Urban heat island effect
Melbourne is already experiencing hotter summers and more frequent heatwaves due to climate change. At the same time, planning reforms are enabling higher-density development across established suburbs, often with reduced landscaping requirements, smaller setbacks, and increased site coverage.
While these changes increase housing supply, they also reduce the natural cooling capacity of urban environments — amplifying the urban heat island effect.
Less vegetation, more heat retention
One of the key drivers of urban heat is the loss of trees and green space.
Under current reforms:
- Tree canopy requirements are reduced
- Private gardens are shrinking due to higher site coverage
- Landscaping space is more limited in new developments
- Mature trees are more likely to be removed during redevelopment
Without sufficient vegetation, less shade is created and less heat is absorbed by the natural environment.
This is particularly significant because a substantial proportion of Melbourneʼs urban vegetation is located on private residential land. Public parks and street trees alone cannot fully offset the cumulative loss of residential gardens and vegetation across established suburbs.
More hard surfaces, higher temperatures
New developments typically include:
- Larger building footprints
- More concrete, asphalt, and paved areas
- Reduced permeable soil for cooling through evaporation
These surfaces absorb and retain heat during the day and release it slowly at night, keeping temperatures elevated even after sunset.
Cumulative warming across suburbs
While a single development may have a limited impact, the widespread application of these planning changes across many suburbs leads to cumulative effects.
Over time, this can result in:
- Higher average local temperatures
- Reduced night-time cooling in dense areas
- More widespread heat stress during summer periods
- Increased reliance on air conditioning
Neighbourhood-scale changes can therefore translate into city-wide temperature impacts.
Reduced natural shading
Tree canopy, gardens and vegetation play a critical role in reducing surface and air temperatures through shading and evapotranspiration.
With reduced space for trees:
- Streets receive more direct solar exposure
- Footpaths and roads become hotter and less comfortable
- Outdoor spaces are less usable during heat events
- Heat is reflected and trapped by built form rather than dissipated
This affects both public and private spaces.
Impacts on health and liveability
Urban heat is not just an environmental issue — it directly affects human health and wellbeing.
Higher local temperatures can contribute to:
- Heat stress and heat-related illness
- Increased energy consumption for cooling
- Reduced outdoor activity and social interaction
- Greater risk for vulnerable populations, including the elderly and young children
Heat also places additional pressure on health services during extreme weather events.
Infrastructure strain during heatwaves
Hotter urban environments increase demand on infrastructure systems.
This includes:
- Higher electricity demand for air conditioning
- Greater strain on power networks during peak heat events
- Increased water usage for cooling and irrigation
- Stress on transport infrastructure exposed to high temperatures
These pressures are compounded in areas with high-density redevelopment and limited green infrastructure.
Why this matters
The urban heat island effect is one of the most direct and measurable consequences of reduced urban greening.
It influences:
- Comfort and safety in daily life
- Public health outcomes
- Energy costs and emissions
- Overall city resilience to climate change
In a warming climate, mitigating heat is not optional — it is essential for maintaining liveability.
What this means for Melbourne
Without stronger protections for tree canopy, gardens, open space and urban greening, increased density risks intensifying heat across already vulnerable suburbs.
The result may be:
- Hotter streets and homes
- Less comfortable outdoor environments
- Increased reliance on mechanical cooling
- Reduced climate resilience at neighbourhood scale
Good planning must ensure that growth does not come at the cost of a more heat-stressed city.