Dans plusieurs territoires agricoles, les débits des rivières pendant l’étiage sont régulièrement inférieurs aux normes, signant des situations de « déséquilibre structurel » entre offre et demande en eau. Les différents acteurs du territoire peinent à s’accorder sur les changements à engager, d’autant que les impacts de ces changements sont incertains. Que valent alors les différentes propositions avancées pour résoudre le déséquilibre hydrique ? Je réponds à cette question en concevant une démarche d’évaluation multicritère multi-acteur que je déploie sur le territoire de l’Aveyron aval – Lère (Sud-Ouest de la France). Quatre scénarios - trois visant à réduire l’irrigation et un à améliorer le stockage de l’eau - sont comparés au travers de simulations informatiques (modèle MAELIA) et de jugements d’acteurs (outil KERBABEL DST). Les scénarios se différencient en termes d’intensité et de diversité des impacts simulés, d’intérêts ou préjudices perçus par les acteurs, et de capacité à produire du consensus ou de la discorde. Les connaissances développées à l’issue de cette thèse sont d’ordres agronomique, socioéconomique et méthodologique. / In many agricultural landscapes, river flows during the low-water period regularly fall below regulatory thresholds, indicating situations of structural imbalance between the water offer and demand. The various stakeholders disagree on the changes to implement, especially since the impacts of these changes are uncertain. In this context, how valuable are the different proposals to solve the water imbalance? I answer this question by designing a multi-actor multicriteria evaluation method, which I adapt to the downstream Aveyron watershed (South-Western France). Four scenarios – three aiming to reduce irrigation withdrawals and one improving water storage – are compared based on computer simulations (MAELIA model) and stakeholder judgments (KERBABEL deliberation support tool). Scenarios differ from each other in terms of magnitude and diversity of the simulated impacts, perceived advantages and weaknesses, and capability to generate consensus or discord among stakeholders. Agronomic, socioeconomic and methodological knowledge is derived from this thesis.

[pt] O objetivo geral do presente estudo é sustentar que a consideração da literatura existente sobre julgamento e tomada de decisão (JTD), oriunda da psicologia e das ciências cognitivas, (i) não apenas confirma a direção acertada de nosso modelo constitucional de processo democrático pautado em um contraditório substancial, como também (ii) demonstra-se imprescindível ao seu aprimoramento. De início, apresentam-se os contornos teóricos daquilo que se entende por processo judicial democrático, focando-se no desenvolvimento dos principais (e novos) aspectos relacionados ao princípio do contraditório - garantidor do fluxo discursivo que permite a construção conjunta (comparticipada e policêntrica) da decisão. Passado o referido ponto, o estudo converge para o terreno da psicologia e das ciências cognitivas. Parte-se das mais conhecidas pesquisas sobre as limitações do raciocínio humano. Posteriormente, introduz-se a provocativa (e recente) teoria sobre o entendimento humano, formulada por Dan Sperber e Hugo Mercier (teoria interacionista do raciocínio). Ao final, concluise que tais estudos e experimentos - intimamente ligados à cognição individual e aos aspectos da deliberação coletiva – nos permitem lançar um novo olhar sobre diversas questões atinentes à (efetiva) adoção de um modelo de processual democrático. / [en] The general purpose of this study is to sustein that the consideration of the existing literature on judgment and decision making, from psychology and cognitive sciences, (i) not only endorses our constitutional model of democratic process, based on a substantial adversarial mechanism, while also (ii) proves to be essential to its improvement. At first, the theoretical contours of what should be understood by a democratic judicial process are presented, focusing on the development of the main (and new) aspects related to the adversarial principle - guarantor of the discursive flow that allows the joint construction (co-participated and polycentric) of the decision. Thereafter, the study steps into psychology and cognitive sciences domain. It is starts with the most acknowledged researches in about the limitations of the human reasoning. Later on, Dan Sperber and Hugo Mercier s recent provocative theory of human understanding is introduced (the interactionist theory of reasoning). Finally, it is concluded that such studies and experiments - intimately connected to individual cognition and the aspects of collective deliberation - allow us to acquire a new perspective over several of pertaining topics related to the (effective) adoption of a democratic procedural model.