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.

Abstract

Adaptation to global change challenges at the river basin scale requires selecting from demand and supply management measures in a context of high uncertainty on 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 define an equitable allocation of the cost of the adaptation plan between the stakeholders involved. The framework developed integrates inputs from the two main approaches commonly used to plan for adaptation. The first, referred to as “top-down”, estimates the impact on the local water resources from different climate change scenarios at the global level. Conversely, the second, called “bottom-up”, starts by assessing vulnerability at the local level to then identify adaptation measures to face an uncertain future. Outcomes from the previous approaches applied in the Orb River basin (France) are integrated to select a cost-effective combination of adaptation measures through a least-cost optimization model developed at the river basin scale. Supply-side infrastructure development measures are considered, as well as demand-side household water conservation measures or irrigation efficiency improvement. The model is then used to investigate the trade-offs between different planning objectives and to identify robust and least-regret adaptation measures. The issue of allocating the cost of the adaptation plan is considered from 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 then compared with cost allocation rules based on social justice principles to provide contrasted insights into a negotiation process. The interdisciplinary framework developed during this thesis combines economics and water resources engineering methods, creating a promising means of bridging the gap between bottom-up and top-down approaches and supporting the definition of cost-effective and equitable adaptation plans at the local level.