Ovens and Tinderboxes in the Golden State

Joint heatwave outage events are a unique compound hazard disaster, as the most immediate solution to heat risk—air conditioning—also exacerbates outage risk. Increasingly frequent and intense heatwaves and wildfires remain some of the biggest climate threats facing California. Climate-induced hazards disproportionately threaten the health and wellbeing of vulnerable populations. They also underscore the vulnerability of the electric power system, precisely when individuals require cooling the most. Few studies have considered the health consequences of simultaneously occurring heatwave and outage events.

This paper examines associations between hazards, outages, and health outcomes for California cities from 2008–2020. Multiple hazard, outage, and patient data sources were compiled. First, an exploratory analysis looked at historical trends among heatwave, wildfire, and outage events. Second, a regression analysis estimated outage likelihood on hazard days, and the relative risk of emergency department visits and hospital admissions during hazard events. Heterogeneous outcomes by climate zone, race, age, and patient diagnosis (using ICD-10-CM codes) were further explored.

Results found that summer outages were 2.24 times more likely on heatwave versus non-heatwave days, and heatwave events were associated with 18 percent more outage customer hours (outage duration × customers without power) compared to non-heatwave events. The relative risk of ED and hospitalizations were greater on joint heatwave outage days compared to heatwave (non-outage) days. Patient rates for heat illness increased by over a 1,000 percent during joint heatwave outage events compared to approximately 800 percent during heatwave events. ED and hospitalization rates for populations with electricity-dependent medical devices or socioeconomic housing challenges were also higher during joint hazard versus single hazard events.

This research adds to the risk analysis literature by providing baseline, empirical estimates of joint heatwave outage likelihoods and outcomes. Ignoring possible health outcomes during outage events significantly underestimates the cost of disruptions, and in turn the value of resiliency during extreme hazard scenarios. Improved likelihood and valuation of outage-related health outcomes can reshape utility decision-making and investments. Electric service providers and local communities should factor in the individuals most endangered by joint hazard outage events in their rotating outage, Public Safety Power Shutoff, and heatwave mitigation plans.