Resumen de Integrating top-down and bottom-up approaches to design a cost-effective and equitable programme of measures for adaptation of a river basin to global change.
Adaptation to the multiple facets of global change challenges the conventional means of sustainably planning and managing water resources at the river basin scale. Numerous demand or supply management options are available, from which adaptation measures need to be selected in a context of high uncertainty of future conditions. Given the interdependency of water users, agreements need to be found at the local level to implement the most effective adaptation measures. Therefore, this thesis develops an approach combining economics and water resources engineering to select a cost-effective programme of adaptation measures in the context of climate change uncertainty, and to define an equitable allocation of the cost of the adaptation plan between the stakeholders involved. A framework is developed to integrate inputs from the two main approaches commonly used to plan for adaptation. The first, referred to as "top-down", consists of a modelling chain going from global greenhouse gases emission scenarios to local hydrological models used to assess the impact of climate change on water resources. Conversely, the second approach, called "bottom-up", starts from assessing vulnerability at the local level to then identify adaptation measures used to face an uncertain future. Outcomes from these two approaches are integrated to select a cost-effective combination of adaptation measures through a least-cost optimization model developed at the river basin scale. The model is then used to investigate the trade-offs between different planning objectives defined in terms of environmental flow requirements, irrigated agriculture development, and the cost of the programme of measures. The performances of a programme of measures are finally assessed under different climate projections to identify robust and least-regret adaptation measures. The issue of allocating the cost of the adaptation plan is considered through two complementary perspectives. The outcome of a negotiation process between the stakeholders is modelled through the implementation of cooperative game theory to define cost allocation scenarios. These results are compared with cost allocation rules based on social justice principles to provide contrasted insights into a negotiation process. This innovative framework has been applied in a Mediterranean case study in the Orb River basin (France). Mid-term climate projections, downscaled from 9 General Climate Models, are used to assess the uncertainty associated with climate projections. Demand evolution scenarios have been developed to project agricultural and urban water demands on the 2030 time horizon. The least-cost river basin optimization model developed in GAMS allows the cost-effective selection of a programme of measures from a catalogue of 462 supply and demand management measures. Nine cost allocation scenarios based on different social justice principles have been discussed through face-to-face semi-structured interviews with 15 key informants and compared with solution concepts from cooperative game theory for a 3-player game defined at the river basin scale. The interdisciplinary framework developed in this thesis combines economics and water resources engineering methods, establishing a promising means of bridging the gap between bottom-up and top-down approaches and supporting the creation of cost-effective and equitable adaptation plans at the local level.
