Landscape and Urban Planning 134 (2015) 127–138

Contents lists available at ScienceDirect

Landscape and Urban Planning
journal homepage: www.elsevier.com/locate/landurbplan

Research Paper

Planning for cooler cities: A framework to prioritise green
infrastructure to mitigate high temperatures in urban landscapes
Briony A. Norton a,1 , Andrew M. Coutts b , Stephen J. Livesley a , Richard J. Harris c ,
Annie M. Hunter a , Nicholas S.G. Williams a,∗
a

School of Ecosystem and Forest Sciences, The University of Melbourne, 500 Yarra Boulevard, Richmond, Victoria 3121, Australia
CRC for Water Sensitive Cities and the School of Geography and Environmental Science, Monash University, Wellington Road, Clayton, VIC 3800, Australia
c
School of Geography and Environmental Science, Monash University, Wellington Road, Clayton, VIC 3800, Australia
b

h i g h l i g h t s
•
•
•
•

Review of cooling potential from green infrastructure in cities with hot, dry summers.
Presents a hierarchical process to prioritise urban areas for green infrastructure.
Framework to strategically select green infrastructure that is ‘fit-for-place’ and ‘-purpose’.
Case study of framework applied to local government planning scale.

a r t i c l e

i n f o

Article history:
Received 25 May 2014
Received in revised form 19 October 2014
Accepted 21 October 2014
Available online 11 November 2014
Keywords:
Urban greening
Climate change adaptation
Heat wave
Public health
Urban planning
Green roof

a b s t r a c t
Warming associated with urban development will be exacerbated in future years by temperature
increases due to climate change. The strategic implementation of urban green infrastructure (UGI) e.g.
street trees, parks, green roofs and facades can help achieve temperature reductions in urban areas while
delivering diverse additional benefits such as pollution reduction and biodiversity habitat. Although the
greatest thermal benefits of UGI are achieved in climates with hot, dry summers, there is comparatively
little information available for land managers to determine an appropriate strategy for UGI implementation under these climatic conditions. We present a framework for prioritisation and selection of UGI for
cooling. The framework is supported by a review of the scientific literature examining the relationships
between urban geometry, UGI and temperature mitigation which we used to develop guidelines for UGI
implementation that maximises urban surface temperature cooling. We focus particularly on quantifying
the cooling benefits of four types of UGI: green open spaces (primarily public parks), shade trees, green
roofs, and vertical greening systems (green walls and facades) and demonstrate how the framework can
be applied using a case study from Melbourne, Australia.
© 2014 Elsevier B.V. All rights reserved.

1. Introduction
Globally, extreme heat events (EHE) have led to particularly
high rates of mortality and morbidity in cities as urban populations are pushed beyond their adaptive capacities. Recent EHE

∗ Corresponding author. Tel.: +61 3 9035 6850.
E-mail addresses: briony.a.norton@gmail.com (B.A. Norton),
andrew.coutts@monash.edu (A.M. Coutts), sjlive@unimelb.edu.au
(S.J. Livesley), rickjharris1@gmail.com (R.J. Harris), annieh@student.unimelb.edu.au
(A.M. Hunter), nsw@unimelb.edu.au (N.S.G. Williams).
1
Present address: Department of Animal and Plant Sciences, University of
Sheffield, Sheffield S10 2TN, UK.
http://dx.doi.org/10.1016/j.landurbplan.2014.10.018
0169-2046/© 2014 Elsevier B.V. All rights reserved.

examples include: Chicago, USA (1995; 31% mortality increase)
(Whitman et al., 1997), Paris, France (2003; 130% mortality
increase) (Dhainaut, Claessens, Ginsburg, & Riou, 2003), Moscow,
Russia (2010; 60% mortality increase) (Revich, 2011) and Melbourne, Australia (2009; 62% mortality increase) (Department of
Human Services, 2009). Many cities expect catastrophic EHEs more
often, as the frequency, intensity and duration of EHEs are projected
to increase with climate change (Alexander & Arblaster, 2009).
There is evidence that increased mortality and morbidity from
EHE are exacerbated in urban populations by the urban heat island
(UHI) effect (e.g. Gabriel & Endlicher, 2011). Modified land surfaces
from urbanisation lead to the formation of distinct urban climates
(Coutts, Beringer, & Tapper, 2007). Natural surfaces and vegetation
are replaced with a complex, three-dimensional impervious surface

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B.A. Norton et al. / Landscape and Urban Planning 134 (2015) 127–138

Table 1
Existing grey and green infrastructure to be documented as part of the process of
selecting and integrating new green infrastructure to mitigate high temperatures in
high priority, vulnerable neighbourhoods.
Urban green infrastructure

Grey infrastructure

Irrigated and non-irrigated green space
Location of trees
Trees species mapping
Tree health mapping
Green roofs
Green walls

