Present and future European heat wave magnitudes: climatologies, trends, and their associated uncertainties in GCM-RCM model chains

Abstract

Abstract. This study investigates present and future European heat wave magnitudes, represented by the Heat Wave Magnitude Index-daily (HWMId), for regional climate models (RCMs) and the driving global climate models (GCMs) over Europe. A subset of the large EURO-CORDEX ensemble is employed to study sources of uncertainties related to the choice of GCMs, RCMs, and their combinations. We initially compare the evaluation runs of the RCMs driven by ERA-interim reanalysis to E-OBS (observation-based estimates), finding that the RCMs can capture most of the observed spatial and temporal features of HWMId. With their higher resolution compared to GCMs, RCMs can reveal spatial features of HWMId associated with small-scale processes (e.g., orographic effects); moreover, RCMs represent large-scale features of HWMId satisfactorily (e.g., by reproducing the general pattern revealed by E-OBS with high values at western coastal regions and low values at the eastern part). Our results indicate a clear added value of the RCMs compared to the driving GCMs. Forced with the emission scenario RCP8.5, all the GCM and RCM simulations consistently project a rise in HWMId at an exponential rate. However, the climate change signals projected by the GCMs are generally attenuated when downscaled by the RCMs, with the spatial pattern also altered. The uncertainty in a simulated future change of heat wave magnitudes following global warming can be attributed almost equally to the difference in model physics (as represented by different RCMs) and to the driving data associated with different GCMs. Regarding the uncertainty associated with RCM choice, a major factor is the different representation of the orographic effects. No consistent spatial pattern in the ensemble spread associated with different GCMs is observed between the RCMs, suggesting GCM uncertainties are transformed by RCMs in a complex manner due to the nonlinear nature of model dynamics and physics. In summary, our results support the use of dynamical downscaling for deriving regional climate realization regarding heat wave magnitudes.

Record-breaking and unprecedented compound hot and dry summers in Europe under different emission scenarios

“…HWMId was successfully used to classify observed and future heat waves both globally (Zampieri et al 2016, and regionally (Russo et al 2015, Dosio 2017, Molina et al 2020, Lin et al 2022.…”

“…Although many studies exist analysing future projections for Europe of either droughts (Potopová et al 2018, Spinoni et al 2018, Toreti et al 2019, Hari et al 2020 or heatwaves (Molina et al 2020, Lin et al 2022, studies analysing future CHD events mainly focus on either the global scale (e.g. Liu et al 2021, Wu et al 2021, De Luca and Donat 2023, Tabari and Willems 2023, Tripathy et al 2023 or specific regions only, such as central Europe (Sedlmeier et al 2018, Zscheischler andFischer 2020).…”

Climatology and Trends in Concurrent Temperature Extremes in the Global Extratropics

“…We impose a minimum duration threshold of 4 days, again in line with previous work that often adopts thresholds of 3-5 days (e.g. Xu et al, 2016;Brown, 2022;Lin et al, 2022), and show here the results for clustering based on centroid distances below 1000 km. We further enforce a minimum areal extent of clustered temperature extremes of 2×10 5 km 2 .…”

“…display results for percentile thresholds of 90 (10) in Appendix A, as these have also often been adopted in the 100 literature (e.g. Peings et al, 2013;Lin et al, 2022 andHolmberg et al, 2023). The percentiles are applied to the temperature anomalies at each gridbox.…”

A satellite view of the exceptionally warm summer of 2022 over Europe

“…The mechanisms involved in feedbacks between these processes are still under debate, not only due to the remaining uncertainties within the theoretical framework but also due to the lack of suitable observations to support it (Miralles et al, 2014Seneviratne et al, 2021;Barriopedro et al, 2023). This means that there is a significant spread in the heatwave metrics that are provided by different global and regional models, even at higher spatial resolutions (Petrovic et al, 2024;Lin et al, 2022;Furusho-Percot et al, 2022;Molina et al, 2020;Hundhausen et al, 2023).…”