Numerical Analysis about Urban Climate Change by Urbanization in Shanghai

Transcription

1 Numercal Analyss about Urban Clmate Change by Urbanzaton n Shangha Hafeng L 1, Wejun Gao 2 and Tosho Ojma 3 1 Research Assocate, School of Scence and Engneerng, Waseda Unversty, Japan 2 Assocate Professor, Faculty of Envronment Engneerng, The Unversty of Ktakyushu, Japan 3 Professor, Department of Archtecture, School of Scence and Engneerng, Waseda Unversty, Japan Abstract After the ndustral revoluton, megalopols beyond the populaton of 10,000,000 appears one after another, and makes bg mpact to the earth envronment. The urbanzaton n Asan developng countres s tremendous. Especally the rapd urban sprawl and the change of land use are brngng urban clmate changng such as heat sland phenomenon n Chna Shangha n recent years. To evaluate heat sland phenomenon n Shangha by urbanzaton, ths study constructed a land use database usng land use map of Shangha. Usng a numercal analyss method, the nfluence on urban clmate wth the urban sprawl and the change of land use of Shangha was evaluated from 1845 to As a result, analyzed the nfluence on the urban clmate affect by the urbanzaton of 25kmx19km range, the maxmum temperature and average temperature rose by about 1.7 because of the rapd sprawl of urban area and the changes of land use for ths 150 years n Shangha. Keywords: Shangha; urban clmate; urbanzaton; heat sland; numercal analyss 1. Introducton After the ndustral revoluton, megalopols beyond the populaton of 10 mllon appears one after another, and makes bg mpact to the earth envronment. The urbanzaton n Asan developng countres s tremendous. Especally the rapd urban sprawl and the change of land use are brngng urban clmate changng such as heat sland phenomenon n Shangha, Chna n recent years. Now, the heat sland phenomenon of Shangha s collectng a lot of attenton, and a large-scale temperature observaton s gong ahead. To evaluate heat sland phenomenon n Shangha by urbanzaton, ths study construct a land use database usng land use map of Shangha. Usng a numercal analyss method, the nfluence on urban clmate wth the urban sprawl and the change of land use of Shangha was evaluated from 1845 to The Urbanzaton n Shangha After the ndustral revoluton, accompanyng the rapd growth of urban populaton n an earth scale, varous urban problems were brought about n the metropols n the 20th century. In London, the growth of metropols was controlled by the greenbelt polcy. But n Japan, metropolses lke Tokyo were formed wth hgh economc Contact Author: Hafeng L, Research Assocate, School of Scence and Engneerng, Waseda Unversty Okubo, Shnjuku-ku, Tokyo, Japan Tel: Fax: e-mal: hafeng@ojma.arch.waseda.ac.jp (Receved May 8, 2002; accepted August 19, 2002) growth postwar. From the second half of the 20th century, urban populaton ncreases explosvely n Asan developng countres at the speed that has not been experenced n advanced naton. Many Asan metropolses are faced wth very serous envronmental problems. Fgure 1 shows the urban area changes n 50km range of fve megalopolses n the past 100 years. The urban area of New York, London, and Tokyo has already been over the range of 50km, but the Asan developng countres, such as Shangha and Bangkok, kept n the range of 30km n the 1990's. When seen from the urban zone and the populaton of central area of each metropols, Asan developng countres, such as Shangha and Bangkok, had already reached the almost same level as London, New York, and Tokyo (Fgure 2) 1). Compared wth the metropols of advanced countres, the metropolses of Asan developng countres are holdng large populaton n the small urban area can be consdered. Shangha was establshed n 1292, and the total area was about 2,000km 2. In1997, t has already exceeded 6,341km 2, and the urban area and the constructon dstrct area have reached to 2,057km 2 and 412km 2. The changes of the urban area and the populaton n Shangha are shown n Fgure 3 2). Compared wth 1845, the urban area ncreased more than 10 tmes and the populaton also to about 40 tmes for the 150 years. 3. Constructon of Urban Thermal Envronment Evaluaton Database by Usng Land Use Map 3.1 Outlne of Thermal Envronment Evaluaton Database Constructon System In Japan, many dgtal databases, such as remote Journal of Asan Archtecture and Buldng Engneerng/November 2002/

