Overview
DELWP has worked in partnership with RMIT University, CSIRO, and the Clean Air and Urban Landscapes (CAUL) Hub of the National Environmental Science Program to map and analyse vegetation, land use, and urban heat across Melbourne. The project has been supported by our implementation partner Melbourne Water.
The project used UrbanMonitor – a digital aerial photography monitoring system developed by the CSIRO – to create the first high-resolution map that records the baseline of urban vegetation across Melbourne. This project mapped imagery in 2014 and 2018.
For the first time, we can precisely measure the area of tree, shrub and grass cover at a land parcel level and track changes in this area over time.
Mapping and analysing vegetation helps us to understand the relationship between urban vegetation cover and the urban heat island effect. We have also prepared a vulnerability assessment to identify areas that are vulnerable to heat waves. This assessment takes into account the location of vulnerable members of the community, such as the elderly, very young and those with lower capacity to adapt to heat.
The project delivers an important component of the ‘Cooling and Greening Melbourne’ work program (Action 91) of Plan Melbourne 2017-2050 and will support the creation and expansion of urban forests and cooling measures throughout metropolitan Melbourne. It will also enable us to track our progress towards a cooler and greener city.
Project Progress
Vegetation, Urban Heat, and Heat Vulnerability Index Data
The completion of 2018 vegetation, urban heat, and heat vulnerability data is a significant milestone in the project. This data has been added to the 2014 data available on Spatial Datamart. Cooling and greening datasets can be accessed here:
- 2018 vegetation cover
- 2014 vegetation cover
- 2014 – 2018 change in vegetation cover
- 2018 urban heat
- 2018 heat vulnerability index
- 2014 heat vulnerability index
An interactive Mapshare tool that consolidates 2014 and 2018 data in a single platform has also been developed: Cooling and Greening Melbourne Interactive Map. The map provides a visual representation of vegetation cover, land surface temperature and the urban heat vulnerability assessment.
Summary Reports
A series of reports produced in partnership with RMIT University, which provide an overview of the vegetation cover and urban heat data for metropolitan Melbourne, are available for download:
- Urban Vegetation Cover Change 2014-2018 (PDF, 13.0 MB)
- Urban Vegetation Cover 2018 reports for each metropolitan region:
- Urban Vegetation, Urban Heat Islands and Heat Vulnerability Assessment in Melbourne, 2018
Key findings from the data
Metropolitan Melbourne has an urban tree canopy cover of 15.3 per cent, based on 2018 data.
The breakdown of 2018 urban tree cover by region is shown below.
Figure 1 - 2018 % urban tree cover in Melbourne by region
Of Melbourne’s metropolitan regions, the Eastern region has the highest urban tree canopy cover of 25.9 per cent. Of Melbourne’s Local Government Areas (LGAs), Yarra Ranges and Nillumbik have the highest urban tree canopy cover (36.7 per cent and 31.1 per cent respectively).
The Western region has the lowest urban tree canopy cover of 5.5 per cent. Melton and Wyndham LGAs have the lowest tree canopy cover (4.1 per cent and 4.2 per cent respectively).
Figure 2 - 2018 % tree cover in Melbourne by Local Government Area
In urban areas, residential land, parkland, and infrastructure such as streets account for the highest proportion of the total tree canopy cover (46.7 per cent, 18.5 per cent, and 15.7 per cent respectively).
Note: Due to the larger area of vegetation data available for 2018, the tree canopy cover findings presented in the ‘Melbourne Urban Vegetation Cover 2018’ report may be different than those in the ‘Urban Vegetation Cover Change 2014-2018’ report. The 2018 study area includes outer parts of the Eastern and Southern regions, which are typically highly vegetated. The additional data coverage is shown in purple shaded areas on Map 1 in the '2014-2018 tree cover change' tab.
Source: Clean Air and Urban Landscapes Hub 2018, Urban Vegetation Cover Analysis, Melbourne Metropolitan Region 2018, Clean Air and Urban Landscapes Hub, Melbourne.
Based on the data available for the 2014 vegetation coverage (refer to Map 1 below), metropolitan-wide urban tree canopy cover declined from 32,980ha (2014) to 32,295ha (2018), representing a change from 13.6% to 13.4% tree cover and a loss of 0.3 percentage points or 686 ha (values do not sum due to rounding).
Map 1 – Vegetation data coverage
Across the Inner, Western and Northern regions there were areas where tree canopy cover stagnated or moderately increased, and a few areas where tree cover declined. In the Western and Northern regions this change is off a low baseline.
Across the Eastern, Inner South East, and Southern regions there were more extensive areas of average tree canopy cover loss (particularly in the Eastern region). In these regions, baseline tree cover is generally high compared to the Melbourne average.
Tree canopy cover loss is concentrated in areas where there is significant existing vegetation and urban redevelopment activity. The loss is most evident on residential land and parkland, which provide the largest areas of tree cover.
Tree canopy cover gain is concentrated in areas where there is limited existing vegetation.
Percentage point change in urban tree canopy cover by Local Government Area
Change by land use
Residential land
Between 2014 and 2018 residential land in Melbourne lost 737ha of tree canopy cover. This is a change from 15.0% cover in 2014 to 14.3% cover in 2018, representing a loss of 0.7 percentage points.
Urban redevelopment, landowner land-management practices, and climatic effects are combining to reduce urban vegetation cover on residential land.
