Integrated assessment of urban water supply security and resilience: Towards a streamlined approach

Urbanization and competing water demand, as well as rising temperatures and changing weather patterns, are manifesting as gradual processes that increasingly challenge urban water supply security. Cities are also threatened by acute risks arising at the intersection of aging infrastructure, entrenched institutions, and the increasing occurrence of extreme weather events. To better understand these multi-layered, interacting challenges of providing urban water supply for all, while being prepared to deal with recurring shocks, we present an integrated analysis of water supply security in New York City and its resilience to acute shocks and chronic disturbances. We apply a revised version of a recently developed, quantitative framework ('Capital Portfolio Approach', CPA) that takes a social-ecological-technological systems perspective to assess urban water supply security as the performance of water services at the household scale. Using the parameters of the CPA as input, we use a coupled systems dynamics model to investigate the dynamics of services in response to shocks - under current conditions and in a scenario of increasing shock occurrence and a loss of system robustness. We find water supply security to be high and current response to shocks to be resilient thanks to past shock experiences. However, we identify a number of risks and vulnerability issues that, if unaddressed, might significantly impact the city's water services in the mid-term future. Our findings have relevance to cities around the world, and raise questions for research about how security and resilience can and should be maintained in the future.