2 1900 s New York London 1990 s Megalopols (Tokyo+Satama+et al.) Shangha Bangkok Fg.1. Comparson of Urban Area Changes n the 50km s Area of Megalopolses (the nner sde s the rad of 10km outsde s the rad of 20km) Shangha London New York Megalopols (Tokyo+Satama+et al.) urban area (km 2 ) urban zone central area mllon Fg.2. Comparson of Megalopolses Populaton n 1990s urban populaton urban area year urban populaton (mllon) Fg.3. The Change of Urban Area and Populaton n Shangha sensng and GIS data, are used well n urban thermal envronmental evaluate smulaton. However, n Asan developng countres, there are few such databases and the constructon of database requred for evaluaton smulaton takes much tme. Snce urban land use maps are easy to come to hand n Asan ctes, ths study created a database constructon system for evaluatng urban thermal envronment by usng land use map (Fgure 4) 3). The system flow s shown n Fgure 4. Frst, resoluton s set up and land use maps can be downloaded from scanner to personal computer. It s panted over wth the color decded as every classfcaton of each type of land use such as green etc., and the colors wll be corrected to enhance color dstncton precson. Then the maps can be taken n the specal software (color of pxels can be changed nto numbers), and the mesh data based on the color numbers of pxels are outputted to a text fle. Furthermore, mesh sze necessary for the thermal envronmental evaluate smulaton s set up, and by the mesh converson program, land use database for performng thermal envronment evaluaton can be created automatcally. Ths system can create the mesh data of varous mesh szes by the settlement of the take-n resoluton of scanner. 3.2 Create the Land Use Database of Shangha Usng the database constructon system, the land use database for analyzng urban temperature by usng land use map of Shangha from 1845 to 1995 was created The layer attrbute of land use mesh data s set up wth water, green, road, nakedness area, and buldng. The mesh sze s set up wth 500m, and the evaluaton area s 25kmx19km range. 4. Thermal Envronmental Smulaton 4.1 Thermal Envronment Evaluaton Smulaton Model 4) In order to observe urban heat sland phenomenon, a three dmensons model has been used n ths study. The conservaton equaton for momentum, mass, and energy can be generally descrbed as below, Energy Formula dt T Q D dt x x C p 144 JAABE vol.1 no.2 November 2002 Hafeng L

3 Land use map setup of takng-n resoluton of the land use map Scanner take nto a personal computer Personal computer rasng color dscernment accuracy Color compensaton creatng mesh-data automatcally by land use color Mesh-data of land use automatc creaton Mesh converson program setup of the output mesh sze setup of the color recognton number by land use Urban thermal envronmental smulaton evaluaton change the color of pxels nto numbers Fg.4. Thermal Envronmental Evaluaton Database Constructon System by Usng Land Use Map Contnuaton Formula du 0 dx Momentum Formula du P U D g dt x x x Where, T : ar temperature ( ) U: (U, V, W): average wnd veloctes at X, Y, Z drectons (m/s) D (DX, DY, DZ): dsperson coeffcents of X, Y, Z drectons (m 2 /s) Q: nternal heat source (kw/m 3 ) P: ar pressure (N/m 2 ) ρ: the densty of the ar (kg/m 3 ) C p: ar specfc heat (kj/kg ): g: ar gravty (m/s 2 ) In ths model, the followng assumpton has been used to smple the above equaton as below, 1) Ar flow s unform wth a constant ar gravty and thermal capacty. 2) Turbulent eddy dffusve for energy and momentum are equvalent. 3) The effect of thermal capacty of buldngs s neglected. 4) The ar flow s dvded nto two parts. One s the general current and the natural current defned as follows, U U u P P p 5) The vortctes are defned as follows, U U j x j x 6) The natural current flow (a, b) s generally smaller than the general current flow (A, B). Therefore, the follow assumpton can be assumed. AB ( A a)( B b) AB ab Ab ab AB ab Ab The calculated area has been selected n ths study shown n fgure 5. Lx, Ly, Lz are the length of X, Y, Z drecton. The urban has been assumed to be contnuous. The boundary condton above the Z drecton has been assumed to the same clmate condton, whch s a general weather condton recorded n the weather staton, and the wnd pattern n Z drecton s stable where there s no turbulence. So the boundary condton can be descrbed by fgure 5. In the ground surface, the heat balance can be wrtten by the followng equaton, Q Q s cv Q rd Q vp Q cd Where Qs=solar radaton absorbed by the ground surface (kj/m 2 h) Qcv=convecton heat flow (kj/m 2 h) Qrd=long-wave radaton heat flow (kj/m 2 h) Qvp=evaporaton heat flow (kj/m 2 h) Qcd=heat conducton of the walls(kj/m 2 h) Although the ar temperature and wnd dstrbuton should be ganed through solvng the above equaton together wth the energy and momentum equaton, the JAABE vol.1 no.2 November 2002 Hafeng L 145

