© 2025 SURF
This paper presents five design prototypes for cool urban water environments developed in the 'Really cooling water bodies in cities' (REALCOOL) project. The REALCOOL prototypes address an urgent need: urban water bodies, such as ponds or canals, are often assumed to cool down their surroundings during days with heat stress, whereas recent research shows that this is not always the case and that urban water bodies may actually have warming effects too. There are, however, indications that shading, vaporising water, and proper ventilation can keep water bodies and their surroundings cooler. Yet, it is necessary to explore how these strategies can be optimally combined and how the resulting design guidelines can be communicated to design professionals. The REALCOOL prototypes communicate the spatial layout and biometeorological effects of such combinations and assist design decisions dealing with urban water environments. The micrometeorological simulations with Envimet showed that the prototypes led to local reductions on daytime PET from 1 °C to 7 °C, upon introducing shade. Water mist and fountains were also cooling solutions. The important role of ventilation was confirmed. The paper discusses and concludes about the use of the prototypes as tools for urban design practice.
Het Knowledge Mile Park (KMP), momenteel de drukste verkeersader van Amsterdam, wordt de komende jaren uitgebreid vergroend. Op diverse locaties langs de KMP werd steekproefsgewijs hittemetingen uitgevoerd om hittestress op te sporen, verkoelingscapaciteit van het aanwezige groen te meten en het thermisch comfort van de KMP voor de gebruiker te inventariseren. Er werd volgens het Cool Towns Heat Stress Measurement Protocol (Spanjar e.a., 2020) hittemetingenuitgevoerd met mobiele weerstations, infraroodcamera’s en vragenlijsten. Uitgevoerd op twee opeenvolgende dagdelen tussen 17.00 tot 20.00 uur. Dit vond plaats op 21 en 22 augustus 2023 toen de luchttemperatuur 23-25 °C bereikte. De resultaten geven het hitteverloop van een milde warme zomerdag weer. Uit de enquête afgenomen onder KMP-gebruikers blijkt dat meer dan de helft van de respondenten op zowel het Weesperplein als het Wibautpark het als een beetje warm of neutraal ervaren. De meetresultaten komen overeen met Europees hitteonderzoek (Spanjar e.a., 2022) en laat zien dat op locaties in de zon zoals op het stenige Weesperplein en het grasveld, mensen tussen 17.00 en 18.30 uur te maken hebben gehad met een sterke tot extreme hittestress condities (35 tot 45 °C PET, zie Grafiek 1). Op de drie andere locaties verminderen boomkronen de hittestress tot licht of niet aanwezig. Verharde locaties blootgesteld aan de zon warmen op en verminderen het thermisch comfort verder door de werking van infraroodstraling. De uitkomsten van de enquête maakt het belang van het goed reguleren van het thermisch comfort op de KMP zichtbaar.
Built environments are increasingly vulnerable to the impacts of climate change. Most European towns and cities have developed horizontally over time but are currently in the process of further densification. High-rise developments are being built within city boundaries at an unprecedented rate to accommodate a growing urban population. This densification contributes to the Urban Heat Island phenomenon and can increase the frequency and duration of extreme heat events locally. These new build-up areas, in common with historic city centres, consist mainly of solid surfaces often lacking open green urban spaces.The Intervention Catalogue is the third publication in a series produced by the Cool Towns project and has been designed as a resource for decision makers, urban planners, landscape architects, environmental consultants, elected members and anyone else considering how to mitigate heat stress and increase thermal comfort in urban areas. Technical information on the effectiveness of the full array of intervention types from trees to water features, shading sails to green walls, has been assessed for their heat stress mitigation properties, expressed in Physiological Equivalent Temperature (PET). The results shown in factsheets will help the process of making an informed, evidence based, choice so that the most appropriate intervention for the specific spatial situation can be identified.
In face of climate change and urbanization, the need for thermally comfortable outdoor urban spaces is increasing. In the design of the thermally comfortable urban spaces and decision making about interventions that enhance thermal comfort, scientists and professionals that work for cities use meteorological measurements and models. These measurements can be done by professional and accurate meteorological sensors, but also by simpler mobile instruments such as the easy-to-use Kestrel weather meters. In using these simple type of sensors, it is important to know what the performance of these sensors is for outdoor thermal comfort assessments and how they can be used by scientists and professionals in decision making about urban designs that enhance thermal comfort.To answer these questions, we carried out three experiments in the summer of 2020 in Amsterdam, in which we tested the 11 Kestrel 5400 heat stress sensors and assessed the performance of this equipment for thermal comfort studies. We concluded that Kestrel sensors can be used very well for assessing differences in air temperature and PET (Physiological Equivalent Temperature) between outdoor built environments. For both air temperature and PET, the RMSE between the 11 Kestrel sensors was 0.5 °C maximum when measuring the same conditions. However, Kestrel sensors that were placed in the sun without a wind vane mounted to the equipment showed large radiation errors. In this case, temperature differences up to 3.4 °C were observed compared to Kestrels that were shaded. The effect of a higher air temperature on the PET calculation is, however, surprisingly small. A sensitivity analysis showed that an increase of 3 °C in the air temperature results in a maximal PET reduction of 0.5 °C. We concluded that Kestrel sensors can very well be used for assessing differences between air temperatures and PET between two locations and assessing the thermal effects of urban designs, but care should be taken when air temperature measurements are carried out in the sun. We always recommend using the wind vanes to deviate from high radiant input orientations for the temperature sensor, and placing the stations next to each other at the beginning and at the end of the measurements to check whether the stations actually measure the same values. Any differences can be corrected afterwards.
