Spatial and temporal variation characteristics of the drought-flood abrupt alternations over Haihe River Basin

The research on the occurrence regularity of the drought-flood abrupt alternation in Haihe River Basin can provide scientific reference for flood control and drought relief. Based on the daily precipitation data of 159 meteorological stations in Haihe River Basin from 1961 to 2019, the Standardized Antecedent Precipitation Index (SAPI) is calculated. Based on the SAPI, according to the drought-flood grade standard and drought-flood abrupt alternation conditions, the drought-flood abrupt alternation events since 1961 are screened out, and the frequency and intensity characteristics of drought-flood abrupt alternation in Haihe River Basin are analyzed. The results show that the annual average frequency of drought-flood abrupt alternation in Haihe River Basin is 33 times, which basically increases year by year, with an average of 37 times in recent 10 years. The intensity of drought-flood abrupt alternation also showed an upward trend, and increased to above the average value after 2000; it showed a jumping increase with reaching the maximum value especially in recent 10 years. The drought-flood abrupt alternation occurred mostly in May, June and mid September, and less in midsummer. The intensity of drought-flood abrupt alternation presents a single peak distribution, and the maximum value appears from the middle of June to the first ten days of July. The corresponding frequency of drought-flood abrupt alternation is also more in this period, which increases the risk of flood disaster. From the perspective of spatial distribution, the frequency and intensity of drought-flood abrupt alternation are high value areas in the southern part of Luanhe River system, the western part of Beisanhe River system and the central part of TuhaiMajia River. That is to say, the frequency and intensity of drought-flood abrupt alternation are high in these areas, consequently, the risk of drought-flood abrupt alternation is high. These areas may become the focus of flood control.