Flood Season Division Using Statistical Analysis Methods and Verifying by Regional Rainy Characteristics

Seasonal variation information is very important information for reservoir operation and water resources management. Traditional flood season division relies primarily on statistical methods and does not consider the specific regional rainy patterns. This study used several statistical methods to divide the flood season for the Danjiangkou Reservoir basin in the upper Han River, and verified the results by considering the regional characteristics of the Meiyu and Autumn Rain in the Yangtze River basin. The whole flood season is finally divided into three periods: the summer flood season (20 June to 10 August), a transition period (11 August to 31 August), and the autumn flood season (1 September to 10 October). The Meiyu occurs mainly in June and July, which can produce large floods. The latest end date of the Meiyu is on 8 August, which signals a reduction of flood prevention pressure in the downstream Han River. After 10 August, the Danjiangkou Reservoir flood prevention storage can be released gradually. Autumn Rain occurs from late August to mid-September, and contributes significantly flow discharge, which is an opportunity for reservoir early refill operations. This study will provide a practical approach for flood seasonal division in other regions with seasonal rainfall characteristics.