How do you cool a city?

In the heart of Vienna’s First District, the hum of cooling pumps echoes through the basement of the Old Post building. The air here is cool, almost frosty, thanks to a network of silver metal pipes that snake through the underground space. A sign reads “Kaltwasser”, cold water, in white letters against a green background, with arrows indicating the direction of flow. Burkhard Hölzl, a remote cooling expert for Wien Energie, explains that this system provides seven-degree Celsius water, ensuring comfort even during the hottest days. As temperatures soar above 35 degrees Celsius, city dwellers seek refuge in shaded street corners, avoiding direct sunlight. This second heatwave of the summer has intensified, with records being broken across the region. On early August, 11 weather stations recorded temperatures of 40 degrees Celsius or higher, adding 63 new station records. Nighttime temperatures also reached unprecedented levels, marking the warmest night since record-keeping began. Urban areas feel the effects of extreme heat more acutely than rural regions, despite similar air temperatures. Concrete and asphalt absorb and radiate heat throughout the day, keeping urban environments warmer long after sunset, akin to functioning heaters. This phenomenon, known as the urban heat island effect, explains why nighttime temperatures remain high in cities. The number of tropical nights, defined as nights with minimum temperatures of at least 20 degrees Celsius, has increased significantly. This year, many capital cities recorded more such nights than the average between 1991 and 2020. For example, Linz had 14 tropical nights, Eisenstadt 17, and the Viennese inner city 34. At one of these stations, the lowest temperature recorded was 27.4 degrees Celsius, the coldest ever measured in the city center overnight. Even outside the city, the heat persists. In the market town of Hornstein in Burgenland, nighttime temperatures remained at 28.5 degrees Celsius, slightly warmer than in Vienna. As the heat continues, residents increasingly look for ways to stay comfortable indoors. One solution is external shading, such as roller shutters, awnings, or facade shades. These can help keep indoor spaces cooler, especially when combined with proper ventilation and window treatment. The city of Vienna promotes the installation of such measures in residential buildings, though approval from property management or homeowners is required. For those living in protected zones, additional permits from the building authority are necessary. These authorities assess whether the exterior appearance and uniformity of facades are preserved. While the government aims to make air conditioning easier to install, the environmental impact of these devices remains a concern. Although they provide relief indoors, their operation contributes to outdoor heat, creating a cycle that exacerbates the overall warming effect. To address this challenge, the government has agreed to simplify the process of approving air conditioners. By reducing bureaucratic hurdles, the goal is to make these systems more accessible. A draft law is expected to be available by autumn. However, even with these changes, the broader implications of widespread air conditioning usage on urban climate conditions remain a topic of ongoing discussion.