Environmental Engineering Reference
In-Depth Information
leads to a reduction in the wind speed and higher PBL. These
modified meteorological conditions lead to detectable ozone-
concentration increases of 2.9-4.2% and 4.7-8.5% for day- and
night-time surface-ozone concentrations.
Civerolo
et al
. (2007) quantified the effects of increased
urbanization on surface meteorology and ozone concentrations
in the New York City metropolitan region. A land use change
model was used to extrapolate urban LULC over this region from
''present-day'' (ca. 1990) conditions to a future year (ca. 2050),
and these projections were subsequently integrated into MM5
and CMAQ simulations. The results suggest that extensive urban
growth in this metropolitan area has the potential to increase
afternoon near-surface temperatures by more than 0
.
6
◦
C, ozone
by about 1-5 ppb, and episode-maximum 8-hour ozone levels
by more than 6 ppb across much of the New York City area.
The focus of this study is on regional atmospheric modeling.
There are also efforts going on to better represent urban areas
in climate models. For example Oleson
et al
. (2008) included
a single layer UCM in the land model for the Community
Climate System Model (CCSM). However to fully make use of
the recent development of improvements in regional atmospheric
modeling high-resolution dynamical downscaling to urban areas
is necessary that can resolve heterogeneity of urban LULC.
A good example of such a study is Jiang
et al
. (2008) who
applied WRF-chem with the single-layer UCM to investigate
the impacts of climate and LULC changes on surface ozone
in the Houston area for August of current (2001-2003) and
future (2051-2053) years. The model was forced by downscaled
6-hourly Community Climate System Model (CCSM) version
3 outputs. High-resolution current year land use data from
National Land Cover Database (NLCDF) and future year land
use distribution based on projected population density for the
Houston area were used. The simulations show in the urban
area, the effect of climate change alone accounts for an increase
of 2.6 ppb in daily maximum 8-h O3 concentrations, and a 62%
increase of urban land use area exerts more influence than does
climate change. The combined effect of the two factors on O3
concentrations can be up to 6.2 ppb.
TABLE 21.2
EHE and the highest recorded maximum and
minimum daily temperatures during each period for Phoenix Sky
Harbor station (1961-2008) based on Huth
et al
. (2000) criteria.
Highest observed daily temperature (
◦
C)
Maximum
EHE
Minimum
25-28 June 1979
47.2
26.7
07-09 June 1985
46.1
27.8
21-23 June1988
46.7
31.7
03-05 July 1989
47.8
30.6
25-28 June1990
50.0
33.9
26-29 July 1995
49.5
31.7
12-16 July 2003
46.7
35.6
12-17 July 2005
46.7
33.9
21-24 July 2006
47.8
35.0
03-06 July 2007
46.7
33.9
1991. Table 21.2 lists EHEs identified for the Phoenix metropoli-
tan region between 1961 and 2008 plus the highest recorded
maximum and minimum temperatures. WRF simulations were
carried out for each EHE using LULC classification data for
the years 1973, 1985, 1998 and 2005. The scientific question
asked was whether urban development caused an intensification
and expansion of the area characterized by extreme tempera-
tures. Landsat Multispectral Scanner (MSS), Landsat Thematic
Mapper (TM) and Landsat ETM
derived LULC data for 1973
(Moeller, 2005), 1985, 1998 (Stefanov, 2000) and 2005 (Buyan-
tuyev, 2005) are used to provide the basis for model parameter
values. Landsat MSS, TM, and ETM
+
- based12-category LULC
data (rescaled to 30 m pixels) for 1973, 1985, 1998 and 2005 were
analyzed using the procedure of Stefanov, Ramsey and Chris-
tensen (2001). The data were incorporated by recoding classes
to conform to the 33-category 30 s global USGS Land Use/Land
Cover System currently used in WRF. The classification is part of
the USGS ''North America Land Cover Characteristics Data Base
Version 1.2'' (USGS, 2008) and contains 24 of the 37 categories
of the Anderson
et al
. (1976) Level II classification (U.S. Geo-
logical Survey, 2008). Additional categories in WRF's global 30-s
classification are: ''Playa'' (25), ''Lava'' (26), ''White Sand'' (27),
''Unassigned'' (28-30), ''Low intensity Residential'' (31), ''High
intensity Residential'' (32) and ''Industrial or Commercial'' (33).
WRF in conjunction with a single-layer UCM (Kusaka and
Kimura, 2004) as applied in this study includes three urban
land use classes characterized as commercial, high-intensity
and low-intensity residential. Here, these have been adjusted:
commercial/industrial, urban mesic residential and urban xeric
residential, which are distinguished by the type of vegetation
and irrigation (no vegetation, well-watered flood or overhead
sprinkler irrigated, and drought-adapted vegetation with drip
irrigation, respectively).
For each LULC class we adjusted the urban fraction according
to detailed vegetative cover measurements that were obtained
from an extensive field survey carried out in 30
+
21.4.2
Case study for Phoenix
The impact of 1973-2005 LULC changes on near-surface air
temperatures during four recent summer extreme heat events
(EHEs) are investigated for the arid Phoenix metropolitan area
using WRF.
During three decades of rapid urbanization the population of
the Phoenix metropolitan region increased by
∼
45% per decade
from about 971 000 to nearly 4 million currently. It is expected
that the population will grow to
∼
10 million by 2050 (Maricopa
Association of Governments, 2007). Understanding the effects
of urbanization on near-surface air temperature is particularly
importantinthisaridregioninordertoenhancetheadaptive
capacity of a city that regularly experiences high average daily
summertime temperatures and extendedperiods without rainfall.
Multiday EHEs strongly influence human comfort and health.
Between the years 1993-2002 Arizona led the United States in
deaths from heat exposure (CDC, 2005). EHEs were identified
based on criteria developed by Huth, Kysely and Pokorna (2000)
and Meehl and Tebaldi (2004) using the distribution of maxi-
mum recorded summer time air temperatures between 1961 and
×
30 m field
plots at 200 randomly selected sites across the entire urban
area (Grossman-Clarke
et al
., 2005). Development across the
Phoenix area is largely suburban in nature, with an urban core
of very limited spatial extent, unlike many older cities in more
temperate regions. The fraction of the surface cover types in the
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