基于REOF分区的海河流域旱涝急转事件时空特征分析OA

Drought and flood abrupt alternation(DFAA)events refer to a phenomenon of abnormal intra-seasonal precipitation.Compared with single drought or flood events,DFAA events tend to cause more severe damage to human lives,water conservancy projects,food production,and food security.However,existing stud-ies have paid little attention to the evolutionary characteristics of DFAA events in northern China,and their re-gional concurrent characteristics have not yet been fully recognized.Therefore,by adopting an identification method for DFAA events based on the run length theory at a daily scale and by using daily precipitation data from 159 meteorological stations in the Haihe River Basin(HRB)during 1961-2023 and rotated empirical orthogo-nal function(REOF)precipitation zoning,the spatiotemporal variation characteristics of DFAA events(only fo-cusing on"drought-to-flood"abrupt alternation events)and regionally concurrent DFAA events in the study area are investigated.The results show that:①From 1961 to 2023,both the frequency and intensity of DFAA events in the HRB exhibited an increasing trend with significant interannual variations.Specifically,the frequency of DFAA events increased in all five subareas;the intensity of DFAA events slightly increased in Subarea I,while no obvious trends were observed in the other four subareas.②DFAA events occurred more frequently in parts of the northwest,central-western,and downstream regions of the Haihe River Basin.Relatively high DFAA intensity was detected in parts of the northern,central-western,and southern regions.Notably,both the frequency and in-tensity of DFAA events were higher in the northwest and central parts of the Beisan River Basin,suggesting that more attention should be paid to these high-risk areas with frequent or high-intensity DFAA events.③This study also defined a method for identifying regionally concurrent DFAA events.Based on this method,a total of 115 re-gionally concurrent DFAA events occurred in the HRB during 1961-2023,and both their frequency and compre-hensive intensity showed an increasing trend.May and June were the peak periods for regionally concurrent DFAA events,with strong comprehensive intensity.These events were more likely to occur in Subareas Ⅲ,Ⅳ,and Ⅴ,which are precipitation-abundant regions in the HRB,indicating a close correlation between regional pre-cipitation and the occurrence of regionally concurrent DFAA events.