Analysis of evolutionary characteristics and causes of drought-flood abrupt alternation in middle and lower reaches of Yangtze River BasinOA

[Objective]Under the influence of the subtropical monsoon climate,drought-flood abrupt alternation(DFAA)events frequently occur in the middle and lower reaches of the Yangtze River Basin(MLRYRB),posing a serious threat to the sustainable development of the river basin.Therefore,accurately identifying and analyzing the evolution patterns and causes of DFAA events is of great significance for formulating regional disaster prevention and mitigation strategies.[Methods]The short-cycle drought-flood abrupt alternation index(SDFAI)was employed as an indicator for identifying DFAA events to examine the spatiotemporal characteristics of drought-to-flood(DTF)and flood-to-drought(FTD)events in the middle and lower reaches of the Yangtze River,including their frequency,spatial extent,and intensity.Furthermore,the multiscale geographically weighted regression(MGWR)model and the random forest(RF)model were used to quantify the meteorological and atmospheric circulation factors of DFAA events.[Results]The result showed that:(1)DTF and FTD events occurred alternately,with the annual maximum intensity of DTF events showing a decreasing trend and that of FTD events showing an increasing trend,indicating a shift from DTF-dominated to FTD-dominated patterns.(2)The number of occurrences of both DTF and FTD events was primarily concentrated between 22 and 26 times,with the slight events exhibiting the broadest spatial extent and moderate-intensity events being the most frequent.Spatially,western Hunan,southern Anhui,and southern Jiangsu were DTF-prone areas,while southern Hunan and southern Hubei were more susceptible to FTD events.(3)Temperature(TRE)and precipitation(PRE)were the dominant meteorological drivers of DFAA events,serving as the primary or secondary influencing factors in more than 50%of the region.However,sunshine duration(SSD)was the primary influencing factor for FTD events in 29.12%of the region.The El Niño-Southern Oscillation(ENSO)and Sunspot were the major atmospheric circulation factors influencing DFAA events.[Conclusion]Compared to FTD events,DTF events exhibited greater intensity,frequency,and spatial extent in the MLRYRB.Hunan,central Hubei,and southern Anhui are regions with frequent occurrences of DFAA events.TEM and PRE are the dominant meteorological drivers of DFAA events,while the ENSO and Sunspot were the key atmospheric circulation factors.These findings can provide scientific guidance for improving the monitoring,prediction,and management of DFAA events in this region.