Urban trees and people’s yards mitigate extreme heat in western Adelaide: final summary report

Extreme heat in cities poses a significant threat to public health and urban livability. More frequent, prolonged and intense heatwaves are predicted under future climate change, posing unprecedented challenges for Australia’s urban systems. Urban green infrastructure, forests and nature-based solutions have been suggested as inexpensive and effective strategies for climate change adaptation in cities. Urban trees in particular can significantly decrease land surface temperature across entire suburbs and cities. However, little knowledge exists on the more localised cooling benefits that trees might provide, particularly where these are needed the most ˗ the residential landscapes where people live.

This study assessed the effects of trees and other vegetation in people’s yards at reducing day time and night time heat during an extreme heatwave event in Western Adelaide. Despite covering about 20% of urban land, people’s yards contained more than 40% of the total tree cover and 30% of herbaceous (grass) cover. The number of private gardens, as well as the percentage of vegetation cover within these gardens, both contributed significantly in providing widespread cooling benefits across the Western Adelaide region with localised reductions in land surface temperatures of up to 5-6˚C compared to non-vegetated areas and land parcels. Vegetated cover overall provided the greatest day time cooling benefits further away from the coastline.

Findings suggest that the vegetation in people’s yards is of utmost importance for decreasing urban land surface temperature during extreme heat. Ambitious canopy cover targets (e.g., doubling of the current canopy cover from 13.5% to 27%) will require significant greening interventions across both the public and private realms. Private spaces offer significant untapped opportunities for urban greening and cooling, particularly in suburbs with lower vegetation cover. Where possible, urban development and densification must be carefully planned and performed to ensure that vegetation is retained and possibly expanded over time.