Introduction Of Vegetation Components In Polyhedral Urban Canopy Model And Its Simulation Study

The park city is a new concept proposed to solve the heat island and environmental problems brought about by urbanization.In this paper,the influence of vegetation components was introduced on the basis of the traditional single-layer urban canopy model,and the polyhedral urban canopy model is constructed with reference to the park city.The model is evaluated by observation data from October 28 to October 31,2017,and the contribution of different natural surfaces to the canopy temperature and humidity environment was discussed.At the same time,the effects of changes in urban canopy morphology,roof materials and vegetation parameters?such as natural surface ratio,leaf area index,leaf water content?on radiant heat,surface temperature and canopy temperature and humidity characteristics were analyzed using the offline polyhedral urban canopy model.The results show:?1?The model can better simulate the temperature and humidity characteristics of the urban canopy.Compared with the traditional single-layer urban canopy model,the introduction of vegetation components can improve the simulation effect of the model to a certain extent,and can more accurately reproduce the observed values.The correlation coefficient of roof temperature,roof long-wave radiation flux and canopy temperature between the simulated and observed values is greater than 0.9,and the standard error?SE?of each physical quantity is basically controlled within 0.05,and the SE value is smaller after introduction of vegetation.That is,the intensity of the mean value fluctuation is reduced.At the same time,the root mean square error?RMSE?of roof temperature,sensible heat flux,long-wave radiant flux,and canopy temperature were reduced by 1.09,3.18,5.54,and 0.85,respectively,in other words,the dispersion between the simulated and observed value decreases.?2?Comparing the contribution of different underlying surfaces to the temperature and humidity of the canopy,it is found that the contribution of the pavement to the sensible heat flux is much larger than that of the natural surfaces,it account for about 60%of the total sensible heat during the daytime and about 85%of the nighttime.Conversely,the contribution of the natural surfaces to the latent heat flux is much larger than that of the pavement,accounting for about 85%of the total latent heat during the daytime and about 50%at nighttime.For the three natural surfaces,the change of canopy specific humidity is basically less than 1 g?kg^-1 after replacing the trees with the lawn,and the canopy temperature is significantly increased,the maximum daily temperature can be increased by more than 0.5K.After replacing soil with lawn,the daily maximum of canopy specific humidity will increase by 4-6 g?kg^-1,and the cooling range will be less than 0.1k.That is to say,the lawn in the canopy can increase the canopy specific humidity to a greater extent compared with soil,and the trees among the three planted components have the most obvious cooling effect.?3?The model is sensitive to the morphological and material parameters of the building.The natural surface ratio,leaf area index and leaf water content also have certain influence on the temperature and humidity environment in the canopy.For the same degree of change of each morphological parameter,surface temperature is most sensitive to the width of the street?the ground temperature increases by about 4K,the wall temperature decreases by about 1.5K,and the canopy temperature can be reduced by 0.6K?.Compared with the gray cement roof,the high albedo white paint reduces the net radiation flux loss of nearly 380 W·m^-2 and roof temperature by about 12K.Among the natural surface parameters,the natural surface ratio has a greater influence on the canopy specific humidity.When the ratio decreases from 0.3 to 0.1,the maximum daily canopy specific humidity can be reduced by about 0.005 kg?kg^-1.An increase of 0.5 in vegetation proportion or 0.3 in leaf moisture content would lead to a decrease of about 1K in daytime canopy temperature,and when the three vegetation parameters change the same,the effect on the temperature and humidity environment of the night canopy is significantly less than the daytime.