Performance Analysis of CMA-BJ Model for "23·7" Extreme Heavy Rainstorm

Typhoon “Doksuri” weakened to low pressure in the north, and it was blocked by a high-pressure dam and moved slowly. From July 29 to August 2, 2023, an extremely heavy precipitation event occurred in the Beijing-Tianjin-Hebei region, which lasted for a long time, and the cumulative precipitation at a single station exceeded the historical extreme, causing huge floods. Based on precipitation observations, this paper comprehensively evaluates the CMA-BJ v2.0 performance of the precipitation event the spatial distribution characteristics of the cumulative precipitation and precipitation period in the CMA-BJ v2.0 forecast were consistent with the observed precipitation, and the overall rainfall was large, among which the D02 forecast was the closest to the observation; when the GFS global background field was used, the rain belt moved southward, and the high precipitation value area appeared in the central and southern part of Hebei Province, which deviated greatly from the observation, while the EC-driven forecast was closer to the observation. Compared to the cold run and single assimilation, the increasing wind speed of multiple assimilations brought a large amount of water vapor, and the distribution of precipitation was more consistent with the observations. The choice of boundary layer parameterization scheme has a certain impact on the forecast of wind field, and then affects the distribution and magnitude of precipitation. The YSU scheme has a better forecast effect than ACM2 and Boulac schemes in this precipitation event.