Risk perception, but not response efficacy, linked risk communication to protective action during an atmospheric river in California

Abstract Whether and how risk communication motivates individuals to take protective action over the course of extreme weather events is a central question for public policy. Yet to date, such evidence has been difficult to obtain due to the challenges of forecasting events, rapidly recruiting populations in at-risk locations, and fielding longitudinal studies as conditions unfold. In February 2026, forecasts of an atmospheric river threatening northern California provided an opportunity to examine how risk communication related to protective action in real time. As the atmospheric river approached and made landfall, we surveyed 513 at-risk adults twice daily over one week (n = 5,099 observations) and applied preregistered Bayesian within-person mediation models to the resulting intensive longitudinal data. We found that when participants received more risk communication than their personal average, they were more likely to take protective action. This within-person relationship was explained by changes in risk perception, but not response efficacy. Unexpectedly, receiving more risk communication than usual was associated with lower response efficacy, even though higher levels of response efficacy were associated with a higher likelihood of taking protective action. Taken together, these findings lend empirical support to policy priorities that use risk communication to promote protective action during extreme weather events, such as the United Nations’ Early Warnings for All initiative. Still, risk communication could be even more effective by building confidence that specific actions reduce harm, in addition to raising awareness of the threat.