A Study of the Beijing Super-Storm of 21 July 2012 using WRF model

A once-every-60-year storm hit the Beijing metropolitan areas on 21 July 2012 with 460 mm of rainfall in 18 hours. This extreme weather event was part of the mesoscale convective system (MCS). The storm, which started in the afternoon and continued late into the night, caused major flooding and life loss. Surface Pressure continued to fall until 21 July, 18UTC when a cold front passed Beijing. At this time, a wind-shift line moving northward into southern Beijing slowed down due to topographical blocking at Mt. Taihang. It was accelerated after passing the mountain. The MCS developed at this time remained quasi-stationary due to westerly flow and appeared to be the main reason for the extreme rainfall. Beijing was the worst affected due to the amount of rainfall it received. We use high-resolution Weather Research and Forecasting (WRF)-Urban modeling system to conduct numerous simulations to address the following questions: 1) Is the rainfall at Beijing solely due to the large weather pattern which moved over northern China? And 2) have the urbanization processes in the large Beijing metropolis (such as urban heat island) contributed to this event in terms of rainfall structure, location and amount? In order to isolate the effects of urbanization, we perform series of simulations that represent different degrees of urbanization and effects of urban dynamic and thermodynamic processes using three nested domains in WRF, and the finer domain has a grid spacing of 1 km. The preliminary results are encouraging and the details would be discussed at the conference. We will also discuss the influence of recycling of water from the previous storm of 21 July on subsequent storms occurred in the week of 23 July 2012 in that area.