Dortmund is a major city in Germany’s Ruhr region, with roughly 586,000 inhabitants (2021) in a 280.7 km² city surface area. Its dense infrastructure and steadily increasing summer temperatures raise concerns about its vulnerability to heatwaves. Although the highest temperatures recorded so far are not considered critical, in 2018, Dortmund experienced 23 hot days in a row (with daily maxima above ~30 °C) in a city with a summer average of 17.9 °C, and since then, meteorological records show a progressive increase in temperature.
In an endeavour to stay ahead of potential emergencies and anticipate the effects of extreme heat, the city developed a Heat Action plan as part of the city’s first Climate Adaptation Plan. In doing so, they found that they lacked detailed, local data to support the plan’s implementation. Consequently, Dortmund’s municipality – through a joint, collaborative action bringing together different departments and scientific partners –started its heat management strategy by establishing the status quo, identifying the city’s hotspot and understanding where the vulnerable citizens reside. The data was collected through an innovative sensor technology, making it possible to identify and address urban heat islands.
Dortmund’s Heat Action Strategy
Carolin Ondera, Environmental Officer of the city of Dortmund, explained how the city is addressing heatwaves through a data-driven strategy developed following a climate adaptation planning process, started in 2021, updating the broader Integrated Climate Action Plan. The city’s Heat Action Plan was developed in recognition of the need for cross-cutting partnerships, such as the connection with doctors and pharmacies, key to reaching people and spreading measures to cope with heatwaves.
In 2023, Dortmund municipality went further with its Heat Action Plan’s data collection strategy by including two projects, both founded through the ICLEI Action Fund 2.0, in partnership with Google.org.
The first project, CATCH4D - Climate Adaptation through Thermographic Campaign and Heatmapping (June 2023 to May 2025), utilised thermal imaging flights to create a comprehensive three-dimensional thermographic model of the entire city of Dortmund. This imaging was specifically conducted in winter to identify issues with energy efficiency and heat leakage in buildgins, such as problems with roofs, facades, or window insulation. Crucially, the data collected from the CATCH4D project was then employed to identify urban heat islands and help pinpoint the cooler, shady areas suitable for citizens in times of heat.[AC1]
The second core project, Data2Resilience (June 2023 – July 2025), established a dense biometeorological measurement network of 70 sensors across the city. These sensors collect temperature and humidity data every half an hour, focusing on parameters that affect human thermal comfort. This provides real-time, local climate data essential for developing targeted heat protection strategies.
The collection of data from the sensors enables Dortmund to integrate heat prevention effectively into its planning and Heat Action Plan. The thermal data from CATCH4D is then used by the city to offer free consultation services to homeowners on renovations needed to comply with building regulations and improve energy efficiency. The sensor data also feeds into a public dashboard, designed for integration into the Smart City dashboard, making real-time thermal information publicly accessible and supporting further applications.
© Vanessa Reinhart (2024, LinkedIn): D2R sensor network
© Vanessa Reinhart (2025, LinkedIn): D2R heatmapping dashboard
Projects’ partners and stakeholders
The projects rely heavily on collaboration with scientific and academic partners such as the Ruhr-Universität Bochum, Leibniz Universität Hannover and NTNU (Norwegian University of Science and Technology). These partners were crucial for providing the necessary scientific expertise, personnel, and resources to implement and host the network, as well as for processing the complex data.
Internally to the City of Dortmund, the initiative involves multiple departments. This includes the Housing department, which has been heavily involved in the buildings’ heat mapping and subsequent retrofitting suggestions. Another active department was the Smart City team, in charge of managing the sensor network and covering maintenance costs until 2027.
Citizens were engaged through participatory workshops like the "Klimakomfort-Labor" events involving the city’s Environmental, Health, and Social offices, as well as neighbourhood walks where citizens were made aware of the city’s hotspots. Many of them showed great interest in how to access funding and building renovation advice.
Main challenges in addressing heatwaves
One of the early challenges faced by Dortmund’s heat adaptation initiatives was achieving internal and public buy-in. Because the city has not yet experienced extremely severe or prolonged heatwaves compared to southern European regions, many citizens initially questioned the urgency of implementing heat adaptation measures. This scepticism extended to some local actors who perceived the risks as abstract or distant.
To address this, the project teams placed a strong emphasis on communication and awareness-raising, using the data from the sensor network and thermographic campaigns to make the impacts of heat visible and relatable. Demonstrating local evidence of urban heat islands and temperature variations across neighbourhoods helped shift perceptions and build support for proactive adaptation.[AC2]
Another significant challenge is related to data governance and public trust. Especially during the CATCH4D project, concerns emerged among residents that the thermal imaging data could be used by the municipality to identify and enforce building renovation requirements.
