Urban Climate

Introduction

Our laboratory’s research is focused on the urban heat island phenomenon and related themes.
 (1) Urban climate projection for the 2070s by the Weather Research and Forecasting model
 (2) Heavy rainfall events in urban areas
 (3) Urban heat island measurements

Urban climate projection using the WRF model    

 Urban warming is one of the most pressed issues in metropolitan areas in Japan.
 Temperatures in large cities have been increasing due to urbanization and climate change, and are expected to continue rising in the 21st century. As urban warming has a significant impact on economy and human health, there is a strong demand for urban climate projection at detailed scales. However, existing global climate models (GCM) are not well suitable for urban climate projection due to their coarse horizontal resolution. Alternatively, GCM may be combined with a fine resolution regional climate model via dynamical downscaling technique to produce high-resolution climate scenarios.
 Kusaka research group conducts various urban climate projections using regional climate model WRF. We mainly focus on various aspects of urban climate in Tokyo, including temperature rise and precipitation change.
 We also include several urban planning scenarios in our simulations to test their impacts on urban climate. Our projection target spans from 2050s to 2100.

(Asuka SUZUKI-PARKER)

August average temperature calculated by WRF model, Aug 2008 (Left), Aug 2050(Right)
With the calculation of forecasting model, we predicted that even the average temperature in 2050 summer is also the same as the highest temperature now. Maybe in 2070, we even cannot fall in sleep because of the hotness.

(Keiko FUJITA, 2011)
→For more details
Papers
  • Doan, Q.V., and H. Kusaka, 2016: Numerical study on regional climate change due to the rapid urbanization of greater Ho Chi Minh City's metropolitan area over the past 20 years, International Journal of Climatology, 36(10), 3633–3650, DOI: 10.1002/joc.4582,2016/08/01 (Acknowledgments: CCS) .
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  • Doan, Q., H. Kusaka and Q.B. Ho, 2016: Impact of future urbanization on temperature and thermal comfort index in a developing tropical city: Ho Chi Minh City, Urban Climate, 17, 20-31, DOI: :10.1016/j.uclim.2016.04.003, 2016/06/08 (Acknowledgments: CCS) .
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  • Kusaka, H., A. Suzuki-Parker, T. Aoyagi, S. A. Adachi, Y. Yamagata, 2016: Assessment of RCM and urban scenarios uncertainties in the climate projections for August in the 2050s in Tokyo., Climatic Change., 137 (3), DOI 10.1007/s10584-016-1693-2, 427-438, 2016/05/23(Acknowledgement: S-5-3,RECCA, SOUSEI,CCS) .
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  • Takane, Y., Kusaka, H., Hara, M., 2012: Urban climate projection in the 2070’s Augusts for the three major metropolitan areas under the IPCC SRES A2 emission scenario: Dynamical downscaling by the WRF-UCM. Journal of Heat Island Institute International., 7, 18-26. 2012/11/29 (Acknowledgement: RECCA,S-8) .
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  • Kusaka, H., Hara, M., Takane, Y., 2012: Urban climate projection by the WRF model at 3-km horizontal grid incremet: Dynamical downscaling and predicting heat stress in the 2070’s August for Tokyo, Osaka, and Nagoya metropolies. J. Meteor. Soc. Japan., 90B, 47-64. (Acknowledgement: S5) .
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Press Release
    • Nikkei Inc. (5.10,2012)
    • The Ibaraki-Shimbun (6.29,2012)
    • The Chunichi Shimbun(6.29,2012)


Other

Short-time heavy rainfall in urban areas       

 Studying heavy rainfalls in urban areas is important. In our laboratory, the impact of urbanization on such heavy rainfalls has been examined by statistical analysis using observation data and numerical models.
 In an urban city scale, short time heavy rainfall are much easier to happen, with this reason, to figure out the factor and mechanism of the phenomena is very meaningful. In our laboratory, we try to use the statistical way to analyze our real observation data, and we also run the numerical experiment with weather models. Which will help us to expound the short time heavy rainfall phenomena in urban areas.

