LETTER • OPEN ACCESS

Seasonal hydroclimatic impacts of Sun Corridor
expansion
To cite this article: M Georgescu et al 2012 Environ. Res. Lett. 7 034026

You may also like
- From legacy contamination to watershed
systems science: a review of scientific
insights and technologies developed
through DOE-supported research in water
and energy security
Dipankar Dwivedi, Carl I Steefel, Bhavna
Arora et al.
- Mapping mountain torrent hazards in the
Hexi Corridor using an evidential
reasoning approach
Youhua Ran, Jinpeng Liu, Feng Tian et al.

View the article online for updates and enhancements.

- Climate regionalization of various wine
grape varieties in Hexi Corridor, China
Yan Hao, Yanjun Wang, Yashan Li et al.

This content was downloaded from IP address 184.182.36.54 on 10/05/2022 at 23:53

IOP PUBLISHING

ENVIRONMENTAL RESEARCH LETTERS

Environ. Res. Lett. 7 (2012) 034026 (9pp)

doi:10.1088/1748-9326/7/3/034026

Seasonal hydroclimatic impacts of Sun
Corridor expansion
M Georgescu1,2,3 , A Mahalov2 and M Moustaoui2
1

School of Geographical Sciences and Urban Planning, Arizona State University, Tempe,
AZ 85287-5302, USA
2
School of Mathematical and Statistical Sciences, Global Institute of Sustainability, Arizona State
University, Tempe, AZ 85287-1804, USA
E-mail: Matei.Georgescu@asu.edu

Received 14 May 2012
Accepted for publication 22 August 2012
Published 7 September 2012
Online at stacks.iop.org/ERL/7/034026
Abstract
Conversion of natural to urban land forms imparts influence on local and regional
hydroclimate via modification of the surface energy and water balance, and consideration of
such effects due to rapidly expanding megapolitan areas is necessary in light of the growing
global share of urban inhabitants. Based on a suite of ensemble-based, multi-year simulations
using the Weather Research and Forecasting (WRF) model, we quantify seasonally varying
hydroclimatic impacts of the most rapidly expanding megapolitan area in the US: Arizona’s
Sun Corridor, centered upon the Greater Phoenix metropolitan area. Using a scenario-based
urban expansion approach that accounts for the full range of Sun Corridor growth uncertainty
through 2050, we show that built environment induced warming for the maximum
development scenario is greatest during the summer season (regionally averaged warming
over AZ exceeds 1 ◦ C). Warming remains significant during the spring and fall seasons
(regionally averaged warming over AZ approaches 0.9 ◦ C during both seasons), and is least
during the winter season (regionally averaged warming over AZ of 0.5 ◦ C). Impacts from a
minimum expansion scenario are reduced, with regionally averaged warming ranging between
0.1 and 0.3 ◦ C for all seasons except winter, when no warming impacts are diagnosed.
Integration of highly reflective cool roofs within the built environment, increasingly
recognized as a cost-effective option intended to offset the warming influence of urban
complexes, reduces urban-induced warming considerably. However, impacts on the hydrologic
cycle are aggravated via enhanced evapotranspiration reduction, leading to a 4% total
accumulated precipitation decrease relative to the non-adaptive maximum expansion scenario.
Our results highlight potentially unintended consequences of this adaptation approach within
rapidly expanding megapolitan areas, and emphasize the need for undeniably sustainable
development paths that account for hydrologic impacts in addition to continued focus on mean
temperature effects.
Keywords: urban heat island, adaptation, hydroclimatic modeling, megapolitan areas,
Arizona, Sun Corridor, cool roofs, sustainability
S Online supplementary data available from stacks.iop.org/ERL/7/034026/mmedia

3 Address for correspondence: School of Geographical Sciences and Urban

Content from this work may be used under the terms
of the Creative Commons Attribution-NonCommercialShareAlike 3.0 licence. Any further distribution of this work must maintain
attribution to the author(s) and the title of the work, journal citation and DOI.
1748-9326/12/034026+09$33.00

