A climatological study of heat waves in Grenoble over the 21st century

We investigate heat waves (HWs) affecting the valley of Grenoble in a future climate. In this study, heat waves are defined as periods of at least 3 consecutive days of daily maximum and minimum temperature exceeding the 92nd historical percentile. This definition has been chosen to select HWs that might impact human health. Even though only the strongest HWs are potentialy harmful, the definition allows to identify a suficient number of events to perform a statistical study. The HWs are characterised by their duration, peak temperature and mean daily maximum temperature. Additionally, each HW is studied per year using a framework measuring heat wave number, duration, participating days, and the peak and mean magnitudes. The HW characteristics are calculated with the results of simulations from the regional climate model MAR. MAR was forced by reanalysis and by a global model for the entire 21st century. The uncertainty of future anthropogenic forcing is taken into account by analysing results for the shared socio-economic pathways SSP2 and SSP5. The simulations are evaluated against in-situ measurements in the past period. MAR captures well daily maximum and minimum temperatures as well as observed HWs. Under future climate conditions, the increase in very hot daily maximum and minimum temperatures is mainly due to the shift rather than the broadening of their probability density functions. Additionally, the HWs become more frequent and have a longer duration, higher peak temperature and mean daily maximum temperature. Finally, a sensitivity analysis to the HW de ning threshold is carried out.