The Techem Heat Atlas highlights hotspots in Germany—where heat poses a challenge inside buildings

Eschborn, June 22, 2026. The current heat wave in Germany vividly illustrates just how much high temperatures now shape everyday life. This development is part of a larger trend: Europe is considered the fastest warming continent in the world due to climate change—with noticeable consequences for Germany as well.

The new Techem Heat Atlas of Germany visualizes this development at the city and state levels, showing which regions are currently particularly affected by heat and where temperatures have risen most significantly over the past decades. The analysis is based on cooling degree days. These indicate how frequently and intensely high temperatures lead to a need for cooling and are thus a reliable indicator of heat stress.

Germany's Hottest Cities and Districts in 2025
The analysis reveals a clear geographic concentration: Many of the hottest cities in 2025 are located in southwestern Germany—Baden-Württemberg, Rhineland-Palatinate, and Hesse are particularly affected.

Top 10 Hottest Cities and Counties in 2025:

1. Speyer (Rhineland-Palatinate)
2. Heidelberg (Baden-Württemberg)
3. Germersheim (Rhineland-Palatinate)
4. Rhein-Pfalz District (Rhineland-Palatinate)
5. Ludwigshafen am Rhein (Rhineland-Palatinate)
6. Mannheim (Baden-Württemberg)
7.  Southern Wine Route (Rhineland-Palatinate)
8. Frankfurt am Main (Hesse)
9. Groß-Gerau (Hesse)
10. Neustadt an der Weinstraße (Rhineland-Palatinate)

A clear pattern also emerges at the state level: Southwest Germany, in particular, experienced the highest heat stress. In 2025, Saarland topped the list with about 44 cooling degree-days, followed by Rhineland-Palatinate (38) and Baden-Württemberg (29). Hesse also ranked high on the list with about 26 cooling degree-days. The national average was around 19 cooling degree days. States such as Bavaria and Saxony-Anhalt were roughly at this level, while northern regions such as Lower Saxony, Mecklenburg-Western Pomerania, and Schleswig-Holstein were significantly below it.

This is where the heat has increased the most
While the current heat stress is concentrated regionally in the southwest, the long-term trend reveals an even broader picture of these dynamics. This makes it clear where heat stress has increased particularly sharply over the past 45 years.

Top 10 Cities and Counties with the Sharpest Rise in Temperature (1980–2025):

1. Speyer
2. Heidelberg
3. Rhein-Pfalz County
4. Germersheim
5. Mannheim
6. Ludwigshafen am Rhein
7.  Frankfurt am Main
8. Karlsruhe
9. Rhein-Neckar District
10. Groß-Gerau

What stands out is that many cities that were particularly hot in 2025 are also among the regions that have experienced the sharpest rise in heat over the past 45 years.

A comparison of the federal states also reveals significant differences in the rate of increase in heat stress: Berlin has seen by far the sharpest rise, with an increase of about 55 cooling degree days since 1980. It is followed by Brandenburg (37) and Saxony (32). Rhineland-Palatinate and Saarland also show significantly rising values. In Bavaria, by contrast, the increase is more moderate. Schleswig-Holstein has recorded the comparatively smallest increase, at 4 cooling degree days. This means that, even in the long-term trend, the state remains well below the national average of just under 18 cooling degree days. Hamburg and Mecklenburg-Western Pomerania are also at this national average level.

Heat Is Becoming a Challenge for Buildings
As temperatures rise, the demands placed on buildings are also changing fundamentally. Longer heat waves cause indoor spaces to heat up more, cool down less at night, and put increasing pressure on thermal comfort. “Heat is increasingly becoming a key challenge in building operations,” says Matthias Hartmann, CEO of the Techem Group. “It is crucial to make the effects transparent and to regulate buildings based on data in such a way that comfort and efficiency remain guaranteed even as temperatures rise.”

Modern building technologies can help significantly improve heat management: Heat pumps are becoming increasingly important because they can be used not only for heating but also—depending on the system—for cooling. In combination with smart metering solutions, they also provide transparency regarding when and how energy is used for cooling—an important foundation for efficient operation.  At the same time, dynamic electricity rates open up additional economic potential: By cooling a building specifically when electricity prices are low or even negative, operators can reduce operating costs and use energy particularly efficiently. Sensor-based solutions such as Techem’s Multisensor Plus collect temperature and indoor climate data and enable targeted, data-driven ventilation management.

Heat Calls for a New Approach
Overall, it is clear that managing heat is increasingly becoming a key task in building operations and requires a combination of technology, data, and intelligent management. For the housing industry, municipalities, and building operators, this means that heat must be given greater consideration in the planning, design, and operation of buildings. Data-driven analyses and intelligent solutions will play a crucial role in this process.

Image caption: The new Techem Heat Atlas of Germany illustrates this trend at the city and state levels, showing which regions are currently particularly affected by heat and where temperatures have risen the most significantly in recent decades (Image source: Techem).

Methodology
For the Techem Heat Atlas, cooling degree days (CDD) were used as the key indicator to describe heat stress. A cooling degree day is counted whenever the daily average temperature is greater than or equal to a defined threshold value. The cooling demand for each day is determined as the difference from a threshold temperature. The source used (agri4cast.jrc.ec.europa.eu) employs 24°C as the threshold value and 21°C as the limit temperature. The monthly CDD values provided by agri4cast were aggregated into annual totals.

The analysis is based on data from the NUTS 3 regions (counties and city districts). To present the data at the federal state level, area-weighted averages for the respective regions were calculated to account for the regions’ sizes.

The current heat stress is presented based on the CDD values for the year 2025. To assess the long-term trend since 1980, the data was smoothed using three-year averages.