Street orientation
Building heights (H)
Street widths (W)
Height to width ratio (H:W)

that absorbs large amounts of solar radiation during the day and this
energy is then slowly released at night, keeping urban areas warmer
than the surrounding rural countryside and leading to the UHI (Oke,
1982). Rainfall is rapidly drained via stormwater pipes leaving little
moisture in the urban landscape, which reduces evapotranspiration
and increases sensible heating of the local atmosphere (Coutts et al.,
2007). Several studies have shown that higher night time temperatures limit people’s recovery from daytime heat stress (Clarke &
Bach, 1971). Consequently, many urban populations must adapt to
the compounding effects of the UHI, climate change and EHE (Bi
et al., 2011).
Many governments are now strategically planning for EHE
(O’Neill et al., 2009), often with a focus on short-term preparation and prevention, for example warning systems, promoting
behavioural change and preparing emergency services (Kovats &
Hajat, 2008; Queensland University of Technology, 2010). Increasing the amount of vegetation, or green infrastructure, in a city
is one way to help address the root cause of the problem, by
reducing urban air and surface temperature maxima and variation (Bowler, Buyung-Ali, Knight, & Pullin, 2010). However, to
substantially reduce the UHI, widespread implementation of green
infrastructure is required. For example, measurements during an
EHE in Melbourne, Australia, suggested a 10% increase in vegetation cover could reduce daytime urban surface temperatures by
approximately 1 ◦ C (Coutts & Harris, 2013).
Urban green infrastructure (UGI) can be defined as the network
of planned and unplanned green spaces, spanning both the public
and private realms, and managed as an integrated system to provide
a range of benefits (Lovell & Taylor, 2013; Tzoulas et al., 2007). UGI
can include remnant native vegetation, parks, private gardens, golf
courses, street trees and more engineered options such as green
roofs, green walls, biofilters and raingardens (Table 1). This paper
focuses on the integration of UGI into the public realm to mitigate
high urban temperatures and considers the various UGI types and
possible locations.
UGI research is not well integrated with urban design and planning, which contributes to the lack of guidance on how best to
implement UGI (Bowler et al., 2010; Erell, 2008). UGI is a particularly good option for temperature mitigation in Mediterranean or
warm temperate climates due to the greater relative cooling benefits in hot, dry climates (Ottelé, Perini, Fraaij, Haas, & Raiteri, 2011),
particularly if water is available to maintain vegetation health and
evapotranspiration. Yet, there is a dearth of empirical evidence
regarding the benefits of UGI in cities experiencing a Mediterranean
climate, nor information on successful and cost effective UGI implementation strategies (Williams, Rayner, & Raynor, 2010). Clearly a
cross-disciplinary approach is required.
We present a framework, supported by relevant literature, for
green space managers, planners and designers to most effectively
integrate UGI into existing urban areas for the primary goal of
improved urban climate. With the aid of thermal mapping, a decision framework was developed for local government authorities
in Melbourne, Australia. A step by step case-study implementing
the framework is provided, drawing on high resolution, airborne

thermal mapping as a tool within this framework. Melbourne
(37◦ 49 S; 144◦ 58 E), on the southern coast of south eastern
Australia, has a warm Maritime Temperate climate (Peel, Finlayson,
& McMahon, 2007), but has long periods of summer drought and
extreme heat. This framework can be applied to cities with classic
Mediterranean climates (e.g. Perth, San Francisco, Seville, Beirut
and Athens) and those that experience extended summer periods
of hot, dry conditions, such as Adelaide and Melbourne. Cities in
colder or more humid climates may have different considerations,
for example in humid areas there can be a greater emphasis on
maximising air flow (Emmanuel, 2005).
2. A framework for using UGI to mitigate excess urban heat
We propose a hierarchical, five step framework to prioritise
urban public open space for microclimate cooling (Steps 1–4) using
the most appropriate ‘fit for place’ UGI (Step 5) (Fig. 1). The same
principles will apply to privately-owned outdoor space, although
this may be complicated by issues of multiple ownership (Pandit,
Polyakov, Tapsuwan, & Moran, 2013).
The framework operates firstly at the ‘neighbourhood’ scale,
then the ‘street’ scale and finally the ‘microscale’ (Fig. 1). While
the actual area would be defined by organisation implementing
the framework, a neighbourhood would encompass hundreds of
houses and urban features such as a shopping precinct, a school, a
railway station, parks and playing fields. The street scale is a smaller
unit within a neighbourhood, for example some houses and a strip
of shops. The microscale is an area within a street canyon, equivalent to one or more property frontages perhaps. Integrating these
three scales is central to this framework, and is important to the
strategic integration of UGI for microclimate cooling (Dütemeyer,
Barlag, Kuttler, & Axt-Kittner, 2014). This framework is flexible and
can be applied and adapted by green space mangers, planners and
designers to meet their local circumstances. Local stakeholders can
also be involved in the decision framework at any, or all, stages
as determined by budget, time and engagement philosophy of the
local government authority.
2.1. Step 1—Identify priority urban neighbourhoods
Specific neighbourhoods are prioritised by identifying areas
with the largest numbers of people that may be exposed and/or are
vulnerable to excessive urban heat. A risk of mortality and morbidity from excessive urban heat is based on a combination of heat
exposure, vulnerability to extreme heat (Dütemeyer et al., 2014), as
well as the behavioural exposure occurring, in terms of the number of people using public open spaces (Fig. 2). When these three
risk drivers intersect (C), a high priority neighbourhood has been
identified. However, it is hard to predict the amount of behavioural
exposure in public open spaces such as community health centres,
so neighbourhoods where heat exposure and vulnerability intersect
(B orange) can also be regarded as a priority (Fig. 2).
2.2. Heat exposure
Areas within cities that experience extreme heat are not evenly
distributed spatially and ‘hot-spots’ occur where there is intense
urban development with little vegetation and/or water. Consequently, air temperatures predicted from coarse resolution models
(e.g.100–200 km) can frequently be exceeded in susceptible urban
neighbourhoods or ‘hot-spots’ (McCarthy, Best, & Betts, 2010). To
adequately assess how exposed a neighbourhood population may
be to high temperatures, temperature information that is specific
to that location is important (Kovats & Hajat, 2008). Satellite or
airborne remotely sensed thermal data can provide a snapshot
in time of land surface temperature across a large spatial area,

