Improvement of urban parameters for the single-layer UCM in the WRF model
Sachiho A. Adachi,1 Hiroyuki Kusaka,2 Michael G. Duda,3 Manabu Kanda,4Alvin C.G. Varquez,4 Makoto Nakayoshi, 4 Motohiko Tsugawa,1 and Fujio Kimura1

1 Japan Argency for Marine-Earth Science and Technology,
3 The National Center for Atmospheric Research,

4 Tokyo Institute of Technology(Fig. 1). The grid of the inner domain has 500 x

1. Introduction
Anthropogenic heat, urban fraction, andbuilding

2 University of Tsukuba

height(roughnessdisplacementheight)

areparameters

expressing

lenght,majorurbantheurban

characteristics such as human activity, landuse, and urban geometric structure in an urban
model. In the single-layer urban canopy model(UCM) of the current Weather Research andForecast model (WRF), urban areas are
categorized into only three types of urban,

500 grid cells with the horizontal resolution of 4km. The simulation was conducted from July25, 2010 to September 1, 2010, and the output
only in August was used for analysis.
Table 1. Model settings
Boundary data

20km, 4km (Horizontal)

ResolutionLand

31 levels (Vertical)

surfacedefined by different sets of values of urban

schemeparameters.

Urban scheme

To reproduce the urban effects to local
climate caused by inhomogeneity in the urban
area, this study modified the WRF/UCM toNCEP/NCAR reanalysis I

Noah land surface model
Single-layer urban canopy
model (Kusaka et al., 2001)
Mellor-Yamada-Janjic TKE

PBL scheme

schemeincorporate the gridded urban parameters into
the model, and then conducted the sensitivity
analyses of spatially inhomogeneous urban
texture to the local climate.
2. Model and Experimental DesignThe version used in this study was WRF
version 3.3.1 (Skamarock et al., 2008). The
applied schemes and model setting are listed inTable 1. The outer domain covers the most partof main island in Japan, while the innerFig 1. Model domains. The dashed squaredomain covers the central part of Japan

indicates

including the Tokyo metropolitan area (TMA)

metropolitan area).

theanalyzedarea(TokyoTable 2. Experimental design
Simulation

Urban fraction

AH

Roughness length

Displacement(Z0C)

height (ZDC)

CTL_org

0.7*

17.5*

0.71*

7.185*

CTL_LU

0.7*

00.71*

7.185*

EXP_LU

map

0

0.71

7.185

CTL_AH

map

17.5*

0.71

7.185

EXP_AH

map

map

0.71

7.185

EXP_z0map

map

map

7.185

EXP_zdmap

map

0.71

map

EXP_allmap

map

map

map

* only at grid cells with LU_INDEX ( the dominant land use) = urban
The four urban parameters given as theThese11or12

land-use

types

weregridded data in new WRF/UCM are as

reclassified to eight land-use types used infollows: (1) urban fraction, (2) anthropogenic

USGS land-use types in the WRF model. Theheat (AH), (3) momentum roughness length,

anthropogenic heat release is based on theand (4) displacement height. The urban

AH value in August reported in NIRE (1997),

fraction is defined as a ratio of urban area towhich is estimated using energy consumption

an entire grid cell.

rates. The momentum roughness length

The gridded urban parameters used inabove canyon and the displacement height

this study are illustrated in Fig 2. The urban

arefraction is created using the fine land coverequations set up based on a number of large

data (FLCD) from the Digital National Land

eddy simulations in the Tokyo metropolitan

Information (DNLI) dataset, published by thearea (Kanda et al., 2012).

Ministry of Land, Infrastructure, Transport,

calculated

accordingtoempirical

To evaluate the impacts of the griddedand Tourism. The FLCD categorizes land use

data

into 11 or 12 types for every 100-m square.

analyses are conducted. The experimental

tourbanclimate,thesensitivity

Fig 2. Distributions of (a) the anthropogenic heat flux, (b) urban ratios, (c) the roughness length, and(d) the displacement height.

