Climate change will result in more intense, more frequent and longer lasting heat waves. The most hazardous conditions emerge when extreme daytime temperatures combine with warm night-time temperatures, high humidities and light winds for several consecutive days. Here, we assess present and future heat wave impacts on human health in Europe. Present daily physiologically equivalent temperatures (PET) are derived from the ERA-Interim reanalysis. PET allows to specifically focus on heat-related risks on humans. Regarding projections, a suite of high-resolution regional climate models - run under SRES A1B scenario - has been used. A quantile-quantile adjustment is applied to the daily simulated PET to correct biases in individual model climatologies and a multimodel ensemble strategy is adopted to encompass model errors. Two types of heat waves differently impacting human health - strong and extreme stress - are defined according to specified thresholds of thermal stress and duration. Heat wave number, frequency, duration and amplitude are derived for each type. Results reveal relatively strong correlations between the spatial distribution of strong and extreme heat wave amplitudes and mortality excess for the 2003 European summer. Projections suggest a steady increase and a northward extent of heat wave attributes in Europe. Strong stress heat wave frequencies could increase more than 40. days, lasting over 20. days more by 2075-2094. Amplitudes might augment up to 7. °C per heat wave day. Important increases in extreme stress heat wave attributes are also expected: up to 40. days in frequency, 30. days in duration and 4. °C in amplitude. We believe that with this information at hand policy makers and stakeholders on vulnerable populations to heat stress can respond more effectively to the future challenges imposed by climate warming. © 2014 Elsevier B.V.

This work has been partially sponsored by the CGL2008-01271/CLI (MEDICANES) and CGL2011-24458 (PREDIMED) projects from the Spanish Ministerio de Ciencia e Inovación; and by ESTCENA project (200800050084078), a strategic action from Plan Nacional de I+D+i 2008–11 funded by Ministerio de Medio Ambiente y Medio Rural y Marino. The authors also acknowledge the ENSEMBLES project, funded by the European Commission's 6th Framework Programme, through contract GOCE-CT-2003-505539

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