*Article* **Analysis on the Return Period of "7.20" Rainstorm in the Xiaohua Section of the Yellow River in 2021**

**Shuangyan Jin \*, Shaomeng Guo and Wenbo Huo**

Hydrology Bureau of Yellow River Conservancy Commission, Zhengzhou 450004, China

**\*** Correspondence: yrccjinzi@163.com

**Abstract:** The "7.20" rainstorm and flood disaster in 2021 occurred in Zhengzhou and adjacent areas of Henan province. According to the Maximum Rainfall Data of Different Periods and the "7.20" rainstorm data of the section from Xiaolangdi to Huayuankou of the Yellow River in 2021, i.e., thirteen kinds of automatic monitoring rainfall data in minutes and six kinds of manual monitoring rainfall data in hours, the rainfall frequency curves of two representative periods of ten reference stations are established using Pearson-III distribution. The return periods of "7.20" rainstorms with maximum 24 h greater than 300 mm and maximum 6 h greater than 100 mm are calculated. The results show that the influence of "7.20" rainstorms on the rainfall return period is obvious. For the ten reference stations, all the maximum 24 h rainfall of "7.20" rainstorms ranked in the first of the series. When establishing the frequency curve, if this value is considered, the largest return period occurs at Sishui station, with a return period of 486 years. Otherwise, the return period of Sishui, Mangling, Minggao, and Xicun stations will exceed 10,000 years. Among ten reference stations, the largest proportion of the maximum 6 h rainfall between "7.20" rainstorms and historical series is Minggao station. Taking Minggao station as an example, the return period is about 200 years when considering the "7.20" value to establish the frequency curve, otherwise it is about 3000 years. The results can provide technical support for the analysis of the rainstorm return period and the flood control operation in the lower Yellow River.

**Keywords:** return period; Pearson-III distribution; "7.20" rainstorm; Yiluo River basin; Xiaohua section
