What would a recent heatwave look like in a warmer world?

Storyline simulations of the July 2019 heatwave show strong and inhomogeneous temperature amplification compared to the global average warming signal.

How would a heatwave that we experienced in the recent past develop in a warmer climate? As part of the Innovation Pool SCENIC project (https://earthenvironment.helmholtz.de/changing-earth/innopool-projects/scenic/), scientists at IMKTRO and AWI have jointly developed a methodology to place the July 2019 heatwave into different climates. This is achieved by forcing a global climate model AWI-CM-1.1-MR to have the same jet stream position as in ERA5 reanalyses, but under global warming of, e.g., +4 Kelvin (K). Based on the global simulations, regional analogues of this heatwave were created by running the regional climate model ICON-CLM over a European (12 km) and ahigh resolution Central European (3 km) domain.

Figure 1. Daily maximum temperature on the 25th of July 2019 in present-day, +3K, and +4K climates (a,c,e) over Euope at 12 km horizontal resolution and (b,d,f) with a focus over Germany at 3 km horizontal resolution.

This method is known as a storyline approach and is becoming increasingly emergent in climate science (Shepherd, 2018). The study of Klimiuk et al. (2025) estimates that in some areas, the daily maximum temperatures could rise by up to 3 K per degree of global warming. This would mean that the maximum temperatures of 38°C in 2019 would translate into temperatures as high as 46°C if the same heatwave would occur in 2095 (based on the applied scenario of a +4 K world).

Moreover, they found that the temperature response in the hottest areas is limited: the hottest regions over France, which reached 41 °C on the 25th of July 2019, heated up only by about 2 K per degree of global warming. In this case, the maximum temperature would also reach 46 °C if this event occurred in 2095.

The summer of 2019 is just one of a sequence of hot and dry summers that were modelled within the SCENIC project. The period from 2018 to 2022 is available in pre-industrial, present-day, +2 K, +3 K, and +4 K climates. With this dataset, the impacts of global warming on hydrology, agriculture, health, and other branches can be estimated and communicated to stakeholders. One such study has already been conducted and shows the impact of global warming on crop yield (Martin et al., 2025). The results show that the timing and severity of a heatwave can have a much higher impact on crop yields than the mean warming level itself.

References

Shepherd, T. G., Boyd, E., Calel, R. A., Chapman, S. C., Dessai, S., Dima-West, I. M., Fowler, H. J., James, R., Maraun, D., Martius, O., Senior, C. A., Sobel, A. H., Stainforth, D. A., Tett, S. F. B., Trenberth, K. E., van den Hurk, B. J. J. M., Watkins, N. W., Wilby, R. L., and Zenghelis, D. A. (2018) Storylines: an alternative approach to representing uncertainty in physical aspects of climate change, Clim. Change, 151, 555–571, https://doi.org/10.1007/s10584-018-2317-9.

Klimiuk, T., Ludwig, P., Sanchez-Benitez, A., Goessling, H. F., Braesicke, P., and Pinto, J. G. (2025) The European summer heatwave of 2019 – a regional storyline perspective, Earth Syst. Dynam., 16, 239–255, https://doi.org/10.5194/esd-16-239-2025.

Anker Lucia Martin, L., Smerald, A., Kiese, R,, Klimiuk, T., Ludwig, P., Sanchéz-Benítez, A., Goessling, H., and Scheer, C. (2025) The Vulnerability of European Agricultural Areas to Anthesis Heat Stress Increases with Climate Change, Environmental Research: Food Systems 2 (2): 025002. https://doi.org/10.1088/2976-601X/adb03d.