Effect of urbanization on the urban climate in coastal city, Fukuoka-Kitakyushu metropolitan area, Japan Yoichi Kawamoto [email protected] Assistant Professor, Faculty of Design, Kyushu University 4-9-1, Shiobaru, Minami-ku, Fukuoka, Japan

1. Objective Table 1. Rate of air temperature change in last one century. To investigate the effect of urbanization in (Extract from “Heat island monitoring report”, JMA, 2015) Fukuoka-Kitakyushu metropolitan area, the Rate of National Land Numerical Information (NLNI) land- Site urban land Average Daily maximum Daily Minimum use data provided by Ministry of Land, use (%) Annual Spring Summer Fall Winter Annual Spring Summer Fall Winter Annual Spring Summer Fall Winter Infrastructure, Transport and Tourism of Japan Tokyo 92.9 3.2 3.1 2.0 3.4 4.5 1.5 1.6 1.1 1.7 1.8 4.5 4.5 2.8 4.4 6.1 for 1976 and 2009 were utilized in the WRF Osaka 92.1 2.7 2.6 2.3 3.2 2.8 2.2 2.3 2.1 2.2 2.2 3.7 3.6 3.5 4.3 3.4 Nagoya 89.3 2.9 3.0 2.2 3.2 3.0 1.1 1.3 0.7 1.1 1.3 4.0 4.4 3.3 4.4 3.9 simulation. Fukuoka 64.3 3.1 3.3 2.4 3.8 3.0 1.7 1.9 1.4 1.7 1.6 5.1 5.9 3.9 6.2 4.6 Avg. of 15 lowly 2. Target Area 18.5 1.5 1.8 1.0 1.5 1.7 1.0 1.3 0.7 0.8 1.2 1.9 2.1 1.5 1.9 2.0 Fukuoka-Kitakyushu metropolitan area is the urbanized sites fourth largest metropolitan area after Tokyo, Kitakyushu Kitakyushu Osaka, and Nagoya. At Fukuoka observation site, located at the central part of Fukuoka- ② ③ ② ③ Kitakyushu metropolitan area, apparent air ① ① temperature rise in the last one century has Fukuoka ④ Fukuoka ④ observed (“Heat island monitoring report”, Japan ⑤ ⑤ Meteorological Agency (JMA), 2015). ⑦ ⑧ ⑦ ⑧ ⑥ ⑩ ⑥ ⑩ 3. Outline of NLNI land-use data ⑨ ⑨ The NLNI land-use data are stored with a resolution of approximately 1 km2 and a grid ⑪ ⑪ spacing with latitude and longitude of 30 and “Urban” land-use fraction “Urban” land-use fraction 0.0001 - 0.1000 ⑫ 0.0001 - 0.1000 ⑫ 0.1001 - 0.2000 0.1001 - 0.2000 45 , respectively. Fig. 1 shows the fraction of 0.2001 - 0.3000 0.2001 - 0.3000 land-use under the Urban category in Fukuoka 0.3001 - 0.4000 ⑬ 0.3001 - 0.4000 ⑬ 0.4001 - 0.5000 0.4001 - 0.5000 prefecture in 1976 and 2009. Fig. 2 shows the 0.5001 - 0.6000 0.5001 - 0.6000 0.6001 - 0.7000 0.6001 - 0.7000 increment in the Urban land-use fraction from 0.7001 - 0.8000 0.7001 - 0.8000 0.8001 - 0.9000 0.8001 - 0.9000 1976 to 2009. 0.9001 - 1.0000 ⑭ a) 1976 0.9001 - 1.0000 ⑭ b) 2009 4. Analysis conditions Figure 1. ‘Urban’ land-use fraction in Kyushu Prefecture. The dark Analysis period was summer of 2013; during tone indicates the fraction of ‘Urban’ land-use within each mesh. this period, the average air temperature in the Kitakyushu western part of Japan was the highest among observations by Japan Meteorological Agency ② ③ since 1946. ① Fig. 3 illustrates the analysis domains for WRF model simulation. Fukuoka ④ To evaluate the climatological effect of the ⑤ ⑦ ⑧ urbanization process over the three decades, ⑥ ⑩ numerical simulations were performed using two ⑨ Tokyo different land-use datasets. For simplicity, these Nagoya ⑪ Osaka two datasets are abbreviated as ‘case 76’ for “Urban” land-use increment Fukuoka- land-use dataset for 1976, and ‘case 09’ for -0.2000 - 0.0000 ⑫ Kitakyushu 0.0001 - 0.2000 2009. To evaluate the influence of urbanization, 0.2001 - 0.4000 0.4001 - 0.6000 ⑬ the same meteorological datasets were adopted 0.6001 - 0.8000 as the initial conditions for both cases. 0.8001 - 1.0000 5. Results ⑭ 5.1. Frequency of sultry nights Figure 3. Analysis domains for the WRF Table 2 shows the frequency of sultry nights Figure 2. Increase in the ‘Urban’ land-use in July and August for cases 76 and 09. fraction. The red tone indicates increase in Compared with cases 76 and 09, the frequency the ‘Urban’ land-use fraction from 1976 to km with a resolution of 5 km) and domain 3 of sultry nights was higher in 11 sites (red tone 2009 and the blue tone indicates decrease. in Table 2). This result suggested that Table 2. Frequency of sultry nights urbanization in the targeted area worsens the for simulation cases 76 and 09. In urban environment at night. this study, a sultry night is treated 5.2. Surface air temperature as a day in which the minimum air Fig. 4 shows the difference in air temperature at 2 m above ground level between case 76 and Site Case 76 Case 09 case 09. Hourly data of air temperature for 62 1. Munakata 19 20 days of July and August were averaged only on 2. Yahata 27 34 the land surface. 3. Kuko- Central parts of Fukuoka and Kitakyushu 40 39 (darker colour in Fig. 1 were already urbanized in kitamachi the 1970s, so air temperature rise caused by 4. Yukuhashi 15 24 urbanization in this area was small. On the other 5. Iizuka 24 28 hand, because of urban sprawl, urban heat 6. Maebaru 23 33 island phenomenon had expanded. Although 7. Fukuoka 49 50 some parts in Fig. 4 show air temperature drop, air temperature difference averaged over the 8. Hakata 39 49 9. Dazaifu 20 39 10. Soeda 16 15 Acknowledgment This work was supported by “Japan Society 11. Asakura 16 21 Fig. 4. Difference of averaged air temperature for the Promotion of Science” Grant-in-Aid for 12. Kurume 19 32 between case 76 and case 09 over July and August. Young Scientists (A) (Grant Number: 25709053). 13. Kurogi 10 7 Blue tone shows temperature drop and red tone 14. Omuta 35 39 shows temperature rise from case 76 to case 09.