Indirect Effects of Binary Typhoons on an Extreme Rainfall Event in Henan Province, China From 19 to 21 July 2021: 1. Ensemble‐Based Analysis

Abstract

AbstractThe extreme rainfall from 19 to 21 July 2021, which caused massive flooding and loss of life, is the second heaviest rainfall that has occurred in Henan province, central China. To identify the key factors controlling this rainfall event, we conducted an ensemble‐based analysis using ECMWF operational global ensemble forecasts. The forecasts of extreme rainfall had a relatively large spread and there was a large bias in the ensemble mean precipitation, indicating uncertainties in the forecast. The extreme rainfall was closely related to the Huang‐Huai cyclone and the southerly and southeasterly flows. Although they had little influence on the southeasterly flow, the uncertainty and predictability of typhoons In‐fa and Cempaka probably caused the variation in the southerly flow and the maintenance of the Huang‐Huai cyclone, which determined the amount of precipitation for this extreme event in the ensemble forecast model. When typhoon In‐fa was located further northwest, the northeasterly airflow generated by the binary interaction between typhoons In‐fa and Cempaka weakened the intensity of the southerly flow, reduced the transport of water vapor to the rainstorm area and weakened the Huang‐Huai cyclone, thus reducing precipitation in the control area. The results of this study indicate that ensemble‐based analysis can improve our understanding and forecasting of extreme precipitation events under the influence of multiple remote tropical cyclones.