# 
Urban
Heat
Subdivision design can reduce urban heat, manage the effects of urban heat within the subdivision area and maintain human health and wellbeing through periods of extreme heat.
# Why do subdivisions need to reduce urban heat?
With the changing climate, Victoria is expected to have more days of extreme heat as well as higher average temperatures of at least 1.5 degrees by 2070. (opens new window)
Studies show that air temperature in built-up areas, can range from 4°C to 10°C warmer (opens new window) than in neighbouring, less built-up regions.
Elevated temperatures from urban heat islands can affect the environment and impact quality of life. It increases the need for active cooling (such as air conditioning) while also contributing to general discomfort as well as more severe heat related health conditions (e.g. heat stress and heat related mortality).
The negative impacts of urban heat also extend to increased energy demand, disruption to transport operation and damage to infrastructure, (opens new window) degradation of vegetation and wildlife, and has even shown to have a negative influence on crime rates. (opens new window)
These impacts can have a significant economic impact. A study conducted by the City of Melbourne showed that the urban heat island effect contributed 16% of the overall cost of hot weather on the City equating to a discounted value of $300 million between 2012 and 2050. Climate change is expected to have a compounding effect on this as the number of days over 30 degrees increases (Economic Assessment of the Urban Heat Island Effect | City of Melbourne, 2015).
Paved and dark surfaces such as car parks absorb heat and will continue to exacerbate urban heat island effect as the climate changes. Whereas areas with more vegetation and irrigated landscapes have a cooling effect.
# Benefits of cooler subdivisions
Developers can take advantage of:
- Enhanced market appeal of the subdivision to prospective purchasers
- The economic benefit of urban heat mitigation
- Demonstrating best practice to create climate resilient neighbourhoods
A new resident can expect:
- Lower energy bills due to less reliance on active heating and cooling systems
- Improved living comfort (internal and external)
- Future proofing of building and community asset
- Less disruption during extreme heat events
# Reducing urban heat in subdivisions
“ Increasing numbers of people are moving into urban areas, where temperatures are higher than the surrounding rural areas as a result of reduced natural, vegetated landscapes and increased dark, paved surfaces that store heat, an effect known as the urban heat island (UHI). ”
# Urban heat mitigation
There are several strategies that can be undertaken through the subdivision design process to mitigate the impact of urban heat. Urban heat mitigation principles include:
- Providing shading of roads and carparks to reduce urban heat
- Irrigating streets and open space to cool the landscape
Strategies to mitigate urban heat include introducing irrigated and vegetated landscapes into the subdivision - these create evapotranspiration which helps to naturally cool the outdoor environment.
However, there are also opportunities to use materials that have a higher solar reflective index (SRI) to lower the heat absorption. The SRI is an indicator of how hot a material is likely to become when exposed to solar radiation (the lower the SRI, the hotter it is likely to become).
Choosing lighter materials is a low cost, effective method of mitigating urban heat, for example, by using design guidelines to ensure the use of light-coloured roofs.
# Access to shelter
With more days of extreme heat already being experienced, and this number expected to grow, ensuring adequate access to shelter throughout the subdivision will ensure future residents can continue to move freely.
The access to shelter principle is providing shelter for pedestrian and cyclist movement.
Future residents should be able to move around the subdivision using ‘cool routes’. ‘Cool routes’ are active transport routes between destinations that provide protection from direct heat such as through a physical shade structure or relatively uninterrupted canopy cover.
By ensuring adequate shelter for pedestrian movements and places of respite from harsh conditions within the urban environment, the public realm can remain functional for active transport under a greater range of conditions.
The choice of materials used for physical shade structures can also support urban heat mitigation by ensuring they have a higher SRI.
# Health and wellbeing
Urban heat mitigation strategies must ultimately enable future residents to move safely and comfortably around the subdivision without compromising their health and wellbeing.
Health and wellbeing principles include:
- Providing places with cooler microclimates which provide relief from hot conditions
- Maintaining human health and wellbeing through periods of extreme heat
The opportunity to develop microclimates within the subdivision is strongly linked to the ecology and integrated water management categories. The use of vegetated and irrigated landscapes can reduce urban heat while protecting resident health and wellbeing.
Design guidelines can also be used to ensure that private realm landscaping supports urban heat mitigation, ultimately improving the health and wellbeing of residents within their homes as well as supporting public realm outcomes.
Subdivision design should include shelter and continuous shaded pathways for comfort during extreme heat.
# Case study
| Location | Alkimos Beach, City of Wanneroo (opens new window) |
| Site Area | 224 ha |
| Number of Dwellings | 2,200 |
| Development Type | Residential + community infrastructure |
| Year / Status | 2012 / Ongoing |
| Sustainability Accreditation | 6-star Green Star - Communities EnviroDevelopment |
| Key Stakeholders | DevelopmentWA (State Government land development agency / Development Partner) Lendlease (Project Management / Development Partner) City of Wanneroo (Local Government) |
| Key Features | - Maintaining minimum 30% of developable area dedicated to parks and open space. - Roof colour requirements in the Residential Design Guidelines outlining minimum Solar Absorptance (SA) values and colour options (e.g. no black roofs). - Mandatory landscaping requirement in the Residential Design Guidelines that every detached dwelling must include a mature tree in their front garden to help establish tree-lined streets. - Water wise plant selections providing residents with green space including tree canopy shading. - Interpretive signage trail educating residents on sustainability issues such as urban heat. - Complimentary front landscaping packages provided to residents to help improve greening outcomes on private land. |
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