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129

Fig. 1. The steps in the prioritisation operate at the neighbourhood scale (Steps 1–3), where the physical environment and people’s vulnerability are characterised for the
area; and the street (Step 4) and microscales (Step 5), at which scales UGI that is fit for place is selected and implemented. See text for details.

and can be used as a proxy for air temperature (Saaroni, BenDor, Bitan, & Potchter, 2000) although the correlation may be poor
under unstable (windy) conditions (Stoll & Brazel, 1992). While
land surface temperature and air temperatures are clearly different, mitigating high surface temperatures in cities is an appropriate
target, as these reflect locations where both air temperature and
absorbance of solar radiation is high, which impacts directly on
human thermal comfort (Matzarakis, Rutz, & Mayer, 2007). Satellite
remotely sensed data are low-resolution but often freely available,
whereas airborne remotely sensed data can provide higher resolution (1–5 m) but can be costly and time-consuming to process
(Coutts & Harris, 2013; Tomlinson, Chapman, Thornes, & Baker,
2011).

circumstances are particularly vulnerable (Bi et al., 2011). Prioritising neighbourhoods for high temperature mitigation is therefore
a social justice issue, as well as a preventative health measure
(Wolch, Byrne, & Newell, 2014). Assessing vulnerability of a population to high temperatures requires demographic information (e.g.
Huang, Zhou, & Cadenasso, 2011; O’Neill et al., 2009). Loughnan,
Tapper, Phan, Lynch, and McInnes (2013) have developed methods
for assessing vulnerability in Australian cities primarily using Australian census information (Australian Bureau of Statistics, 2011c)
collected every five years, including a vulnerability index for all
Australian capital cities.

2.3. Vulnerability

Areas in a city where large numbers of the public are active
outdoors should rate highly for heat mitigation, such as public transport interchanges, recreational spaces, outdoor shopping
strips, schools and pedestrian thoroughfares. These areas may be
prioritised to modify the human thermal comfort of large proportions of the population. For instance, during an extreme heat
event the public transport network can be interrupted, leaving
commuters waiting in extreme heat for transport services. Furthermore, public areas of activity where vulnerable populations
may be exposed should be identified, including outside aged care
facilities, schools and community centres, health care centres,
socio-economic support locations, and social housing complexes.
Such information can be sourced from census data, local planning
schemes, and other institutional resources.
Heat related stress, stroke or death do not occur spontaneously
or rapidly, it is prolonged exposure to higher than normal temperatures, often over several days, that causes heat related illness
(e.g. Harlan, Brazel, Prashad, Stefanov, & Larsen, 2006; Luber &
McGeehin, 2008; McGeehin & Mirabelli, 2001). Hence, people are
exposed to thermal stress throughout the day and night, and
respond negatively after different periods of time depending upon
their vulnerability and the temperatures they experience. The aim
of this framework to prioritise UGI implementation for heat mitigations is really an aim to reduce the overall outdoor exposure
of vulnerable individuals (and all people) to high temperatures
throughout the course of the day. Furthermore, this framework
applies to public spaces where local governments can more easily
intervene.

A wide range of factors influence the vulnerability of urban
populations to extreme heat. Socially disadvantaged neighbourhoods (those with lower household income and lower quality
parks, shops and transport) often experience greater negative
health impacts from extreme heat. The elderly, those with preexisting physical (i.e. heart disease, obesity) or mental illness, the
very young and those living alone and in low socio-economic

Fig. 2. Factors required to identify neighbourhoods of high (C), medium (B) and
moderate (A) priority for UGI implementation for surface temperature heat mitigation. The key factors are high daytime surface temperatures (Heat exposure)
intersecting with areas with more vulnerable sections of society (Vulnerability) and
identifying the zones of high activity (Behavioural exposure) with this area.

2.4. Behavioural exposure

2.5. Step 2—Characterise UGI and grey infrastructure
Once priority neighbourhoods have been identified, it is important to characterise the built form (grey infrastructure) in a

