Student research results - more thermal walks

One of our master students civil engineering student, Gianluca Belardo, has now finished his MSc thesis, expanding on the results from thermal walks. He also developed site specific recommendations for each of the locations tested and check their feasibility with the municipality Hengelo. The title is 'Urban Heat Stress Assessment in Hengelo Through Thermal Walks to Guide the Implementation of Green-Blue Infrastructure for Urban Cooling'. The summary is below, and the repository link to download the full thesis is here. An overview of the tested locations is in the image. 

"Since the 1940s, global temperatures have steadily increased as a result of climate change. At the same time, rapid urbanisation has driven cities to expand, replacing natural landscapes with built-up areas dominated by materials like concrete and asphalt. These surfaces absorb and retain heat, while the loss of vegetation reduces the natural cooling capacity of the environment. As urban areas grow denser and greener spaces become more limited, cities begin to experience significantly higher temperatures than their rural surroundings, a phenomenon known as the Urban Heat Island (UHI) effect. This rise in urban temperatures not only worsens environmental conditions but also poses growing risks to public health and overall quality of life.
This thesis explores how urban design interventions, specifically Green-Blue Infrastructure (GBI), can improve outdoor thermal comfort in city centres. The research focuses on Hengelo, a medium-sized city in the Netherlands that, like many European cities, is increasingly dealing with the consequences of extreme heat, yet lacks detailed microclimate data or clear strategies for site-specific interventions. While Hengelo has made some progress in implementing GBI, many public spaces remain exposed to heat stress, and decision-makers face challenges in balancing spatial constraints, public use, and climate adaptation goals.
To address these challenges, the thesis first evaluates the existing conditions in Hengelo’s urban centre and then proposes targeted GBI strategies to improve thermal comfort in its most heat-stressed areas. This begins with a comprehensive literature review, examining the UHI effect, thermal comfort theory, and the effectiveness of various GBI types in mitigating urban heat in different spatial contexts. The review also explores participatory and observational methods for assessing heat perception, laying the foundation for the fieldwork approach adopted in this thesis.
Building on insights from the literature, the methodology integrates multiple research approaches that shaped both the data collection and the analysis of findings. A spatial analysis was first conducted using the available urban heat maps for Hengelo, helping to identify priority areas that might benefit most from interventions. Due to the low spatial resolution of these maps, assumptions had to be made about which areas were most heat-stressed, based on available information on urban form, surface materials, and existing vegetation. To build on this preliminary assessment, the core of the field research involved thermal walks, a novel method in which participants walked through five different locations while environmental data was recorded and subjective thermal perceptions were gathered. Environmental conditions were measured using two Kestrel 5400 trackers. At each location, one tracker was placed at a reference point and the other at an intervention point to assess the cooling performance of the existing GBI. At the same time, participants at the intervention point completed a questionnaire covering comfort ratings, thermal sensation, and preferences for shade, wind, and cooling.
The results showed a strong correlation between dense green infrastructure and improved thermal comfort. The location with the most dense tree cover recorded a reduction in Physiological Equivalent Temperature (PET) of over 20°C between reference and intervention points and was consistently rated as the most comfortable by participants. Locations with partial vegetation, also showed moderate cooling effects and improved participant comfort. In contrast, blue infrastructure without shade, such as the pond and the fountain locations, produced limited physical relief. Tracker data even showed PET increases in some cases due to radiant heat from surrounding paving or water reflections, despite participants perceiving these areas as slightly cooler, likely due to the psychological effects of water.
After this analysis, a strategy was developed to improve the less effective locations analysed in the thermal walks and also for the most heat stressed areas that were analysed at an earlier stage. The study then included feedback from municipal representatives, who helped assess the feasibility of the proposed interventions. While some locations, such as the pond area, were deemed realistic for near-term implementation (adding climbing vegetation), all others locations posed challenges due to underground infrastructure and competing land uses. Additionally, the municipality emphasized the importance of maintaining visual openness and ecological balance, where new trees could disrupt existing plant life. As a result, the recommendations reflect not only environmental performance but also practical limitations. The discussion with the municipal representatives also sparked internal reflection within the municipality about whether long-term heat resilience should take precedence over occasional public uses in certain urban spaces.
Based on the findings, this thesis recommends a site-specific approach to urban cooling. Priority should be given to increasing shade through tree planting where feasible, combining green and blue infrastructure in areas with enough space, and using artificial shading (e.g. pergolas or vertical greenery) in more constrained locations. Overall, the research shows that evidence-based interventions, informed by local context, can support effective climate adaptation. Moreover the methodology applied here, specifically the use of thermal walks, builds on existing research and demonstrates their value in connecting environmental data with user experience. In doing so, this study contributes new, location-specific insights and helps further develop the practical application of thermal walks in urban heat research." 

