Numerical Study On The Mitigation Effect Of Roof/Ground Scheme On The Thermal Environment Of Yangtze River Delta

Due to the population growth and socioeconomic development in urban areas,urban construction is constantly expanding,resulting in the change of urban regional spatial pattern and surface properties,resulting in urban heat island effect.The urban heat island effect affects the thermal environment of urban areas,and makes the air pollutants gather in the central area.Its warming effect can also lead to the increase of the probability and frequency of heat wave events in the city,which endangers people's health and even lives.How to alleviate the urban heat island effect has always been a hot issue in urban meteorological research.Reasonable urban planning can effectively alleviate the urban heat island effect,improve the urban thermal environment,enhance human thermal comfort,and reduce building energy consumption.In this paper,the WRF3.9 coupled single-layer urban canopy model(UCM)is used to simulate the effects of different mitigation schemes.The test includes the control test(CTRL)and 18 sensitivity tests including roof scheme(high-reflective roof HR1-4 and green roof GR1-4),ground scheme(high-reflective ground HG1-4 and urban vegetation GG1-4)and superposition scheme(HR4&GG4 and GR4&GG4).The summer of 2013(June,July and August)is divided into normal summer and heat wave weather,and the different mitigation effects of mitigation schemes under different weather conditions are further analyzed to study the impact of different mitigation schemes on urban thermal environment,human thermal comfort and energy consumption of Yangtze River Delta urban agglomeration under different weather conditions.The results show that:(1)All the mitigation schemes have the ability of cooling,humidifying,reducing the intensity of heat island and improving human thermal comfort,and the superposition scheme has the best mitigation effect,the daily maximum cooling range is 1.32 ?,the humidification range is 8.07%,and the heat island intensity is reduced by 0.89 ?.At the same time,there is a strong linear relationship between the cooling and humidifying effect of roof / ground scheme and the proportion of different schemes,and the mitigation effect of roof scheme is stronger in the daytime,and that of urban vegetation is better at night.According to the analysis of urban surface energy balance,the higher the albedo of the reflection scheme,the greater the output short wave radiation and the smaller the net radiation flux;the larger the green area of the greening scheme,the greater the evaporation and the more latent heat released.(2)Comparing the different mitigation effects of normal summer and heat wave weather,it is found that no matter which scheme,the mitigation effect of urban thermal environment in heat wave weather is more obvious than that in normal summer,the average cooling range is58% higher and the humidification range is 64% higher.This is because,in heat wave weather,the incident solar short wave radiation is enhanced,and the reflection scheme can reduce the net radiation flux to a greater extent,and the greening scheme can release more latent heat.Therefore,the cooling effect of the two schemes in heat wave weather is stronger than that in the normal summer.Under heat wave weather,the comfort time decreased by8.08% on average,and the thermal discomfort time increased by 17.87%.Compared with Hangzhou,the cooling range of Changzhou is 0.06-0.28 ? higher,and the humidification range is about 0.2-1.5% higher.Therefore,previous studies may underestimate the amplification effect of urban agglomeration.(3)Based on the model of residential and commercial electricity consumption,it is found that the electricity consumption of the control test is the highest,reaching 18.423 billion KWh,while the total electricity consumption of the superposition scheme is the lowest,saving 12.80% compared with the control test,and the energy saving potential of the superposition scheme is 1.66-2.28% more than that of the roof / ground scheme alone.Compared with the energy-saving potential of different days,the electricity consumption of heat waves accounted for 68.5% of the total electricity consumption,and GR4&GG4 had the largest energy-saving potential of 17.70%.