Planning, Arizona State University, PO Box 875302, Tempe, AZ 85287-5302,
USA.
1

c 2012 IOP Publishing Ltd Printed in the UK

Environ. Res. Lett. 7 (2012) 034026

M Georgescu et al

1. Introduction

second half of the century, shifting economic priorities
directed the region away from a mostly agrarian lifestyle to a
major metropolitan area. The outcome was considerable urban
land-use development at the expense of agricultural plots and
native semi-desert landscapes [21]. Recent work indicates that
projected Sun Corridor expansion through mid-century could
induce summer season local- to regional-scale near-surface
temperature impacts at least as important as those owing
to large-scale climate change [22]. In addition to locally
simulated summertime warming approaching 4 ◦ C for a
maximum expansion scenario, the vast conversion of natural
to impermeable surfaces was shown to lower summertime
evapotranspiration (ET) by 1–2 mm day−1 over newly
urbanizing urban areas.
Here we extend previous scenario-based Sun Corridor
expansion work by emphasizing seasonally varying hydroclimatic consequences, and fully characterize impacts on
near-surface temperature and precipitation throughout the
calendar year. Our numerical simulations, using the Weather
Research and Forecasting (WRF) modeling system, account
for a maximum and minimum Sun Corridor expansion
scenario, as well as integration of highly reflective cool
roofs within the built environment to assess the alleviation
potential of UHI-induced warming. In evaluating impacts
on accumulated precipitation we also hope to shed light on
potential consequences for renewable water resources. For
example, the Salt River watershed, a highly managed system
of dams and reservoirs provides nearly half of the annual
water supply for the Phoenix metropolitan area [23], and
evaluation of regional-scale precipitation change is justified
given the combined effects of urban-induced and large-scale
climate change impacts on this semi-arid urban region [22].
Finally, although our focus is on the rapidly expanding
Sun Corridor, we hope our scenario-based approach,
accounting for the full range of urban expansion uncertainty,
will be extended to other rapidly expanding megapolitan
areas, particularly in the developing world where the large
share of future (urban-related) population rise is expected [2].

Although an overall world population increase of 2.3 billion
is projected by 2050 relative to 2011, urban growth is
estimated at 2.6 billion, as urban complexes, in addition
to absorbing all of the world’s additional inhabitants,
are expected to draw in 0.3 billion rural residents [1].
To meet the ever-increasing population-driven demand of
urban infrastructure during the next few decades, substantial
conversion of natural landscapes to urban land forms is
anticipated [2]. The landscape modification associated with
emergence and expansion of large urban agglomerations will
necessarily modify the surface radiation and moisture balance,
with implications for local and regional hydroclimate.
Considering the likely prospects of future urban growth,
research addressing hydroclimatic consequences of emerging
and expanding megapolitan areas is essential to provide
guidance for city planners, and energy and water providers,
focused on undeniably sustainable development paths with
minimum environmental consequences.
The most documented mechanism whereby urban
complexes modify their own and that of surrounding
environments is the urban heat island (UHI) [3–10]. Defined
as a thermal difference between urban and nearby rural areas,
the characterization of the UHI depends on the biome in
which the urban complex resides [9, 11], with considerable
sustainability implications (e.g., timing of peak energy
demand and delivery for air conditioning use associated with
maximum UHI-induced warming impacts) for the placement
of newly emerging and rapidly expanding megapolitan areas.
In addition to their thermal influence, mounting evidence
also suggests that urban agglomerations modify local to
regional-scale precipitation [12–16]. While much of this
work has fundamentally advanced our understanding of
hydroclimatic impacts of urban regions, there has been
relatively less research addressing consequences arising from
rapidly expanding megapolitan areas [17]. Since projected
global urban expansion is expected to dwarf urbanization
witnessed thus far [2], likely hydroclimatic effects of urban
development (e.g., rapidly expanding megapolitan areas)
should be expected to exceed similar impacts studied to date.
Within the US, Arizona’s Sun Corridor is the fastest
growing megapolitan area, a designation for a housing and
urban land-use corridor anchored by two or more large cities
at its geographical termini [18]. The state of Arizona is
projected to reach a top ten national ranking as one of the most
populous in the US by 2030 [19], with mid-century population
estimates ranging between 8 and 16 million people [20].
Since precise forecasts of Sun Corridor growth through
mid-century are unlikely to produce accurate placement of
urban land forms, scenario-based projections that account
for the full range of growth uncertainty are required to
evaluate hydroclimatic impacts resulting from urban-induced
landscape modification.
The Greater Phoenix area, at the heart of the emerging
Sun Corridor and the largest metropolitan area within the
Colorado River Basin, has undergone substantial landscape
modification throughout the 20th century [21]. During the

