A new heatwave sweeps across Europe: "We have buildings for a climate that no longer exists"

BarcelonaEurope is currently facing a new heatwave; the umpteenth of this exceptionally warm summer, which particularly affects France and the United Kingdom, where meteorological services have officially classified it as an extreme heat episode. In France, 80 departments are on orange alert for heatwaves, while in England, an advisory remains in place covering much of the south and centre of the country. The episode also brings very high temperatures across the Iberian Peninsula and other parts of Western Europe, although not all of these areas necessarily meet the official heatwave criteria of their respective meteorological services.

Mercury peaks are becoming increasingly common. But beyond meteorological alerts, this extreme heat also tests the capacity of our cities and buildings. "We are building buildings for a climate that no longer exists," asserts Pablo Martínez, architect and founder of the think tank Trescientosmil. He is one of the authors of the 'Atlas of heat vulnerability, developed in conjunction with the earth sciences department of the Barcelona Supercomputing Center - National Supercomputing Centre (BSC-CNS).

This is a visual tool that compiles up to 70 climate simulations to map out which cities in the country will suffer more heatwaves in the future, which will require more cooling, and which are least prepared to face climate change. All this, with a study horizon between the years 2000 and 2050. The conclusions paint an uninviting scenario. Across the analyzed municipalities, the number of days with heatwaves will triple on average by 2050 compared to the year 2000. At the same time, the need for cooling in homes will increase by 65%.

However, this does not mean that all cities suffer the same: the atlas shows significant territorial differences and focuses not only on rising temperatures, but also on the resources available to adapt to them. To understand why the cooling demand for homes will increase by 65%, we need to look at one of the most technical indicators in the atlas: cooling degree days (CDD). "It's not the average temperature, but how many degrees you deviate each day from the comfort temperature," explains Martínez. In this case, the reference temperature is 23 degrees. It is a common indicator in the construction sector, but not very intuitive for the general public. For this reason, the architect himself recommends focusing more on the percentage variation than on the absolute value.

The example of Europe, the clearest

The most important thing, however, is that these projections do not start from a single model. The climate data comes from the European project Impetus4Change and incorporate up to 70 global and regional climate models, run with large computing infrastructures. Martínez emphasizes that even though the models "roughly say" the magnitude of the increase, "they all point in the same direction." And that direction is clear: more heat and, above all, a sustained increase in temperatures.

What is happening this week in a large part of Europe is the irrefutable demonstration of this premise: today, temperatures can locally reach or exceed 37 °C in the warmest areas of southern England, while France can reach 40 °C in large areas and exceed them locally. In Catalonia, 40 °C will also be reached or exceeded in Ponent and the Ebro valley, a situation that will be repeated in the warmest areas of the interior of the country.

The origin of this situation is an area of very high atmospheric pressure, a kind of plug that prevents hot air from escaping and favors many sunny days and a progressive warming of the continent. This has allowed a very warm air mass to spread from the Iberian Peninsula towards France and the British Isles. Forecasts indicate that from Friday onwards, the heat will begin to lose strength in Western Europe, although it will move eastwards and could maintain very high temperatures over the weekend in Germany, the Alps, and other areas of Central Europe.

But the objective of this atlas is precisely to move away from the idea that temperature increases are temporary or seasonal episodes. What the projections show is a continuous trend towards a warmer climate. However, not all cities will face this future from the same starting point.

Inequalities in preparedness

The atlas allows these differences to be seen. The peninsular south concentrates the most important predicted increases in cooling needs, while the Catalan and Balearic coast appears among the areas where heat waves will increase the most. In fact, Catalonia, Baix Llobregat, and Garraf top the state ranking for the increase in heat waves. On the other hand, no Catalan city is among those that will experience the highest increases in cooling needs in the State, a ranking dominated by Andalusia and the peninsular interior.

However, vulnerability does not depend solely on how hot it will be. The tool also incorporates the quality of housing, urban green spaces, access to daily supplies, and residents' income. In other words, it tries to relate the climate threat to the real capacity of cities and their inhabitants to adapt to it. "If the city is better prepared, then it will be easier for it to adapt to the new situation," summarizes Martínez.

This is where one of the architect's main warnings appears. The problem is not just that it will be hotter, but that a large part of the current housing stock is not designed for these conditions. "Current building regulations are more concerned with protecting us from the cold than from the heat," he states. And he focuses on the Technical Building Code, which uses historical climate series from the period 1970-2000. "We are building for a climate that no longer exists," he insists.

According to Martínez, this forces us to look at climate change from an urban perspective. Three more degrees may seem like a relatively small variation when looking only at the thermometer, but when transferred to buildings, it can mean a much greater need for cooling and more hot days. "This leap has a brutal magnitude when we approach it from a territorial perspective," he summarizes.

The atlas, therefore, does not want to limit itself to pointing out which cities will be hotter. The intention is to show where this heat may coincide with worse housing, less green space, fewer services, or fewer economic resources to face the transformations. "There is a very big gap between the future that awaits us and how prepared we are to face this future," concludes Martínez. And this is, probably, the main warning that the tool leaves us with: climate change will not only arrive in the form of higher temperatures. It will also arrive in homes, streets, and the (unequal) capacity that each city will have to protect its inhabitants.