Seasonal and diurnal surface temperatures of urban landscape elements

In the context of the Urban Heat Island effect, landscape professionals need practical guidance to design for managing surface urban heat. The apparent surface temperatures of samples of 19 hard and soft landscape elements (LEs) found in Perth (Australia) were measured. Thermal images of LE samples on an oval were taken at a 1 m height. The study was conducted in two phases. Phase 1 LE surface temperatures relative to ambient (∆T) were measured over one day in all four seasons. LEs were ranked by average ∆T, and maintained a similar order across seasons, with summer LEs the hottest. Some LEs were 30–44 ◦C above ambient in spring and autumn, so these seasons are also significant. Phase 2 repeated the summer test, but used only 14 larger LEs, which were well-coupled to the ground, i.e. more representative of in situ LEs. ∆T values were averaged over daytime and evening periods. Larger LEs were generally hotter than corresponding smaller LEs, with the effect more evident for heavier, denser LEs in the evenings. Future tests should be performed as per phase 2. Averaged measured values of grey pavers were the hottest, whilst ground-cover plants were the coolest. In the evening, grey pavers were also the hottest, whilst decking, soil and turf grass were the coolest. This data will help landscape professionals to assess and compare the thermal performance of different landscape designs, particularly when considering the time of use.