(Nana FURUHASHI)

The amount of precipitation caused by the short-time heavy rainfall in the past 15 years.
From the picture we can know that the precipitation in the mountains area and Tokyo (23 area) is much more than other areas.
(Mayumi MIZUNARI, 2010)→For more details
Papers
  • Kusaka, H., Nawata, K., Suzuki-Parker, A., Takane, Y. and Furuhashi, N., 2014: Mechanism of precipitation increase with urbanization in Tokyo as revealed by ensemble climate simulations, J. Appl. Meteor. Clim., 53, 824-839. 2014/04/01(Acknowledgement: SOUSEI, RECCA) .
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  • Nakano, K., Nakayoshi, M., Alvin C.G. Varquez,Kanda, M., Adachi, S., Kusaka, H.2013: Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) , 69(4), I335-I360. 2013/02/01 .
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  • Kusaka, H., Hanyu, T., Nawata, K., 2010: Case study of local heavy rainfall, focusing on GPS precipitable water vapor-rainfall event observed in Tokyo on July 4, 2000-. Geophysical Review of Japan., 83(5), 479-492. 2010/09/01 (Acknowledgement: S5) .
    Details
Press Release
  • TV Asahi「HOUDOU Station」(Prof. Kusaka)(5.10,2012)
  • TV Asahi「MORNINGBIRD」(7.28,2011)
  • Yomiuri Telecasting Corporation「MIYANEYA」(8.2,2011)
  • Nikkei Inc. (7.17,2011)

Urban heat island measurement and simulation     

 The urban heat island phenomenon causes an uncomfortable thermal environment, leading to heat stroke, sleep disruption, and higher energy consumption for air conditioning. Field experiments are important in mitigating the urban heat island phenomenon. In particular, we have been measuring the urban heat islands in the cities of Tsukuba and Tajimi. In recent years, we have been observing the thermal environment in and around parks in Tsukuba to understand the impact of these small parks on the surroundings.

(Shiori ABE)

The observed surfce air temperature around the Tsukuba City, Japan

 We did the observation work in 2008.2.17(6:00 a.m.) in Tsukuba city. The figure shows horizontal distribution of 1.5 m temperature in Tsukuba City.
 From the figure, we can see that the UHI effect was so obvious, the temperature in central part of Tsukuba city is much higher than rural areas.

(KUSAKA, 2009)
→For more details
Papers
  • Lin, C., C. Su, H. Kusaka, Y. Akimoto, Y. Sheng, J. Huang, and H. Hsu 2016: Impact of an improved WRF urban canopy model on diurnal air temperature simulation over northern Taiwan. Atmospheric Chemistry and Physics, 16, 1809–1822. DOI: :10.5194/acp-16-1809-2016, 2016/02/16 .
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  • Adachi, S. A., F. Kimura, H. Kusaka, M. Duda, T. Yamagata, S, Seya, K. Nakamichi, T. Aoyagi, 2014: Moderation of summertime heat-island phenomena via modification of the urban form in the Tokyo metropolitan area. J. Appl. Meteor. Clim., 53, 1886-1900, 2014/08/08(Acknowledgement: **) .
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  • Okada, M., H. Kusaka, M. Takaki, S. Abe, Y. Takane, Y. Fuji and T. Nagai, 2014: Distribution of air temperature in Tajimi city in summer, Tenki, 61(1), 23-29. 2014/01/31(Acknowledgement: RECCA) .
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  • Takane, Y., Kusaka, H., Takagi, M., Okada, M., Abe, S., Nagai, T., Fuji, Y., Iizuka, S.,2013: Observational Study and Numerical Prediction Experiments on Wet-Bulb Globe Temperature in Tajimi,Gifu Prefecture:Consideration of Uncertainty with a Physics Parameterization Scheme and Horizontal Resolution of the Weather Research and Forecasting Model. Geophysical Review of Japan., 86(1), 14-37. 2013/01/01 (Acknowledgement: RECCA) .
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  • Kusaka, H., Takane, Y., Abe, S., Takagi, M., Shigeta, Y., Ohashi, Y., Buhe, B., 2012: Urban heat island phenomenon observed in open spaces in Tsukuba city on clear summer days: An evaluation of uncertainty in urban-rural temperature difference. Journal of Heat Island Institute International., 7, 1-9. 2012/07/27 (Acknowledgement: Grant-in-Aid for Young Scientists B, Grant-in-Aid for Scientific Research B, RECCA) .
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  • Kusaka, H., Ohba, M., Suzuki, C., Hayashi, Y., Mizutani, C., 2009: Preliminary Analyses of Urban Heat Island Phenomenon on a Typical Winter Day in Tsukuba City. Journal of Heat Island Institute International, 4, 10-14. 2009/02/01 (Acknowledgement: Grant-in-Aid for Scientific Research B) .
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  • Kusaka, H., Kimura, F., 2004: Thermal effects of urban canyon structure on the nocturnal heat island. J. Appl. Meteor., 43, 1899-1910. 2004/12/01 (Citations:48times) .
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  • Kusaka, H., Kimura, F., 2004: Coupling single-layer urban canopy model with a simple atmospheric model : Impact on urban heat island simulation for an idealized case. J. Meteor. Soc. Japan, 82, 67-80. 2004/02/25 (Citations:47times) .
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  • Kusaka, H., Kimura, F., Hirakuchi, H., Mizutori, M., 2000: The effects of land-use alteration on the sea breeze and daytime heat island in the Tokyo metropolitan area. J. Meteor. Soc. Japan, 78, 405-420. 2000/08/25 (Citations:55times) .
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  • Kusaka, H., Chen, F., Tewari, M., Dudhia, J., Gill, D.O., Duda, M. G., Wang, W., Miya, Y., 2012: Numerical Simulation of Urban Heat Island Effect by the WRF Model with 4-km Grid Increment: An Inter-Comparison Study between the Urban Canopy Model and Slab Model. J. Meteor. Soc. Japan., 90B, 33-45. (Acknowledgement: S5, T2K) .
    Details
Press Release
  • Tokyo Broadcasting System Television, Inc. 「NSUTA」(Prof. Kusaka)(7.22,2010)

