The Influence of Series Length and Current Maximum Value on the Estimation of the Rainfall Return Period

According to the rainfall data of Lijiahe and Dingjiagou hydrological stations from 1960 to 2017 in Wudinghe basin, the influence of series length on the variation coefficient is calculated and analyzed. Taking “7.26” rainstorm in Wudinghe as an example, using P-III distribution, rainfall frequency curve of the maximum 24h and 12h of the two stations in the following three cases were established, i.e. not considering the current rainfall, considering the current rainfall, transplanting adjacent extra-large rainfall, and the return period of rainfall at each station was calculated. The results showed that: (1) When the series length reaches 30-35 years or more, the variation coefficients of the six different time scales tend to be stable. (2) The influence of current maximum value on the rainfall recurrence period is obvious. The max 24h rainfall of the “7.26” rainstorm in Lijiahe station ranks first of the series, the return period is about 90 years when considering the value, otherwise it is about 500 years. The max 24h rainfall of the “7.26” rainstorm in Dingjiagou station doesn’t rank the first of the series, whether the value is involved in the establishment of frequency curve, return period is 20∼30 years. (3) Considering the transplantation of rainstorm, it is suggested that in the analysis of rainfall return period, the current maximum value should be considered, and the adjacent extra-large value should be transplanted.