A Review of the European Summer Heat Wave of 2003

Abstract This paper reviews the European summer heat wave of 2003, with special emphasis on the first half of August 2003, jointly with its significant societal and environmental impact across Western and Central Europe. We show the pattern of record-breaking temperature anomalies, discuss it in the context of the past, and address the role of the main contributing factors responsible for the occurrence and persistence of this event: blocking episodes, soil moisture deficit, and sea surface temperatures. We show that the anticyclonic pattern corresponds more to an anomalous northern displacement of the North Atlantic subtropical high than a canonical blocking structure, and that soil moisture deficit was a key factor to reach unprecedented temperature anomalies. There are indications that the anomalous Mediterranean Sea surface temperatures (SSTs) have contributed to the heat wave of 2003, whereas the role of SST anomalies in other oceanic regions is still under debate. There are methodological limitations to evaluate excess mortality due to excessive temperatures; however, the different studies available in the literature allow us to estimate that around 40,000 deaths were registered in Europe during the heat wave, mostly elderly persons. Despite previous efforts undertaken by a few cities to implement warning systems, this dramatic episode has highlighted the widespread un-preparedness of most civil and health authorities to cope with such large events. Therefore, the implementation of early warning systems in most European cities to mitigate the impact of extreme heat is the main consequence to diminish the impact of future similar events. In addition to mortality (by far the most dramatic impact), we have also analyzed the record-breaking forest fires in Portugal and the evidence of other relevant impacts, including agriculture and air pollution. KEY WORDS: heat wavesextreme eventsclimate impacts ACKNOWLEDGMENTS Ricardo Trigo and Ricardo García-Herrera received support from the Portuguese-Spanish integrated action (E-27/2005) funded by CRUP and MCYT and also from Gulbenkian Foundation through project IMPACTE (no. 1568). Erich Fischer was funded by the Swiss National Centre of Competence in Research on Climate (NCCR Climate). The authors would like to thank the ECMWF and NCEP/NCAR for providing their reanalysis data, and the Belgium institute VITO for providing the images from satellite VEGETATION. The authors would like to acknowledge Daniel Paredes, David Barriopedro, Bernardo Mota, José Miguel Cardoso Pereira, Célia Gouveia, and Martin Hirschi for all their comments and contribution to several figures. We also acknowledge the comments and suggests from the reviewers.