Comment on esd-2022-53

Abstract

Due to climate change, years with positive temperature anomalies are becoming more frequent in Europe, requiringhigh-resolution climate data to plan for climate change mitigation and adaptation. However, many regional climate models(RCMs) simplify the representation of groundwater processes, leading to biases in simulated extreme heat events. Here, westudy the characteristics of summer heat events in a unique dataset from the regional Terrestrial Systems Modeling Platform(TSMP) simulations, compared to an ensemble of EURO-CORDEX climate change scenario control simulations, for the historicaltime period 1976–2005. Our results show that in TSMP, the impact of groundwater coupling on the frequency of hot summer days depends on theconsidered time period and the region, associated with respective evaporative regime. An increasing trend of the frequencyof hot summer days averaged across Europe is the lowest in TSMP compared to the other RCMs considered. Groundwatercoupling has a systematic effect on the duration and intensity of heat events: summer heat events with long duration and highintensity are less frequent in TSMP compared to the CORDEX ensemble. In particular, extended heat events with a durationexceeding 6 days, i.e. heat waves, occur on average in Europe about 1.5–8 times less often in TSMP, while single-day heatevents happen slightly more often in TSMP compared to the CORDEX ensemble. The frequency of high-intensity heat wavesin TSMP is up to 12 times lower on average in Europe compared to the CORDEX ensemble. Thus, an explicit groundwaterrepresentation in RCMs may lead to rarer and weaker heat waves in Europe also in climate projections. The findings of thiswork indicate an existing discrepancy in the ensemble of EURO-CORDEX climate change scenario control simulations andemphasize the importance of groundwater representation in RCMs.