Changes in the Global Pattern and Magnitude of Summertime Heatwave Metrics Are Largely Explained by a Mean Shift

Abstract Heatwave severity has increased over time, and the degree of change varies over the globe. We demonstrate that the observed spatial pattern of changes in common heatwave metrics can largely be explained by local mean warming. We further show that the climatological variance and skewness of the daily maximum temperature distribution regulate the effect of the mean shift on heatwave frequency, duration, and intensity. Using only the mean shift and the first three climatological moments, we generate baseline estimates of heatwave change across space. Among the metrics, the shift model best explains spatial changes in heatwave frequency. Further, the model reveals the distinct pattern of change that comes with intensity‐based metrics like cumulative heat compared to the temporal‐only metrics of heatwave frequency and duration. Our results suggest that the use of threshold‐based metrics can result in apparent differences in heat trends that can be unified through the proposed shift framework.