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基于深度学习的降水临近预报方法及其在2023年江苏汛期的应用评估

Evaluation of deep learning-based precipitation nowcasting methods during the 2023 flood season in Jiangsu

  • 摘要: 与传统外推类临近预报方法相比,深度学习降水临近预报方法能够预报强降水的生消演变。目前应用较多的深度学习方法有PhyDNet、PredRNN-v2、GAN三种,前两种为深度学习框架下不同网络架构的时空卷积神经网络,第三种则是以PhyDNet为生成器,多层卷积为判别器构成的生成对抗网络。本文评估了上述三种方法在2023年江苏汛期(4—8月)的应用效果,并通过典型个例分析了各方法在不同降水类型中的适用性。结果表明:(1) 从整体时段的评估结果看,PhyDNet和PredRNN-v2的TS表现优于GAN,而GAN对于主要降水雨带的BIAS有着最优表现,可消除前两种方法中出现的随预报时效趋于平滑的问题。(2) 系统性暴雨时段三种方法的评估结论与整体评估时段 基本一致,但在局地强降水时段中,GAN的TS和BIAS表现均优于PhyDNet和PredRNN-v2。(3) 典型个例分析结果表明三种方法均能刻画降水系统的生消演变,在系统性暴雨过程中,PredRNN-v2对降水增强过程的预报能力优于其他两种方法,而在局地强降水过程中,GAN不仅能够克服“模糊”导致的降雨区偏大的问题,还能更好表述降水中心强度及位置。以上结果表明,三种预报方法针对两类强降水预报预警场景各具优势,PhyDNet整体评分表现最优,PreRNN-v2适用于较长时效预报,GAN则适用于局地强降水预报,在实际业务中需根据各自特点择优参考。

     

    Abstract: Compared to the traditional nowcasting methods based on extrapolation, deep learning-based precipitation nowcasting methods can effectively forecast the trigger, development, and dissipation of heavy rainfall processes. Currently, there are three widely used deep learning methods, which are PhyDNet, PredRNN-v2, and GAN. The first two are spatiotemporal convolutional neural networks under the deep learning framework, while the third is the generative adversarial network with PhyDNet as the generator and multilayer convolution as the discriminator. This study evaluates the application of the above three deep learning-based precipitation nowcasting methods during the flood season of 2023 (April to July) in the Jiangsu region. The applicability of these methods in different precipitation types was also discussed through the representative case studies. The results indicate that: (1) From the entire evaluation period, PhyDNet and PredRNN-v2 show better TS performance than GAN. However, GAN performs the best in terms of BIAS for the main precipitation bands, which helps eliminate the "blurry" issue observed in the first two methods with the increase of forecast lead time. (2) During the systematic heavy precipitation periods, the evaluation results for all three methods are consistent with the overall period assessment. However, during the localized heavy precipitation periods, GAN outperforms PhyDNet and PredRNN-v2 in both TS and BIAS. (3) The results of the typical case analysis show that all three methods can capture the evolution of precipitation systems. In the case of systematic heavy rainfall events, PredRNN-v2 exhibits better performance in precipitation intensification compared to the other two methods. In localized heavy rainfall events, GAN not only overcomes the issue of precipitation overestimation caused by "blurriness" but also provides a better representation of the intensity and locations of the heavy precipitation centers. The above results suggest that each of the three forecasting methods has its advantages for different scenarios in heavy precipitation forecasting and warning. PhyDNet performs the best overall, PredRNN-v2 can be used for forecasts with longer lead time, while GAN is suitable for localized heavy rainfall events. Therefore, in practical operational applications, the choice of method should be based on their respective strengths and characteristics.

     

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