Does Groundwater Dynamics Impact Heat Waves Simulations and Projections? Explicit Groundwater Representation in a State-of-the-art Regional Climate Model Ensemble over Europe

Recent record-breaking heat wave events around the world raised awareness and concerns that these extremes are more likely to happen due to global warming. Previous studies showed that coupling a 3D groundwater representation to the land surface of regional climate models impacts near-surface air temperatures (Keune et al., 2016; Barlage et al., 2021). However, the effect of groundwater dynamics on long-term simulations and climate projections remains to be explored. In order to advance our physical understanding, in climate time scale simulations, we applied the Terrestrial Systems Modelling Platform (TSMP, Shrestha et al., 2014), which closes the terrestrial water cycle and includes a 3D variably saturated groundwater flow representation. First, we evaluated the TSMP heat waves climatology forced by ERA-Interim (Furusho-Percot et al., 2019) in the context of a representative EURO-CORDEX Regional Climate Model ensemble, and an observational reference data (E-OBS). In our evaluation, TSMP shows consistently improved statistics with respect to observations in comparison to the RCM ensemble. Then, we used TSMP with 3D groundwater to downscale a CMIP5 Global Climate Model (MPI-ESM-LR, r1i1p1 experiment by the Max-Planck Institute) simulation over Europe and compared to RCM similar EURO-CORDEX downscaling experiments for the periods of 1976-2005 and 2006-2099 using the RCP2.6 and RCP8.5 scenarios. With the fully coupled TSMP simulations, we are able to address the following questions: How are future heat waves going to evolve in Europe under near-natural conditions? How does the evolution differ from the projections of climate models that do not consider groundwater dynamics explicitly? Future work will additionally consider groundwater use scenarios to identify the role of groundwater for drought and heat wave mitigation.