The Influence of the Green Field in the park

 The built-up area in a city is covered mainly with artificial surface. Hence, such area has the high air temperature and affects the human health like as heat stroke. To mitigate urban thermal environment, urban green area is expected to be one of the countermeasure. Urban green area is expected not only to decrease air temperature but also to provide places for the rest and the evacuation in the time of disaster. Thus, urban green area plays a variety and an important role in an urban are with a few green area.

 Generally, air temperature in an urban green area is lowered than that in the built-up area. This has been investigated by observations, numerical simulations and remote sensing. However, there are many types of the area and the vegetation forms in an urban green area even if they say merely green area. Is the urban green area really cooler than the built-up area? Is it also cooler as the human thermal sensation if the urban green area is cooler? Is there any differences of its effect between big green area and small green area? Furthermore, it is considered that the urban green area cools the surrounding area (Is it true?). Kusaka Labo. studies these themes by observations, scale experiments and numerical simulations.

(Maki OKADA)

Figure B: Urban fabric of the Meji Shrine and Yoyogi Park in Tokyo, Japan. (Map datasets provided by 2008/2009 Zmap-TOWNII). From the map, we can know that temperatures in the Yoyogi Park are 2 to 3 degrees lower than high-rise areas (Fig A).

(OKADA, 2013)
Figure A: The temperature distribution around the Meji Shrine and Yoyogi Park in Tokyo, Japan. (12.1.2012 5am - 7am)

Papers
  • Okada, M., M. Okada, and H. Kusaka,2016: Dependence of Atmospheric Cooling by Vegetation on Canopy Surface Area During Radiative Cooling at Night: Physical Model Evaluation Using a Polyethylene ChamberJournal of Agricultural Meteorology,72(1),1-9. DOI: 10.2480/agrmet.D-15-00015,2016/03/10(Acknowledgement: RECCA) .
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  • Okada, M., M. Okada and H. Kusaka, 2014: A Polyethylene Chamber for Use in Physical Modelling of the Heat Exchange on Surfaces Exposed to a Radiation Regime. Boundary-Layer Meteorology, 153(2), 305-325. 2014/06/12(Acknowledgement: RECCA) .
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  • Okada, M.,Kusaka, H., 2013: Proposal of a new equation to estimate globe temperature in an urban park environment. J. Agric. Meteor.69(1), 23-32.2013/04/30 .
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  • Okada, M., Y. Wakazuki, S. Inukai, R. Hirota, and H. Kusaka, 2013: An Investigation of air temperature distribution in-and outside of a wooded area in early winter morning -A case study for the Yoyogi-park and the Meiji-shrine-. Journal of Heat Island Institute International., 8, 7-12. 2013/04/16(Acknowledgement: S-8) .
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      Fair Weather Cumulus

      Now describing.