Regional Warming Related with Land Use Change during Past 135 Years in Japan

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1 Present and Future of Modeling Global Environmental Change: Toward Integrated Modeling, Eds., T. Matsuno and H. Kida, pp by TERRAPUB, Regional Warming Related with Land Use Change during Past 135 Years in Japan T. ICHINOSE Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba , Japan Abstract LUIS (Land Use Information System) is a digital land use data set covering all of Japan with a 2 km grid. The land uses for each grid point circa 1850, circa 1900, circa 1955 and circa 1985 were compiled in LUIS. By using numerical simulations with a mesoscale model referenced to LUIS, the author attempted to determine the influence on surface air temperature by regional warming related to land use changes during the past 135 years. During the 4 periods, the area showing regional warming related to land use changes has expanded. This feature was significant around Tokyo and Osaka. Urbanization during the 4 periods weakened the daytime penetration of sea breezes in south Kanto (around Tokyo) which produced regional warming. The warming area moved to the north by expanding on the Kanto Plain due to a sea breeze from the daytime to midnight. In the Osaka Plain, the movement of the warming area by the sea breeze was smaller than in the Kanto Plain. The daily maximum and minimum temperatures around 1850, estimated from the observed data (monthly averages of daily maximum and minimum temperatures) in Tokyo (Otemachi) since 1876, were compared with the computed results. The computed daily maximum temperature agreed well with the estimated value. INTRODUCTION In Japan, around 120 years have past since meteorological observations were started. A warming trend of 1 degree Celsius per 100 years was observed as an influence of urbanization in the Japanese mega-cities (Fujibe, 1995). On the other hand, nowadays, the computing of regional wind systems and distribution of surface air temperatures have been established, when land use map with a high resolution for the detailed surface boundary condition was developed (Kimura and Takahashi, 1991; Ichinose et al., 1998, 1999). LUIS (Land Use Information System), a database on land use with a 2 km mesh covering all of Japan in 4 stages (circa 1850, circa 1900, circa 1955 and circa 1985) was constructed (Himiyama, 1995) and published as a GRID-Tsukuba original database by the National Institute for Environmental Studies (NIES) in Japan. For example, 1) expansion of urbanized area into plains (Fig. 1), e.g., south Kanto (around Tokyo), and 2) recovery of forest in the mountainous areas of central Japan, were noticeable as major characteristics on land use changes between circa 1850 and circa 1985 in central Japan. Such a significant change in the ground surface is expected to bring 433

2 434 T. ICHINOSE Fig. 1. Urbanization around 5 big cities in Japan. Percentages of urbanized area circa 1850 (upper) and circa 1985 (lower) are shown. X-axis shows scales (10 km). Urbanization in the analyzed area (see Fig. 3) around Tokyo was noticeable. a) around Sapporo, b) around Sendai, c) around Tokyo, d) around Osaka, e) around Fukuoka.

3 Regional Warming Related with Land Use Change during Past 135 Years in Japan 435 Fig. 2. Diurnal variability of computed surface air temperature on a calm and clear day in late July in 2 stages. a) Sapporo, b) Sendai, c) Tokyo (Otemachi), d) Osaka, e) Fukuoka. a regional climate change through the change in surface heat budget. It is thought to be possible to compute the regional wind system and distribution of surface air temperature emerging in the past, when land use in the former stage was input as a surface boundary condition to the mesoscale numerical model.

4 436 T. ICHINOSE Fig. 3. Surface air temperature (degrees Celsius) on a calm and clear day in late July around Tokyo circa X-axis shows scales (km). Legend shows height (m). T: Tokyo, Y: Yokohama, U: Urawa, M: Maebashi, K: Kofu.

5 Regional Warming Related with Land Use Change during Past 135 Years in Japan 437 Fig. 4. As in Fig. 3, but surface horizontal wind system. METHODS The numerical simulation model used in this study was based on the Colorado State University Mesoscale Model (CSU-MM) (Pielke, 1974) with some modifications (Ulrickson and Mass, 1990; Kessler and Douglas, 1992) and with small changes to input values for several surface boundary conditions like the albedo or anthropogenic heat in each grid cell (Ichinose et al., 1999). A hydrostatic equilibrium and the Boussinesq approximation are assumed in this model. The model consists of equations of motion, moisture and continuity within a 3-dimensional terrain-following coordinate system and it includes a thermodynamic equation, a diagnostic equation for pressure and an equation for surface heat budget. Each rectangular area around Tokyo, Osaka, Sapporo, Fukuoka and Sendai with the horizontal scale of several hundred kilometers was divided into a grid system. The atmosphere (up to 8000 m) was divided into 23 layers of different thicknesses. The soil to a depth of 0.5 m was also divided into 11 layers of varying thicknesses. The surface boundary conditions in each grid cell, i.e., albedo, evaporation efficiency, roughness length, density, specific heat capacity and heat diffusion coefficient, were calculated by the method using a weighted average for each share of land use type by referring to LUIS. The surface parameters for each land use type were determined by referring to Anthes et al. (1987). The time step for the numerical integration was chosen as 60 seconds and the results were calculated for 48 hours from 0AM on July 26 in 4 periods. The results were analyzed for 24 hours from 0AM on July 27. Anthropogenic heat with its diurnal variability (Ichinose et al., 1994) was given only to urbanized area. Its daily average for circa 1985 was assumed to be 25 W m 2. For former periods, 75%, 50% and 25% of the intensity for circa 1985 were assumed for circa

6 438 T. ICHINOSE Fig. 5. As in Fig. 3, but difference between circa 1850 and circa Positive value means warming. Wind system was enforced in this direction.

