Green infrastructure has the potential to cool urban environments and reduce the health burden due to heatwaves. This study develops a new method to quantify the benefits of urban heat mitigation technologies on human heat balance and population mortality. The Heat Health Impact (HHI) method is based on the state-of-the-art, multi-parameter model, Universal Thermal Climate Index (UTCI).

A proof-of-concept exercise applied the HHI method to Sydney, Australia (population = 5.7 million). All available weather stations (10) were selected for full spatial coverage of the Sydney region (12,367 km2), and average hourly UTCI was calculated from meteorological observations spanning the entire year 2017. In the baseline analysis, average daily UTCI values were calculated for each of the 10 observation sites, and then spatially interpolated across the entire Sydney region for Feb 9, 2017, a representative heatwave day for Sydney. Three different greening intervention scenarios were investigated, and daily average change in UTCI (ΔUTCI) was calculated under each by comparison with the baseline scenario; this ΔUTCI was named Urban Cooling Effect (UCE). We implemented a health impact assessment methodology to estimate the change in attributable mortality due to each greening scenario for the Sydney GMR population for the representative heatwave day. Urban greening infrastructure scenarios reduced daily average UTCI between −0.2 and −1.7 °C on the heatwave day, with the health impact assessment indicating heat attributable deaths reducing up to 11.7 per day across the Sydney GMR compared to the baseline scenario. Our results highlight the health benefits of greening infrastructure to cool urban environments.