9.15 STUDY ON URBAN HEAT ISLANDS IN TOKYO METROPOLITAN AREA USING A METEOROLOGICAL MESOSCALE MODEL INCORPORATING AN URBAN CANOPY MODEL Ryozo Ooka*, Kazuya Harayama**, Shuzo Murakami***, Hiroaki Kondo**** *Institute of Industrial Science, University of Tokyo, Tokyo, Japan **Yamatake Corporation, Tokyo, Japan ***Faculty of Science and Technology, Keio Gijuku University, Yokohama, Japan ****National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan 1. Introduction thermal environments [3,4]. Although this model can The temperature increase due to urbanization, i.e. predict thermal the environment at pedestrian level urban heat islands, is becoming very serious in easily, it is not possible to consider the effect of local Japanese cities. Urban heat island phenom ena have climate due to the assumption of a horizontally been analyzed by many researchers. The three- homogeneous flow and temperature field. dimensional meteorological meso-scale model is often In this study, a meteorological meso-scale model used to solve the mechanism of urban heat islands based on the Mellor-Yamada model level 2.5 [5] which [1,2]. On the meso-scale analysis , which was originally incorporates the urban canopy model proposed by developed in order to predict the climate above the Kondo et al [3] as the boundary conditions (see Fig.1) surface boundary layer, a one-dimensional heat is developed to bridge the urban climate and urban balance model is usually used for the ground thermal environment. boundary conditions. In this conventional model, a roughness parameter is employed in order to present 2. Incorporating the Urban Canopy Model into the the effect of the building complex. As the vertical grid Meteorological Meso-scale Model size adjacent to the ground surface must be made several times larger than the roughness length in the The following five factors due to the building conventional model, physical phenomena within the complex are incorporated into the meteorological surface layer cannot be estimated. Furthermore, the meso-scale model : (1) wind reduction by the building definition of surface temperature is quite vague in the complex, (2) production of turbulence by the building conventional model because its relationship with complex, (3) solar radiation heat transfer inside and ground, roof and wall surface temperatures is unclear. outside of the building complex, (4) long wave Therefore, it is necessary to include the effect of urban radiation heat transfer inside and outside of the canopy exactly in order to analyze the thermal wind wind environment at pedestrian level in an urban area. On the other hand, the one-dimensional urban canopy model is also used commonly to analyze urban * Corresponding author address: Ryozo Ooka, IIS, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, （1）conventional model （2）urban canopy model Japan, e-mail: [email protected] Fig. 1 The concept of urban canopy model building complex and (5) sensitive and latent heat ¶ æ ¶U ö H ¶ ç ÷ 2 2 2 + K + (- uw)-hC daU (U + V + W ) (1) ¶y ç xy ¶y ÷ H - z ¶z* transfer from the building surface. The four factors è ø g due to plant canopy are also incorporated into the , where h is the ratio of the city block or planting meteorological meso-scale model: (1) wind reduction area to the grid area, Cd is the drag coefficient and by the plant canopy, (2) production of turbulence by a is the building or leaf area density. In the building the plant canopy, (3) solar radiation absorption by the canopy, the building area density a is assumed as plant canopy and (4) transpiration from the plant 4b /(w + b)2 . canopy. These processes are explained as below. The underlined terms are added to the following turbulent energy q2/2 and turbulent length scale q2l 2.1 Modeling the Building Complex. equations respectively. The effects of the building complex are D æq 2 ö ¶ é K ¶ æ q 2 öù ¶ éK ¶ æ q2 öù ç ÷ = ê xx ç ÷ú + ê yy ç ÷ú incorporated into the meteorological meso-scale ç ÷ ç ÷ ç ÷ Dt è 2 ø ¶x ëê s q ¶x è 2 øûú ¶y ëê s q ¶y è 2 øûú model as additional terms. In this analysis, a uniform 2 æ ö é 2 ù ç H ÷ ¶ ¶ æ q ö H æ ¶U ¶V ö + ê(qlSq ) ç ÷ú - çuw + vw ÷ city block, i.e. a series of buildings with the same ç H - z ÷ ¶z* ¶z * ç 2 ÷ H - z ç ¶z * ¶z* ÷ è g ø ëê è øûú g è ø height (h) , width (b), and interval (w), is assumed 3 3 q 2 2 2 2 - bV gwq v - +hC da(U + V + W ) (2) within each grid in the meso-scale analysis as shown B1l in Fig. 2. The three-dimensional detailed