Research On The Impact Of Urbanization On Heavy Rain In The Warm Area Of South China Based On Wind Profile Observation And Numerical Simulatio

Urban flooding events caused by the warm-sector heavy rainfall(WSHR)are frequent in the coastal areas of Guangdong.The WSHR features strong and concentrated precipitation and no significant obvious synoptic-scale baroclinic pressure system appears before the occurrence,so the forecast accuracy is very limited in the current meteorological operations.And the occurrence of WSHR in the coastal is usually closely related to the 950 h Pa boundary layer low-level jet(BLJ)and700h Pa synoptic-system-related low-level jet(SLLJ).Therefore,this paper is based on the wind profile radar observation data with the weather research and forecasting model(WRF)to investigate WSHR,and the conclusions are as follows:1)For the 10 WSHR events in 2019,the four precursor signals I(low-level jet index),ΔV(horizontal wind shear),N(atmospheric uplift intensity)and Z(boundary layer height)calculated from the wind profile radar data showed an increasing trend in the 2 hours before the precipitation occurred.And the outbreak of the South China Sea Summer Monsoon will cause I(low-level jet index)to increase significantly 75 minutes before precipitation.N(atmospheric uplift intensity)and Z(boundary layer height)in the PRD region is significantly greater than that in other regions,and the increase of I(low-level jet index),ΔV(horizontal wind shear)and N(atmospheric uplift intensity)can better indicate the occurrence of heavy precipitation.Before the occurrence of WSHR,the four precursor signals in the city center changed more strongly than in the surrounding areas.2)Five kind of urban undersurfaces and anthropogenic heat designed for the Pearl River Delta region were introduced into the urban canopy model of WRF,and the WSHR of the urban agglomeration on April 20,2019 was selected for simulation study.With the new urban canopy model,increased roughness of the urban subsurface causes enhanced convergence and deceleration of the near-surface wind,precipitation is mainly concentrated in the urban center,and the simulated precipitation results are improved.The anthropogenic heat element strengthens the thermal lifting effect in the urban area resulting in local convergence shifting southward and increased precipitation in the southern part of the urban areas.The evaluation of simulated precursor signals shows that the new urban canopy model can provide some improvement in the simulation of precursor signals in urban areas.The above studies provide a new approach for forecasting the WSHR along the coastline,and help to improve the simulation of the warm-sector heavy rainfall in urban agglomeration.