Association and causes of intra-seasonal droughts and floods variations during summer in Hubei Province

Under the combined influence of climate change and anthropogenic activities, persistent and transitional drought-flood events have become increasingly frequent during summer in Hubei Province. To clarify the relative contributions and their evolutionary characteristics, this study investigates the dominant modes and causes of intraseasonal summer drought-flood variability in Hubei, using daily precipitation data and NCEP/NCAR reanalysis datasets, along with statistical methods such as Empirical Orthogonal Function decomposition and regression analysis. The results show that: (1) The intra-seasonal drought and flood variations in Hubei summer are primarily characterized by two modes: a persistent drought-flood mode and a transitional drought-flood mode. The former accounts for a higher proportion of explained variance than the latter. (2) Different drought-flood modes correspond to distinct atmospheric circulation evolution characteristics. In persistent drought-flood years, a stable East Asia-Pacific teleconnection wave train plays a crucial role, accompanied by the ‘Silk Road’ teleconnection wave train in early summer. In transitional drought-flood years, the circulation undergoes significant adjustments, shifting from a semicircular wave train over Eurasia in early summer to a Eurasian-like wave train in mid-summer. (3) Further research reveals notable spatio-temporal differences in the key sea surface temperature regions influencing persistent and transitional drought-flood events. Seasonal-scale SST anomalies in the equatorial central-eastern Pacific, tropical Indian Ocean, and North Atlantic can induce the formation and maintenance of the EAP and ‘Silk Road’ teleconnection wave trains, making Hubei prone to persistent drought-flood conditions in summer. In contrast, monthly-scale SST anomalies associated with the North Atlantic tripole can excite different Eurasian mid-high latitude wave trains, thereby favoring transitional drought-flood occurrences in Hubei during summer. The research findings can provide scientific support and decision-making references for subseasonal climate prediction and refined water resource management in the middle reaches of the Yangtze River region.