Evaluating the May 2026 heatwave with storyline simulations of DestinE's Climate Digital Twin

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Evaluating the May 2026 heatwave with storyline simulations of DestinE’s Climate Digital Twin

24 June 2026

© KASUEMA SALAE – stock.adobe.com.

May 2026 was the world’s second-warmest May on record according to the Copernicus Climate Change Service (C3S). Using a ‘Storyline’ simulation approach, Destination Earth’s Climate Change Adaptation Digital Twin (Climate DT) was used to explore how this heatwave would unfold under different climate conditions. The simulations showed that in warmer climate scenarios, the heatwave becomes more intense, lasts longer and affects a larger area.

Storyline simulations of the Climate DT allow to replay observed extreme weather events under different climate scenarios. Each scenario represents a different ‘storyline’ for how the same event could unfold: in the cooler climate of the 1950s, in today’s climate, and in a future scenario with +2 °C warming.

Within the European Commission’s DestinE initiative, scientists working on the Climate DT used this storylines approach to explore how the May 2026 heatwave would look like under these different climate scenarios. The Climate DT is implemented through a partnership led by CSC – IT Center for Science in close collaboration with ECMWF, bringing together climate research institutions, supercomputing centres, national meteorological services, and academic partners from across Europe. The simulations show that the same weather pattern would have produced a heatwave in all three scenarios. However in the future warmer scenario the heatwave becomes hotter, lasts longer, and affects a larger area of Europe.

Figure 1 shows how the heatwave would unfold under the three different climate scenarios. The top three maps show the number of days that the May heatwave would last for in the three different climate scenarios. A heatwave is defined a maximum daily temperature exceeding the 98th percentile of the 1961 – 1990 reference period and exceeding more than 28 °C for 3 days or more. The bottom panel of the figure shows the maximum temperature that would be reached over Europe during the heatwave under the three different climate scenarios. While it is clear that this weather pattern would have lead to a heatwave in a cooler climate, an increase in intensity, spatial, and temporal extent of the heatwave can be seen, while the maximum temperature over Europe is seen to increase by 4°C from the coolest to warmest climate scenario. Credit: Alfred Wegener Institut (AWI).

Figure 2 shows he Universal Thermal Climate Index (UTCI) for 27th May 2026 in the three climate scenarios. The UTCI is a thermal comfort metric that combines various variables such as temperature, humidity, and wind to assess how the human body responds to different thermal conditions. In Figure 2, the spatial extent of the ‘very strong heat stress’ category is seen to greatly extend across Western Europe, covering larger areas of Portugal, Spain, France and Italy. This level of stress indicates a significant risk of heat exhaustion and severe discomfort. Credit: Alfred Wegener Institut (AWI).

Spectral km-scale nudging technique

The storyline simulations of the Climate DT are produced by a team led by scientists from the Alfred Wegener Institute (AWI), the Barcelona Supercomputing Center (BSC), CNR-ISAC, and CSC-IT Center for Science. They use a technique called spectral nudging, in which the simulations are constrained to follow the observed large-scale atmospheric circulation – in different climate conditions – while allowing regional and near-surface processes to evolve within the simulation. This large-scale atmospheric state is taken from ERA5, ECMWF’s global reanalysis produced for the Copernicus Climate Change Service, which combines observations and modelling to provide a consistent reconstruction of past weather. This allows the simulations to retain the observed weather situation that led to the extreme events – in this case the May 2026 heatwave – while exploring how its impacts change under cooler, present-day and warmer climate conditions.

Spectral nudging uses reference data, such as observations or the ERA5 reanalysis produced for the Copernicus Climate Change Service, to keep the large-scale atmospheric evolution in the simulation close to the observed event, while allowing local weather and climate processes to evolve. Credit: Amal John and Helge Goessling, AWI

At kilometre-scale resolution and with hourly output, this approach provides information at a level of detail that is much closer to the scales at which impacts of extreme events are felt. It can therefore support the analysis of locally relevant aspects of an event, such as heat stress, rainfall, wind or coastal conditions, while keeping the analysis anchored in the observed weather situation.

Learn more about the Climate DT storyline simulations in the Climate DT user guide.

Access the data via the DestinE platform https://platform.destine.eu/

The Climate DT, procured by ECMWF in the framework of Destination Earth is developed through a contract led by CSC-IT Center for Science and includes Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), Barcelona Supercomputing Center (BSC), Max Planck Institute for Meteorology (MPI-M), Institute of Atmospheric Sciences and Climate (CNR-ISAC), German Climate Computing Centre (DKRZ), National Meteorological Service of Germany (DWD), Finnish Meteorological Institute (FMI), Hewlett Packard Enterprise (HPE), Polytechnic University of Turin (POLITO), Helmholtz Centre for Environmental Research (UFZ) and University of Helsinki (UH), in close collaboration with ECMWF.

Destination Earth is a European Union funded initiative launched in 2022, with the aim to build a digital replica of the Earth system by 2030. The initiative is being jointly implemented under the leadership of DG CNECT, by three entrusted entities: the European Centre for Medium-Range Weather Forecasts (ECMWF) responsible for the creation of the first two ‘digital twins’ and the ‘Digital Twin Engine’, the European Space Agency (ESA) responsible for building the ‘Core Service Platform’, and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), responsible for the creation of the ‘Data Lake’.

We acknowledge the EuroHPC Joint Undertaking for awarding DestinE  strategic access to the EuroHPC supercomputers LUMI, hosted by CSC (Finland) and the LUMI consortium, Marenostrum5, hosted by BSC (Spain) Leonardo, hosted by Cineca (Italy) and MeluXina, hosted by LuxProvide (Luxembourg) through a EuroHPC Special Access call. 

More information about Destination Earth is on the Destination Earth website and the EU Commission website.

Evaluating the May 2026 heatwave with storyline simulations of DestinE’s Climate Digital Twin

Spectral km-scale nudging technique

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