Scientific identification of the spatial sources of mainstream flood events in the middle and lower Yangtze River basin is of great significance to the design of a regional flood control strategy and its engineering application. This study uses an improved method of principal component analysis (PCA) to screen significant flood fluctuation samples

based on the 2003-2022 daily average discharge series from this basin’s mainstream and major tributaries. Major flood events are determined using warning water levels

through combining a three-zone Flood Combination Index (FCI)

high-FCI years

and primary discharge combination patterns for different zones. The results indicate that the improved PCA extracts discharge fluctuating characteristics effectively

and significant samples with the first principal component (PC1) score above the threshold 1.36 are in good agreement with the real cases in the high range of flow discharge. Inter-annual variations occur in the distribution of consecutive significant-sample periods. In 2021

significant flood periods occurred quite late under the influence of autumn floods from the Han River

while in 2022

early-season inflow impacts were evident due to a "dry flood season". The year of 2020 was marked by typical basin-wide flood events

and regional floods dominated 2010

2012

2016

and 2017

consistent with historical flood records.