Resilient California water portfolios require infrastructure investment partnerships that are viable for all partners

In May 2021, California Governor Newsom announced a $5.1 billion package for “immediate drought response and long-term water resilience investments” (Office of Governor Gavin Newsom, 2021). This follows the administration's Water Resilience Portfolio Initiative (WRPI), an ambitious blueprint for bolstering the state's water security (Newsom et al., 2020). The WRPI recommends a suite of actions to overcome challenges such as population growth, groundwater overdraft, and aging infrastructure, as well as climate change, which is already making droughts more frequent and severe (AghaKouchak et al., 2014, 2021; Berg & Hall, 2017; Diffenbaugh et al., 2015). Focal point recommendations in the WRPI include (a) expanding, improving, and diversifying the state's water storage and conveyance infrastructure, (b) developing flexible institutions for water sharing (e.g., groundwater banking), and (c) preparing for more climate change-related extreme droughts and floods. The WRPI envisions a future in which separate agencies, utilities, and stakeholder groups collaboratively develop and manage a shared network of water infrastructure that bridges local, regional, and statewide scales. However, at present, it is not clear that planners have the tools they need to build this “cohesive, resilient ‘water system of systems’ across California” (Newsom et al., 2020). In this work, we show that traditional water supply planning tools are unsuitable for the task at hand. Exploratory modeling contributes new insights for designing and evaluating collaborative water investment partnerships under uncertainty. These insights have broad relevance beyond California, including the entire Western U.S. and other water-scarce regions around the world seeking to develop more resilient water supply systems.