Sustainable water management under future uncertainty with eco-engineering decision scaling

1 Securing the supply and equitable allocation of fresh water to support human well-being while sustaining healthy, functioning ecosystems is one of the grand environmental challenges of the twenty-first century, particularly in light of accelerating stressors from climate change, population growth and economic development. Rehabilitation of ageing infrastructure and construction of new infrastructure are now widely viewed as engineering solutions to mitigate future climatic uncertainty in the hydrologic cycle1. Indeed, the construction of tens of thousands of dams in the twentieth century helped secure water supplies and fuel economic development in industrialized countries, and developing economies are now pursuing massive new infrastructure projects with thousands of new dams proposed for hydropower production and water supply security2. Despite the economic stimulus provided by many dams historically, the global experience with dam building warns that traditional approaches to water infrastructure development in a rapidly changing world carry severe risks of economic and environmental failure. First, large water projects are very capital-intensive and long-lived, costing billions of dollars to plan, build and maintain. Yet, they are vulnerable to biased economic analyses3, cost overruns and construction delays, and changing environmental, economic and social conditions that can diminish projected benefits4,5. Under a variable and changing climate, large water infrastructure may even risk becoming stranded assets6. Second, the principles of economic efficiency inherent in cost-benefit analysis dominate project design and performance assessment, making integration of social and environmental benefits and costs into a comprehensive economic Sustainable water management under future uncertainty with eco-engineering decision scaling