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Robust Decision Making Gives Policymakers Insight About an Uncertain Future

• Under historical climate conditions and access to new anticipated supplies in 2020, EID's current plan is 100 percent reliable in the western portion of its service area and 94 percent reliable in the eastern portion of its service area.
• Evaluating the EID system across a wide range of climate, growth, and supply availability futures shows that reliability for both regions would be substantially degraded for many plausible futures.
• Vulnerability analysis determined that the western portion of EID's service area is vulnerable primarily to the availability of new supplies from a particular project, regardless of climate and growth rates. For the east, vulnerable outcomes occur even with the new supplies, and they are associated with conditions that are only slightly drier than those in the historical record.
• Increasing urban water use efficiency and expanding surface storage is shown to mitigate some of the vulnerabilities due to climate change and new supply uncertainty.

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.

• Chapter One

  Introduction

• Chapter Two

  An Approach for Addressing Climate Change by Local Water Agencies

• Chapter Three

  Application to Local Water Agency Planning

• Chapter Four

  Results

• Chapter Five

  Discussion