How \u2018hot\u2019 is too hot? Evaluating acceptable outdoor thermal comfort ranges in an equatorial urban park

Su Li Heng,Winston T L Chow

doi:10.1007/s00484-019-01694-1

Su Li Heng, Winston T L Chow

Open Access

https://doi.org/10.1007/s00484-019-01694-1

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Abstract

Urban green spaces offer vital ecosystem services such as regulating elevated temperatures in cities. Less information exists, however, on how urban green spaces influence outdoor thermal comfort (OTC), which is dependent on people’s perceptions of the complex interactions amongst ambient humidity, wind and both air and radiant temperatures. In this study, we analysed an existing OTC dataset compiled within a large Singapore urban park and calibrated OTC thresholds for physiological equivalent temperatures (PET) by analysing PET against thermal perception survey responses from the park visitors (n = 1508). We examined OTC according to (i) neutral, (ii) acceptable and (iii) preferred temperatures, where respondents felt ‘comfortable’ outdoors in the park. We estimated that neutral temperature, when all respondents experience neither heat nor cold stress, is 26.2 °C; acceptable temperatures, when only slight heat or cold stress is experienced, range between 21.6 and 31.6 °C; and preferred (‘ideal’) temperature for all respondents is 24.2 °C. Respondents residing for more than 6 months in Singapore achieved thermal neutrality, suggesting that a greater degree of thermal adaptation likely developed during acclimatisation to local climate through a combination of physiological, behavioural and psychological circumstances. Comparisons with other OTC studies showed differences in synoptic climates are linked to variations in the magnitude and ranges of perceived PET. Lastly, respondents in this study perceived lower neutral and preferred temperatures compared to respondents surveyed over a variety of urban land use categories in another local study. The differences in neutral and preferred temperatures between studies suggest that lower park temperatures and different environmental attitudes influence perceived OTC.

Highlights

Urban greenery and outdoor thermal comfortUrban greenery, e.g. street trees, parks and rooftop gardens, offer important provisional, support, cultural and regulatory ecosystem services (Gómez-Baggethun et al 2013)
Neutral temperatures can be estimated by probit analysis of sensation votes (e.g. Spagnolo and de Dear 2003; Kántor et al 2016), most other studies estimate neutral temperatures from linear regression of mean thermal sensation vote (MTSV) vs. physiological equivalent temperatures (PET) (e.g. Lin 2009; Middel et al 2016; Krüger et al 2017)
We analyse an outdoor thermal comfort (OTC) dataset in a large Singapore urban park to estimate the ranges of perceived (i) neutral, (ii) acceptable, and (iii) preferred temperatures respondents felt was ‘comfortable.’ The findings enhance the results of a previous study (Chow et al 2016), which was based on this same dataset but did not examine aspects of rational heat based on the PET index

Summary

Introduction

E.g. street trees, parks and rooftop gardens, offer important provisional, support, cultural and regulatory ecosystem services (Gómez-Baggethun et al 2013). The latter service manifests through regulation of the urban heat island (UHI), a phenomenon where enhanced heat within cities is caused by the alterations to. Research on individual outdoor thermal comfort (OTC) occurs less compared to city-wide UHI impacts or its mitigation (Johansson et al 2014). This disparity exists despite acknowledgement amongst scientists and policymakers that achieving appropriate conditions for urban OTC is beneficial. These uncertainties arise from the understanding of what thermal comfort is, and from the array of methodological approaches to assess OTC in various contexts

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