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.
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Vijf studenten aan Hogeschool Van Hall Larenstein (VHL) hebben in 2019/2020 als onderdeel van de minor ‘Bomen en Stedelijke Omgeving’ onderzoek uitgevoerd naar het effect van groen/beplanting op de gevoelstemperatuur in 'bloemkoolwijken'. De opdrachtgever voor dit onderzoek was dr. ir. Jelle Hiemstra van Wageningen University & Research. Op het gebied van ENVI-met kregen zij begeleiding van dr. ir. Cor Jacobs van Wageningen University & Research, die hen hielp met het bouwen van het model en het berekenen van de temperatuur, luchtvochtigheid, windstromen en gevoelstemperatuur. De studenten werden begeleid door docent dr. Mart Vlam. Dit artikel is geschreven op basis van vragen die ex-redactielid Jozé ’t Hoen en redactielid Jaco Houweling de studenten hebben voorgelegd.
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As a consequence of climate change and urbanization, many cities will have to deal with more flooding and extreme heat stress. This paper presents a framework to maximize the effectiveness of Nature-Based Solutions (NBS) for flood risk reduction and thermal comfort enhancement. The framework involves an assessment of hazards with the use of models and field measurements. It also detects suitable implementation sites for NBS and quantifies their effectiveness for thermal comfort enhancement and flood risk reduction. The framework was applied in a densely urbanized study area, for which different small-scale urban NBS and their potential locations for implementation were assessed. The overall results show that the most effective performance in terms of flood mitigation and thermal comfort enhancement is likely achieved by applying a range of different measures at different locations. Therefore, the work presented here shows the potential of the framework to achieve an effective combination of measures and their locations, which was demonstrated on the case of the Sukhumvit area in Bangkok (Thailand). This can be particularly suitable for assessing and planning flood mitigation measures in combination with heat stress reduction.
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