Outdoor human thermal comfort in Melbourne's botanic gardens

Climate change is likely to increase the frequency of hotter days, which will affect the thermal comfort of visitors to botanic gardens and outdoor parks. Urban green space has previously been shown to reduce the perception of thermal discomfort under hot conditions. However, the overall cooling benefits of gardens in Australia are not well understood. In this study we aim to demonstrate the importance of landscape design for thermal comfort using the Royal Botanic Garden (RBG) in Melbourne as our case study. RBG Melbourne has a mixture of native and exotic plants, as well as a regular irrigation regime.

Data gathered during the Australian summer of 2013/2014 included visitor surveys and meteorological data. During that summer 2204 visitors were surveyed in the RBG Melbourne. In total 148 surveys were conducted in Chinese. This provides a unique understanding of how Chinese tourists perceive thermal comfort in Australia. Furthermore, a network of 11 automatic weather stations was established in the RBG Melbourne during the summer season (18 December 2013 to 26 March 2014).

The study included several periods of extremely hot weather when temperatures reached close to 45 °C. Preliminary analysis indicates that there are mean daytime temperature differences in the order of 2 °C between well-irrigated areas and unirrigated areas at the RBG Melbourne during very hot weather. This temperature difference could contribute substantially to visitors' relative comfort levels during hot days in summer.

Our study provides empirical evidence of the relative thermal comfort perception of visitors from different countries. The multiple nationalities of visitors and the diverse microclimates inside the garden offer novel insight into the roles of various factors that affect thermal comfort perception. Since the garden visitors are from different climate zones, they have different clothing behaviour. Therefore it is important to appreciate how cultural and ethnic differences in dress affect the thermal comfort of visitors in the garden. Moreover, the project compares the visitors' thermal comfort perception with weather measurements.

Understanding the variability of temperature and thermal comfort in the RBGs can assist in improving garden design, so that RBG management can prepare for future changes in climate. Our work can be used to inform garden landscape planning, and ultimately improve visitor comfort levels, especially during hot weather. Currently, microclimate and thermal comfort play a minor role in landscape and urban planning since planners frequently have little knowledge of urban climatology and human biometeorology. In light of the future rising temperature, it is essential to emphasise the role of parks and gardens in mitigating the urban heat island and promoting human thermal comfort.