adaptação para a Bacia Lagos São João. Através da aplicação da metodologia desenvolvida, foi possível realizar uma análise multicriterial que identificou, por um lado, os principais estressores afetando a integridade ecológica da bacia, e sua severidade e frequência, mediante avaliação colaborativa de um painel de especialistas; por outro lado, avaliou-se a sensibilidade da bacia aos estressores selecionados. O uso de ferramentas de sistemas de informação geográfica permitiu espacializar, localizar e quantificar as ameaças (estressores), gerando mapas de risco ecológico, identificando em especial, as unidades mais desequilibradas do território em análise. Estas são indicadas como prioritárias para as ações de conservação dos ecossistemas aquáticos, e dos serviços ecossistêmicos providos, do qual depende grande parte da população da bacia. Esta dissertação apresenta, portanto, duas principais contribuições: um estudo global e preliminar da integridade ecológica da bacia Lagos São João; e, sobretudo, adaptações e detalhamentos da base metodológica desenvolvida pela Rede WWF, replicáveis em outras bacias hidrográficas. Ressalte-se que esta análise constitui etapa preliminar para a definição de estratégias de adaptação e resiliência de bacias hidrográficas às mudanças ambientais globais associadas às variabilidades e mudanças climáticas. / This study aims to contribute to the development of a methodology for the analysis of watersheds ecological vulnerability, focusing on freshwater ecosystems. It Was developed from a methodological base proposed by WWF and its adapted application to Lagos São João Basin. With this methodology, it was possible to perform a multi-criteria analysis identifying, by one side, the major stressors affecting the ecological integrity of the basin, and its severity and frequency, by collaborative evaluation of a panel of experts; on the other side, was evaluated the basin sensitivity to stressors identified. The use of geographic information system tools allowed spatialize, locate and quantify the treats (stressors), generating maps of ecological risk, identifying in particular, the units more unbalanced of the territory in question. These are priority in actions of aquatic ecosystems conservation, and provided ecosystems services, which depends much of the population of the basin. Can be conclude, therefore, that this dissertation presents two main contributions: a global and preliminary study of Lagos São João Basin ecological integrity, and, above all, the adaptations and detailing of the methodology base developed by WWF, replicable to other watersheds. Should be noted that this analysis is the preliminary step for the definition of basins adaptation and resilience strategies to global environmental changes associated with climate variability and change.

Este trabalho objetiva contribuir para o desenvolvimento de metodologia de análises de vulnerabilidade ecológica de bacias hidrográficas, com foco nos ecossistemas de água doce. Partiu-se de uma base metodológica proposta pela Rede WWF e de sua adaptação para a Bacia Lagos São João. Através da aplicação da metodologia desenvolvida, foi possível realizar uma análise multicriterial que identificou, por um lado, os principais estressores afetando a integridade ecológica da bacia, e sua severidade e frequência, mediante avaliação colaborativa de um painel de especialistas; por outro lado, avaliou-se a sensibilidade da bacia aos estressores selecionados. O uso de ferramentas de sistemas de informação geográfica permitiu espacializar, localizar e quantificar as ameaças (estressores), gerando mapas de risco ecológico, identificando em especial, as unidades mais desequilibradas do território em análise. Estas são indicadas como prioritárias para as ações de conservação dos ecossistemas aquáticos, e dos serviços ecossistêmicos providos, do qual depende grande parte da população da bacia. Esta dissertação apresenta, portanto, duas principais contribuições: um estudo global e preliminar da integridade ecológica da bacia Lagos São João; e, sobretudo, adaptações e detalhamentos da base metodológica desenvolvida pela Rede WWF, replicáveis em outras bacias hidrográficas. Ressalte-se que esta análise constitui etapa preliminar para a definição de estratégias de adaptação e resiliência de bacias hidrográficas às mudanças ambientais globais associadas às variabilidades e mudanças climáticas. / This study aims to contribute to the development of a methodology for the analysis of watersheds ecological vulnerability, focusing on freshwater ecosystems. It Was developed from a methodological base proposed by WWF and its adapted application to Lagos São João Basin. With this methodology, it was possible to perform a multi-criteria analysis identifying, by one side, the major stressors affecting the ecological integrity of the basin, and its severity and frequency, by collaborative evaluation of a panel of experts; on the other side, was evaluated the basin sensitivity to stressors identified. The use of geographic information system tools allowed spatialize, locate and quantify the treats (stressors), generating maps of ecological risk, identifying in particular, the units more unbalanced of the territory in question. These are priority in actions of aquatic ecosystems conservation, and provided ecosystems services, which depends much of the population of the basin. Can be conclude, therefore, that this dissertation presents two main contributions: a global and preliminary study of Lagos São João Basin ecological integrity, and, above all, the adaptations and detailing of the methodology base developed by WWF, replicable to other watersheds. Should be noted that this analysis is the preliminary step for the definition of basins adaptation and resilience strategies to global environmental changes associated with climate variability and change.

L’idée de ce sujet de thèse a émergé du constat des difficultés auxquelles sont aujourd’hui confrontés les aménageurs de grands projets d’infrastructures linéaires. Le contexte actuel leur impose de prendre en compte les enjeux environnementaux, notamment en termes de préservation des milieux naturels et de la biodiversité, à différentes échelles, tout en veillant à faire aboutir leurs projets dans de bonnes conditions, sans surcoûts. Cependant, les maîtres d’ouvrage de grands projets d’infrastructures linéaires peinent pourtant à intégrer ces enjeux efficacement faute de méthodes et d’outils adaptés. Dans ce contexte, cette thèse propose une lecture et une analyse de l’évaluation environnementale au travers du prisme d’une géographie environnementale et d’une géographie de l’aménagement expérimentales et de l’étude d’un projet à enjeux environnementaux à échelles emboîtées, du niveau européen au niveau local, avec son lot de contradictions scalaires : le projet Seine-Nord Europe. Tout d’abord, au travers de la présentation et de l’évaluation de ce projet au regard de la prise en compte de ces enjeux, cette thèse se veut une contribution théorique à la connaissance des dynamiques et des stratégies d’aménagement et de leur trajectoire en matière d’intégration des enjeux environnementaux : la biodiversité et la question de la préservation des milieux naturels constituent l’enjeu environnemental plus particulièrement envisagé. D’autre part, cette thèse est aussi conçue comme une recherche-action et un accompagnement de la maîtrise d’ouvrage. Trois outils d’évaluation de la vulnérabilité écologique des milieux le long du tracé du projet ont ainsi été élaborés pour répondre à cet objectif. / This thesis is led by difficulties experienced by planners during linear infrastructure studies and developments. In the present context, they have to ensure a successful project without any extra cost while also taking into account environmental issues at different scales, as natural habitats and biodiversity protection. Until recently, these issues were not a main source of concern and studies were carried out to simply cover regulatory requirements as environmental assessment. Nevertheless, since The Grenelle Environment Forum, environment concerns have been considered as a key challenge for linear infrastructure projects in spite of difficulties due to a lack of process and efficient tools. Therefore this thesis provides an environmental assessment analysis based on environmental and experimental spatial planning geography and focused on the North-Seine canal project with some inconsistencies from European to local scale. Firstly, based on the description and analysis of this project, this thesis is a contribution to the knowledge improvement of planning strategies and the way they take into account environment issues: biodiversity and natural resources and environment protection are the main environmental concerns. Furthermore, this thesis is also designed as an “action research” and a help for project planners and managers with effective help. Three different ecological vulnerability assessment tools have been created to analyze natural resources and environments along the route proposition and they are described in this paper.