Urban Heat: Causes, Consequences and What Municipalities Can Do

In short. Cities heat up more than their surroundings because sealed surfaces and dense development store heat and allow almost no evaporation. The consequences range from health impacts to overloaded infrastructure. Effective countermeasures are well known: shading, desealing, water and a heat action plan. The challenge lies less in the technology than in prioritisation and implementation across several departments.

Why this matters for your municipality. Heat is the extreme weather risk with the highest death toll in Germany. The Robert Koch Institute (RKI, Germany's federal public health institute) estimates around 3,100 heat-related deaths for 2023 and around 2,800 for 2024; for summer 2025 the RKI cites around 2,600 (as of: RKI, July 2026). Summer 2026 clearly exceeds all previous years: by calendar week 33, the RKI estimates around 15,800 heat-related deaths, and the estimate is still incomplete (as of: RKI, 27 August 2026). Those affected are mainly older people and people with pre-existing conditions, a group for which municipalities bear direct responsibility through care, social services and health.

Why is it hotter in the city than in the countryside?

The effect is called the urban heat island. Asphalt, concrete and roof surfaces absorb solar energy during the day and release it again at night. Where greenery and open ground are missing, evaporative cooling is also missing. Germany's Federal Environment Agency (UBA) describes that city centres can be several degrees warmer at night than the surrounding countryside. The night is often the decisive factor: if temperatures stay above 20 degrees Celsius (a tropical night), the body gets no recovery.

What are the concrete consequences of urban heat?

Three levels are affected. First, health: cardiovascular strain, dehydration, worsened outcomes for chronic illnesses. Second, infrastructure: heat stress for trees, strain on rail tracks and bridges, higher cooling loads in buildings. Third, social participation: daycare centres, schools, care homes and public swimming pools reach their limits. These consequences are distributed unevenly: the same city has cool districts and heavily burdened ones. A heat map shows exactly where.

What can municipalities effectively do?

The measures are proven and can be divided into two groups. Short-term and organisational: use the German Weather Service's (DWD) heat warning system, provide drinking water, adapt operating procedures in care facilities and daycare centres, and set up a heat action plan. Long-term and structural: shading through urban trees, desealing, light-coloured surfaces, building greening and water features. The greatest benefit comes from first identifying the hotspots and then targeting measures where high exposure and vulnerable use coincide.

The spokes of this topic. Creating a heat action plan (a guide from responsibilities to the warning chain) · Heat map and heat register (what they show, how they are created) · Urban heat islands (causes and countermeasures) · Heat protection for vulnerable groups (care, daycare, hospitals) · Shading, urban trees and cooling · Identifying heat hotspots.

The honest limitation. No single measure solves the problem. A tree only takes effect after years, desealing costs time and money, and a heat action plan only saves lives if it is actually put into action in an emergency. No finished list of measures can be promised from a distance: priorities depend on your data, your building stock and your population structure.

When KomAdapt is worthwhile. If you want a reliable picture of how your urban area is heating up and want to derive a well-founded order of priorities from it, the risk and exposure analysis by KomAdapt helps. It combines heat data with usage and vulnerable facilities, as was done for the heat maps for the town of Meinerzhagen. The result is not an abstract map but a traceable basis for your decisions.

_How many heat deaths are there in Germany per year?_ The number varies greatly with the summer. The RKI estimates around 3,100 for 2023, around 2,800 for 2024 and around 2,600 heat-related deaths for summer 2025. Summer 2026 is far outside the range: around 15,800 by calendar week 33 (as of: RKI, 27 August 2026). These are statistical estimates based on excess mortality. _What is the difference between heat and a heatwave?_ Heat generally refers to high temperatures. A heatwave is a multi-day phase of exceptionally high strain. The DWD works with the perceived temperature: it warns of strong heat stress from 32 degrees and extreme heat stress from 38 degrees. _Which measures work fastest?_ Organisational measures take effect immediately: translating DWD heat warnings into fixed procedures, providing drinking water, adjusting operating hours. Structural measures such as trees take years. It makes sense to start both in parallel. _Who is responsible within the administration?_ Heat is a cross-cutting task: environmental, urban and green space planning, the health and social welfare department, and department heads. A heat action plan sets out responsibilities.

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