City Cooling - Mitigation of the Urban Heat Island (UHI) Effect

 

Australian heatwaves are getting hotter and more frequent, with the largest impacts occurring in cities due to the urban heat island (UHI) effect.

The term UHI refers to how built up areas have a greater capacity to absorb, hold and emit the sun’s heat compared to rural areas. This absorption of energy can increase day and night time temperatures in cities by several degrees. The effect can increase summertime peak energy demands, air conditioning costs, and heat-related illness and mortality. This challenge is driving a new form of urban planning called ‘climate sensitive urban design’. This involves the creation of thermally comfortable, resilient, attractive and sustainable outdoor urban environments by enhancing positive natural and man-made features through architecture, planning and landscape design.

Thermal image taken in a heatwave show the impact of urban heat islands in Melbourne. Source: City of Melbourne

Thermal image taken in a heatwave show the impact of urban heat islands in Melbourne. Source: City of Melbourne

Thermal images taken in a January 2017 heatwave show the impact of urban heat islands in Melbourne. Source: City of Melbourne

Growing evidence is showing an effective method of delivering human thermal comfort is via introducing shade and moist soil environments (i.e. irrigated vegetation). This suggests the UHI effect could be mitigated through the establishment of healthy tree canopy supported by water sensitive urban design (WSUD) approaches. The specific connection of WSUD ensures tree canopies are large, healthy and actively release water vapour via transpiration. The CRC for Water Sensitive Cities (CRCWSC) have demonstrated that urban heat impacts are mitigated by means of passive watering practices and green infrastructure solutions (such as irrigated trees) and these practices can lower the Urban Thermal Climate Index by up to 10 °C.

This method is beginning to translate into policy for many Victorian cities with state green-blue infrastructure guidelines now available and the adoption of urban forestry strategies and targets of up to 40% tree canopy cover by 2040 committed to by progressive municipalities (such as, City of Melbourne and City of Ballarat).

Land surface temperature showing cooler areas around irrigated ovals and tree canopy on a day with a maximum temperature of 37 deg C. Source: CRC Water Sensitive Cities Land surface temperature showing cooler areas around irrigated ovals and tree canopy on a day with a maximum temperature of 37 deg C. Source: CRC Water Sensitive Cities

Previous CRCWSC research was able to show the clear physical urban cooling benefits of different levels and types of urban greening. As part of the Integrated Research Projects (IRP2) portfolio this project will take this knowledge a step further to provide a credible estimate of the economic value of the cooling produced under different scenarios of WSUD adoption. This will allow UHI mitigation to be used as a policy position or business case for greening cities and integrated water management policy changes. The E2Designlab team are collaborating with the CRCWSC and RMCG to apply the latest research and modelling capabilities for UHI effect to quantify the benefits of integrating blue-green infrastructure across urban spaces and built form.  Outputs will be dollar value estimates of the UHI mitigation value produced under different greening and integrated water management settings.

Interested in cooling your city and building heatwave resilience? Follow the links below to learn more or contact E2Designlab at: [email protected]

The role water sensitive urban design (WSUD) can take in achieving climate sensitive streets, neighbourhoods and cities. Source: CRC Water Sensitive CitiesThe role water sensitive urban design (WSUD) can take in achieving climate sensitive streets, neighbourhoods and cities. Source: CRC Water Sensitive Cities.

How-to guide for planning urban greening and enhanced stormwater management in Victoria. Source: DELWP

A green-blue city action plan. Souce: City of Ballarat