Vulnerability and risk: climate change and water supply from California’s Central Valley water system


Water allocation institutions globally must operate within legal and political contexts established by precedent and codified in operating rules, even as they flex and adjust to climate change. California’s Central Valley Water System (CVS) is a prime example. Recent global, national, regional, and local climate change assessments have highlighted climate-change-driven impacts on the CVS; however, these previous studies have not discussed the relative likelihood of performance decline, making it difficult to use the information for planning. In response, this paper presents a systematic climate change stress test that utilizes a physically based hydrologic model linked with a water resources system model representing the infrastructure, operations, and policy constraints of the interconnected system of natural river channels and man-made facilities that comprise the CVS. The results provide a summary of the sensitivity of the system to climate change, indicating the specific climate changes that cause performance of the system to decline below historical norms, and an estimation of the General Circulation Model (GCM) informed probability of those changes by 2050. Degraded performance is especially likely for State Water Project (SWP) deliveries (> 85%), and September carryover/drought storage in the Oroville Reservoir (the SWP’s largest reservoir, ~ 95% likely to degrade). A decline in Net Delta Outflow is likely in all seasons except summer and early fall (when regulations require supplemental releases to combat salinity from sea level rise). For most of these metrics, the modeled performance drop is more severe in dry years than in wet years.

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The authors gratefully acknowledge the financial and technical support provided by the California Department of Water Resources, and the efforts of the anonymous reviewers in improving the quality of this manuscript. Water system data supporting this analysis are available upon request from the California Department of Water Resources.

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Correspondence to Patrick Ray.

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Key points

•A climate change stress test of the CVS required development of internally consistent scenarios, statistically linking hydrological and non-hydrological inputs.

•The GCM-informed likelihood of climate-change-induced degradation of CVS performance by 2050 is greater than 60% for 5 of the 7 evaluated metrics.

•Substantial (> 10%) increases in precipitation would be required to offset the performance losses that would occur with 1 or 2 °C of warming.

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Ray, P., Wi, S., Schwarz, A. et al. Vulnerability and risk: climate change and water supply from California’s Central Valley water system. Climatic Change 161, 177–199 (2020).

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  • California Central Valley
  • Climate change
  • Water year type
  • Hydrologic model
  • Decision scaling