With climate change, heatwaves in Australia are set to become more frequent and severe (i.e. more common, hotter and lasting longer). Heatwaves, such as those that occurred in Brisbane in 2004, Melbourne in 2009 and Sydney in 2011, pose significant threats to human health as measured by increased heat-related illness and deaths. The health risk from heatwaves is not only a function of extreme weather, but also influenced by thermal performance of housing  and the heat sensitivity of occupants seeking shelter to reduce exposure during extreme heat.

Using building simulations, this study investigated the impacts of tree planting on reducing indoor heat risk in Australia's three largest cities, using weather data from recent heatwave events. Indoor thermal comfort and annual energy savings for space cooling were analysed. 

The initial results show that during the heatwave, the highest temperature inside the dwelling with maximum external tree shading may decrease by 4.5°C, with a reduction in the energy required for cooling of 24% compared to no tree shading. The use of tree planting to reduce heat-related health risk in poor performing housing is recommended.  It is also important to note, however, that in the short-term and without careful species selection and positioning of trees in relation to the house, there could also be a penalty with regard to increased energy required for heating purposes in winter. This penalty is expected to diminish over time with climate change, as the requirements for cooling energy increase and heating energy decrease.