Verification and Assessment of Real-time Forecasts of Two Extreme Heavy Rain Events in Zhengzhou by Operational NWP Models

In the present study, the performances of the NWP models on two heavy rainfalls on 20 July and 22 August2021 over Henan Province were investigated. The impacts of the water vapor transport to the extreme rainfall were further discussed. The results showed that the regional model system in the Guangzhou Meteorological Service generally showed high scores on the extreme rainfall over Henan. The maximum 24 h accumulative rainfall by the 24 h forecasts by the CMA-GD reached 556 mm over Henan Province. The 24-h and 48-h Threat Score(TS) of heavy rainfall reached0.56 and 0.64. The comparisons of the Fraction Skill Score(FSS) verifications of the heavy rainfall by CMA-GD and CMA-TRAMS at the radium of 40 km reached 0.96 and 0.87. The water vapor transport to the extreme rainfall showed that the vertically integrated water vapor transport(IVT) of the whole layer before the occurrence of the heavy rainfall exhibited a double-eyes distribution in case 7 · 20. The north eye over Henan reached the same magnitude of IVT as the typhoon eye(Cempaka) over south China. The IVT over the lower troposphere(<500 hPa) showed an overwhelming magnitude than the upper level, especially in the planetary boundary layer(<700 hPa). More practical technique needs to be developed to improve its performances on the forecasting of extreme rainfall, as well as more experiments need to be conducted to examine the effects of the specific terrain and physical schemes on the extreme rainfall.