4 separate step has been appled that the surface temperature dstrbuton frstly s determned by assumng the ar temperature s known and then the ar temperature and wnd dstrbuton can be calculated usng the surface temperature dstrbuton. T y 0 T y L y Qs u y 0 u y L x v v y 0 y L x L z Z T y 0 u y 0 v y 0 w y 0 T x 0 u x 0 v x 0 w x 0 T z L z T a u z L z 0 v z L z 0 w z L z 0 Q artfcal heat release w y 0 w y L x T x 0 T x L x u x 0 u x L x v x 0 v x L x Y Fg.6. The Buldngs Densty Dstrbuton Map of Shangha w x 0 w x L x L x L y X Fg.5. Thermal Envronment Smulaton Model 4.2 Thermal Envronment Evaluaton of Shangha Frstly, a thermal envronment evaluaton of Shangha was performed to confrm the valdty of the system. Mesh sze s set up wth 500m, and the range of the area for evaluaton s 25kmX19km. In order to rase the accuracy of mesh data, the buldngs densty dstrbuton map (Fgure 6, to calculate the rate of buldngs) and the populaton densty dstrbuton map (Fgure 7, to calculate artfcal heat release) were also used except for the land use map of Shangha. Furthermore, the populaton mesh data, created from Fgure 7, multply the amount of Shangha 1 person per energy consumpton 5) to calculate the artfcal heat release. Smulaton was started from 13:00 n typcal summer day. The other ntal condtons are shown n Fgure 8. Fgure 9 showed the temperature dstrbuton by land use data only smulaton and Fgure.10 showed the temperature dstrbuton by land use + artfcal heat release smulaton. In heght of 1.5m above ground level, the maxmum temperature of 34.7 and 35.5 s shown respectvely. It s found that because there are few bg green lands, the cool sland s hard to form snce the bgger heat sland n the center of Shangha s beng formed. And, the coolng effect by the rver was confrmed, too. In Table 1, the case of only land use smulaton showed that the dfference between mnmum temperature and maxmum temperature s 3.1. But n the case of land use + artfcal heat release smulaton, the dfference went up to 3.8, and the Fg.7. The Populaton Densty Dstrbuton Map of Shangha ntal temperature temperature : 31 buldng: 47.5 road : 47.5 nakedness area : 47.5 green : 29.5 water : 26.4 Fg.8. The Intal Condtons of Smulaton temperature rse by artfcal heat release reaches 0.7. It s predcted that ncrease of the energy consumpton accompaned by the rapd economc development n Shangha from now on wll has bg nfluence on the urban temperature. In Shangha, there are many hgh temperature days of 35 or more n July and August, and the maxmum temperature dfference between the urban area and the suburbs reaches 4.8 n recent years. The smulaton 146 JAABE vol.1 no.2 November 2002 Hafeng L

5 result s close to t havng been observed. Table 1. Comparson of the Ar Temperature n 13:00 Land use only Land use + artfcal smulaton heat release smulaton Max value of temperature( ) Average value of temperature( ) Mn value of temperature( ) Numercal Analyss about Urban Clmate Change of Shangha by Urbanzaton By analyzng the nfluence on the urban clmate due to the urbanzaton, the central area of 25kmx19km range n 1845, 1911, 1978 and 1995 of Shangha was selected. The numercal smulaton result showed n Fgure 11. In 1845, the urban area s 38km 2, the average temperature and the maxmum temperature s 31.7 and In 1995, the urban area expanded to about 400km 2, the average temperature and the maxmum temperature rose to 33.5 and The maxmum temperature and average temperature of Shangha rose by about 1.7 compared wth 150 years ago Rver 35.5 Rver Rver Rver Fg.9. The Temperature Dstrbuton by Land Use Data Only Smulaton(1.5m heght above ground level) Fg.10. The Temperature Dstrbuton by Land Use + Artfcal Heat Release Smulaton(1.5m heght above ground level) the change of urban area n Shangha(25km 19km range) the rse of urban temperature n Shangha(1.5m heght above ground level ) Fg.11. The Urban Clmate Changes Due to the Urbanzaton n Shangha JAABE vol.1 no.2 November 2002 Hafeng L 147

6 6. Concluson In ths study, a database constructon system for the thermal envronment evaluaton by usng urban land use map of Shangha was presented. Usng ths system, wthout the exstng dgtal mesh databases, we can also create mesh data from the urban land use map easly and apply to thermal envronment evaluaton. It expects greatly beng used for the thermal envronment evaluaton n Asan developng countres. By usng the land use map of 1845,1911,1978,1995 of Shangha, we analyzed the nfluence on the urban clmate affect by the urbanzaton of 25kmx19km range. As a result, the maxmum temperature and average temperature rose by about 1.7 because of the rapd expanson of urban area and the changes of land coverng for ths 150 years followng wth urbanzaton of Shangha. In ths tme, the nfluence on the urban clmate due to the sprawl of urban area and the changes of land use was studed. The analyss wth consderng the artfcal heat release of Shangha wll be studed by future study. Acknowledgments A part of ths study was supported by the Mtsubsh Foundaton Natural Scence Research Grant. References 1) Tokyo Metropols (1996) Tokyo Metropols Whte Paper. 2) Chna Natonal Statstcs Bureau (1996) Shangha Statstcal Yearbook. 3) HaFeng L, Wejun Gao and Tosho Ojma (2000) Research about urban thermal envronment evaluaton method by usng land use map--a case study n 50km bloc of metropols. Journal of Archtecture, Plannng and Envronmental Engneerng of AIJ, No ) Hafeng L, Wejun Gao and Tosho Ojma (1999) Thermal envronment evaluaton of cty area by usng geographc nformaton system. Journal of Archtecture Plannng and Envronmental Engneerng of AIJ, No518, pp ) Shangha Map Edt Commttee (1997) Collecton of Shangha Maps. 148 JAABE vol.1 no.2 November 2002 Hafeng L