463 / 2024-03-29 10:17:27

Characterization of drought-flood abrupt alternation events in the Yangtze River basin based on improved multi-scale standardized dry-flood abrupt alternation index

drought-flood abrupt alternation; multi-scale; standardized index; Yangtze River basin; Spatiotemporal distribution

Subtheme 1: Water-related Hazard and Risk Reduction > Topic 1: Water Hazard Under Climate Change

Drought-flood abrupt alternation (DFAA) events are often cause severe disasters that affect economic growth and ecological security. Since the current monthly to sub-seasonal drought-flood abrupt alternation index (DFAI) has the limitations of misjudgments, omissions and neglecting alternation speed, this paper proposes a multi-scale standardized drought and flood abrupt alternation index (MSDFAI) that takes into account the combined effect of intensity and speed of alternation, and uses the Yangtze River basin (YRB) as an example to analyze its characteristics of DFAA. The results show that the MSDFAI index makes a conditional judgment on whether a drought or flood event occurs based on the standardized precipitation index (SPI) value, which can effectively avoid these misjudgments and omissions. Meanwhile, the MSDFAI index describes the DFAA events in a more comprehensive manner by introducing the speed factor. The drought to flood events among DFAA (DTF) in the YRB show a spatial pattern of high frequency in the upper reaches of the Yangtze River Basin (UYRB), the Han River and the lower reaches of the Yangtze River (LYRB), and relatively low frequency in the Poyang Lake water system and the  middle reaches of the Yangtze River Basin (MYRB), while the flood to drought events among DFAA (FTD) show a pattern of relatively more in the central part of the YRB and less in the western and eastern parts. The intensity of long-cycle DFAA events is stronger than that of short-cycle events, with light and midding events occurring most frequently in short-cycle, and midding events occurring most frequently in long-cycle. In the context of climate change, there is no significant interannual trend in the intensity of the average DFAA events in the YRB, but there is a significant increasing trend in the intensity of local extreme DFAA events. The interdecadal variability of severe DFAA events in the YRB is characterized by a turning point in the 1990s, when severe DTF events increased and FTD events decreased after the 1990s.