To safeguard trust and ensure compliance with data protection standards, the scientific partner took responsibility for managing and processing the raw thermal imagery, while the city received the processed data. This separation of responsibilities ensures transparency, protects privacy, and reinforces the message that the project aims to inform and support citizens, not impose obligations .
Ensuring long-term resource continuity is also a vital challenge. The Smart City team, which manages the Data2Resilience sensor network, is currently funded to maintain operations only until 2027. While this provides a medium-term horizon, there remains uncertainty about who will sustain the network and integrate its data beyond that point. The city is exploring potential partnerships and funding sources to secure the long-term future of the system. Maintaining continuity will be essential to preserve the value of the dataset, enable trend analysis, and ensure that the data-driven tools continue to inform Dortmund’s climate resilience strategy over the coming decade.
Lessons learnt and next steps
Through these heat-related projects, the city of Dortmund understood the value of collaborating with scientific partners as highly beneficial for municipalities’ climate adaptation initiatives. Scientific institutions bring critical resources that city administrations may not possess internally, including specialised research personnel, advanced analytical tools, and the capacity to process and interpret datasets.
The involvement of academic partners enabled the effective deployment of the Data2Resilience sensor network and the analysis of thermal imaging data from the CATCH4D project. These partnerships enhanced the technical quality of the projects, allowed the city to leverage evidence-based insights for informed decision-making, and provided a solution to alleviate public apprehensions about data privacy.
Community engagement has been proven to be most effective when it combines interactive, participatory activities with concrete, actionable information. In Dortmund, initiatives like thermal walks allowed residents to visualise local heat risks tangibly. Guidance on practical measures, such as available funding for building renovations or strategies for creating cooler outdoor spaces, helped translate awareness into action. Peer-to-peer exchange among citizens who have undertaken heat protection measures with those who still have not has been highlighted as a key catalyst.
As for the next steps ahead, the city is currently working on integrating the interactive thermal comfort dashboard into the existing city dashboard to ensure its usability for both general citizens and technical experts. They are looking to ensure the long-term availability of the Smart City dashboard beyond 2027 through strategic partnerships.
Replicability and key takeaways
For other cities, the suggestion is to start by establishing a clear need for heat adaptation measures, then leveraging scientific knowledge from partners, to then finally embed projects within a broader Climate Adaptation Strategy driven by cross-departmental collaborations.
Cities looking to strengthen their heat resilience strategies should start by partnering with scientific institutions and take advantage of the great human and knowledge capital at their disposal.
Dortmund is part of the Cities Refresh campaign, creating lively and safe places for all.
Dortmund' Refresh
Solutions to address heatwaves: Data2Resilience sensor network and CATCH4D thermal imaging
Maximum temperature reached during extreme heat events: 34°C (August 2025 heatwave)
- Urban Design and Technology
- CATCH4D Thermal Imaging: First comprehensive three-dimensional thermographic model of the city of Dortmund to analyse building energy efficiency and urban heat islands.
- Data2Resilience Biometeorological Measurement Network: A network of 70 sensors in the city that measure temperature and humidity every half hour.
Expected results with the solutions implemented:
- Providing the city with highly resolved climate data and tools for targeted heat prevention to be included in urban planning.
- Using thermal data to identify urban heat islands and cool/shady locations, to then share the information with citizens.
- Incentivising and advising homeowners on measures to increase energy efficiency and renovate buildings.
Covenant Figures
Signatory to the Covenant of Mayors since: 2009
Emission reduction ambitions:
- Overall CO2 emission reduction target: Climate neutrality by 2035
- % GHG emissions reductions by 2030: Climate neutrality by 2035 (council decision), corresponding to a GHG emission reduction of approximately 88.9 % in 2030. Due to its status as a Mission City and the pending official receipt of the EU Mission label, this goal will be officially adjusted to climate neutrality by 2030.
- % GHG emissions reductions by 2050: 100%
City Awards
- EU Mission City (100 Climate-Neutral and Smart Cities)
Related links
Financing the project
Budget:
- CATCH4D: about 975,000 EUR
- Data2Resilience (RUB + LUH): about 1 million EUR
Sources of funding (rough breakdown):
Both projects received funding from Google.org, the non-profit arm of Google, as part of the ICLEI Action Fund 2.0 competition.The Smart City team at the City of Dortmund is expected to cover the maintenance costs for the sensor network until 2027.