2. Methods
We have used version 3.2.1 of the WRF modeling
system [24, 25] to conduct sensitivity experiments assessing
hydroclimatic consequences of Sun Corridor expansion. A
detailed summary (e.g., parameterization options, forcing
data) of the modeling approach has been presented in
preceding work [22]; therefore we provide only an overview
here.
We performed three-year (2006–8) continental-scale,
ensemble-based simulations at 20 km resolution, for both a
modern-day Sun Corridor representation and scenario-based
expansion (figure 1). The domain utilized includes portions
of the Atlantic and Pacific Oceans, northern Mexico and
Southern Canada [22]. Each numerical experiment consists of
four independent realizations (realization 1 has a start time
of October 2005; realization 2 has a start time of November
2005; realization 3 has a start time of December 2005;
realization 4 has a start time of January 2006; all analysis
2

Environ. Res. Lett. 7 (2012) 034026

M Georgescu et al

We account for urban expansion by incorporating
Maricopa Association of Governments (MAG)-projected
high and low development mid-century Sun Corridor
growth scenarios. MAG, serving as the regional agency
for metropolitan Phoenix (www.azmag.gov/) and dedicated
to long-range and strategic planning, conducted statewide
growth analyses based on land ownership patterns. Military
lands, forests, parks and national monument lands, and
Native American residential lands, were deemed slowly or
non-developing, leaving privately owned land and state trust
lands as areas where conversion to urban land-use was
projected to occur. A maximum geographical expansion
scenario (hereafter ‘SUNCORR High’) was based on a
designation that required a minimum number of MAGprojected dwelling units per unit area to meet urban land-use
criteria. This scenario resulted in the greatest possible urban
land-use spatial extent, and these pixels were converted to
high intensity/commercial class within WRF’s single-layer
urban canopy model (UCM) [25, 26]. The UCM accounts
for urban geometry, shadowing from and reflection of
buildings, roof, road, and wall biophysical representation,
and diurnal cycle of anthropogenic heating. SUNCORR High
therefore consists of the greatest spatial extent and greatest
urban land-use intensity. A minimum geographical expansion
scenario (hereafter ‘SUNCORR Low’) was based on a
designation requiring a maximum number of MAG-projected
dwelling units per unit area to meet urban land-use
criteria. This scenario resulted in the most restrictive urban
land-use spatial extent, and these pixels were converted to
low intensity residential class within WRF’s single-layer
UCM. SUNCORR Low therefore consists of the most
restrictive spatial extent and least urban land-use intensity.
Consequently, our approach embraces the full range of
Sun Corridor megapolitan expansion uncertainty rather than
relying on specific forecasts for which precise predictions (of
urban land forms) are unlikely to be attainable.
Integration of highly reflective cool roofs within the
built environment, increasingly recognized as a cost-effective
adaptation option intended to offset the warming influence
of urban complexes [27, 28], was based on modification
of SUNCORR High experiments. Roof albedos were set to
an EPA Energy Star SOLARFLECT coating value of 0.88
(hereafter ‘SUNCORR Adapt’). The value of 0.88 was based
on the solar reflectance after three years of wear and tear (EPA
Energy Star Roof Product List: http://downloads.energystar.
gov/bi/qplist/roofs prod list.pdf?8ddd-02cf; accessed 1 June
2011). Usage of this, rather than a lower value, is intended to
quantify the greatest possible offset of UHI-induced warming
over this rapidly urbanizing semi-arid megapolitan area.
We utilize the US Geological Survey’s National Land
Cover Database 2006 [29] to represent urban features
of modern-day central Arizona (figure 1(a); hereafter
‘CONTROL’), and replace this landscape with MAGgenerated projections of high and low development Sun
Corridor growth scenarios to characterize projected midcentury expansion (figures 1(b) and (c)).
Finally, our reference to regional/area averages discussed
in the sections to follow refers to means calculated

Figure 1. Representation of Sun Corridor urban landscape extent
used within (a) Control, (b) SUNCORR Low, and
(c) SUNCORR High WRF simulations. Urban land-use is bounded
by red contours. Approximate geographic extent of the cities of
Prescott (north-central AZ), Tucson (southeast AZ), and the
Phoenix metropolitan area (central AZ) are denoted by blue squares.
Topography is overlaid in meters with higher altitudes appearing
darker.

