An evaluation method suitable for precipitation forecasts and services

Based on the thread score (TS), an improved verification index, the double-sided thread score (DTS), is proposed for precipitation forecast and service. TS only focuses on the forecasting skills of occurrence of events, but DTS takes into account the forecasting skills for both occurrence and non-occurrence of the events. The theoretical analysis and real cases show that DTS can help to improve the subjective or objective forecasts with BIAS closer to 1. The verification of annual precipitation forecast from 2007 to 2018 and daily precipitation forecast in 2019 shows that the DTS score decreases with the increase of the grade, and the scores of each grade are mostly higher than 0.5, so the score results are easier for the public to understand. In addition, the growth trend and fluctuation of prediction skills reflected by DTS are consistent with those by TS, which is convenient for comparison with historical scores.