Resilience of urban water systems: an 'infrastructure ecology' approach to sustainable and resilient (SuRe) planning and design
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Increasing urbanization is a dominant global trend of the past few decades. For cities to become more sustainable, however, the infrastructure on which they rely must also become more efficient and resilient. Urban infrastructure systems are analogous to ecological systems because they are interconnected, complex and adaptive, are comprised of interconnected components, and exhibit characteristic scaling properties. Analyzing them together as a whole, as one would do for an ecological system, provides a better understanding about their dynamics and interactions, and enables system-level optimization. The adoption of this “infrastructure ecology” approach will result in urban development that costs less to build and maintain, is more sustainable (e.g. uses less materials and energy) and resilient, and enables a greater and more equitable creation of wealth and comfort. Resilience, or the capacity of a system to absorb shocks and perform under perturbations, can serve as an appropriate indicator of functional sustainability for dynamic adaptive systems like Urban Water Systems. This research developed an index of resilience (R-Index) to quantify the “full-spectrum” resilience of urban water systems. It developed five separate indices, namely (i) Index of Water Scarcity (IWS), (ii) Relative Dependency Index (RDI), (iii) Water Quality Index (WQI), (iv) Index of Network Resilience (INR), and (v) Relative Criticality Index (RCI), to address the criticalities inherent to urban water systems and then combines them to develop the R-Index through a multi-criteria decision analysis method. The research further developed a theoretical construct to quantify the temporal aspect of resilience, i.e. how quickly the system can return back to its original performance level. While there is a growing impetus of incorporating sustainability in decision making, frequently it comes at the cost of resilience. This is attributable to the fact that the decision-makers often lack a life-cycle perspective and a proven, consistent and robust approach to understand the tradeoff between increased resilience and its impact on sustainability. This research developed an approach to identify the sustainable and resilient (SuRe) zone of urban infrastructure planning and design where both sustainability and resilience can be pursued together.