consists of the period January 2006 through December 2008),
with variable spin-up times, an invaluable approach for
reduction of internal model noise and sensitivity to initial
conditions.
Since each scenario comprises of 12 years of numerical
experiments (three years of model integration times four
independent realizations), all model simulations are averaged
to produce a corresponding scenario mean.
3

Environ. Res. Lett. 7 (2012) 034026

M Georgescu et al

Figure 2. Simulated 2 m air temperature difference (◦ C) between SUNCORR High and Control simulations for (a) spring, (b) summer,
(c) fall and (d) winter, seasons.

between the SUNCORR High and Control experiments.
The greatest regionally averaged warming influence due to
Sun Corridor expansion occurs during the summer season
(1.04 ◦ C), with warming impacts remaining significant during
the spring and fall seasons (warming of 0.89 ◦ C and
0.87 ◦ C, respectively). During winter season, warming is
primarily constrained to areas undergoing transition to urban
land forms, with regionally averaged simulated warming
of 0.53 ◦ C. Contrasting the impacts during winter season,
urban-induced warming has a spatial sphere of influence
extending beyond areas undergoing urbanization, although
this characteristic appears most pronounced for the summer
and fall seasons as more than two-thirds of the state
experience warming in excess of 0.5 ◦ C. In addition, for
all seasons except winter, warming over newly urbanized
areas exceeds 2 ◦ C, and local maxima for each season range
between 3.5 and 4 ◦ C.
Integration of highly reflective cool roofs within the
built environment offsets about half of urban-induced
warming, leading to small regional-scale cooling during the
winter season (figure 3). Regional-scale warming impacts
remain greatest during the summer season (0.27 ◦ C) with
maximum local warming reduced by nearly half relative
to urban expansion without this adaptation approach (from
3.86 to 2.0 ◦ C). Regional-scale warming during spring

across the illustrated spatial domain. Specifically, the
extent encompasses a 6◦ latitude (31.25◦ N–37.25◦ N) X
7.5◦ longitude (−115◦ W to −108.5◦ W) box.

3. Results
A detailed assessment of WRF’s ability to appropriately
reproduce the summer climate of semi-arid urban regions
within the southwest US demonstrates excellent agreement
in the representation of daily to monthly diurnal cycle
of near-surface temperatures, and accurate simulation of
maximum daytime temperature timing and trend [11]. In
addition, we present an evaluation of the seasonally varying
near-surface temperature and precipitation representation of
the Control WRF simulation in the supplemental section (see
also figures S1–S3 available at stacks.iop.org/ERL/7/034026/
mmedia). Generally, WRF Control experiments compare well
with observationally based gridded product data, and provide
confidence in the model’s ability to reproduce Arizona’s
climate during the simulated time period.
3.1. Thermal impacts of Sun Corridor expansion
Figure 2 presents the seasonally varying (spring, summer,
fall, and winter) simulated 2 m air temperature difference
4

Environ. Res. Lett. 7 (2012) 034026

M Georgescu et al

Figure 3. Simulated 2 m air temperature difference (◦ C) between SUNCORR Adapt and Control simulations for (a) spring, (b) summer,
(c) fall and (d) winter, seasons.

(0.06 ◦ C) and fall (0.17 ◦ C) is considerably reduced with
cool roof implementation, in agreement with previous
research [30–32]. For all seasons (except winter, when cooling
is simulated) urban-induced warming remains an entirely
local phenomenon, and non-urbanizing locales undergo little
or no warming.
Consideration of a lower Sun Corridor expansion
scenario (i.e. SUNCORR Low simulations) reveals regionalscale urban-induced warming less than 0.3 ◦ C for all seasons.
Greatest warming occurs during summer (0.28 ◦ C), slight
warming during spring (0.14 ◦ C) and fall (0.12 ◦ C), and
no change in near-surface temperature is noted during
winter (figure 4). As noted in the SUNCORR Adapt relative
to Control simulations (figure 3), urban-induced warming
remains a primarily local phenomenon, with non-urbanizing
locales experiencing little change in near-surface temperature.
Locally greatest warming resulting from expansion to
SUNCORR Low does approach 2 ◦ C during the summer
season, but remains less than 1 ◦ C for both the spring and fall.

