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基于分级跨级权重评分的短临模式集合降水预报订正技术研究

Research on Short-term Model Ensemble Precipitation Forecasting Correction Technology Based on Hierarchical Cross-level Weighted Scoring

  • 摘要: 基于CMA-GD-R3、CMA-SH3、CMA-MESO三个模式(简称原模式)的24 h内逐1 h、3 h起报降水产品以及湖南区域自动站降水实况资料,在传统降水检验方法的基础上创建了分级跨级权重降水评分法(Cross-magnitude Weight, CMW),并设计了基于CMW优选的时间滞后和空间平移短临模式集合降水订正预报模型(STDA-CMW),实现了效果更优的逐时更新的未来12 h内逐时定量降水预报。将该模型与三个原模式以及为验证STDA-CMW各模块有效性而设置的三组对比试验(分别为缺失空间平移模块、缺失强降水融合模块、将CMW优选替换为TS评分优选方案,简称对比模型)进行比较,以检验各模块的独立贡献。结果表明:(1) 对于一般性降水0.1,20) mm·h−1,STDA-CMW模型TS (0.325)优于所有原模式及对比模型。三个增强模块(空间平移模块、CMW优选模块、强降水融合模块)均有正贡献,其中CMW优选模块贡献最大,明显优于传统TS评分优选模块,空间平移与强降水融合模块贡献接近。(2) 对于强降水(≥20 mm·h−1),STDA-CMW模型在TS (0.011)、空报率 (0.971)、平均绝对误差 (25.141)和CMW(−0.004)上均优于原模式及对比模型。三个模块均有正贡献,但只有三个模块同时集成时,预报效果才能优于所有原模式预报。(3) 三个模块贡献各有侧重,空间平移模块主要提升强降水命中率,强降水订正模块同时提升命中率并降低空报率,CMW优选模块主要降低强降水空报率,且对强降水量级的贡献明显大于另外两个模块。上述研究成果为基于快速更新中尺度数值模式的短临降水订正提供了一种可行路径,在降低空报率和减少平均绝对误差等业务关键指标上具有相对优势,三个增强模块对短临降水预报的贡献各有侧重,且仅在三者协同集成时才能达到最优的强降水预报效果。

     

    Abstract: Based on the 1-hourly and 3-hourly updated precipitation products within 24 hours from three models (CMA-GD-R3, CMA-SH3, and CMA-MESO, hereinafter referred to as the original models) and the precipitation observations from regional automatic weather stations in Hunan Province, this study develops a novel verification metric named Cross-magnitude Weight (CMW) on the basis of traditional precipitation verification methods. A short-term ensemble correction and forecasting model (STDA-CMW) is designed, which incorporates time-lagging and spatial shifting techniques optimized by CMW, to achieve more effective hourly-updated quantitative precipitation forecasts for the next 12 hours. The proposed model is compared with the three original models and three sets of comparative experiments designed to validate the effectiveness of each module of STDA-CMW (namely, the scheme without the spatial shifting module, the scheme without the heavy precipitation fusion module, and the scheme replacing CMW optimization with the traditional TS score optimization), in order to examine the independent contributions of each module. The results are as follows. (1) For general precipitation 0.1, 20) mm·h−1, the STDA-CMW model achieves a TS score (0.325) superior to all original models and comparative models. All three enhancement modules (spatial shifting module, CMW optimization module, and heavy precipitation fusion module) make positive contributions, among which the CMW optimization module contributes the most, significantly outperforming the traditional TS score optimization, while the contributions of the spatial shifting module and the heavy precipitation fusion module are comparable. (2) For heavy precipitation (≥20 mm·h−1), the STDA-CMW model outperforms the original models and comparative models in terms of TS score (0.011), false alarm rate (0.971), mean absolute error (25.141), and CMW (-0.004). All three modules make positive contributions, but the forecast performance can surpass that of all original models only when the three modules are integrated simultaneously. (3) The contributions of the three modules have distinct focuses. The spatial shifting module primarily improves the hit rate of heavy precipitation; the heavy precipitation correction module enhances both the hit rate and reduces the false alarm rate; the CMW optimization module mainly reduces the false alarm rate of heavy precipitation and makes a significantly greater contribution to the magnitude of heavy precipitation than the other two modules. The above findings provide a feasible pathway for short-term precipitation correction based on rapidly updated mesoscale numerical models, demonstrating relative advantages in reducing false alarm rates and mean absolute error—key operational early warning metrics. The three enhancement modules contribute differently to short-term precipitation forecasting, and optimal heavy precipitation forecasts can only be achieved when the three modules are integrated synergistically.

     

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