digital map 2 2 é 2 ù éK 2 ù æ ö é 2 ù D(q l) ¶ K xx ¶(q l) ¶ yy ¶(q l) ç H ÷ ¶ ¶(q l) = ê ú + ê ú + ê(qlSl ) ú information system is also utilized to represent the Dt ¶x s ¶x ¶y s ¶y ç H - z ÷ ¶z* ¶z* ëê t ûú ëê t ûú è g ø ë û properties of the real building complex, such as the 2 é H æ ¶U ¶V ö ù q3 é æ l ö ù -lF ê çuw + vw ÷ + b gwq ú - ê1+ F ç ÷ ú building height, width, and interval. The shapes of the 1 ç * * ÷ V v 2ç ÷ ëêH - zg è ¶z ¶z ø ûú B1 ëê è kz ø ûú building complex are measured by an airborne laser 3 2 2 2 + 2hC alU + V + W 2 scanner. Fig. 3 shows the distribution of building d ( ) (3) height and building width (averaged within a 2km × 2km grid) in Tokyo city area obtained from a Digital h Surface Model (DSM) and a Digital Elevation Model b (DEM). w w b Fig.2 Modeling the Building Complex 2.2 Effect of the Building and Plant Canopy on the Flow Field 6m The underlined term is added to the following 8m 16m 5m momentum equation for the resistance of the building 20m 15m 40m and plant canopy, referring to the forest canopy model Tokyo bay 25m proposed by Yamada [6]. 12m Tokyo bay * æ Q ö ¶z 16m DU æ ö H -z ç v ÷ g ¶ æ ¶U ö = f çV - V ÷ - g ç1 - ÷ + çK ÷ Dt g Q ¶x ¶x ç xx ¶x ÷ è ø H ç v ÷ è ø (1) building height (2) building width è ø （2km grid average） （2km grid average） Fig.3 Distribution of building height and width in Tokyo 2.3 Effect of the Building and Plant Canopy on the Increase of cooling load Radiation Field of a building In order to incorporate the effect of the building canopy External heat on the radiation field, it is necessary to consider complex radiation heat exchange between the ground Internal heat load Q H surface, roof surface, wall surface, and sky. The ①hot-water Promotion of ②lightning Heat Release from Air Conditioner Urban Heat Island authors have developed an estimation method based ③OA apparatus on the Monte Carlo Simulation to analyze the radiant ④kitchen heat transfer in complex urban areas [7]. While this ⑤human method is expected to give a highly accurate Fig.4 Schematic View of Building Energy Model estimation, it is not suitable to be used as a sub-model Wall Constitution Outside → Inside of the meteorological meso-scale model here, ① Concrete : 150mm ② Outside Inside Insulating material : 25mm because it increases the computational load. ③ Air space Therefore, an improved and simplified method based ④ Plaster board : 9mm ⑤ Sound absorbing board : 12mm on Kondo et al. [3] is adopted in this paper as a Roof Constitution Outside relatively simple urban radiation heat transfer model. Outside → Inside ① Mortar : 20mm ② Concrete :150mm 2.4 Modeling of the Air-Conditioning Exhaust Heat ③ Insulating material : 18mm Inside ④ Plaster board : 10mm In this research, the building energy model shown in Fig.5 Constitution of Wall and Roof Fig.3, are also incorporated into the building canopy internal heat generation in the building. This air- model in order to estimate the exhaust heat from air conditioning heat load is released with the energy conditioning in the buildings. The building energy consumed by the air-conditioner from air-conditioner‘s model is developed for both commercial and external unit. The ratio of the air-conditioning area to residential buildings. Usually, the air-conditioning heat total floor area of a building is assumed to be 0.4 and load is composed of (1) the heat load through the walls, 0.6 for commercial and residential buildings (2) the heat load through the windows, (3) the heat respectively. The heat load through the walls is load due to ventilation, and (4) the heat load due to obtained by calculating the one-dimensional heat ］ ］ 2 50 2 50 45 機器発熱機器発熱 45 OA OA機器発熱 W/m W/m OAOA機器発熱 ［ 40 照明発熱照明発熱 ［ 40 Lighting 照明発熱Light照明発熱ing 35 人体発熱 35 Human人体発熱 人体発熱人体発熱Human 30 30 発熱量 厨房発熱 発熱量 Kitchen厨房発熱 給湯発熱Hot-water 25 給湯発熱 25 20 Hot給湯発熱-water 20 あたりの 15 あたりの 15 10 10 5 5 0 0 単位床面積 0 6 12 18 24 単位床面積 0 6 12 18 24 Time[h] 時刻Time[h]［h］ 時刻［h］ （1）戸建住宅Residential 、Building集合住宅 （2）Commercial事務所系ビル Building Fig. 6 Internal Heat Generation per Unit Floor Area［W/m 2］ conduction of the wall. The heat load through the parameters, such as albedo, roughness length Z0, windows is calculated from the transmission of solar heat capacity, and moisture availability b [9][10] are radiation through the walls. The ventilation rate is 480 km -3 3 2 -4 3 2 The Japan Sea(25℃) Grid1 (mesh size:8km) N assumed to be 1.1×10 m /m s and 3.5×10 m /m s for commercial and residential buildings respectively.