Simulation Study On The Influence Of Cooling Roof On Thermal Environment In Beijing

With the rapid development of China's economy and the acceleration process of urbanization,the issue of Urban Heat Islands(UHI)has become more and more prominent.An effective method to study the urban heat islands problem is the Weather Forecasting and Forecasting Model 3.8(WRFV3.8)with the Single-Layer City Canopy Model(SLUCM).To mitigate the warming effect of the UHI and the Heat Waves in summer,this paper discusses the mitigation effects of two types of cooling roofs(green roofs and high albedo roofs)in summer.Beijing is selected to study,which has it's typical high-density building.Combining 1km high-modis(30s)satellite remote sensing data,the numerical experiment are made from the 12:00 third day of July to its 00:00 seven day(the spin-up time for the first 12 hours)under the summer high pressure control of 2010,and in the highest peak of high temperature and drought weather,no precipitation,good weather conditions,and few sunny clouds.There are 8 sets(case1-8)of numerical experiments that with different proportions of roof.According to the observation data of Beijing Institute of Urban Meteorology,the control case(case1)has a good simulation effect.Other 7 sets that with different albedo roof cases(case2-4)and different cover ratios of green roof cases(case5-case8)are conducted to make the sensitivity experiments.The results of the study showed that:(1)In Beijing urban areas,the roof which albedo is 0.85(case4)has a better cooling effect than 100%(case8)green roof.During the three days,the average temperature of case4 drops 0.9?,and the cooling of the case8 is 0.46?.(2)With the albedo of the roof increases by 0.1,that the maximum temperature in Beijing will decrease 0.27?.And the increase of the proportion of green roofs will also result in a decrease in temperature.With each increase by 10%,the maximum temperature will decrease by 0.16?.(3)There is significant impact on urban heat islands that caused by cooling roofs.During the daytime from 13:00 to 14:00,compared with case 1 the maximum UHI drop of case4 is 1.47?,which is higher than the cooling effect of case8.(4)The cooling effect of the cooling roof can reach the height of 1.2km above the city,and the turbulence movement is also significantly reduced.At the 12:00-18:00 of the three days,compared with case1,the height of the boundary layer of case4 and case8 are respectively average reduced by 669 m,430m.