Synoptic analysis and urban signatures of a heavy rainfall on 7 August 2015 in Beijing

A heavy rainfall event that occurred in Beijing on 7 August 2015 was investigated by means of several nonconventional observational data and the Beijing Rapid Update Cycle Model (v3.0). A cold front guided by an upper trough and the wind shear line are main factors influencing this rainfall event. The two factors combined were enhanced after passing the Beijing downtown area. A Nourban land use scenario was employed to analyze the impact of urbanization on this rainfall event. The results show that the urban land use type, which induces the wind shear line, is indispensable in forecasting the rainstorm. The urban land use type leads to gradients of the sensible heat flux, temperature, and wind increasing in the suburban area, which may allow the synoptic systems to merge and enhance. Urbanization caused the precipitation to increase in the downstream suburban area and the spatial distribution of precipitation to become more concentrated. Ensemble tests of different parameterization schemes confirm that the results are reliable.