Small urban water bodies, like ponds or canals, are often assumed to cool their surroundings during hot periods, when water bodies remain cooler than air during daytime. However, during the night they may be warmer. Sufficient fetch is required for thermal effects to reach a height of 1–2 m, relevant for humans. In the ‘Really cooling water bodies in cities’ (REALCOOL) project thermal effects of typical Dutch urban water bodies were explored, using ENVI-met 4.1.3. This model version enables users to specify intensity of turbulent mixing and light absorption of the water, offering improved water temperature simulations. Local thermal effects near individual water bodies were assessed as differences in air temperature and Physiological Equivalent Temperature (PET). The simulations suggest that local thermal effects of small water bodies can be considered negligible in design practice. Afternoon air temperatures in surrounding spaces were reduced by typically 0.2 °C and the maximum cooling effect was 0.6 °C. Typical PET reduction was 0.6 °C, with a maximum of 1.9 °C. Night-time warming effects are even smaller. However, the immediate surroundings of small water bodies can become cooler by means of shading from trees, fountains or water mists, and natural ventilation. Such interventions induce favorable changes in daytime PET.
Since it is insufficiently clear to urban planners in the Netherlands to what extent design measures can reduce heat stress and which urban spaces are most comfortable, this study evaluates the impact of shading, urban water, and urban green on the thermal comfort of urban spaces during hot summer afternoons. The methods used include field surveys, meteorological measurements, and assessment of the PET (physiological equivalent temperature). In total, 21 locations in Amsterdam (shaded and sunny locations in parks, streets, squares, and near water bodies) were investigated. Measurements show a reduction in PET of 12 to 22 °C in spaces shaded by trees and buildings compared to sunlit areas, while water bodies and grass reduce the PET up to 4 °C maximum compared to impervious areas. Differences in air temperature between the locations are generally small and it is concluded that shading, water and grass reduce the air temperature by roughly 1 °C. The surveys (n = 1928) indicate that especially shaded areas are perceived cooler and more comfortable than sunlit locations, whereas urban spaces near water or green spaces (grass) were not perceived as cooler or thermally more comfortable. The results of this study highlight the importance of shading in urban design to reduce heat stress. The paper also discusses the differences between meteorological observations and field surveys for planning and designing cool and comfortable urban spaces. Meteorological measurements provide measurable quantities which are especially useful for setting or meeting target values or guidelines in reducing urban heat in practice.
The liveability of cities worldwide is under threat by the predicted increase in intensity and frequency of heatwaves and the absence of a clear spatial overview of where action to address this. Heat stress impairs vital urban functions (Böcker and Thorsson 2014), hits the local economy (Evers et al. 2020), and brings risks for citizens’ health (Ebi et al. 2021). The ongoing densification of cities may escalate the negative consequences of heat, while rising climate adaptation ambitions require new pathways to (re)design public places for a warmer climate. Currently, policy makers and urban planners rely on remote sensing and modelling to identify potential heat stress locations, but thermal comfort models alone fail to consider socio-environmental vulnerabilities and are often not applicable in different countries (Elnabawi and Hamza 2020).In the Cool Towns Interreg project, researchers collaborated with municipalities and regions to model urban heat stress in nine North-Western European cities, to find vulnerabilities and to measure on the ground (see Spanjar et al. 2020 for methodology) the thermal comfort of residents and the effectiveness of implemented nature-based solutions. Using the Physiological Equivalent Temperature (PET) index, several meteorological scenarios were developed to show the urban areas under threat. The PET maps are complemented by heat vulnerability maps showing key social and environmental indicators. Coupled with local urban planning agendas, the maps allowed partner cities to prioritize neighbourhoods for further investigation. To this end, community amenities and slow traffic routes were mapped on top of the PET maps to identify potential focus areas.A comparative analysis of the collated maps indicates certain spatial typologies, where vital urban activities are often influenced by heat stress, such as shopping areas, mobility hubs, principal bicycle and pedestrian routes. This project has resulted in the development of a multi-level Thermal Comfort Assessment (TCA), highlighting locations where vulnerable user groups are exposed to high temperatures. Standardized for European cities, it is a powerful tool for policy makers and urban planners to strategically identify heat stress risks and prioritize locations for adapting to a changing climate using the appropriate nature-based solutions.
MULTIFILE