to the semi-arid area’s total regional precipitation [33],
is expected to diminish as falling precipitation previously
stored within the soil column is no longer available for
evapotranspiration (ET) during subsequent days. To evaluate
simulated hydroclimatic impacts owing to Sun Corridor
expansion, five-day means of ET were calculated for
all experiments (for their duration) in order to remove
high-frequency variability. Figure 5 presents the area averaged
(i.e. the box bounded by: 31.25◦ N to 37.25◦ N and −115◦ W
to −108.5◦ W) ET difference between SUNCORR High
and Control (figure 5(a)), SUNCORR Low and Control
(figure 5(b)), and SUNCORR Adapt and Control (figure 5(c)).
To denote variability of ensemble members, and therefore
estimate the degree of simulated uncertainty, the green
rectangles depict ±1 standard deviation from the mean
differences, and the blue whiskers denote extreme ensemble
member difference values.
Sun Corridor expansion, for all scenarios, leads to an
overall mean reduction in ET that peaks during the summer
season (extending into September) but is less pronounced
(although still negative) during remaining seasons. For all
scenarios, the largest ensemble member variability (i.e., the
degree of green rectangle extent about the mean) occurs
during the summer season (i.e., during the monsoon season),
likely associated with simulated differences in parameterized
convective motions and ensuing precipitation. Despite this

3.2. Hydroclimatic impacts of Sun Corridor expansion
Encroachment of urban infrastructure upon previously
permeable surfaces alters the local to regional-scale water
balance. Precipitation recycling, an important component
5

Environ. Res. Lett. 7 (2012) 034026

M Georgescu et al

Figure 4. Simulated 2 m air temperature difference (◦ C) between SUNCORR Low and Control simulations for (a) spring, (b) summer,
(c) fall and (d) winter, seasons.

variability, the overwhelming majority of SUNCORR High
and SUNCORR Adapt members lead to less ET (relative
to the CONTROL member counterpart) for all seasons,
including summer, when area-averaged reductions between
0.5 and 1 mm day−1 are predominant. Notably, ET impacts
owing to SUNCORR Adapt expansion appear to be more
consistently negative when compared to SUNCORR High
expansion, as only one (SUNCORR Adapt) ensemble
member leads to noticeably positive ET differences (relative
to CONTROL) during the entire length of simulated years,
in contrast to somewhat greater simulated variability for
SUNCORR High experiments.
Predictably, the reduction in evapotranspired water
results in a substantial total precipitation decrease (figure 6),
with greatest impacts (relative to CONTROL experiments)
occurring for expansion to SUNCORR High (12% less
total precipitation) and SUNCORR Adapt (16% less total
precipitation). Implementation of cool roofs therefore leads
to a 4% total accumulated precipitation decrease relative to
the non-adaptive expansion scenario. Urbanization-induced
precipitation reduction primarily occurs during the monsoon
months (figure 7), unlike similar impacts expected from
large-scale climate change, which indicate a decrease in mean
winter precipitation of approximately 8% over portions of
the southwestern US [34]. Progressively greater differences

in total precipitation between the urban expansion scenarios
and CONTROL experiments occur with the passage of
each simulated year, with the least intense urban expansion
scenario (SUNCORR Low) modifying regional precipitation
least. Expansion to SUNCORR High further reduces regional
precipitation while the SUNCORR Adapt simulations result
in least simulated total precipitation by the end of the
period, highlighting unintended but potentially significant
consequences via modification of the regional hydrologic
cycle associated with this adaptation approach.

4. Discussion and conclusions
This research evaluates hydroclimatic impacts of the fastest
growing megapolitan area in the US: Arizona’s Sun Corridor.
We use scenario-based expansion projections to assess
seasonally varying hydroclimatic consequences and account
for feedback effects to large-scale climate [35], which are
necessary for a more thorough accounting of climate system
impacts due to rapidly expanding megapolitan areas.
While we consider our results robust, we recognize
the value of a model intercomparison and differing
parameterization selection (e.g., incorporation of various
convective schemes) that could improve simulated diagnosis
of uncertainty quantification. Analysis performed at a
6

