Study On The Process Of Air-Ground-Water Heat Exchange In Urban Surface Space At The Micro-Scale

With the rapid development of urbanization,artificial impervious surfaces,characterized by large thermal inertia,gradually replace natural vegetation and soil.The expansion of the impervious surface reduces the infiltration of surface water,reduces the amount of atmospheric evaporation,and the surface absorbs more energy from solar radiation,resulting in the urban heat island effect,which causes the urban ecological environment to gradually deteriorate.When rainfall occurs in summer,the thermal runoff on the impervious surface flows into urban rivers and lakes,resulting in a rapid rise in surface water temperature,which has a serious impact on the urban water environment.However,the existing research on the heat exchange process of the urban underlying surface only stays at the surface layer,and the exploration of the formation mechanism of surface thermal runoff is lacking.In order to explore the heating efficiency of the urban underlying to the surface runoff,the effects of weather conditions,hydrological conditions and underlying conditions on the runoff temperature were analyzed.Based on UAV remote sensing data and in-situ observation data,this study constructed a surface-air heat transfer model and a surface-water heat transfer model with four common urban underlying surfaces,namely asphalt,concrete,permeable brick and lawn as the surface types.Model.This paper analyzes the near-surface heat exchange process in urban space and reveals the formation mechanism of thermal runoff.The study quantified the contribution rates of wind speed,initial surface temperature,rainfall intensity,thermal conductivity of the underlying surface and water permeability of the underlying surface to the surface runoff temperature.The main conclusions of the study are:1)The results show that in the surface-air heat transfer model,0.96?R~2?0.97,0.65??RMSE?1.18?,0.54??MAE?1.01?;in the surface-water heat transfer model,0.97?R~2?0.98,0.53??RMSE?1.14?,0.47??MAE?0.96?.Both the surface-air and surface-water heat transfer models can effectively and accurately simulate the heat exchange process.2)The four types of asphalt,concrete,permeable brick and lawn have different heat transfer rates under solar radiation.The higher the thermal conductivity of the underlying surface,the faster the temperature transfers from the surface to the interior,thereby slowing the surface heating.During rainfall,the thermal compensation effect inside the underlying surface will prolong the heating effect of surface runoff.3)The initial surface temperature of the surface is the most critical factor in the heat exchange process.The initial surface temperature,wind speed,rainfall intensity,thermal conductivity of the underlying surface and water permeability of the underlying surface can explain 95.4%and 91.9%of the changes in surface runoff temperature difference and surface runoff heating rate,respectively.4)The reduction of urban ventilation will intensify the thermal effect of surface runoff.Compared with the permeable subsurface,the impervious subsurface is the main driving force for the formation of surface thermal runoff pollution.