June 2026 brought Vienna 39.7 degrees and records at 157 weather stations. Why cities heat up so much — and what Vienna, Graz and Linz are doing about it.
Illustration: AI-generated
On the night of 29 June, the temperature at the Jubiläumswarte in the west of Vienna never dropped below 27.3 degrees. That was the low, mind you: it got no cooler than that all night. According to GeoSphere Austria, the national weather service, it was the warmest night ever measured in Austria; the previous record of 26.9 degrees dated from 2 August 2017. At the end of June, the Hohe Warte weather station registered 39.7 degrees, beating two marks at once: Vienna's June record of 36.1 degrees from 1950 and the all-time annual record of 38.5 degrees from August 2013 (GeoSphere Austria, heat report of 1 July 2026).
The heatwave, which began on 18 June and only ended in the east of the country on 1 July, was — according to GeoSphere Austria's analysis — the most severe since measurements began in Bregenz, Innsbruck, Vienna and, on a par with 2015, Linz; in Vienna, the records stretch back to 1872. New June highs were set at 157 of GeoSphere's 277 weather stations, and 66 stations even recorded new all-time annual highs. Below 800 metres above sea level, depending on the region, there were ten to 14 consecutive hot days — days of at least 30 degrees. The summer of 2026 had only just begun, and it was already confronting Austria's cities with the question they have been trying to answer for years: how do you live in a city that no longer cools down?
A June for the record books
What the climatologists stress most is not so much any single peak reading as the duration. The strongest heatwaves in the provincial capitals now last, according to GeoSphere Austria, an average of around seven days longer than around 1960 — an increase of roughly 140 per cent. The margin by which the new records fell is unusual, too: on average, the June highs of 2026 exceeded the previous best marks by 1.4 degrees, and at 46 stations by two degrees or more. On the night of 29 June, 94 weather stations recorded a tropical night, in which the temperature never fell below 20 degrees (GeoSphere Austria, 1 July 2026).
The long-term trend points in the same direction. At Vienna's Hohe Warte, the 1961–1990 average was ten hot days a year; in 2024 there were 45 — a new record (GeoSphere Austria, Vienna climate review 2024, May 2025). How the warming is affecting the country as a whole, from glacier retreat to crop failures, is something we have compiled in our analysis of the consequences of climate change in Austria. For cities, however, there is an additional factor that has only an indirect connection to the global climate: they heat up more than their surroundings.
Why the city doesn't cool down
The difference can be read directly off the map in Vienna. In 2024, the Innere Stadt weather station in the city centre counted 52 hot days; the Hohe Warte, on the greener edge of the city, 45 (Vienna climate review 2024). Asphalt, concrete and dense construction store heat during the day and release it again at night, while the evaporation that soil and plants would provide is missing. Experts call this the urban heat island effect, and every additional square metre of sealed surface intensifies it.
This is precisely where Austria's structural problem lies. According to the monitoring of ÖROK, the Austrian spatial planning conference, an average of around 6.5 hectares of land per day were newly taken up between 2022 and 2025; on average, 52.8 per cent of the land taken up is sealed (ÖROK monitoring of land take and soil sealing, December 2025). Sealed ground cannot absorb water and cannot cool; it turns summer heat into a health risk.
Just how serious that risk is can be seen in the estimates of AGES, Austria's agency for health and food safety. For June to September 2024 it arrives at 989 heat-related deaths in Austria, for the same period of 2025 at 449. For June to August 2026 it now estimates 995, the highest figure for those three months since 2017 (AGES, climate change and heat, updated 2 October 2026). These are modelled estimates with a wide uncertainty range, not a count. Those most affected are elderly people, the chronically ill and those who cannot afford a cool home.
What Vienna is actually doing
Vienna has its own heat action plan, combining short-term protective measures for vulnerable groups with long-term urban redesign. Its most visible element is the Cool Zones (Coole Zonen): in 2026 there are 34 freely accessible, staffed spaces across 20 districts, among them libraries, pensioners' residences, the district offices in Währing and Brigittenau and premises of social organisations. They have been open since 1 June, two of them since 1 July (City of Vienna, press release of 28 May 2026); since the end of June they have also been marked on the city's online map.