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three-dimensional sense, and to identify existing UGI. Step 2 helps
identify opportunities for micro-climate improvements, and documents the landscape for later steps. The aim is to identify the
location of existing, healthy vegetation, and where UGI is lacking,
i.e. which parts of the current built environment could be retrofitted
with UGI (Table 1). If thermal mapping data (Step 1) are unavailable,
this step increases in importance. Characterising street width and
building height will determine street openness to solar radiation,
and self-shading by buildings. This information can be gathered
from a combination of visual surveys, aerial imagery, LiDAR data,
GIS databases, etc.
2.6. Step 3—Maximise the cooling benefit from existing UGI
Many cities already have well-established urban forests and
other green infrastructure networks. Their cooling benefit is most
important during very hot, dry periods, however this is when urban
vegetation can be most water stressed. Stress from low water availability during hot weather can lead to defoliation and possibly
death. The impacts of this are most serious when large trees die due
to the large reduction in cooling they provide and high replacement
cost (Gill, Handley, Ennos, & Pauleit, 2007). Vegetation that is water
stressed has higher surface temperatures than irrigated vegetation
(Coutts & Harris, 2013). Inadequate water availability will also lead
to reduced plant transpiration when it is most desired (Leuzinger,
Vogt, & Körner, 2010; Shashua-Bar, Pearlmutter, & Erell, 2011).
Consequently, supplementary irrigation of UGI in cities that experience hot, dry summers is a wise investment to ensure long-term
temperature mitigation, as well as other ecosystem services (May,
Livesley, & Shears, 2013). However, some cities (e.g. Melbourne),
introduce water use restrictions in response to extended drought,
even though this approach immediately reduces and threatens
the long-term temperature mitigation benefits from UGI (Coutts,
Tapper, Beringer, Loughnan, & Demuzere, 2013; May et al., 2013).
Some supplementary water can also be supplied through water
sensitive urban design that utilises stormwater runoff rather than
potable water (Coutts et al., 2013), but this will require increased
investment in stormwater capture and storage within the urban
landscape.
2.7. Step 4—Develop a hierarchy of streets for new UGI
integration
After selecting priority neighbourhoods for temperature mitigation, particular streets that are most vulnerable to high
temperatures can be targeted. Urban streets can be viewed as
canyons, with a floor (the road, walkway, verge and front yards) and
two walls (the building frontages up to the top of the roof). Our fivestep hierarchy focuses on street canyons because: (1) they occupy
a large proportion of the public domain in cities; (2) a lot of urban
climate research is based around street canyons; (3) street features
relevant to assessing the thermal environment are relatively easy to
measure and often already available to local government agencies;
(4) street geometry and orientation are important determinants
of surface and air temperatures in urban areas (Bourbia & Awbi,
2004a, 2004b); and (5) the principles for cooling based on canyon
geometry can be usefully applied to other urban open spaces, e.g.
car parks (Onishi, Cao, Ito, Shi, & Imura, 2010) and intersections
(Chudnovsky, Ben-Dor, & Saaroni, 2004; Saaroni et al., 2000).
An important goal in using UGI to reduce surface temperature
is to replace or shade impervious surfaces with vegetation (Oke,
Crowther, McNaughton, Monteith, & Gardiner, 1989). Selection of
UGI should therefore focus on the properties of the street canyon
that determine level of solar exposure. These are building height
(H), street width (W), height to width ratio (H:W), and orientation, but providing sufficient capacity for ventilation at night is also

important. The street canyon H:W ratio determines the amount of
shade cast by the buildings themselves across the canyon floor.
Wide, open canyons (low H:W ratios) experience higher daytime
temperatures due to high solar exposure, as compared to deep,
narrow canyons (high H:W ratios) where buildings self-shade the
canyon (Johansson, 2006). Canyon orientation influences the level
of solar exposure, as east-west canyons receive more hours of direct
solar radiation than north-south orientated canyons (Ali-Toudert
& Mayer, 2006). If street H:W ratio is low (e.g. 0.5), an east-west
oriented street will receive direct solar radiation while the sun is
up, whereas north-south streets are solar exposed only in the middle hours of the day (Bourbia & Awbi, 2004a). The number of solar
exposed hours is also related to a street canyon’s H:W ratio and solar
zenith angle, which changes predictably throughout the year. For
Melbourne’s latitude (37.8◦ S), a street canyon H:W ratio of between
0.5 and 1.0 would provide some self-shading during the day, but be
able to dissipate heat at night (Bourbia & Awbi, 2004b; Mills, 1997;
Oke, 1988).
Implementing UGI is one of the easiest ways to modify street
canyon microclimates, other than façade awnings and overhangs
to shade footpaths (Ali-Toudert & Mayer, 2007). Ranking canyon
geometry and orientation can help prioritise streets for tree
planting or other UGI interventions. Using the RayMan model
(Matzarakis, Rutz, & Mayer, 2010), we hierarchically prioritised
streets of different geometry, based on self-shading by buildings
at the summer solstice (Fig. 3). For east-west oriented canyons the
proportion of the street canyon floor exposed to the sun is calculated at solar noon (Fig. 3a), and for north-south oriented canyons
the proportion of the day that the canyon floor is shaded is calculated (Fig. 3b). The amount of shading was then equally divided into
four priority classes (Fig. 3a and b). It should be noted that these
priorities are specific to Melbourne and will vary with geographic
location. This hierarchical approach demonstrates that wide/very
wide, east-west orientated streets should be prioritised for street
trees because of high solar exposure (Fig. 3c). Street trees would
provide less benefit in narrow street canyons with a high degree
of self-shading. In an analysis of daytime thermal imagery, Coutts
and Harris (2013) found that street trees in Melbourne were particularly effective at reducing surface temperatures in canyons with
a H:W < 0.8, whilst above this H:W the effects of trees on surface
temperature were reduced, which is consistent with our findings.
In narrow canyons, where there is adequate light, green walls
and façades as well as ground level vegetation should be prioritised
over trees due to reduced space, and because they allow better ventilation and long wave cooling at night. Appropriate plant selection
is very important in these situations. As H:W increases, light levels drop and wind turbulence may increase, and few plant species
are likely to tolerate these conditions. There is a paucity of empirical data on the performance of plants suitable for green walls and
facades in deep, narrow urban canyons (Hunter et al., 2014; Rayner,
Raynor, & Williams, 2010).
2.8. Step 5—Select new UGI based on site characteristics and
cooling potential
The final step selects and implements new UGI that is ‘fit-forplace’. The order of UGI elements presented in this section reflects
their priority given the goal of surface temperature reduction.
The primary goal for new UGI implementation should be to maximise ‘overhead’ vegetation canopy cover, to reduce canyon surface
temperatures as well as provide shading of pedestrian space and
transpirative cooling. The secondary goal should be to implement
either ground or wall ‘surface’ vegetation cover, also to reduce surface temperatures and provide transpirative cooling, but no (or
little) shading. Surface vegetation cover includes vertical greening
systems, green roofs and grassed ground surfaces. Table 2 presents a

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131

Fig. 3. Classification of streets for the implementation of street trees to mitigate daytime surface temperatures at the summer solstice in Melbourne, Australia (37.8136◦ S,
144.9631◦ E) based on the extent of self-shading by buildings. Figs. (a) and (b) show the percent of the street canyon floor shaded at solar noon for streets of different H:W
ratios. Calculations use the RayMan model. Fig. (c) demonstrates how this can be used to prioritise street tree installation for cooling assuming no existing UGI, where sites
with high solar exposure and resulting high temperatures are high priority targets for mitigation. Numbers inside the boxes are H:W ratios.

simple guide to how different UGI elements provide surface cooling
benefits.

2.8.1. Trees
In most cases, tree canopies are the optimal solution for
shading both canyon surfaces and the pedestrian space, and they
also provide evapotranspirative cooling (Rosenzweig et al., 2006;
Spronken-Smith & Oke, 1999) (Table 2). The amount of shade
trees provide depends on their architectural form and canopy density (Pataki, Carreiro, et al., 2011; Shashua-Bar, Potchter, Bitan,
Boltansky, & Yaakov, 2010). Thick or dense canopy trees provide
particularly good shade, meaning that broadleaf trees are generally
more effective than needle-leaf trees (Leuzinger et al., 2010; Lin &
Lin, 2010). However, trees that provide the greatest shade during
hot summer days can also trap heat under their canopy at night
(Spronken-Smith & Oke, 1999). To minimise heat trapping, street

trees should not form a continuous canopy, thereby allowing ventilation and long-wave radiation to escape (Dimoudi & Nikolopoulou,
2003; Spronken-Smith & Oke, 1999). A mix of tree species, with
different canopy architectures, could be considered for the same
reason (Pauleit, 2003).

2.9. Urban green open spaces
Urban green open spaces are primarily grassed areas with a relatively sparse (or absent) tree canopy, such as ornamental parks,
sporting fields and golf courses. Depending on their design and
irrigation regimes, urban green open spaces can potentially provide
‘islands’ of cool in hot urban areas, so it is important they be easily accessible to people (Giles-Corti et al., 2005). Depending on
their size and the wind direction, they can also cool urban areas
downwind (Dimoudi & Nikolopoulou, 2003; Spronken-Smith &

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Table 2
Modes of cooling provided by different urban green infrastructure options during summer and priority locations to optimise those cooling benefits.

Oke, 1998). Urban green open spaces cool more effectively if they
contain scattered trees and receive irrigation (Spronken-Smith &
Oke, 1998, 1999), and their spatial layout and vegetation structure
will be important in determining their cooling potential (Lehmann,
Mathey, Rößler, Bräuer, & Goldberg, 2014).
Greatly increasing the total area of green open space within a
city may significantly reduce temperatures at the city scale (Bowler
et al., 2010) but this is unlikely to be an option in most cities. Providing many small, distributed green open spaces could benefit a
larger number of neighbourhoods (Coutts et al., 2013; ShashuaBar & Hoffman, 2000), and the spatial prioritisation of green open
space for urban cooling is an area of ongoing research (Chang, Li,
& Chang, 2007; Connors, Galletti, & Chow, 2013). As cooling benefits are focussed downwind of any urban green open spaces, they
would be best placed upwind of particularly hot areas or vulnerable
populations.
2.10. Green façades
Green façades are climbing plants grown up a wall directly or
on a trellis or similar structure set away from the wall (Hunter
et al., 2014). Green façades can be planted in the ground or in
planter boxes at any height up the walls of a building. As well as
preventing heat gain to building walls, green façades can provide
cooling through evapotranspiration (Köhler, 2008). Unlike green
walls, green façades are a realistic option for wide spread UGI
implementation because of lower installation and maintenance
costs (Ottelé et al., 2011).
Green façades are particularly beneficial on walls with high
solar exposure and where space at ground-level is limited (Wong
& Chen, 2010), or where aerial obstructions limit tree growth.
Dark coloured walls should be prioritised for green façade covering
over light coloured walls, which do not become as hot (Kontoleon
& Eumorfopoulou, 2010). To benefit pedestrians, green façades
should be installed adjacent to walkways (Table 2).
2.11. Green roofs
During the day, roofs are some of the hottest surfaces in urban
areas (Chudnovsky et al., 2004). Greening those roofs can greatly
mitigate urban surface temperatures, as well as reducing air-space
cooling requirement inside those buildings. Green roofs may be
extensive, with thin substrates (2–20 cm) and a limited range of
plants, or, where building structure is sufficiently strong, intensive,

with a thicker substrate layer that can support a wider range of
plants (Oberndorfer et al., 2007; Wilkinson & Reed, 2009).
Modelling suggests that green roofs can cool at a
neighbourhood-scale if they cover a large area (Gill et al., 2007;
Rosenzweig et al., 2006). To be effective, green roofs need to be
irrigated and maintain a high leaf area index before they become
comparable to the cooling provided by roofs painted with high
albedo paint (Santamouris, 2014) but their influence on cooling
at street level will be low (Ng, Chen, Wang, & Yuan, 2012). Green
roofs reduce surface temperatures best when they are covered in
taller vegetation (Lundholm, MacIvor, MacDougall, & Ranalli, 2010;
Wong & Chen, 2010) and irrigated (Liu & Bass, 2005). Achieving
a balance between maximising cooling performance during hot
summer conditions, whilst keeping plants alive in shallow soils
with minimal irrigation is an ongoing research challenge (Williams
et al., 2010). Green roofs have multiple benefits but for urban
surface cooling that has human health benefits, we recommended
adding green roofs to large, low buildings, or in areas with little
ground level green open space (Table 2).

3. Case study—city of Port Phillip, Melbourne, Australia
The City of Port Phillip comprises 20.62 km2 of predominantly
pre-1900 suburbs on the north shore of Port Phillip Bay in inner
city Melbourne, Australia (City of Port Phillip, 2014) and is home to
over 91,000 people (Australian Bureau of Statistics, 2011b). The City
of Port Philip was a key partner in this research and keenly aware
of the impacts of heat on communities especially from the 2009
extreme heat event in Melbourne which contributed to 374 excess
deaths (Department of Human Services, 2009). In the summer of
2011–12 the City of Port Phillip undertook airborne thermal remote
sensing of their municipality, a primary input to the prioritisation
framework, to help understand where areas of heat occurred in the
municipality in order to inform planning decisions. The City of Port
Phillip is an affluent, high density suburb populated by many city
professionals, yet pockets of disadvantage remain as it has the second highest amount of community and social housing in Victoria.
The elderly in the City of Port Phillip make up 6.8% of the population
which is slightly lower than the average for Greater Melbourne of
8.2% (City of Port Phillip, 2014). The interest and positive collaboration with the City of Port Phillip including the provision of thermal
data made this local government area an excellent case study. In
the 2011 census, the City of Port Phillip contained 228 statistical
areas (Statistical Area Level 1) which have an average population

B.A. Norton et al. / Landscape and Urban Planning 134 (2015) 127–138

of around 400 people (Australian Bureau of Statistics, 2011a). We
averaged the thermal data over the statistical areas to correspond
with demographic data. Steps 1–3 were undertaken with the support of the City of Port Phillip (Coutts & Harris, 2013) and a trial of
Steps 4 and 5 was undertaken with local council representatives
from across Melbourne.

3.1. Step 1—Identifying priority neighbourhoods
Heat exposure was assessed using high resolution (0.5 m) airborne thermal remote sensing data for solar noon and midnight
on the 25 February 2012, during an EHE (daytime max. 37.1 ◦ C;
overnight minimum 24.7 ◦ C) (Coutts & Harris, 2013). The data were
corrected for emissivity effects and then averaged for each statistical area to identify hot spots (Fig. 4a and b). The coolest location in
the City of Port Phillip both during the day and night is Albert Park, a
large park with a lake in the north east of the study area (see Fig. 4f).
More information on the use of thermal imagery, data processing,
and prioritising areas of high heat exposure can be found in Coutts
and Harris (2013).
To assess vulnerability in the City of Port Phillip, several common
indicators were used:
• elderly population (>65 years) (Fig. 4c)
• population of the very young (<5 years) (Fig. 4d) and
• the Index of Relative Socio-Economic Disadvantage (IRSD)
(Fig. 4e).
These commonly identified contributors to vulnerability draw
on information that is readily available and easily accessible at an
appropriate resolution. Local knowledge of communities and what
influences vulnerability in a neighbourhood can assist decisions
regarding what contributors to include.
Finally, to determine zones of behavioural exposure, local knowledge can be supplemented with information on planning zones. In
the City of Port Phillip we identified several planning zones (Fig. 4f)
that are likely to experience high population activity;
• Park and Public Recreation Zone;
• public use zone (education, health and community, transport);
• mixed use zone (neighbourhood centres with residential and
non-residential development around train stations); and
• commercial zones.

133

3.2. Step 2—Characterising UGI and grey infrastructure
To classify existing UGI and grey infrastructure, we created a
detailed land cover map using a combination of aerial imagery and
multispectral data and LiDAR data. Using a supervised classification in GIS software that was trained using these data sources, a
map was produced comprising seven land cover classes: vegetation
(trees), irrigated and non-irrigated green space, rooftops, concrete,
asphalt (roads) and water (Fig. 6). We documented building heights
based on height information from the LiDAR data in GIS software
and manually measured street widths, also in GIS. If such data are
not available, mapping of grey infrastructure can also be completed
using visual surveys or products such as Google Earth, while local
governments may also have tree inventories that can be drawn
on. The characterisation information in Fig. 3 provides a guide for
identifying the types of streets in our City of Port Phillip priority
neighbourhood that are likely to experience poorer thermal comfort, with little shading and high levels of imperviousness leading
to high land surface temperatures during the day.
3.3. Step 3—Maximising the cooling value of existing UGI
Vegetation health information, obtained from remotely sensed
data (Step 2) or on-ground surveys, can be used to identify where
water sensitive urban design can be used most efficiently to
enhance existing UGI (Fig. 6). In the City of Port Phillip, annual
stormwater runoff into Port Phillip Bay is estimated to be 4764 ML,
while a further 11,460 ML flows through the municipality and into
to the bay from neighbouring areas (City of Port Phillip, 2010). Not
all of this large water resource can be captured and stored but if suitable technologies and distributed storage can be implemented this
can greatly assist in optimising existing and new UGI performance.
Water sensitive urban design and stormwater harvesting help capture and retain stormwater in the urban landscape for irrigation
(Coutts et al., 2013). Modes of capture and storage that were considered were (1) bioretention pits, (2) curb cut-outs that direct water
to tree root zones, and (3) roof runoff harvesting and storage in
rainwater tanks for irrigation. Urban green open spaces in the priority neighbourhood are mostly unirrigated, and during the day can
experience surface temperatures greater than roads and concrete.
A 2009 streetscape assessment (City of Port Phillip, unpublished
data) found that 40% of streets were rated fair for stocking, health
and vigour of trees. Providing water to the other 60% of street trees
can help improve health and vigour, increasing transpiration, leaf
density and hence shading capacity.
3.4. Steps 4 and 5—Selecting and integrating new UGI

