21世纪中国极端降水事件预估

评估分析了欧洲中期天气预报中心（European Centre for Medium-range Weather Forecasts，ECMWF）细网格模式（以下简称EC-thin）在长三角地区汛期（5-9月）的暴雨预报评分及ECMWF降水极端天气预报指数（EFI）对暴雨预警的指示作用。研究发现：（1）EC-thin降水和降水EFI对暴雨预报的ETS评分随着预报时效的延长而明显降低，在短时效内，细网格模式降水预报占优，超过60 h后，降水EFI的评分相对更好。（2）对EC-thin降水而言，在不同的预报时效采用不同的降水阈值来预报暴雨，可望达到最佳的评分效果。短期时效内该阈值随着预报时效的延长，大致从55 mm逐渐下降到35 mm。（3）对于降水EFI而言，12-36 h内EFI为0.65~0.7时，暴雨预报ETS评分最高。随着预报时效的延长逐渐下降，60-84 h内EFI为0.55~0.6时，暴雨预报ETS评分最高。（4）在不同预报时效内，采用合理的方式和阈值综合考虑EC-thin降水和降水EFI，可望得到更高的暴雨预报评分。

Improvements in IFS forecasts of heavy precipitation

European Center for Medium-range Weather Forecasting (ECMWF) high-resolution model and ECMWF Extreme Weather Forecast Index (EFI) are evaluated and compared for heavy rainfall during the flood season (May to September) in Yangtze River Delta. The studies show the following results. (1) The ETS score of ECMWF model and EFI of precipitation for heavy rainfall forecast are significantly reduced with the extension of forecast period. In a short time period, ECMWF model precipitation forecast is superior, but EFI tends to be better after 60 h. (2) In different forecast time periods, using different precipitation thresholds to predict the heavy rainfall is expected to achieve the best score. In the short term period, the threshold is gradually reduced from 55 mm to 35 mm with the extension of forecast period. (3) For the EFI of precipitation, when the EFI is 0.65~0.7 in 12-36 h, the ETS score of heavy rainfall forecast is the highest. The threshold of EFI also decreases with the prolongation of the prediction period. The ETS score is the highest when the EFI takes 0.55~0.6 at 60-84 h. (4)The combination of EC-thin precipitation and EFI of precipitation by reasonable methods and thresholds can obtain higher score of heavy rainfall forecast in different forecasting time periods.