The current heatwave in Germany demonstrates vividly how strongly high temperatures now shape everyday life. This development is part of a larger trend: Europe is considered the continent warming fastest worldwide as a result of climate change, with noticeable consequences for Germany too.
The new Techem Germany Heat Atlas makes this development visible at city and federal-state level. It shows which regions are currently affected particularly severely by heat and where temperatures have risen most sharply in recent decades. The analysis is based on cooling degree days. These indicate how often and how intensely high temperatures create a need for cooling, making them a reliable indicator of heat exposure.
Germany’s hottest cities and districts in 2025
The analysis reveals a clear geographical concentration: many of the hottest cities in 2025 are in south-west Germany, with Baden-Württemberg, Rhineland-Palatinate and Hesse particularly affected.
Top 10 hottest cities and districts in 2025:
- Speyer (Rhineland-Palatinate)
- Heidelberg (Baden-Württemberg)
- Germersheim (Rhineland-Palatinate)
- Rhein-Pfalz district (Rhineland-Palatinate)
- Ludwigshafen am Rhein (Rhineland-Palatinate)
- Mannheim (Baden-Württemberg)
- Südliche Weinstraße (Rhineland-Palatinate)
- Frankfurt am Main (Hesse)
- Groß-Gerau (Hesse)
- Neustadt an der Weinstraße (Rhineland-Palatinate)
A clear pattern also emerges at federal-state level: south-west Germany in particular had the highest heat exposure. Saarland led in 2025 with around 44 cooling degree days, followed by Rhineland-Palatinate (38) and Baden-Württemberg (29). Hesse was also near the top, with around 26 cooling degree days. The national average was around 19 cooling degree days. States such as Bavaria and Saxony-Anhalt were approximately at this level, while northern regions such as Lower Saxony, Mecklenburg-Western Pomerania and Schleswig-Holstein were well below it.
Where heat has increased the most
While current heat exposure is concentrated regionally in the south-west, the long-term trend presents an even broader picture. It shows where heat exposure has risen particularly sharply over the past 45 years.
Top 10 cities and districts with the largest increase in heat (1980–2025):
- Speyer
- Heidelberg
- Rhein-Pfalz district
- Germersheim
- Mannheim
- Ludwigshafen am Rhein
- Frankfurt am Main
- Karlsruhe
- Rhein-Neckar district
- Groß-Gerau
One striking finding is that many cities which were particularly hot in 2025 are also among the regions where heat has increased most over the past 45 years.
There are also clear differences between the federal states in the rate at which heat exposure is changing. Berlin has recorded by far the largest increase, around 55 cooling degree days since 1980. Brandenburg (37) and Saxony (32) follow. Rhineland-Palatinate and Saarland also show significant increases. In Bavaria, by contrast, the increase is more moderate. Schleswig-Holstein has the smallest increase by comparison, at 4 cooling degree days. The state therefore also remains well below the national average of nearly 18 cooling degree days over the long term. Hamburg and Mecklenburg-Western Pomerania are also around this national average.
Heat is becoming a challenge for buildings
Rising temperatures are also fundamentally changing the demands placed on buildings. Longer periods of heat cause interiors to warm up more, cool down less at night and come under growing pressure in terms of thermal comfort. “Heat is increasingly becoming a central challenge in building operation,” says Matthias Hartmann, CEO of the Techem Group. “The crucial task is to make the effects transparent and use data to control buildings so that comfort and efficiency continue to be assured as temperatures rise.”
Modern building technologies can help improve the response to heat considerably. Heat pumps are becoming more important because, depending on the system, they can be used not only for heating but also for cooling. Combined with smart-metering solutions, they also make it transparent when and how energy is used for cooling, providing an important basis for efficient operation. Dynamic electricity tariffs create further financial opportunities: anyone who deliberately cools a building when electricity prices are low or even negative can reduce operating costs and use energy particularly efficiently. Sensor-based solutions such as Techem’s Multisensor Plus record temperature and indoor-climate data and enable targeted, data-based ventilation management.
Heat requires a rethink
Overall, dealing with heat is increasingly becoming a central task in building operation and requires technology, data and intelligent management to work together. For the housing industry, local authorities and building operators, this means that greater consideration must be given to heat when planning, equipping and operating buildings. Data-based analyses and intelligent solutions will play a decisive role.
Methodology
The Techem Heat Atlas uses cooling degree days (CDD) as the central indicator for describing heat exposure. A cooling degree day is recorded when the mean daily temperature is greater than or equal to a defined threshold. The cooling requirement for each day is determined as the difference from a threshold temperature. The source used sets the threshold at 24°C and the base temperature at 21°C. The stated monthly CDD values were aggregated into annual totals.
The analysis is based on data for NUTS 3 regions (districts and independent cities). Area-weighted averages for the respective regions were calculated for presentation at federal-state level in order to account for differences in their size.
Current heat exposure is presented using CDD values for 2025. Three-year averages were used to smooth the data when assessing the long-term trend since 1980.