Addressing Climate Change in Local Water Agency Plans

Water agencies are increasingly seeking to address climate change in their long-term planning. Doing so, however, requires moving beyond traditional planning approaches to ones that can incorporate information about future hydrologic conditions, demographic changes, and other management conditions that are deeply uncertain or not statistically well characterized. This report describes an approach for planning under deep uncertainty, called Robust Decision Making (RDM), and demonstrates its application in a research study with the El Dorado Irrigation District (EID), a water agency located in the California Sierra Nevada Mountains. Using RDM, the authors, in collaboration with EID, tested the robustness of their current long-term plan across more than 50 futures reflecting different assumptions about future climate, urban growth, and the availability of important new supplies. The analysis finds that, although the system is highly reliable under traditional assumptions of historical climate and successful implementation of its long-term plan, significant vulnerabilities arise under climate change and uncertainty about the availability of new supplies. RDM structures an analysis of additional strategies and shows how additional urban water use efficiency and surface storage could mitigate some of these vulnerabilities. The report concludes by presenting key trade-offs among the strategies and showing how EID's expectations for future vulnerable conditions can guide decisions to augment its long-term plan.