Student research results - thermal walks Hengelo

Last May two thermal walks were conducted with participants in Hengelo to test five different locations where the municipality has implemented blue/green infrastructure. While some findings were in line with expectations, large trees with more shadow providing a more comfortable environment than small trees, the results on water fountains were more difficult to interpret. 

The summarized results: "dense-canopy trees were the most effective intervention, lowering Wet Bulb Globe Temperature (WBGT) by up to 5.3 °C and having the highest comfort ratings. Sparse-canopy trees also provided substantial cooling (up to 4.1 °C decrease in WBGT) and are more feasible to plant with their lower spatial requirements and easier to implement in narrower streets of Hengelo’s city centre. The green square presented moderate cooling and mostly positive thermal comfort ratings, although, its use is spatially and financially constrained. Water features were less effective, since the sensors at the water pond recorded consistent warming effects despite positive feedback from the participants, while the water fountain recorded measurable cooling, but had low perceived comfort, as it lacked shade and surrounding vegetation."  

You can read more details in the thesis by Katarzyna MartaOłdak, titled 'Evaluation of the Local Cooling Effect of Existing Green-Blue Infrastructure in Hengelo Through Thermal Walks', at the UTwente repository. 

What are thermal walks?

As developed at the University of Applied Sciences Amsterdam, "A thermal walk is a research method that is used to map out the heat measured and perceived in a particular area, and to obtain answers to questions such as: how heat-proof is a particular walking route in the city, a shopping street, a residential area, the area around a train station, or a market square? A thermal walk maps out which planning layouts are hottest, coolest, most pleasant, and most unpleasant. One of the determining factors is the perceived temperature. Is a location situated in direct sunlight or is it shaded? In addition to air temperature and perceived temperature, the thermal walk considers thermal perception, i.e., how is a particular location perceived in terms of heat? The psychological effect is another important factor in heat-proof spatial planning."

What this means in practice is that a researcher team uses both sensors and participants' experience to determine how heat is experienced in different areas. These results can be used to determine the performance of urban green infrastructure in terms of reducing the urban heat island effect. For the sensor part, two devices are used that register temperature, humidity, wind speed and direction, and importantly, the Wet Bulb Globe Temperature. The device in question we apply is the Kestrel 5400 heat stress tracker. 

 

For participants a questionnaire is held at each location to be tested. Questions relate to topics such as clothing worn, experienced comfort level, and desired changes in environment. At the same time, the sensors calibrate to each environment which takes some 10-15 minutes. If locations are within 2 km, up to 5 locations can be tested in an hour, making thermal walks a practically effective method for measuring the performance of urban green infrastructure. For warm days, the practice is now well established. It is of course crucial to ensure participants are not exposed to extreme heat so temperatures up to 25 degrees are preferred. What would be interesting is how effective this method is during colder days, and what would be an acceptable minimum temperature for thermal walks during winter. Our current students are testing thermal walks for heat in Hengelo, and we hope to test winter conditions as well. 

Results from an Urban Green Infrastructure Walk Shop during class

As last year, 3rd year students from the course Smart Solutions for Sustainable Cities were invited to do a walk shop where green infrastructure projects on campus are visited for inspiration, and subsequently design a green infrastructure solution. The main question centered again around performance of the design. 

The first question to answer is 'What is the main benefit you want to design green infrastructure for?' Students could choose from five themes: energy consumption, extreme temperatures, extreme precipitation, flood peaks, and CO2 sequestration. They had to choose one location they are familiar with. While most often locations on campus or in Enschede are selected, this year we also had a group designing for Almelo, and even a city in Mexico. 

Students next chose one type of green infrastructure to reach this benefit, and for the sake of performance, a sensor and measurement frequency to gather data that helps prove their infrastructure actually contributes to the benefit they want to achieve. You can see examples of their work below. Despite the short amount of time, the groups came up with actionable ideas for implementing green infrastructure at the locations.

Carbon sequestration:

 

 Energy consumption:

Flood peaks:

 

 Extreme temperatures:

 

 Extreme precipitation: