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Erratum: Prioritizing urban sustainability solutions: coordinated
approaches must incorporate scale-dependent built environment
induced effects (2015 Environ. Res. Lett. 10 061001)
M Georgescu1,4, W T L Chow2, Z H Wang3,4, A Brazel1,4, B Trapido-Lurie1, M Roth2 and V Benson-Lira1
1
2
3

School of Geographical Sciences and Urban Planning, Arizona State University, Tempe, AZ 85287, USA
Department of Geography, National University of Singapore, Kent Ridge, Singapore 117570
School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, AZ 85287, USA
Global Institute of Sustainability, Arizona State University, Tempe, AZ 85287, USA

Any further distribution of 4
this work must maintain
E-mail: Matei.Georgescu@asu.edu
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and DOI.

Due to an error in the production process, the
incorrect version of figure 2 was mistakenly published
on 9 June 2015. The correct version of the figure is

below. This error has no bearing on the interpretation
and conclusions drawn.

Figure 2. Geographical considerations, in terms of micro-, to local/neighborhood, to meso-/regional-, and finally global scale linkages
in physical processes and aspects are often downplayed or underconsidered when implementing urban adaptation measures.

© 2015 IOP Publishing Ltd

Environ. Res. Lett. 10 (2015) 061001

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Prioritizing urban sustainability solutions: coordinated approaches
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M Georgescu1,4, W T L Chow2, Z H Wang3,4, A Brazel1,4, B Trapido-Lurie1, M Roth2 and V Benson-Lira1
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School of Geographical Sciences and Urban Planning, Arizona State University, Tempe, AZ 85287, USA
Department of Geography, National University of Singapore, Kent Ridge, Singapore 117570
School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, AZ 85287, USA
Global Institute of Sustainability, Arizona State University, Tempe, AZ 85287, USA

E-mail: Matei.Georgescu@asu.edu
Keywords: urban, sustainability, adaptation, mitigation, climate

Abstract
Because of a projected surge of several billion urban inhabitants by mid-century, a rising urgency
exists to advance local and strategically deployed measures intended to ameliorate negative
consequences on urban climate (e.g., heat stress, poor air quality, energy/water availability). Here we
highlight the importance of incorporating scale-dependent built environment induced solutions
within the broader umbrella of urban sustainability outcomes, thereby accounting for fundamental
physical principles. Contemporary and future design of settlements demands cooperative participation between planners, architects, and relevant stakeholders, with the urban and global climate
community, which recognizes the complexity of the physical systems involved and is ideally fit to
quantitatively examine the viability of proposed solutions. Such participatory efforts can aid the
development of locally sensible approaches by integrating across the socioeconomic and climatic
continuum, therefore providing opportunities facilitating comprehensive solutions that maximize
benefits and limit unintended consequences.

1. Introduction
The share of urban relative to rural dwellers has rapidly
surpassed the 50% threshold of global population
(figure 1(a)). Anticipated increases of urban inhabitants (a surge of roughly 3 billion by mid-century
compared to today) will lead to extensive conversion
of natural to engineered landscapes, with recent
estimates indicating likely growth of global land cover
exceeding 1.5 million km2 by 2030 [1], an area roughly
equivalent to the size of Mongolia. Urban, relative to
peri- or ex-urban areas, face combined challenges
from directly induced regional climate modification
owing to the physical infrastructure of the built
environment and impacts resulting from increased
global emissions of long-lived greenhouse gases [2].
Because greenhouse gas emissions continue to
increase, there is mounting urgency to advance existing and develop novel strategies minimizing tradeoffs,
while maximizing the benefits gained from improving
© 2015 IOP Publishing Ltd

the very environment more of the globe’s inhabitants
will reside in. We posit that novel urban solutions
aimed at the provision of sustainable urban environments lie at the intersection of adaptation (i.e.,
adjustment in response to expected changes in
climate) and mitigation (i.e., intervention aimed at
anthropogenic forcing reduction) strategies, aptly
incorporating essential elements of both approaches.
Current attitudes on sustainability of cities
endorse the notion of high-density agglomerations
[3]. This concept, centered on the presumption of
reduced per capita emission of greenhouse gases, has
recently given rise to large expansion campaigns. For
example, Iskandar, Malaysia, a newly minted developmental region in Southeast Asia, is lauded as a sustainable metropolis of international standing with a keen
eye on energy conservation, environmental awareness
and preservation. Regrettably, the notion of energy
conservation exclusive of built environment impacts
(e.g., reduction of the sky view factor, limiting the

Environ. Res. Lett. 10 (2015) 061001

M Georgescu et al

expected for some time. This is fundamentally different relative to developed nations, where management
plans for retrofitting metropolitan areas are of greater
concern, necessitating economic valuation to guide
strategic prioritization [9].
This perspective addresses the opportunity of
choices available for urban regions to ameliorate negative consequences on urban climate (e.g., heat stress,
poor air quality, energy/water availability), illustrates
scale dependent benefits and tradeoffs of individual
choices, and outlines necessary steps forward.

2. Limiting constraints and choices of
opportunity
Figure 1. Historical and projected total global population
(black line), urban population (red line), and rural population (dark yellow line) through 2050, in billions (a). Relative
urban population for Asia (red line), Africa (green line),
North America (blue line), South America (light blue line),
Europe (pink line), and Oceania (yellow line), compared to
total urban population for specified particular period of time
(b). Source: UN.

region’s ability to naturally cool itself during evening
and nighttime hours will require more, not less, energy
consumption) often omits fundamental physical principles. Importantly, current norms designating highdensity equals enhanced sustainability may not offer the
decisive advantage previously thought [4, 5]. Although
such work has not been conducted for a necessarily
diverse number of cities to reach broadly generalizable
conclusions, recent evidence provides support to the
notion that ‘there is no easy single recipe for low-carbon lifestyles’ [6] when lifecycle assessments account
for lifestyle choices plus emissions related to housing
energy and transportation fuels [7].
We emphasize here that urban sustainability, a
term that could broadly be defined as ensuring environmental, socio-cultural, and economic dimensions
of a city meeting the needs of its residents over a longterm period [8], must also incorporate direct built
environment induced effects, thereby accounting for
fundamental physical principles from an energy balance perspective. Prioritizing urban solutions therefore requires place-based awareness, but ought to also
entail temporal aspects describing when such prioritization is expected. For example, the relative share of
urban population for Asia is projected to peak around
2030, but decline subsequently, as urban populations
in Africa begin growing at increasingly rapid rates
(figure 1(b)). Therefore, projected changes of the
urban share of population can be used as a timeline
indicating when the co-evolution of urban growth and
adapting/mitigating infrastructure implementation
can take place—consequently, technological investments today can be utilized in several decades, henceforth, in areas where substantial urbanization is not
2

Commonly used approaches towards ameliorating
deleterious aspects of urbanization on climate (e.g.
urban warmth or air pollution) largely involve directly
modifying several terms of the surface energy balance
[10]. High albedo roofs increase reflectance and
reduce sensible heat and stored energy in the urban
fabric [11], while permeable concrete or asphalt
enables reduced heat storage and larger surface
evaporation [12], and green spaces simultaneously
increase latent heat fluxes and increase direct shading
from vegetated canopies [13]. In addition to the
established methods specified, there also exists a
portfolio of recently developed complementary technologies that serve dual adaptation and mitigation
purposes. These technologies, which include phase
change materials for storing solar energy [14], photovoltaic pavements and canopies [15], and the cogeneration of power with waste heat [16], also alter the
urban surface energy and water cycles, which in turn
reduce the urban heat island (UHI) intensity and
building energy loads, thereby diminishing energy
demand, therefore lowering greenhouse gas emissions. In addition, an indirect but essential energy
saving opportunity is maximized when anthropogenic
heat, an important constituent of the UHI effect [17],
is utilized for cogeneration purposes.
The physical aspects underpinning the abovementioned approaches are well known at the immediate spatial scale of application, but their multi-scale
efficacy and impacts on other natural and urban systems have not been as well elucidated. The lack of theoretical knowledge is unsurprising given the inherent
physical and social complexities of developing and
implementing such solutions in cities. These include:
(i) The availability of developed or undeveloped
spaces in urban areas. In mature cities with
intensive land-use and finite space for development, little room exists for substantial variation
in horizontal and vertical redevelopment. This
limitation may preclude approaches that require
sizeable spaces (e.g. large parks) in favor of other
less space-intensive approaches utilizing urban

Environ. Res. Lett. 10 (2015) 061001

M Georgescu et al

Figure 2. Geographical considerations, in terms of micro-, to local/neighborhood, to meso-/regional-, and finally global scale linkages
in physical processes and aspects are often downplayed or underconsidered when implementing urban adaptation measures.

landscapes with limited functions (e.g. rooftop
gardens or cool roofs).
(ii) The opportunity costs of implementing these
approaches. Maintaining a dedicated space, such
as an urban forest that potentially reduces urban
warmth and improves air quality, may be too
substantial relative to alternate land-uses that
may be of greater short-term economic value.
Quantifying its value under a sustainability
framework is fraught with difficulty, but
approaches (e.g. a cost-benefit life cycle analysis
or an ecosystems services framework) assigning
an economic value to the service provided can be
—and have been—successfully employed in
cities to inform policymakers of the sustainable
value of these parks [18].
(iii) The vertical location (i.e. street- versus rooflevel) and spatial extent (i.e. building or neighborhood-scale) of the approach. First, certain
approaches (e.g. green roofs) will result in
substantial micro-scale benefits towards selected
stakeholders, particularly within or around the
building rooftop. These benefits, however, are
unlikely to be experienced by the majority of city
residents as pedestrians at street levels, especially
if not applied at sufficiently large scales. Second,
the success of these methods is likely to be
piecemeal without co-ordination between urban
stakeholders. The spatial configuration of green
spaces in the context of UHI reduction can be
significant in some cities [19], and an important
corollary would thus be how to maximize the
3

potential
for
configurations?

cooling

with

different

(iv) The city’s larger synoptic climate context. Three
examples of how urban solutions must be aware
of the coupling between geographic scales of
physical processes from the micro- to the globalscale (figure 2) must be considered. First, the
city’s regional or synoptic climate may substantially reduce the selected approach's effectiveness.
Reflective roofs in cities subject to seasonal dust
storms can have substantially lower albedos
through deposition of fine particulate matter and
other debris [20]. Second, unexpected climatological impacts at larger scales may occur. For
example, high reflectivity can have adverse effects
on the hydrological cycle of cities, leading to
reduced regional-scale precipitation [2, 21, 22].
Third, strategies effective within specific climates
may be impeded by larger sustainability contexts,
such as the viability of utilizing non-native, high
water-demand flora within arid environments
that reduce the supply of available urban water
[23, 24]. The tradeoff between localized cooling
vis-à-vis water scarcity in cities susceptible to
drought conditions has yet to be fully examined.
The myriad of biophysical and socio-economic
complexities present in real urban environments
strongly suggest that a portfolio of adaptive and mitigating strategies is likely to be a preferable option,
though it remains to be seen how much, and of what, is
ideal. Certainly, previous assertions endorsing onesize-fits-all type of solutions, by virtue of their neglect

Environ. Res. Lett. 10 (2015) 061001

M Georgescu et al

of multi-scale socio-economic and biophysical considerations, are not recommended [2, 25]. One narrative yet to be widely considered, however, is that of a
spectrum of spatial scales (figure 2) [26]. Reflective
materials, for instance, may be most effective in reducing microscale temperatures when individual building facets are considered, but lose efficiency when
thermal interactions among buildings and street canyons are included at neighborhood scales. Green roofs,
on the other hand, can be a promising option when
implemented extensively at city scales, but its full
potential can be more costly if regional scale advection
is considered within the context of water-energy
trade-offs.

3. Steps forward
It is understandable that urban climatologists are
collaborating with other disciplines (e.g., urban planning, landscape architecture) increasingly often to
enhance communication and apply knowledge
towards advancing solutions to urban problems
[27, 28]. Illustrative examples of interdisciplinary
cooperation include: (i) comparing disciplinary theory, methods, modeling, and aspects of applications to
urban design and planning, as well as (ii) sustainable
policy development emphasizing enhanced coordination between stakeholders, researchers, and policymakers, and (iii) formalizing organizational structures
that enable and facilitate interactions with related
fields (e.g., International Association for Urban Climate, and the Board on the Urban Environment of the
American Meteorological Society).
The field of ecology, for example, has been impacted heavily with new foci on urban ecology and the socalled ecological homogenization of urban USA [29].
Urbanization is a central topic in the emerging field of
macrosystems ecology, which similarly has established
protocols to study multi-scale drivers for ecological
processes in cities. Considerable integration with
knowledge in urban climate is needed in these
endeavors.
While individual buildings that can be built to last
for decadal- or century-time scales have considerable
temporal impacts, decisions made by stakeholders
concerning urban sustainability solutions also have
climate-related spatial impacts. Scale considerations
often impose limits on subsequent or concurrent
planning decisions [27], and require extensive multidisciplinary knowledge potentially beyond individuals
or uncoordinated groups involved in ad-hoc urban
development. For instance, the construction of a
building, which is taller relative to existing structures,
would alter existing surface and near-surface temperatures, shading and wind-flow, in turn modifying thermal comfort and air quality. These impacts may
preclude and limit subsequent development that
potentially reduces the neighborhood’s sustainability,
4

especially when the cumulative impacts from rapid
development are considered. For example, the sum of
rapid development in the Pearl River Delta region in
East China, by virtue of local to regional circulation
changes, has been linked to deteriorating regional air
quality [30]. Thus, stakeholders involved in the more
sustainable design and planning of settlements should
be cognizant of these issues prior to incipient stages of
growth to complement strategies across spatial scales.
One way to enable this is via a centralized planning
process involving contributions from interested participants aware of the limits and impacts on urban climate arising from building development. Clear and
integrated communication between architects, builders, planners and other stakeholders with relevant
urban climate knowledge would yield key insights into
developmental approaches that maximize urban sustainability. For instance, centralized planning of the
new Marina Bay Financial Centre district in Singapore
utilizes several of the aforementioned urban climate
adaptation strategies across building- and localscales [31].
There remains considerable analysis, tool-building, and coordinated value-added collaboration (e.g.,
the World Climate Change Research Programme,
tasked with improving prediction of the Earth system,
omits reference to urban sustainability in its inventory
of six grand challenges) that must emanate from the
urban and global climate community, and related disciplines, who understand the physics of these complex
systems and have the capacity to simulate desirable
features and goals of the strategies noted herein. This
must be a priority rather than applying limited techniques and producing quick solutions without fully
comprehending outcomes that may, in reality, be
inappropriate. Not all strategies should be weighted
equally across all scales and regions, but judiciously
analyzed to optimize what will and will not work in the
climate region and within a societal needs context.

Acknowledgments
This work was supported by NSF Grants EAR1204774, DMS-1419593, CBET-1435881 and by the
National University of Singapore Research Grant
R-109-000-162-133.

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