Environ. Res. Lett. 7 (2012) 034026

M Georgescu et al

Figure 5. Simulated evapotranspiration difference (mm day−1 ) between (a) SUNCORR High and Control, (b) SUNCORR Low and
Control, (c) SUNCORR Adapt and Control, for the duration of the simulations. Red line depicts inter-ensemble mean difference after
averaging over five-day window to smooth out high-frequency variability. Green rectangle depicts ±1 standard deviation from
inter-ensemble mean difference. Blue whiskers represent extreme ensemble member difference values.

range of spatial resolutions [36] to evaluate sensitivity
to horizontal and vertical grid spacing [37] on simulated
hydroclimatic impacts of Sun Corridor expansion also require
attention. Although our approach accounts for a diurnal cycle
representation of anthropogenic heating, it neglects additional
sources likely to occur from diffusion of heat through walls,
roofs and floors, and the consumption of energy due to air
conditioning systems and building occupants [38]. These
topics are the subject of ongoing research.
Near-surface thermal effects depend on the particular
trajectory of Sun Corridor development. For all scenarios, the
greatest regionally averaged warming occurs during summer
season (regionally averaged warming over AZ exceeds 1 ◦ C
for the greatest expansion scenario). Reduced, although still
significant warming occurs during spring and fall (regionally
averaged warming over AZ approaches 0.9 ◦ C for the greatest
expansion scenario), with reduced or no impacts, for all
expansion scenarios, during winter. While the metropolitan
region has already endured substantial UHI-induced warming
due to historical urbanization [39], these results demonstrate
that anticipated urban expansion could modulate regional
climate in years to come, which may pose additional concerns
related to air quality [40, 41] and ecosystem services [42, 43].
In addition, these impacts are layered on top of large-scale

climate change owing to increased emissions of greenhouse
gases [22], adding further stress to an already sensitive
system.
Integration of highly reflective cool roofs within the built
environment offsets about half of urban-induced warming,
leading to small regional-scale cooling during the winter
season. However, impacts on ET appear to be at least as
significant as Sun Corridor expansion without this adaptation
approach. While ET is reduced throughout the calendar
year (chiefly for SUNCORR High and SUNCORR Adapt
simulations, relative to CONTROL), impacts are greatest
during summer, when area-averaged reductions of 0.5–1 mm
day−1 dominate. Whereas expansion to SUNCORR High
decreases total precipitation by 12% (relative to CONTROL),
implementation of cool roofs (i.e., SUNCORR Adapt
experiments) reduces total precipitation by an additional 4%.
The largest share of decreased precipitation occurs over newly
urbanizing areas over higher terrain (e.g., located to the north
of modern-day metropolitan Phoenix), further decreasing
water storage potential over the state’s watersheds, which are
already expected to see less wintertime precipitation [34].
The combined effects of UHI-induced warming and ET
changes act in the same direction and reinforce one another.
UHI-induced warming over this semi-arid metropolitan
7

Environ. Res. Lett. 7 (2012) 034026

M Georgescu et al

Figure 7. Simulated accumulated total precipitation (mm) for
Control (black contour), SUNCORR High (red contour),
SUNCORR Low (green contour), and SUNCORR Adapt (blue
contour) simulations.

Acknowledgments
We appreciate the critique of two anonymous referees, whose
suggestions improved this manuscript. This work was funded
by NSF grant ATM-0934592.

References
[1] United Nations 2012 World Urbanization Prospects: The 2011
Revision Highlights (New York: United Nations,
Department of Economic and Social Affairs, Population
Division) (http://esa.un.org/unup/pdf/WUP2011
Highlights.pdf)
[2] Seto K C, Fragkias M, Guneralp B and Reilly M K 2011 A
meta-analysis of global urban land expansion PLoS ONE
6 e23777
[3] Bornstein R D 1968 Observations of the urban heat island
effect in New York city J. Appl. Meteorol. 7 575–82
[4] Oke T R 1973 City size and the urban heat island Atmos.
Environ. 7 769–79
[5] Arnfield A J 2003 Two decades of urban climate research: a
review of turbulence, exchanges of energy and water, and
the urban heat island Int. J. Climatol. 23 1–26
[6] Collier C G 2006 The impact of urban areas on weather Q. J.
R. Meteorol. Soc. 132 1–25
[7] Grimmond C S B 2006 Progress in measuring and observing
the urban atmosphere Theor. Appl. Climatol. 84 3–22
[8] Tran H, Uchihama D, Ochi S and Yasuoka Y 2006 Assessment
with satellite data of the urban heat island effects in Asian
mega cities Int. J. Appl. Earth Observ. Geoinform. 8 34–48
[9] Imhoff M L, Zhang P, Wolfe R E and Bounoua L 2010
Remote sensing of the urban heat island effect across
biomes in the continental USA Remote Sens. Environ.
114 504–13
[10] Chow W T L, Brennan D and Brazel A J 2012 Urban heat
island research in phoenix, Arizona: theoretical