7 Regional Warming Related with Land Use Change during Past 135 Years in Japan 439 Fig. 6. Daily maximum and minimum temperatures (circle) in Tokyo in 2 stages, estimated from the trend over 121 years. Estimated temperatures (rectangle) and computed results (cross) in late July are shown. Averages of monthly averages in July and August were used. 1955, circa 1900 and circa 1850, respectively. To evaluate the potential warming related with land use changes, the sea surface temperature around each studied area was kept constant during the 4 periods. RESULTS During the 4 periods, the area showing the regional warming related with land use changes has expanded. This feature was significant around Tokyo and Osaka. The maximum difference between circa 1850 and circa 1985 emerged at 9PM and the minimum emerged at 6AM (Fig. 2). The former was 1.8 degrees Celsius in Tokyo (Otemachi). Urbanization during the 4 periods weakened the daytime penetration of the sea breeze in south Kanto and it produced a regional warming (Fig. 5). The warming area moved to the north by expanding on the Kanto Plain due to a sea breeze since daytime till midnight. However, the effect of the recovery of forests in mountainous areas in central Japan was not clear. In the Osaka Plain, the movement of the warming area due to the sea breeze was smaller than that in the Kanto Plain. DISCUSSION The daily maximum and minimum temperatures in circa 1850, estimated from the observed data (monthly averages of daily maximum and minimum temperatures) in Tokyo (Otemachi) since 1876, were compared with the computed results. For this comparison, the method to estimate the daily maximum and minimum temperature on a calm and clear day in the past was developed. In this

8 440 T. ICHINOSE method, the differences between the monthly averages, including the influences by many kinds of synoptic conditions, and the averages on calm and clear days, which were focused on in this study, were regarded as common during the 4 periods. As a result of the comparison in circa 1850, the computed daily maximum temperature was in good agreement with the estimated value (Fig. 6). However, the computed daily minimum temperature was higher than the estimated one. Due to a result of re-computing in the case of a 2 K sea surface temperature decrease, this disagreement was not interpreted by warming in wider scale. This disagreement is related to the difference in the inter-annual warming rate between the daily maximum and minimum temperatures. This difference seems to come from the effect of the urban canopy structure and its characteristic radiation environment. The mesoscale model used in this study could not express this effect. Anyway, the method in this study has a role to fill the temporal and spatial hole of historical climatology depending on the documents available from these historical periods. Acknowledgments The author expresses his sincere thanks to Prof. Dr. Yukio Himiyama of Hokkaido University of Education and Prof. Dr. Shoichiro Arizono of Aichi University, for access to their digital geographic land use data set, and to Prof. Dr. Takehiko Mikami of Tokyo Metropolitan University, for access to the observed data in Tokyo since This work was supported by CREST (Core Research for Evolution Science and Technology) of Japan Science and Technology Corporation (JST). REFERENCES Anthes, R. A. et al Description of the Penn State/NCAR Mesoscale Model Version 4 (MM4). Boulder, NCAR. Fujibe, F Temperature rising trends at Japanese cities during the last hundred years and their relationships with population, population increasing rates and daily temperature ranges. Pap. Meteor. Geophys. 46: Himiyama, Y Atlas. Asakura, Tokyo (in Japanese). Ichinose, T. et al Analyses on geographical distribution of urban anthropogenic heat based on very precise geographical information. Proc. Env. Eng. Res. 31: (in Japanese with English abstract). Ichinose, T. et al Impact analysis of three dimensional replacement of urban activity on urban thermal environment. Klimaanalyse fuer die Stadtplanung, edited by Okimura, T. et al., Kobe University, Ichinose, T. et al Impact of anthropogenic heat on urban climate in Tokyo. Atmos. Env. 33: Kessler, R. C. and Douglas, S. G User s Guide to the Systems Applications International Mesoscale Model (Ver. 2.0). California, Systems Applications International. Kimura, F. and Takahashi, S The effects of land-use and anthropogenic heating on the surface temperature in the Tokyo metropolitan area: A numerical experiment. Atmos. Env. 25B: Pielke, R. A A three dimensional numerical model of the sea breezes over South Florida. Mon. Weather Rev. 102: Ulrickson, B. L. and Mass, C. F Numerical investigation of mesoscale circulations over the Los Angeles basin. Part 1, A verification study. Mon. Weather Rev. 118: T. Ichinose ( toshiaki@nies.go.jp)