San Francisco's Urban Water Supply: Assessing Alternatives under Future Climate Uncertainty and Demand Growth Scenarios

Water is a key resource for sustainable development, but urban areas around the world are facing challenges in reliably and efficiently providing water services. Strained water resources and the fragmented management of large centralized urban water systems reveal the need to search for holistic management solutions. San Francisco faces increased drought and formidable freshwater constraints. San Francisco Public Utilities Commission's exploration of alternative water supply options, to improve San Francisco's water sustainability provided a case study for this project. The objective of this study is to develop an alternative planning tool used for systematic urban water supply planning and demand management. This framework will compare water supply options using the Water Evaluation and Planning tool. We developed a model to compare a range of alternative water systems and their combinations (e.g. recycled water, desalination, etc.) under future climate change and population growth scenarios. The results show that the inflows for the years 2020-2060 are characterized by increased variability and frequency of low inflow than prior years. Under a 2% population growth rate the projected annual water use rate increased with notable changes from the year 2042-2060. The annual water use rate increases more rapidly after the year 2042 for both San Francisco residential and whole sale customers. Conservation techniques, Tuolumne River diversions, and in-city desalination offer the most benefits when considering the cost and yield of the projects. The most cost-effective portfolio is portfolio A, which contains the Los Vaqueros reservoir expansion, Tuolumne River diversions, and conservation technique projects. The high population growth scenario had the highest unmet demand, increasing at a rapid rate from year 2022-2060. The amount of unmet demand for the high population growth scenario from the year 2022-2060 was higher than that of the climate change scenario. Additional alternative water supply options were added to the model and the concept of drought resilience has been added to the holistic framework. Results from this study demonstrate the use of an integrated modeling tool, within a framework, and its capability to holistically compare urban water development options under uncertainty.