Using GIS software, we overlayed the data for all three components of the prioritisation framework: heat exposure (daytime and
night time heat), vulnerability (elderly, very young and socially disadvantaged) and behavioural exposure (Public Use Zones, etc.). This
produced a priority neighbourhood map for UGI implementation
in the City of Port Phillip whereby the highest risk neighbourhoods
intersected the highest levels of heat exposure, vulnerability and
behavioural exposure (Fig. 5). Framework Steps 2–5 were applied
to the priority neighbourhood highlighted in the inset of Fig. 5.
This neighbourhood comprises a large number of services that
may increase behavioural exposure including the South Melbourne
Market and nearby shopping strips, the Port Phillip Community
Rehabilitation Centre, and a light rail corridor including South Melbourne Station. The neighbourhood includes the Crawford Court
Flats which house elderly citizens, and the area houses over 50
residents of >65 years. The South Melbourne Market and light rail
station are located within a zone of relatively high heat exposure.
As such, this area comprises vulnerable populations who live and
engage in an area that has high heat exposure.

Steps 4 and 5 of the decision framework were applied in a
field workshop with local council representatives from across Melbourne. Using the high resolution (0.5 m) thermal imagery, two City
of Port Phillip streets were identified that illustrated the role of
canyon geometry in high solar exposure and the potential role of
UGI in public space cooling. Both were east-west facing: Street A
was wide (approximately 30 m) and low (two storeys high, 6 m,
H:W = 0.2), whereas Street B was narrow (5 m wide) and low (two
storeys high, 6 m, H:W = 1.2) (Fig. 7). Street A had scattered, small
trees that would never develop a large canopy, and Street B had no
existing UGI. Based on the decision framework and discussions onsite, it was recommended to install a green wall or narrow hedge on
the north-facing wall of Street B (Fig. 7). In contrast, the workshop
group recommended that Street A would benefit from street trees
that would produce wider, denser canopies, planted at a higher
frequency, especially on the southern side of the street which is
more solar exposed (Fig. 7). The footpaths are wide so additional
UGI planting is possible. Although the road was also wide enough

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B.A. Norton et al. / Landscape and Urban Planning 134 (2015) 127–138

Fig. 4. Identifying priority neighbourhoods across the City of Port Phillip. Panels a and b present daytime and night time exposure respectively; panels c and d present
population aged over 65 and below 5 respectively; panel e presents the Index of Relative Socio-economic Disadvantage; panel f presents areas of population behavioural
exposure.

to accommodate central reservation tree planting, the proximity to
a busy market makes this impractical from a car parking and access
perspective.
The City of Port Phillip had already identified opportunities for
street tree planting, and highlighted the need for water sensitive
urban design elements such as bio-retention tree pits and rain gardens to improve water management (TreeLogic, 2010). The benefit
of applying this case study framework, however, is that the City of
Port Phillip can now prioritise their investment and implementation into neighbourhoods and streets that are ‘high priority’ and can
deliver a greater temperature reduction benefit for this investment.

4. Discussion
We have reviewed the potential of urban green infrastructure
to mitigate high temperatures and integrated this information
with census data and remotely sensed thermal data to provide a
decision framework that prioritises effective implementation of
UGI. Although we make recommendations on what types of UGI
will be most suitable in different circumstances, the selection of
appropriate UGI will always depend on the local climate, soils,
water availability as well as community norms and cultural values
(Bowler et al., 2010; Pataki, Carreiro et al., 2011).

B.A. Norton et al. / Landscape and Urban Planning 134 (2015) 127–138

135

Fig. 5. Priority neighbourhoods for mitigation of high urban temperature using green infrastructure in the City of Port Phillip. Darker colours (purple, orange and green)
represent higher priority locations, and black represents the highest priority locations for heat mitigation and UGI implementation. The inset is an identified priority
neighbourhood surrounded by the red box. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

This framework enables prioritisation of placement and UGI
type at the neighbourhood scale. Most existing studies have measured cooling effects from UGI at the micro-scale, or modelled them
at the city scale. More research is needed to understand the interactions between street canyon geometries, UGI placement and plant
species selection to establish firm connections between UGI spatial
arrangement and street-scale cooling. Increasingly, modelling tools
are available to do this, and there are concerted efforts to improve
the representation and simulation of vegetation in urban climate
models (Grimmond et al., 2011). This is a complex problem and
ultimately a combination of field measurements and modelling are
likely required (Oke et al., 1989). Once a greater understanding is

achieved, it might be possible to develop spatially explicit planning
support tools similar to those used in conservation planning (e.g.
Carsjens & Ligtenberg, 2007).
UGI should be part of any urban heat mitigation strategy, and
the strengths and flexibility of the other components to this strategy, such as alternative surface materials and street design, should
be similarly well understood to enable an informed and optimised
response (Emmanuel, 2005). These need to run in conjunction with
adaptation measures in the public health service and attempts to
invoke behavioural change in the urban population to better cope
with higher temperatures (Bi et al., 2011; O’Neill et al., 2009). Furthermore, UGI will rarely be installed exclusively to mitigate high

Fig. 6. Characterisation of urban green infrastructure using a combination of aerial imagery, multi-spectral data and LiDAR.

