As EPRI’s Climate Resilience and Adaptation initiative began its effort in 2022 to collaboratively develop a comprehensive and consistent framework that power companies could use as a guide to conduct physical climate risk assessments, it quickly became obvious that fragility curves and related analyses would be an important part of the process. Quantifying the relationship between a climate hazard and its impact on the performance, life span, and/or failure rates of specific assets within the power system, can provide critical inputs to system planning models that, when coupled with climate projections, can be used to characterize potential risk to assets and systems through the end of this century. These quantitative analyses, whether using empirical data specific to a company’s individual assets, or derived using physics-based models, or some combination of the two, will very likely result in much more accurate inputs to the models than use of more qualitative thresholds for the assets derived from standards, design specifications, rule of thumb, or other sources.
This document explains what fragility curves are, describes how fragility curves can be used for quantitative physical climate risk assessment of power system assets, and provides examples of how to develop fragility curves to relate climate hazard intensity to probability of an unwanted outcome (such as failure). Key methodologies for developing and modifying fragility curves are discussed, including considerations for aging assets and the impacts of climate change on both hazards and asset degradation. Specific examples are given throughout for utility assets, including showing general methodologies for modifying fragility curves to account for degradation. The examples used primarily focus on the impacts of wind speed on wood poles for simplicity, but the concepts can be readily applied to many other hazard-asset combinations across the power sector.
Also discussed is integration of fragility curves with hazard curves, relating the intensity of the hazard to the frequency of exceedance to determine failure rates, and consideration of evolving hazard and fragility curves to account for climate change. Lastly, a literature review was performed with summary tables developed to highlight some key existing fragility curves for distribution poles as an example that can be replicated for other electric utility assets. This literature review serves as the basis for Climate READi’s fragility curve clearinghouse that will incorporate additional studies for other hazard-asset combinations and is expected to be available by mid-2025.