Application Of LCZ Urban Non-uniform Underlying Surface To Simulation Of High-impact Weather In Shangha

High temperature and typhoon precipitation are high-impact weather in Shanghai.Studying the impacts of heterogeneity of urban underlying surface on high temperature events and typhoon precipitation events not only helps to understand the intersections between urban morphology and urban thermal environment,the intensity of typhoon precipitation and rainfall area,but also provides guidance for refined numerical forecasting of megacities.In this study,a high temperature event and a typhoon precipitation event in Shanghai,China,were simulated using WRF model.We incorporated the LCZ（Local Climate Zone）land use data that resolves heterogeneous urban morphology using complex building parameters.The simulations were compared to control cases based on MODIS land use data matched with single class of urban morphology.The findings are:（1）For high temperature event,LCZ performs better than MODIS for simulating 10-m wind speed.The increase of building height causes the wind speed to decrease by 0.6-1.4m s^-1in daytime and by 0.2-0.7m s^-1 in nighttime.High-rise buildings warm the air by trapping radiation in the urban canyon.This warming effect is in part offset by the cooling effect of building shadows in the day.As a result,the 2-m temperature was increased by 0.8℃in nighttime but only by 0.4℃in daytime.Meanwhile,the heterogeneous urban surfaces can increase 50-m turbulent kinetic energy by 0.4 m² s^-2,decrease 10-m wind speed by 1.8m s^-1 in daytime,and increase surface net radiation by 45.1W m^-2,increase 2-m temperature by 1.5℃in nighttime.LCZ modifies the atmospheric circulation between land and ocean in daytime.The shadowing effect reduces the difference in air temperature between land and ocean and weaken the sea breeze.Meanwhile,high-rise buildings obstruct sea breeze,making it impact a smaller portion（10 km along the wind direction）of inland area than MODIS.The larger areas of buildings in rural caused 2-m temperature increased by 0.5-2.4℃ in nighttime.（2）For typhoon precipitation event,LCZ performs better than MODIS for simulating the spatial distribution of rainfall accumulation,and the heavy rainfall area is closer to that of the observations with the reduction of the error by 30km.The stronger friction and dragging effects in the area of high-rise buildings caused the 10-m wind speed 5.2 m s^-1 lower than that in the area of urban-rural crossover,and along with the compensating effect of downward transmission of upper-level momentum,the horizontal wind speed within 2 km is weakened by 4.7 m s^-1,resulting in the local vorticity being 0.0009 s^-1 lower,which weakens the accumulation and convergence upward motion of vapor.Finally,the rainfall accumulated in the area of urban-rural crossover,suppressed and lagged in the area of high-rise buildings,reproduced the real characteristics of rainfall.