From many futures to one: climate-informed planning scenario analysis for resource-efficient deep climate uncertainty analysis

Water resources managers face decisions related to building new infrastructure to increase water system resilience to climate and demand changes. To inform this adaptation planning process, current decision-making methods commonly use scenario approaches to estimate the benefit of adaptation options. While effective, these new analyses require communication of complicated findings to often nontechnical audiences. This paper introduces a pragmatic approach that uses the results from a bottom-up assessment of vulnerability of the water system with future climate projection-based probabilities of climate change to select a single planning scenario that encapsulates the decision-makers’ chosen level of robustness for their system. Contrary to typical implementation of option analysis under deep climate uncertainty, the proposed pragmatic approach does not require the analyst to evaluate each portfolio of adaptation options against all possible states of the world, significantly reducing the required computational costs and communication challenges. It also aligns with the planning scenario approach used in practice by water utilities. The modeling framework is illustrated for the regional water system operated by the San Francisco Public Utilities Commission (California, United States) for which changes in average temperature, precipitation and urban demand are considered.