基于聚类分析的浙江省汛期OCF降水预报分区订正试验

Regional correction calibration for OCF precipitation in flood season in Zhejiang Province based on cluster analysis

汛期暴雨预报一直是气象预报业务工作中的重点及难点。首先,利用浙江省2227个气象站2016-2021年每年汛期(4-10月)逐日降水资料,以欧式距离作为相似度度量标准,通过Kmeans聚类算法对浙江汛期降水进行分区;然后,对偏差订正法进行时空上的改进;最后,将改进后的偏差订正法与分区结合形成分区订正方法。以未与分区结合的全区订正作为对比,对浙江多模式客观集成预报(OCF)进行分区订正和检验。结果显示:(1)将浙江省划分为7个降水相似区,其结果呈现明显的区域特征,并与浙江省地形地貌密切相关。(2)经2021年汛期检验,相较于OCF预报,分区订正预报优于全区订正预报,其优势主要体现在能有效降低晴雨预报的降水空报率和大幅提升大雨以上量级降水的命中率,特别是暴雨以上量级预报命中率由0.25提升至0.41。(3)典型过程检验表明,对于系统性降水和对流性降水,分区订正预报均能改善暴雨以上量级降水强度和落区预报。特别是系统性降水,分区订正预报效果更明显,能预报出大暴雨以上强降水。

The forecast of rainstorm in flood season has always been the key and difficult point in the meteorological forecasting operation.First,we used the daily precipitation data from 2227 meteorological stations in Zhejiang Province from 2016 to 2021 during the flood season(April to October),and divided the precipitation region by applying the K-means clustering algorithm,which employed the Euclidean dis⁃tance as the similarity measure.Then,the regional correction method is formed by combing the spatial-temporally improved bias correction method and divided regions.Finally,we applied this method to perform the regional correction and validation on the Zhejiang Multi-Model Objective Consensus Forecast(OCF),compared with the overall correction not combined with divided regions.The results are as follows.(1)The K-means clustering algorithm can divide Zhejiang Province into 7 precipitation-similar regions,which show distinct regional character⁃istics closely related to the topographic features of Zhejiang Province.(2)According to validation during the 2021 flood season,the regional correction performed better than the overall correction in the OCF forecasts.Its main advantages lie in effectively reducing the false alarm of precipitation in the clear-rain forecast and substantially increasing the hit rate(POD)for the heavy rain and above,especially for the rain⁃storm and above from 0.25 to 0.41.(3)The typical validation show that,for both systematic and convective precipitation,the regional correc⁃tion can significantly improve the intensity and falling area of precipitation for the rainstorm and above.Especially for the systematic precipi⁃tation,the regional correction demonstrated more remarkable effects,which can predict heavy rainstorms.