Unveiling remote and local drivers for the interdecadal shift of European hot days

The accelerated warming in Europe leaves this region especially vulnerable to severe heatwaves. Previous investigations on heatwaves have focused predominantly on long-term trends, interannual variability, or individual events. Based on multiple observational datasets, this study reveals that the summer hot days over Europe exhibit a significant interdecadal shift around 1998, with the largest increase in southern Europe. Yet, the underlying physical mechanisms for this phenomenon have not been fully understood. Observational analyses and model simulations indicate that the sea surface temperature anomalies associated with the negative-to-positive phase transition of the Atlantic Multidecadal Oscillation (AMO) can generate a Rossby wave train, resulting in an anomalous equivalent barotropic high-pressure structure and descending motions over southern Europe. Consequently, southern Europe receives more incoming solar radiation, which heats the land surface and overlying air, increasing the likelihood of hot days. Meanwhile, soil moisture decreases over southern Europe, which intensifies the land–air coupling strength and partitions more surface net radiation into surface sensible heat flux, consequently resulting in enhanced hot days. Notably, the atmospheric circulation anomalies over southern Europe linked to the AMO phase transition reduce regional soil moisture by approximately 35%, as quantified by a dynamic adjustment approach. Our findings provide a new insight into the ocean–soil moisture–hot days linkage, which is essential for understanding extreme heat events worldwide. 欧洲夏季高温日在1998年发生了显著的年代际突变, 其中南欧地区增幅最大.观测分析与模式模拟表明, 与北大西洋多年代际振荡 (AMO) 由负位相向正位相转换相关的海表温度异常 (SSTAs) , 能激发罗斯贝波列, 在南欧上空形成准正压的高压异常和下沉运动, 使得该区域高温日增加.与此同时, 南欧土壤湿度降低, 增强了陆气耦合强度, 加剧高温日现象.我们的研究为理解海洋-土壤湿度-高温日的关联机制提供了新视角.