Spring Regional Sea Surface Temperatures as a Precursor of European Summer Heatwaves

Different spring and early summer North Atlantic sea surface temperature anomalies (SSTAs) have been shown to precede recent European summer heatwaves (EuSHWs). So far, the limited number of observed events associated with several physical mechanisms has prevented a robust identification of SSTAs as precursors. Here, we extend beyond previous studies by combining 100 historical simulations (1850–2005) of the MPI Grand‐Ensemble with an explainable neural‐network method. We find that the spring tripolar North Atlantic pattern with positive SSTAs in the Subtropical Gyre is a precursor of EuSHWs. In addition, positive SSTAs west of the Iberian Peninsula, and in the North Sea, the Baltic Sea and the Mediterranean Sea relate to distinct early summer soil moisture anomaly patterns and are precursors of western and southeastern EuSHWs, respectively. While the phase of the tripolar North Atlantic pattern indicates whether a EuSHW might emerge, regional SSTAs indicate the spatial characteristics of EuSHWs. Plain Language Summary Past studies have investigated the influence of spring and early summer North Atlantic sea surface temperature anomalies (SSTAs) on recent European summer heatwaves (EuSHWs). These studies have proposed different SSTAs in the North Atlantic as the most important for the development of different EuSHWs. Yet, it has not been possible to generalize which spring North Atlantic SSTAs are the most important to anticipate EuSHWs because we have too few observed events and they showed different spatial and physical characteristics. Here, we analyze 100 historical simulations (1850–2005) of the MPI Grand‐Ensemble in which we identify a large number of EuSHWs. We use an explainable neural‐network method to find which spring North Atlantic SSTAs are the most important to anticipate EuSHWs. We find that warm SSTAs in the Subtropical Gyre surrounded by cold SSTAs in the north and in the south is an indicator of EuSHW occurrence. In addition, different regional SSTAs relate to drier than normal soil moisture in different parts of Europe that influence different EuSHWs. Warm SSTAs west of the Iberian Peninsula, and in the North Sea, the Baltic Sea and the Mediterranean Sea indicate the occurrence of western and southeastern EuSHWs, respectively. Key Points A tripolar North Atlantic sea surface temperature (SST) pattern with an anomalously warm Subtropical Gyre is a precursor of European summer heatwaves Distinct regional spring SST anomalies relate to dist