Are Western US Reservoirs at Risk of Minimum Power Pool Events in Warmer Climates?

Abstract Submission: Extreme droughts have caused significant declines in reservoir levels across the western U.S., severely impacting dams where low water levels restrict both water release and power generation. While detailed assessment tools exist for individual reservoirs and river systems, these tools are typically used to evaluate water management-related questions and it can be difficult to develop consistent information about drought impacts across multiple facilities. We lack reservoir elevation thresholds for critical river and power services, resulting in a lack of a comprehensive analysis of the risk of future minimum power pool (MPP) events—scenarios where reservoir levels drop below the threshold required for electricity generation. This evaluation provides valuable insight into the risks posed by these events to the electricity grid in the western U.S. The potential of reservoirs reaching minimum power pool level has already been evident in Lake Oroville in California and has raised concerns for key reservoirs within the Colorado River Basin, at Lake Mead and Lake Powell. This research evaluates the likelihood of MPP events of various magnitudes and durations under projected warmer climate conditions in the western U.S. Using data from the Bureau of Reclamation, California Data Exchange Center, and ResOpsUS, we develop rating curves to illustrate the storage-elevation relationship for 140 hydropower reservoirs, which account for approximately 21 GW of plant capacity—nearly half of the region’s total reservoir-based hydropower capacity. We hypothesize that the risk of widespread MPP occurrences will vary across different GCMs, with potential for both increase and decrease, particularly for infrequent and severe events. We assess the sensitivity of those risks to uncertainties in elevation thresholds. The findings will provide critical insights into the evolving risks of minimum power pool events due to climate change, informing future strategies for reservoir management and energy infrastructure planning in the western U.S.

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