Added to this is a water infrastructure reaching its largest scale yet in the summer of 2026: around 1,800 public drinking fountains, 123 misting showers and mist columns in parks, 100 street sprinklers and 75 mobile fountains with a spray function that travel from district to district under the name "Brunnhilde". For its urban redesign, Vienna relies on the "Raus aus dem Asphalt" (Out of the Asphalt) programme: according to the city, 344 projects have been carried out across all 23 districts since its launch around five years earlier, with 3,316 trees planted along streets alone. In total, the city says it plants up to 4,500 trees a year on average, and the Vienna city gardens department tends more than 500,000 urban trees (City of Vienna, press release of 25 June 2026).
"Green spaces cool the air by 3–6 degrees Celsius, and trees amplify this effect during heatwaves," writes the City of Vienna.
That more urban greenery not only cools but also creates habitat is demonstrated by the 15 "Wiener Wäldchen", densely planted mini-forests that the city lists in the same overview. The role such spaces play for insects, birds and the ecological balance is something we described in our piece on biodiversity in Vienna, Graz and Linz.
Graz and Linz follow suit
Graz has had its own heat action plan since 1 June 2025. It kicks in as soon as the province of Styria, under the Styrian heat protection plan, declares a pre-warning or warning level for the greater Graz area. Care homes, nurseries, hospitals and mobile care services then receive targeted heat warnings, and the city activates its own measures. As "cool rooms", the plan lists three air-conditioned branches of the city libraries and, in cooperation with the Catholic Church in Styria, ten churches in the city centre; drinking fountains are available at more than 150 locations (City of Graz, heat action plan, version 1.0 of 1 June 2025). The fact that Styria recorded an estimated 93 heat-related deaths in 2025 — the highest figure of any Austrian province, according to AGES — lends the plan added urgency.
Linz experienced June 2026 as a wake-up call. At the GeoSphere Austria station, 38.2 degrees on 28 June beat the previous Linz high of 37.6 degrees, and the city's own measuring network even showed around 39.3 degrees at the main railway station. The heatwave lasted 13 days, and at midnight many measuring points were still above 30 degrees, while green, well-ventilated districts cooled down considerably more (City of Linz, media service of 1 July 2026). The action programme of the Linz climate adaptation strategy provides for a heat emergency plan, additional drinking fountains in the areas with the highest heat risk and more space for trees along streets (City of Linz, adaptation strategy action programme 2023).
What actually works inside buildings
The most effective heat protection in the home is also the least spectacular: not letting the sun in at all. External shading such as window shutters, awnings or external blinds keeps out up to 80 per cent of solar radiation, according to Lower Austria's provincial energy advice service, and is around three times as effective as interior blinds or curtains, because the heat never gets into the room in the first place (Energy and Environment Agency of Lower Austria, guide to summer comfort at home, June 2025). In many flats, that makes an air conditioner unnecessary — along with its electricity costs and the waste heat it blows into the street. It also eases the strain on power grids, which are already under pressure from the energy appetite of AI data centres.
For hot weeks like the one in late June, a few basic rules have proven their worth:
- Keep windows closed during the day and shade them from the outside; ventilate at night and in the early morning, ideally with a cross-breeze through the flat
- Switch off electrical appliances rigorously — every watt of standby consumption is also a small heater
- Use fans strategically; they don't cool the air, but they speed up evaporation on the skin
- When renovating or building, plan external shading, light-coloured surfaces and roof or façade greening in from the start
In the long run, however, the heat resilience of cities will be decided not by the individual roller shutter but by land. Every hectare that is not sealed, every tree planted today that will cast shade in a few decades, lowers the temperature for everyone. June 2026 has shown how short the time for that is: the next heatwave isn't coming someday — it's coming next summer.
