The impact of trees on thermal comfort at playgrounds in Melbourne, Australia

Abstract

Climate change causes warmer living conditions, especially in cities due to the urban heat island (UHI) effect. This increases the risk of heat stress, particularly among vulnerable groups like children. Trees have proven to be an effective way to mitigate heat stress, and the City of Melbourne has implemented this by their ‘Urban Forest Strategy’, developed to increase the number of trees in the city and improve the urban climate. The aim of this study was to investigate how trees impact the thermal comfort at playgrounds in Melbourne by examining i) how much shade was provided at the playgrounds, ii) how often heat stress could be experienced, and iii) how much more frequent it would be without trees. Three playgrounds were selected for the study and two scenarios were modeled during a warm summer day in the SOLWEIG model. One with the current number of trees and one where all the trees were removed. The results showed that the amount of shade was reduced once the trees were removed, which led to higher mean radiant temperatures (Tmrt) and thereby increased heat stress. The heat stress was generally higher in the afternoon, which implies that trees are especially important in the later part of the day. The playground located in the open area showed the highest heat stress, especially when the trees were removed, which implies that trees are more important in open areas than in dense areas, as the playground located in an area surrounded by high rise buildings showed no change of heat stress at midday for the two scenarios. However, the heat stress still increased during other parts of the day and trees should therefore not be excluded from densely built areas either. It was also found that the location of the trees is important to be able to provide shade at the right time of day. Two of the playgrounds had high shade cover in the afternoon, which resulted in significantly lower heat stress than at the third playground, which had lower shade cover. As the playgrounds might be more frequently visited in the afternoon, it could be concluded that it might be beneficial to plant more trees in the west. The result from this study can be used for planning more resilient and sustainable cities in the future.