Performance Indicator: Addressing urban heat

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Addressing urban heat Performance Indicator

Purpose

This indicator helps to understand the value of green infrastructure such as tree canopy, vegetation and waterways in reducing the impact of extreme heat on people’s health and improving local amenity.

Goal

The goal is to increase the contribution that the urban tree canopy can make to the quality of public places, streets and open spaces which improves amenity.

Measures

  • Number of hot days (>35°C)
  • Urban heat
  • Tree canopy cover in the urban area

Hot days and heatwaves represent a significant hazard in the Greater Sydney Region. Extreme heat and heat waves can have a significant impact on people’s health and local amenity, with some people more vulnerable to the effects of heat than others. Over the last 100 years heatwaves have caused more deaths in Australia than any other natural hazard.1

Green infrastructure such as tree canopy can enhance the amenity of dwellings, neighbourhoods, streets and centres. It is also a key component of Greater Sydney's highly valued scenic landscapes. Research shows that trees provide shade, reflect heat and transpire through leaves releasing water into the atmosphere. There is a relationship between tree canopy cover and land surface temperatures. In some instances, a 10 per cent increase in tree canopy cover can lower land surface temperature by 1.13 degrees Celsius.2

Measures

Hot days and heatwaves

Hot days are defined as those above 35 degrees Celsius. Heatwaves occur when temperatures remain unusually high for consecutive days. Penrith (Western City District) experiences more hot days on average than Greater Parramatta in Central City District (measured at North Parramatta). However, both these centres experience significantly more hot days on average than the Harbour CBD in the Eastern City District (measured at Observatory Hill) (see figure below).

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Number of days over 35 degrees Celsius (July 1994 – June 2019)

Number of days over 35 degrees Celsius (July 1994 – June 2019)3

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During the summer of 2018-19, the Harbour CBD (Eastern City District) and Terrey Hills (North District) experienced only six hot days over 35 degrees Celsius. In contrast, Penrith (Western City District) experienced 37 hot days, Parramatta (Central City District) had 19 hot days and Bankstown (South District) had 20 hot days (see figure below).

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Number of days over 35 degrees Celsius (July 2018-June 2019)

Number of days over 35 degrees Celsius (July 2018-June 2019)4

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Urban heat

Cities create their own microclimates by influencing the surrounding atmosphere and interacting with climate processes. Localised warming – caused by factors such as buildings, roads and other hard and dark surfaces that absorb and store heat – creates an urban heat island effect5. This means urban surface temperatures can be 10 to 20 degrees Celsius higher than the air temperatures.

Mapping of the urban heat island (UHI) effect across the Region shows it is highest in the Western City District and lowest in the North District (see figure below). This is reinforced when the urban heat island effect is considered in relation to the distribution of the population (see figure below). It also shows that there are significant urban heat issues in Eastern City District.

The community’s resilience to urban heat can be considered through a multi-faceted model of vulnerability that combines considerations such as age (very young and very old) and socio-economic profiles with urban heat profiles such as areas of extreme heat6. This shows a high coincidence of high levels of urban heat and urban vulnerability across parts of Western City, Central City and South districts.

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Greater Sydney and district urban heat island 2016

Greater Sydney and district urban heat island 20167

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Percentage of residents with exposure to high urban heat 2016

Percentage of residents with exposure to high urban heat 2016 8

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Urban tree canopy cover

In 2016, the total tree canopy cover of the urban area of Greater Sydney was 21 per cent. This excludes the large protected natural areas and the metropolitan rural areas that surround the urban area. The urban area of the North District has almost 40 per cent tree canopy cover. All the remaining districts are much lower (see figures below).

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Percentage of urban tree canopy cover 2016

Percentage of urban tree canopy cover 20169

Download this image tree_canopy.png (format PNG / 56 KB)

Findings and future focus

The Western City, Central City, South and Eastern City districts are all affected by urban heat. At the same time, these four districts also have lower tree canopy cover.

Increasing tree canopy in the urban area is one way to improve amenity and address urban heat. This will progress the evolution to a metropolis of three sustainable cities and enhance place-making.

Projections from NSW and ACT Regional Climate Model (NARCliM) show that air temperatures in Greater Sydney are expected to increase in the future as a result of climate change and increasing urbanisation.10

Other ways we may improve and expand how we monitor urban heat include monitoring how water is incorporated in the landscape. Protecting and integrating waterways near neighbourhoods can both moderate urban heat island affects and support urban tree canopy. We can also identify ways to assist communities vulnerable to urban heat such as access to cooler places and community support networks.

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Greater Sydney and district distribution of tree canopy cover 2016

Greater Sydney and district distribution of tree canopy cover 201611

Download this image pulse_of_greater_sydney_draft_p22-23-2.png (format PNG / 3 MB)

References

  1. Climate Council, Heatwaves Longer, Hotter, More Often, 2014
  2. Western City District Plan Planning Priority W15 Increasing urban tree canopy cover and delivering Green Grid connections pp. 119 /NSW Office of Environment and Heritage Government 2015, Technical Guidelines for Urban Green Cover in NSW, NSW Government, Sydney
  3. Source: Bureau of Meteorology, 2019
  4. Source: Bureau of Meteorology, 2019
  5. Office of Environment and Heritage Adapting to Climate Change – Green Cover (https://climatechange.environment.nsw.gov.au/Adapting-to-climate-change/...)
  6. See Dashboard: Heat vulnerability index 2016, NSW Department of Planning, Industry and Environment, NSW Heat Vulnerability Index to ABS Statistical Area Level 1 2016
  7. Source: NSW Department of Planning, Industry and Environment, NSW Urban Heat Island to Modified Mesh Block 2016
  8. Source: NSW Department of Planning, Industry and Environment, NSW Urban Heat Island to Modified Mesh Block 2016
  9. Source: NSW Department of Planning, Industry and Environment, Greater Sydney Region Urban Vegetation Cover to Modified Mesh Block 2016
  10. NSW Department of Planning, Industry and Environment and Adapt NSW (2015) Heatwaves Climate Change Impact Snapshot
  11. Source: NSW Department of Planning, Industry and Environment, Greater Sydney Region Urban Vegetation Cover to Modified Mesh Block 2016

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