Stability and equity in transboundary river basins facing changes in climate and society

More than half of global freshwater is shared in transboundary river basins, involving competing interests and multiple, institutionally independent, and spatially distributed decision makers. Modern water resources literature has replaced the concept of optimality by that of Pareto efficiency to navigate multisector tradeoffs, tacitly assuming either the presence of a centralized social planner or a fully cooperative attitude by all the parties involved to maximize the system wide performance. Yet, this assumption rarely reflects the real socio-political context in international basins. In this work, we propose a decision-analytic framework that combines advances in multi-objective decision making for capturing competing multisector dynamics with cooperative game theory principles to represent alternative levels of cooperation among the decision makers, also including equity concerns to ensure environmental and climate justice for all the stakeholders. The framework is tested on the Zambezi Watercourse in Southern Africa as a paradigmatic example of most transboundary basins in developing countries as well as in the world. Specifically, we first quantify the potential benefit achievable by implementing a fully cooperative system operations with respect to a baseline scenario implementing uncoordinated strategies among institutionally independent decision makers, acting according to the principle of individual-rationality. We then design a coordination mechanism based on monetary compensation among the hydropower operators to find a solution satisfying both group and individual rationality. The different solutions are then discussed in terms of game-theoretic stability and fairness in the distribution of the benefits. Finally, we stress-test the system against an ensemble of synthetically generated climate and socio-economic scenarios, with our results that discover tipping points that may undermine the success of the international agreements designed under historical conditions