Figure 6. Simulated total precipitation difference, for duration of
simulations, normalized by Control precipitation (units are
percentages) between (a) SUNCORR High and Control,
(b) SUNCORR Adapt and Control, and (c) SUNCORR Low and
Control.

complex is primarily a nighttime phenomenon [11, 39] while
the conversion of natural to impermeable surfaces repartitions
the surface energy balance toward increased sensible heating.
Incorporation of cool roofs act in opposition, via decreased
surface-absorbed radiation, but regional precipitation impacts
further drive the region’s hydroclimate away from its
natural state. In this sense, while incorporation of cool
roofs does indeed lower mean, near-surface temperature,
its overall climate system effect is greater when compared
to similar expansion without this adaptation approach.
Future development therefore must consider consequences
for hydroclimate, in addition to temperature impacts, to
comprehensively evaluate optimal mitigation and adaptation
strategies focused on sustainable development.
8

Environ. Res. Lett. 7 (2012) 034026

[11]

[12]

[13]

[14]

[15]

[16]

[17]

[18]

[19]
[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

M Georgescu et al

contributions and policy applications Bull. Am. Meteorol.
Soc. 93 517–30
Georgescu M, Moustaoui M, Mahalov A and Dudhia J 2011
An alternative explanation of the semiarid urban area oasis
effect J. Geophys. Res. 116 D24113
Burian S J and Shepherd J M 2005 Effect of urbanization on
the diurnal rainfall pattern in Houston Hydrol. Process.
19 1089–103
Shepherd J M 2005 A review of current investigations of
urban-induced rainfall and recommendations for the future
Earth Interact. 9 1–27
Kishtawal C M, Niyogi D, Tewari M, Pielke R A and
Shepherd J M 2010 Urbanization signature in the observed
heavy rainfall climatology over India Int. J. Climatol.
30 1908–16
Niyogy D, Pyle P, Lei M, Arya S P, Kishtawal C M,
Shepherd M, Chen F and Wolfe B 2011 Urban modification
of thunderstorms: an observational storm climatology and
model case study for the Indianopolis urban region J. Appl.
Meteorol. Climatol. 50 1129–44
Li W, Chen S, Chen G, Sha W, Luo C, Feng Y, Wen Z and
Wang B 2011 Urbanization signatures in strong versus
weak precipitation over the Pearl River Delta metropolitan
regions of China Environ. Res. Lett. 6 034020
Trusilova K, Jung M and Churkina G 2009 On climate impacts
of a potential expansion of urban land in Europe J. Appl.
Meteorol. Climatol. 48 1972–80
Grimm N B, Foster D, Groffman P, Grove J M,
Hopkinson C S, Nadelhoffer K J, Pataki D E and
Peters D P C 2008 The changing landscape: ecosystem
responses to urbanization and pollution across climatic and
societal gradients Front. Ecol. Environ. 6 264–72
US Census Bureau 2005 Interim State Population Projections
(Washington, DC: US Census Bureau, Population Division)
Marshall R M, Robles M D, Majka D R and Haney J A 2010
Sustainable water management in the southwestern United
States: reality or rhetoric? PLoS ONE 5 e11687
Georgescu M, Miguez-Macho G, Steyaert L T and
Weaver C P 2009 Climatic effects of 30 years of landscape
change over the Greater Phoenix, Arizona, region: 1.
Surface energy budget changes J. Geophys. Res.
114 D05110
Georgescu M, Moustaoui M, Mahalov A and Dudhia J 2012
Summertime climate impacts of projected megapolitan
expansion in Arizona Nature Clim. Change at press
(doi:10.1038/nclimate1656)
Svoma B M, Balling R C and Ellis A W 2010 Analysis of soil
moisture trends in the Salt River watershed of central
Arizona Theor. Appl. Climatol. 102 159–69
Skamarock W C and Klemp J B 2008 A time-split
nonhydrostatic atmospheric model for research and NWP
applications J. Comput. Phys. 227 3465–85
Skamarock W C, Klemp J B, Dudhia J, Gill D O, Barker D M,
Duda M G, Huang X-Y, Wang W and Powers J G 2008 A
description of the advanced research WRF version 3 NCAR
Tech. Note NCAR/ TN − 475 + STR (Boulder, CO: National
Center for Atmospheric Research)
Kusaka H and Kimura F 2004 Thermal effects of urban
canyon structure on the nocturnal at island: numerical
experiment using a mesoscale model coupled with an urban
canopy model J. Appl. Meteorol. 43 1899–910
Menon S, Akbari H, Mahanama S, Sednev I and
Levinson R 2010 Radiative forcing and temperature

