“SEEPS”降水预报检验评分方法在我国降水预报中的应用试验

The Application Experiment of a New Score for Precipitation Verification Based on the SEEPS Principle

  • 摘要: 介绍了国际上一种新的降水检验方法——概率空间中的稳定公平误差(stable equitable error in probabilityspace,SEEPS)的原理、计算方法和误差特征,并应用于我国定量降水预报检验进行评估试验。SEEPS方法在评分意义、降水分类、评分计算及评分应用等方面,比传统检验评分更加灵活,具有更清晰的实际意义。利用两个降水概率阈值,SEEPS方法将降水气候概率分布划分为“干”、“小雨”、“大雨”三类;该方法基于降水概率计算误差矩阵,根据站点分布密度计算区域平均评分权重系数。SEEPS在不同降水概率下具有不同的误差评分特征,使其能够自动适应不同的降水气候。SEEPS不仅可以定量化给出降水预报能力的高低,还可以通过分析不同观测和预报分类组合的误差评分,给出造成评分高低的成因。利用2007年3月—2013年12月24h累积降水逐日观测资料,对中央气象台预报员定量降水预报进行了SEEPS检验试验,并与传统的检验评分进行比较。结果表明:预报员定量降水预报的误差主要来源为两类——预报“小雨”对观测“大雨”的漏报和预报“小雨”对观测“干”类型的空报,合计占到了总误差的近七成;前者说明预报员降水预报量级较实际降水偏小,后者说明预报员对“小雨”的大范围、高频率空报也可以导致总体预报效果的明显下降。SEEPS方法对降水预报能力的评估结论与传统检验评分总体相当,但SEEPS检验指标更简单直接,便于管理层和决策层面使用,具有较好的推广应用价值。

     

    Abstract: The principles, computation and error characteristics of a new method newly developed internationally for precipitation verification, i.e., SEEPS (Stable Equitable Error in Probability Space), are briefly introduced in this paper. With regard to score meaning, precipitation classification, score calculation and application, SEEPS is more flexible and has clearer practical meaning than traditional verification scores. The SEEPS method is applied in the verification and assessment experiment for quantitative precipitation forecasts in China region, and some issues encountered in the application are talked about. Climatic precipitation probability distribution is divided into three classifications, ‘dry’, ‘light’ and ‘heavy’ by two thresholds in SEEPS. Error matrices are determined by the precipitation probability. Area mean is weighed based on the station density. Possessing different error score characteristics under varying precipitation probabilities makes SEEPS automatically adapt to various kinds of precipitation climate. The ability of precipitation forecasts is quantified by the SEEPS values, and different elements of SEEPS can also be analyzed to find the reason why the SEEPS score is high or low. Daily observations of 24-hour accumulated precipitation from Mar. 2007 to Dec. 2013 are used in the SEEPS verification test for quantitative precipitation forecasts (QPF) of forecasters in the National Meteorological Center of CMA. Results show that the two main categories of forecasters’ QPF errors are misses of heavy precipitation with light precipitation forecasts, and false alarms of “dry” with light precipitation forecasts. These two kinds of errors account for about 70 percent of all errors. The former explains the order of forecast precipitation is lower than observations and the latter states that false alarms with large areas and high frequencies can also obviously deteriorate the whole forecast performance. Conclusions of SEEPS are approximately equivalent to those of traditional verification scores. But the SEEPS score is simpler and more suitable for use in management and decision making, and has more value for popularization and application.

     

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