Risk and resilience to enhance sustainability with application to urban water systems

Many cities in water-stressed environments are seeking sustainable alternatives to traditional solutions such as supply augmentation and water restrictions. One alternative is to upgrade urban water systems in an integrated manner. Design of an integrated urban water system (IUWS) requires an understanding of the risk of the IUWS failing to deliver sustainable outcomes. We present a rationale for enhancing well-established risk assessment and management tools with concepts of ecosystem resilience. Although traditional risk assessment focuses on the states of controls that operate on specific system components and the likelihood and consequences of control failure, resilience theory addresses whole-of-system behavior. In identifying critical controls, risk management focuses on the ability to prevent failure and stabilize a certain system state, whereas resilience focuses on the "uncontrollable" to identify pathways for managing system adaptation to change. Based on conceptual analysis of two key resilience metaphors, the "stability landscape" and the "adaptive cycle," we investigate pathways toward risk-based IUWS design and management that explicitly include system resilience as an over-arching measure of sustainability. Areas for future research include development of methodologies for measuring system adaptive capacity, and identifying and quantifying emerging thresholds. The challenge for the risk assessment community is to reconsider what "risk" is: In a resilience context, events traditionally seen as risky are not necessarily bad, and may become opportunities. The challenge for the resilience community is to identify thresholds and the system's proximity to them.