[28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43]

9

response to changes in urban albedos and associated CO2
offsets Environ. Res. Lett. 5 014005
Gaffin S R, Imhoff M, Rosenzweig C, Khanbilvardi R,
Pasqualini A, Kong A Y Y, Grillo D, Freed A, Hillel D and
Hartung E 2012 Bright is the new black—multi-year
performance of high albedo roofs in an urban climate
Environ. Res. Lett. 7 014029
Fry J et al 2011 Completion of the 2006 national land cover
database for the conterminous United States Photogram.
Eng. Remote Sens. 77 858–64
Oleson K W, Bonan G B and Feddema J 2010 Effects of white
roofs on urban temperature in a global climate model
Geophys. Res. Lett. 37 L03701
Levinson R and Akbari H 2010 Potential benefits of cool roofs
on commercial buildings: conserving energy, saving money,
and reducing emission of greenhouse gases and air
pollutants Energy Efficiency 3 53–109
Millstein D and Menon S 2011 Regional climate
consequences of large-scale cool roof and photovoltaic
array deployment Environ. Res. Lett. 6 034001
Georgescu M, Miguez-Macho G, Steyaert L T and
Weaver C P 2009 Climatic effects of 30 years of landscape
change over the greater phoenix, Arizona, region: 2.
Dynamical and thermodynamical response J. Geophys. Res.
114 D05111
Dominguez F, Rivera E, Lettenmaier D P and Castro C L 2012
Changes in winter precipitation extremes for the western
United States under a warmer climate as simulated by
regional climate models Geophys. Res. Lett. 39 L05803
Jacobson M Z and Ten Hoeve J E 2012 Effects of urban
surfaces and white roofs on global and regional climate
J. Clim. 25 1028–44
Iorio J, Duffy P B, Khairoutdinov M and Randall D 2004
Effect of model resolution and subgrid scale physics on
daily precipitation in the continental United States Clim.
Dyn. 23 243–58
Mahalov A and Moustaoui M 2009 Vertically nested
nonhydrostatic model for multiscale resolution of flows in
the upper troposphere and lower stratosphere J. Comput.
Phys. 228 1294–311
Salamanca F, Krpo A, Martilli A and Clappier A 2010 A new
building energy model coupled with an urban canopy
parameterization for urban climate simulations—part I.
Formulation, verification, and sensitivity analysis of the
model Theor. Appl. Climatol. 99 331–44
Brazel A, Selover N, Vose R and Heisler G 2000 The tale of
two climates–Baltimore and Phoenix urban LTER sites
Clim. Res. 15 123–35
Steiner A L, Davis A J, Sillman S, Owen R C,
Michalak A M and Fiore A M 2010 Observed suppression
of ozone formation at extremely high temperatures due to
chemical and biophysical feedbacks Proc. Natl Acad. Sci.
USA 107 19685–90
Jiang X, Wiedinmyer C, Chen F, Yang Z-L and Lo J C-F 2008
Predicted impacts of climate and land use change on
surface ozone in the Houston, Texas, area J. Geophys. Res.
113 D20312
Kinzing A P, Chapin F S III, Perrings C, Polasky S, Smith K,
Tilman D and Turner B L II 2011 Paying for ecosystem
services: promise and peril Science 334 603–4
Jenerette G D, Harlan S L, Stefanov W and Martin C 2011
Ecosystem services and urban heat riskscape moderation:
water, green spaces, and social inequality in Phoenix, USA
Ecol. Appl. 21 2637–51