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ICUC8 – 8 International Conference on Urban Climates, 6 -10 August, 2012, UCD, Dublin Ireland.

556: Improvement of the single-layer UCM in the WRF model
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1Sachiho A. Adachi *, Hiroyuki Kusaka , Michael Duda , Yuko Akimoto , Masayuki Hara ,1
1
Takao Yoshikane , Fujio Kimura
1*

Research Institute for Global Change, JAMSTEC, Yokohama, Japansachihoa@jamstec.go.jp
2Center for Computational Sciences, University of Tsukuba, Tsukuba, Japan
3Mesoscale and Microscale Meteorology, NCAR, Boulder, USAAbstract
This study modifies the WRF/UCM to incorporate the gridded urban parameters into themodel and reproduce the urban effects to local climate caused by inhomogeneity in anurban area. The simulations of heat island in summer and winter in Tokyo metropolitan area
are conducted using the original WRF/UCM and the modified one.
The reproducibility of heat island in Tokyo metropolitan area is improved in the modified
WRF/UCM compared with the original one. The urban fraction shows large impact on thenighttime surface air temperature in summer and winter. The anthropogenic heat (AH)
affects on the nighttime surface air temperature in winter, while impacts of AH is small insummer. The differences in surface air temperature between the simulations with thespacially-uniform urban data and the gridded urban data are small during daytime in bothseasons. The difference of surface wind speed is large in early evening in summer becauseof the difference in the speed of decline of the mixing layer between urban and other landuse areas.
Keywords: urban canopy model, urban parameters, WRF

1. Introduction

Anthropogenic heat, urban fraction, andbuilding height (roughness length, displacement
height) are major urban parameters expressing
the urban characteristics such as human activity,land use, and urban geometric structure in anurban model.
To reproduce the urban effects to local climate
caused by inhomogeneity in an urban area, thisstudy modified the WRF/UCM to incorporate thegridded urban parameters into the model andconducted the preliminary sensitivity analysis ofspatially inhomogeneous urban texture to thelocal climate.

Table 1: Model settings
Boundary data

NCEP/NCAR reanalysis IResolution

20km, 4km (Horizontal)
31 levels (Vertical)

Land surface
schemeNoah land surface model

Urban scheme

Single-layer urban canopy model(Kusaka et al., 2001)

PBL scheme

Mellor-Yamada-Janjic TKE
schemeSurface layer
schemeMonin-Obukhov (Janjic) scheme

2. Methodology

2.1 Model settings
The version used in this study is WRF version
3.3.1 (Skamarock et al., 2008). The applied
schemes and model setting are listed in Table 1.
The outer domain covers the most part of mainislands in Japan, while the inner domain covers
the central part of Japan including the Tokyometropolitan area (TMA) (Fig. 1).
The grid of the inner domain has 126 x 126 gridcells with the horizontal resolution of 4 km. The
sensitivity simulations are conducted in winterand summer. The summer case is conductedfrom July 25, 2010 to September 1, 2010, theoutput only in August is used for analysis. The
winter case is integrated from January 25, 2008
to March 1, 2008, the output only in February isused for analysis.

Fig 1. Model domains. The dashed square indicates theanalyzed area (Tokyo metropolitan area).

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ICUC8 – 8 International Conference on Urban Climates, 6 -10 August, 2012, UCD, Dublin Ireland.

Fig 2. Distributions of (a) urban ratios, (b) anthropogenic heat flux, (c) roughness length, and (d) displacement height in
ctl_org run. (e)-(h) are same as (a)-(d), but for exp_all run.

2.2 Experimental design
The four urban parameters are given as thegridded data in new WRF/UCM: (1) urban fraction,(2) anthropogenic heat (AH), (3) momentum
roughness length, and (4) displacement height.
The gridded urban parameters used in this study
are illustrated in Fig 2.
The urban fraction is defined as a ratio of urban
area to an entire grid cell, and created using thefine land cover data (FLCD) from the Digital
National Land Information (DNLI) dataset,published by the Ministry of Land, Infrastructure,Transport, and Tourism. The FLCD categorizes
land use into 11 or 12 types for every 100-msquare. These 11 or 12 land-use types werereclassified to eight land-use types used in USGS
land-use types in the WRF model. The
anthropogenic heat release is based on the AH
value in August reported in NIRE (1997), which isestimated using energy consumption rates. The
momentum roughness length above canyon andthe displacement height are calculated according

to empirical equations set up based on a numberof large eddy simulations in the Tokyo
metropolitan area (Kanda et al., 2012).
To evaluate the impacts of the gridded data tourban climate, the sensitivity analyses areconducted. The experimental design was shownin Table 2. The fixed value in Table 2 means theurban parameter is spatially homogenous,
namely, it is provided as constant value. On theother hand, “map” means the urban parameter isgiven as the gridded data.
Table 2: Experimental design.
Simulation
Urban
AH
2fraction(W/m )
ctl_org
0.7
17.5
ctl_LU
0.7
0
exp_LUmap
0
ctl_AHmap
17.5
exp_AHmap
map
exp_allmap
map

Fig 3. Monthly mean surface air temperature: (a)observation, (b) ctl_org run, (c) exp_all run.

Z0(m)
0.286
0.286
0.286
0.286
0.286
map

Zd(m)
4.31
4.31
4.31
4.31
4.31
map

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ICUC8 – 8 International Conference on Urban Climates, 6 -10 August, 2012, UCD, Dublin Ireland.

