Integrating SWAP and SIF anomaly to assess the responses of vegetation to the drought-flood abrupt alternation in the middle and lower reaches of the Yangtze River basin, China

The middle and lower reaches of the Yangtze River basin, China. Under the background of global warming, drought-flood abrupt alternation (DFAA) events are occurred frequently, with substantial impact on ecosystems and water resources. Therefore, this study calculated the Standard Weighted Average Precipitation (SWAP) based on daily precipitation to verify the applicability of SWAP in the middle and lower reaches of the Yangtze River basin (MLRYRB). The response of Solar-Induced Chlorophyll Fluorescence (SIF) anomaly to DFAA events was determined based on lagged time correlation coefficients. Finally, based on Partial Wavelet Coherence (PWC), the impact of atmospheric circulation factors on the response relationship between DFAA events and vegetation was analyzed. The results indicate that: (1) the evolutionary characteristics of DFAA events determined by SWAP were consistent with historical records. (2) the DFAA events frequency with most regions experiencing 8–11 events during 2001–2019, with intensity of 2–3, and in the northern and southwestern Jiangxi and southeastern Hubei regions were more intensive and frequently. (3) the stronger correlations were mainly in eastern Guizhou and eastern Jiangxi, with SIF anomaly more sensitive to SWAP at 2-month lag time. (4) The El Niño-Southern Oscillation (ENSO) and sunspots have a significant influence on the response relationship between DFAA events and vegetation anomaly. This research can provide a scientific basis for the integrated response to DFAA events and ecological management in the MLRYRB.