Persistence of heat waves and its link to soil moisture memory

In this study, we assess the role of soil moisture for heat wave persistence using simulations with a regional climate model. Several studies have investigated changes in the frequency of hot summer days but very few investigated changes in their persistence. We use two different heat wave thresholds, either defined by the 90th percentile of the control run or by the 90th percentile of the respective sensitivity experiment. We identify that simulations in which soil moisture is fixed to a constant value or prescribed seasonal cycle, even with prescribed constant dry conditions, present a lower intrinsic heat wave persistence than simulations with interactive soil moisture. This effect is related to the impact of soil moisture persistence in the interactive simulations and amounts to ca. 5–10% of the spell lengths of the 10% hottest days in the respective simulations. Our results highlight the key role of soil moisture memory for the persistence of heat wave events, beside the known effect of soil moisture on heat wave intensity.