Heat waves across Europe by the end of the 21st century: multiregional climate simulations

We investigated changes in the frequency, duration and intensity of heat wave (HW) events between the 20th and 21st centuries, as simulated across Europe by different regional climate models (RCMs). Based on local climate and on calendar day thresholds, the HW indices studied allow a consistent analysis across Europe and throughout the year. Simulations for 2 emission scenarios of greenhouse gases and for 4 model chains, consisting of 3 RCMs, driven by 2 global climate models (GCMs), were considered. Over the 1961-1990 period, the models reproduce fairly well the spatial distribution of fixed exceedance thresholds of the daily maximum temperature (t(max)), although not the magnitude. On the other hand, they are qualitatively and quantitatively effective at reproducing the observed behaviour of the HW indices. Changes in t(max) and in the HW indices were then studied. Because of changes in both the mean and in the variability of t(max), the heat waves simulated for the future (2071-2100) across Europe are more frequent, more severe and they last longer. Their intensity and frequency increase by at least a factor of 3, with highly differing patterns, depending on season and location. Thus, the increase in heat wave days observed across large parts of Europe during the last 30 yr is expected to continue (winter) or even accelerate (summer) to the end of this century. The boundary conditions are the main source of uncertainty, whereas differences between RCMs driven by the same GCM are small.