Fig 4. Monthly mean surface wind speed: (a)observation, (b) ctl_org run, (c) exp_all run.

3. Results

3.1 Comparison with Observation
The summertime surface air temperature andwind velocity simulated by the current WRF/UCM
and new WRF/UCM are compared withobservation to evaluate the model performance.
Figure 3a shows the observed monthly meansurface air temperature (Tsa). The Tsa in August,2010 exceeds 29 degree in the central part ofTMA. The simulated Tsa in exp_all run captures
well the feature in observation, although thesimulated temperature is slightly overestimated in
the center part of TMA and coastal areas (Fig.
3c). The Tsa in ctl_org run also shows theobserved feature of Tsa. However, thetemperature is overestimated in the center part ofTMA more than that in exp_all andunderestimated in the east area of TMA (Fig. 3b).
The surface wind speed is strong in the coastal
area more than in the inner area (Fig. 4a). The
model results can also reproduce thecharacteristics in observation (Figs. 4b and 4c),although the simulated wind speed overestimates
about 1 m/s. The distributions of wind speed arealmost same between ctl_org run and exp_all run,except for that around Tokyo. The wind speed
weak around Tokyo in the exp_all run, because
the sea breeze from south-west is weaken by thelarge friction due to the high buildings.
3.2 Sensitivity analysis of gridded urban
parameters
The impacts of the gridded data of the urban
fraction and the anthropogenic heat onsummertime surface air temperature areindicated in Fig. 5. Figure 5a shows the surface
air temperature differences between ctl_LU run
and exp_LU run, while Fig 5b is that between
ctl_AH and exp_AH. Tsa is strongly affected by
the land use. The difference of about 20% in
urban fraction corresponds to the difference ofabout 0.6℃ in surface air temperature. The
temperature difference due to anthropogenic heatdata is larger than 0.2℃. The effects of urban
fraction to surface air temperature in winter issmaller than that in summer, while the AH haslarger impacts on the Tsa in winter (Fig.6).
The diurnal variations of sensitivities of gridded
urban parameters are shown in Fig.7 and Fig.8.

For analysis of the sensitivity, mean difference isdefined as spatial average of the absolute valueof the difference in two simulations.
Mean difference in Tsa in summer between theexp_all run and the ctl_org run is large during thenight time from 17LT to 04LT. The temperature
difference in night time is mainly caused by thedifferent urban fraction. This is because thedifference in surface air temperature between theurban area and other land-use areas, such as
grassland, irrigated cropland, and pasture, isdominant in the night time. In wintter, the urban
fraction and the AH have a large impact on Tsa in
the evening and in the nighttime, respectively.
Especially, the AH has strongly affects on the Tsa
in the early morning in wintter; the meandifference is about 0.2 ℃.

Fig 5. Difference in monthly mean surface airtemperature in summer between (a) exp_LU and ctl_LU(exp_LU - ctl_LU), and (b) exp_AH and ctl_AH (exp_AH- ctl_AH).

Fig 6. Same as Fig.5, but in winter.

The diurnal variations of mean differences insurface wind speed are smaller than that in Tsa.
In the summer, mean difference peaks in early
evening around sunset. The analysis of windprofile suggests that the large difference inththth

ICUC8 – 8 International Conference on Urban Climates, 6 -10 August, 2012, UCD, Dublin Ireland.

surface wind speed is caused as a result of thedifference in the decline speed of mixing layer. Inwinter, the diurnal variation of mean difference insurface wind speed is small.

5. Acknowledgements

This research was supported by the Research
Program on Climate Change Adaptation(RECCA) Fund by Ministry of Education, Culture,Sports, Science and Technology (MEXT) ofJapan.

6. ReferencesFig 7. Diurnal change of mean difference in monthly
surface air temperature ad monthly surface wind speed
in summer.

Fig 8. Same as Fig. 7, but in winter.

4. Conclusion

The simulations of heat island in summer andwinter in Tokyo metropolitan area are conductedusing the original WRF/UCM and the modified
WRF/UCM.
The reproducibility of heat island in Tokyo
metropolitan area is improved in the modified
WRF/UCM compared with the original one. The
modified WRF/UCM represent the weakness ofsea breeze as a result of the large roughness
length around Tokyo. The urban fraction shows
large impact on the nighttime surface airtemperature in summer and winter. The
anthropogenic heat affects to the nighttime
surface air temperature in winter, while it is small
in summer. The differences in surface airtemperature between the original WRF/UCM (thespacially-homogeneous data) and the modified
one (the gridded urban data) are small during
daytime in both seasons. The difference of
surface wind speed is large in early evening insummer because of the difference in decline
speed of the mixing layer between urban andother land use areas.
The modified WRF/UCM seems to be better
than the original WRF/UCM. However, thequantitative evaluation due to the modification isadditionally required.

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Wang, W. and Powers, J.G., (2008): A
description of the advanced research WRF
version 3. NCAR/TN-475+STR, 113p.
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Gryschka, S. Raasch, (2012): New aerodynamic
parameterization for real urban surfaces.
Boundary-Layer Meteorology, submitted.
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canopymodelforatmosphericmodels:Comparison with multi-layer and slab models.
Boundary-Layer Meteorology, 101, p.329-358.
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method of warming provision technologies within
metropolitan cities (in Japanese). National
Institute for Resources and Environment Rep.,
311 pp.