Urban Forestry & Urban Greening 101 (2024) 128533
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Original article
Park thermal comfort and cooling mechanisms in present and future climate scenarios Maassoumeh Barghchi a,*, Bill Grace a , Nicole Edwards a , Julian Bolleter a , Paula Hooper a a
Australian Urban Design Research Centre (AUDRC), School of Design, The University of Western Australia, Clifton St, Nedlands, WA 6009, Australia
A R T I C L E I N F O
A B S T R A C T
Keywords: Climate change Diurnal cooling Perth WA Plant transpiration Shade provision Urban parks
Extreme heat is Australia’s most perilous natural hazard, and increasing urban temperatures due to climate change are a growing concern. Consequently, there is growing interest in developing nature-based solutions (i.e., greenery and vegetated surfaces) to cool urban areas. Appropriately designed urban parks are anticipated to be crucial for maintaining thermal comfort as temperatures rise. The two main diurnal cooling mechanisms of urban parks are shade provision and vegetation transpiration. However, limited studies have examined the cooling performance of vegetation through transpiration, especially in the southern hemisphere. This study addresses this gap by examining the microclimatic conditions, cooling benefits, and thermal performance of a typical neighbourhood park in Perth, Western Australia, with a focus on the cooling performance of vegetation through shade and transpiration. Present and future microclimates were modelled and simulated for average and hottest summer days based on 25 years of local weather data and projections for 2090 under the Representative Concentration Pathway (RCP) 8.5 scenario. The findings reveal that trees provided diurnal cooling benefits for park users by lowering the Universal Thermal Comfort Index (UTCI) by up to 17◦ C, with this benefit persisting in projected 2090 conditions. This cooling benefit was predominantly achieved through shade provision, with marginal contributions from transpiration. Additionally, on hot days, as leaf temperature exceeded 30◦ C, increased stomatal resistance led to reduced transpiration. Therefore, more attention must be paid to transpiration cooling limits due to stomatal closure during hot hours to improve cooling performance in park design. Moreover, comparing different plant species’ behaviour and adaptability on hot days is crucial, especially in future climatic conditions.
1. Introduction Climate change is increasing annual average temperatures and the number and duration of extreme heat events across Australia, with the 2011–2020 decade being the hottest on record (Shooshtarian et al., 2020). The Intergovernmental Panel on Climate Change (IPCC) warns of an ‘extremely challenging future’ for Australia, with significant disruptions to human and natural systems (IPCC, 2022). Extreme heat is now considered Australia’s most dangerous natural hazard, causing more deaths than all other natural threats combined (i.e., bushfires, cyclones, earthquakes, floods, and severe storms) (Zander et al., 2015). Urban heat and the associated Urban Heat Island (UHI) effect are predicted to amplify the heat-related impacts of climate change in urban areas. Increasing heat affects outdoor thermal comfort, which is crucial for using urban parks (Zhang et al., 2020). Therefore, maintaining comfortable outdoor conditions is critical for planners and policymakers
(Shooshtarian et al., 2020). Nature-based solutions, particularly vegetation, have been identified as a way to mitigate UHI effects, reduce heat intensity and improve thermal comfort [5]. Urban green spaces can regulate and cool the microclimate, directly enhancing the outdoor thermal environment and comfort levels [6]. The literature identifies two primary cooling benefits of urban parks: (1) the cooling effect within the park (Aram et al., 2019; Aram et al., 2020; Bowler et al., 2010; Morakinyo et al., 2017) and (2) the cooling effect in adjacent areas (Al-Gretawee et al., 2016; Lin et al., 2015; Yan et al., 2018). These benefits are influenced by factors such as vegetation type, local climate, biophysical conditions (water, soil, atmosphere) (Carter, 2011; Meili et al., 2021), and the park’s size, shape, configuration and orientation, which impact the duration of direct solar radiation and Mean Radiant Temperature (MRT) (Taleghani et al., 2015). [MRT is a measure of the average temperature of the surfaces surrounding a particular point and is a critical element affecting human
* Correspondence to: Australian Urban Design Research Centre (AUDRC), The University of Western Australia, Clifton St, Nedlands, WA 6009, Australia. E-mail address: maassoumeh.barghchi@uwa.edu.au (M. Barghchi). https://doi.org/10.1016/j.ufug.2024.128533 Received 17 June 2024; Received in revised form 28 August 2024; Accepted 30 September 2024 Available online 9 October 2024 1618-8667/© 2024 The Author(s). Published by Elsevier GmbH. This is an (http://creativecommons.org/licenses/by/4.0/).
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