Toward an integrated modeling framework to assess water system vulnerability to short-term shocks in combination with climate and demand change

Abstract:

Recent drought episodes and the memory of the severe droughts of the past cause water public utilities to fear the possible impacts of a changing climate. At the same time, the risk of a major infrastructure failure resulting from aging and other natural hazards such as forest fires and earthquake is also paramount concern since a water utility must persevere through such short term shocks as well. The question for urban water utilities around the country is how to maintain system resilience in the face of both climate and other deep uncertainties. To answer this question requires a new analysis approach never before attempted for urban water planning. We extend the typical climate stress test to a more comprehensive stress test that addresses in a single conceptual framework long-term uncertainties stemming from short-term shocks, such as earthquakes and infrastructure aging, with climate and demand changes. We illustrate application of the developed framework with the Hetch Hetchy Regional Water System, the water supply system operated by the San Francisco Public Utilities Commission that supplies drinking water to 2.7 million people in the Bay Area. The results illustrate the system response to several infrastructure and natural hazards (e.g., major pipeline failure due to aging or earthquake) in combination with climate and demand changes. For a given climate and demand condition, the system performance varies for each failure scenario and depends on the timing of the event (e.g., the failure occurs during the high demand season versus during the low demand season; or the failure occurs during a wet period versus during a multi-year drought). Changing climate and demand conditions are shown to reveal system vulnerability to short-term shocks that were typically not a concern under the climate and demand baseline, which emphasizes the need for thoughtful planning accounting for not only climate and demand change but also for short-term shocks.