Parkland
Between 2014 and 2018 parkland in Melbourne lost 158ha of tree canopy cover. This is a change from 21.1% cover in 2014 to 20.6% cover in 2018, representing a loss of 0.5 percentage points.
Infrastructure land
Between 2014 and 2018 infrastructure land (largely the street network) experienced a gain in tree canopy cover (229 ha). This is a change from 13.3% cover in 2014 to 13.9% cover in 2018, representing a gain of 0.6 percentage points.
Note: The extent of vegetation data coverage is different for 2014 and 2018. Coverage was limited to State Government-acquired aerial imagery, which is the primary data required for the Urban Monitor approach. Data covering approximately 674,000 ha was available for 2018, however a smaller area of coverage was available for 2014. As such, the 2014 – 2018 tree canopy cover comparison figures are based on 2018 data which has been clipped to the 2014 data coverage area.
Source: Hurley, J, Saunders, A, Both, A, Sun, C, Boruff, B, Duncan, J, Amati, M & Caccetta, P 2019, Urban Vegetation Cover Change in Melbourne 2014 - 2018, Clean Air and Urban Landscapes Hub, Melbourne.
Definition
Urban Heat Island (UHI): The UHI is a measure of the deviation of urban temperatures above or below a non-urban baseline temperature. The UHI measure was derived from land surface temperature (LST) data based on Landsat 8 thermal infrared data collected by the United States Geological Survey (USGS).
2018 UHI findings
The average UHI reading of small statistical areas (Mesh Blocks) within the study area varied from 10.20°C to -7.16°C. Mesh Blocks are defined by the Australian Bureau of Statistics (ABS) as the smallest geographic unit for which statistical data is collected and processed by the ABS. Mesh Blocks are added together to build up larger geographic areas such as suburbs and larger urban areas.
2018 UHI reading (ºC) by Local Government Area
Four LGAs have an average summer UHI reading over 9.5°C (Brimbank, Casey, Melton, and Moonee Valley).
Except for Mornington Peninsula, Yarra Ranges and Nillumbik, all urban LGAs had an average summer UHI reading over 7.0°C.
Large UHI concentration areas appeared in the western and south eastern suburbs of metropolitan Melbourne, along with some scattered areas of high UHI readings in the northern suburbs. Lower UHI concentration areas were mainly along the coast, eastern and north eastern suburbs, and in highly vegetated areas.
Relationship between UHI and vegetation
Tree canopy cover was found to have the strongest relationship with reducing heat in urban areas. By comparison, there was less evidence to suggest that grass and shrub cover has a large influence in reducing urban heat.
Note: The 2014 and 2018 temperature readings are not directly compared in this project. Land surface temperature derived from Landsat thermal images is subject to the availability of satellite images. This causes significant annual variation between two different years due to climatic factors which are difficult to control for.
Source: Sun, C, Hurley, J, Amati, M, Arundel, J, Saunders, A, Boruff, B & Caccetta, P 2019, Urban Vegetation, Urban Heat Islands and Heat Vulnerability Assessment in Melbourne, 2018, Clean Air and Urban Landscapes Hub, Melbourne, Australia.
Definition
Heat Vulnerability Index (HVI): The HVI identifies which populations are most vulnerable to heat. It consists of three indicators: heat exposure, sensitivity to heat, and adaptive capability. Vulnerability ratings are determined by the sum of the aggregated indicators and are scaled from 1 to 5 (1 = low vulnerability, 5 = high vulnerability).
2018 HVI findings
High-risk areas with a HVI rating of 5 were mainly distributed in the LGAs of Melton, Brimbank, Darebin, Casey, and Wyndham. HVI ratings in some areas were high despite lower UHI readings, due to the concentration of vulnerable members of the community, such as the elderly, very young and those with lower capacity to adapt to heat. Map 2 shows the 2018 distribution of HVI ratings.
The impacts of urban heat are reduced in LGAs with low social vulnerability, which typically have a low proportion of younger or older people and/or higher levels of socioeconomic development (e.g. Nillumbik and some parts of Manningham). By contrast, high social vulnerability intensifies heat health risks as people are less able to adapt (e.g. in Brimbank, Casey and Melton).
Map 2 - 2018 HVI distribution
Note: The 2014 and 2018 temperature readings are not directly compared in this project. Land surface temperature derived from Landsat thermal images is subject to the availability of satellite images. This causes significant annual variation between two different years due to climatic factors which are difficult to control for.
Source: Sun, C, Hurley, J, Amati, M, Arundel, J, Saunders, A, Boruff, B & Caccetta, P 2019, Urban Vegetation, Urban Heat Islands and Heat Vulnerability Assessment in Melbourne, 2018, Clean Air and Urban Landscapes Hub, Melbourne, Australia.
Why do we need to measure and monitor our urban forest?
Vegetation mapping is done locally in many different ways which makes it difficult to have a clear picture of vegetation cover at a metropolitan scale and at a high enough resolution for local decision-making.
Key benefits of improved mapping and monitoring include:
- enabling evidence-based planning and decision-making for urban forests
- informing greening targets and tracking progress
- assisting with identifying priority areas for action and investment
- providing a resource for local government to develop local greening strategies, and
- providing a baseline for monitoring the implementation of greening strategies and regulatory responses.
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Page last updated: 26/11/19