Fig 3. Monthly surface air temperature of(a) observation and (b) model.
design was shown in Table 2. The fixed valuein Table 2 means the urban parameter isspatially homogenous, namely it is provided
as constant value. On the other hand, “map”
means the urban parameter is given thegridded data.

Fig 4. Difference of surface airtemperature due to difference between theconstant value and the gridded data in: (a)four urban parameters, (b) the urban
fraction, (c) the anthropogenic heat, (d)theroughness
length,and(e)displacement height.

3. Results
3.1 Sensitivity analysis of gridded urban
parameters
The model output from new WRF/UCM
is compared with observation to evaluate themodel performance. Figure 3a shows theobserved monthly surface air temperature.
The monthly surface air temperature inAugust exceeds 29 deg. in the central part ofTMA. The model results can capture well theobservation,althoughthesimulated

temperature is slightly overestimated in thecenter part of TMA and coastal areas. Themodelresults

canalso

reproducetheobserved characteristics of surface windspeed and precipitation (not shown).
The impacts of the gridded data of eachurban parameter on surface air temperature
are indicated in Fig 4. Figure 4b shows thesurface air temperature differences between
EXP_LU and CTL_LU, while Fig 4c is thatFig 5. Difference of surface wind speed
due to difference between the constantvalue and the gridded data in: (a) foururban parameters, (b) the urban fraction,(c) the anthropogenic heat, (d) theroughness length, and (e) displacement
height.
between EXP_AH and CTL_AH. The surface
air temperature is strongly affected by theland use and anthropogenic heat.

The

difference of about 20% in urban fraction
corresponds to the difference of about 0.6 deg.

in surface air temperature. On the otheris because the difference in surface air

hand, the differences of roughness length andtemperature between the urban area anddisplacement height show the temperatureother land-use areas, such as grassland,change less than 0.2 deg..

irrigated cropland, and pasture, is dominant

Thewindspeed

issusceptible

toin the nighttime.

roughness length. The difference is morethan 0.6 m/s in the central area (Fig 5).

Acknowledgment
This research supported by the Research

3.2 Diurnal variation of sensitivities ofProgram on Climate Change Adaptation

gridded urban parameters(RECCA) Fund by Ministry of Education,

Hourly variation of responses to surface
air temperature is shown in Fig 6. The

Culture, Sports, Science and Technology(MEXT) of Japan.

difference between the simulations of thenew WRF (EXP_all) and the original WRF

References(CTL_org) is large during the nighttime from

Skamarock, W.C., Klemp, J.B., Dudhia, J.,

17LT to 04LT. The main cause is theGill, D.O., Barker, D.M., Duda, M.G.,

difference in the value of urban fraction. ThisHuang, X.-Y., Wang, W. and Powers, J.G.,
2008: A description of the advanced(a)research

WRF

version3.

NCAR/TN-475+STR, 113p.
Kanda, M., A. Inagaki, T. Miyamoto, M.
Gryschka,S.

Raasch,

2012:

New

aerodynamic parameterization for realurban

surfaces.

Boundary-Layer

Meteorology, submitted.
Kusaka, H., Kondo, H., Kikegawa, Y. and(b)Kimura, F., 2001: A simple single-layerurban canopy model for atmosphericmodels: Comparison with multi-layer andslabmodels.

Boundary-Layer

Meteorology, 1 0 1 , 329-358.
NIRE, 1997: Development of a verification
methodFig 6. Diurnal variations of the differencesof (a) surface air temperature and (b)surface wind speed due to difference
between the constant value and thegridded data on: (a) four urban
parameters, (b) the urban fraction, (c) theanthropogenic heat, (d) the roughness
length, and (e) displacement height.

ofwarming

provisiontechnologies within metropolitan cities(in Japanese). National Institute for
Resources and Environment Rep., 311 pp.