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B.A. Norton et al. / Landscape and Urban Planning 134 (2015) 127–138

Fig. 7. Diagram of the street canyon of Streets A (left) and B (right) in the City of Port Phillip case study. Both streets are east-west oriented and the view is from the west.
The diagrams show suggested UGI placement based on the context. See text for details.

temperatures, so there will likely be trade-offs and compromises
when selecting the type of UGI and the plant species used.
There are two other major knowledge gaps that hinder successful implementation of UGI in hot or warm climates. The first
is the horticultural limitations of UGI, which highlight a disconnect between some architectural and urban design ‘visions’ and
what is biologically or physically possible (Hunter et al., 2014).
There is an urgent need for species-specific (or functional type) data
on plant ecophysiology, thermoregulation, water use and microclimate cooling benefits in urban settings to inform UGI plant
selection, substrate selection, placement and subsequent irrigation.
Related to this is the other major knowledge gap; a quantitative
understanding of the water requirements of different UGI systems
and plant species. Trees have received greatest research attention,
yet there is still little information regarding the water requirements of urban trees (May et al., 2013; McCarthy & Pataki, 2010;
Pataki, Carreiro, et al., 2011; Pataki, McCarthy, Litvak, & Pincetl,
2011). Water use and transpiration by street trees varies greatly
among species (McCarthy & Pataki, 2010; Pataki, McCarthy, et al.,
2011) but providing supplementary irrigation can increase cooling benefits (Gober et al., 2009). Until more detailed information
on plant water requirements is available, strategies to maintain
and maximise water availability to UGI elements during drought
periods would be prudent. Especially so for street trees because of
the direct and profound cooling benefits they provide to pedestrians and because of the many years ‘invested’ in their establishment
and growth that can be lost if they die in one year of poor water
management.
The case study application of the framework to the City of Port
Phillip was very well received by the workshop group, challenging their thinking on prioritisation and implementation of UGI,
especially in the objective of mitigating excess heat. Workshop
participants highlighted the multi-functionality of UGI and that
implementation would not consider urban heat alone. While they
found the framework useful in prioritising neighbourhoods, the
realities of implementation on the ground were complex with
many competing factors such as surrounding infrastructure (e.g.
above and below ground electrical and water services) and interactions between public and private space. Some local governments
also do not have the resources to acquire thermal remote sensing
data. High resolution thermal data are not necessary for this prioritisation purpose, and lower resolution satellite data would suffice
(e.g. Landsat 8 provides 30 m resolution). The selection of key vulnerability risk factors could also be informed by local government
staff knowledge and consultation with local social service and
health professionals with a deep knowledge of local demographics. Applying the framework as we have in the case study requires

suitable GIS software skills and products that may not be available
to all local government authorities. Nevertheless, the framework
can still be broadly followed without the detailed mapping applied
in this study, and practitioners can adapt the framework to suit
their local capacity and circumstance. This framework has already
been taken up by the City of Geelong, Victoria, Australia, where a
consultant has been engaged to apply the framework in prioritising
neighbourhoods for heat mitigation within the municipality.
5. Conclusions
Mitigating extreme heat in urban climates will become
increasingly important as climate change progresses and urban
populations expand. UGI should be an important component of any
urban climate change adaptation strategy because of the multiple
benefits it provides to the community and local ecosystems. However, any UGI initiative should determine what the key objective(s)
is at the outset. This study assumes the key objective is temperature
mitigation. As such, in a situation where a decision may negatively
impact other ecosystem service benefits provided by UGI, the tradeoff would always be in favour of greatest temperature mitigation. If
a UGI initiative has multiple objectives this becomes more difficult
and priorities will have to be ranked, or trade-offs individually discussed with or without local community stakeholder engagement.
Despite the increasing amount of research on how UGI can prevent climatic extremes in urban areas, our understanding remains
fragmented and the level of ‘take up’ by urban planners is low. We
have presented, justified and applied a hierarchical decision framework that prioritises high risk neighbourhoods and then selects the
most appropriate UGI elements for various contexts. Much work
remains to be done, especially in determining the optimal arrangement of UGI in a street canyon or the wider urban landscape but
there is sufficient information available for local governing bodies
to take positive, preventive action and start mitigating high urban
temperatures using UGI.
Acknowledgements
This paper arose from a project funded by the Victorian Centre for Climate Change Adaptation Research (VCCCAR). Sincere
thanks to the City of Port Phillip for making available the thermal
imagery data and supporting GIS layers. The manuscript has benefited from input during the project from Brod Street, all workshop
participants, and Karyn Bosomworth and Alexei Trundle from RMIT
University as well as from two anonymous reviewers. Andrew M.
Coutts is funded by the Cooperative Research Centre for Water Sensitive Cities. Monash University provides research into the CRC for

B.A. Norton et al. / Landscape and Urban Planning 134 (2015) 127–138

Water Sensitive Cities through the Monash Water for Liveability
Centre.
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