"25•7" Beijing Severe Rainstorm: Basic Characteristics and Simululation with CMA-BJv3.0 Model

From July 26th to 27th, 2025, Beijing experienced a rainfall of 315.3 millimeters within 12 hours. Due to the combined effect of a series of local precipitation processes over a period of time, severe floods and casualties occurred in the Miyun area. This paper compared the forecasting performance of five operational numerical weather prediction models for this process, and analyzed the impact of the improvement of physical parameterization schemes and data assimilation on precipitation forecasting based on the CMA-BJv3.0 system. The results showed that the CMA-BJv3.0 forecast was consistent with the spatial distribution and overall timing of the observed precipitation, but there were issues of a northward bias in the precipitation area and a smaller precipitation amount. The other four models underestimated the average precipitation in the target area, and there was a significant underprediction. The numerical sensitivity experiments showed that the coordinated optimization of physical processes and assimilation strategies could improve the forecast of precipitation area and intensity, enhancing precipitation in the northern part of Beijing and shifting the precipitation area southward, and reducing the overprediction in the northern part of Hebei. After optimization, the convergence of the northward and southward winds in the lower layer, the convergence and upward movement of the east-west wind field, and the abundant water vapor convergence and large initial CAPE provided favorable conditions for precipitation. The north wind and east wind in the lower layer may play an important role in this extreme precipitation event. A single scheme optimization could not achieve the above improvement effects.