Increasingly frequent co-occurrence of drought or pluvial in multiple tributaries of the Yangtze River basin

Drought and pluvial respectively represent a region experiencing a period of water deficit and surplus relative to its normal state. The co-occurrence of drought and pluvial across numerous tributaries of a large river would trigger widespread water shortage and extreme flooding. However, little is known about such spatially concurrent hydrological extremes within large river basins throughout historical periods. Here, we select ten tributaries of the Yangtze River basin (YRB) and employ the VineCopula model to assess the probability of simultaneous drought and pluvial using precipitation observations during 1960-2019 from the perspective of dry and rainy seasons. From 1960 to 1989 to 1990-2019, the probability of two or more tributaries with simultaneous drought decreases from 37.7% to 25.3% during the dry season while increases from 26.6% to 27.3% during the rainy season. For the case of simultaneous pluvial, the probability increases in both dry (from 19.2% to 36.7%) and rainy (from 26.2% to 29.6%) seasons. The notable shifts in the probabilities of concurrent drought and pluvial within YRB highlight an escalating threat of widespread water scarcity and heightened risks of severe flooding. These changes necessitate immediate attention and proactive measures to address the imminent challenges faced by both natural and societal systems along the Yangtze River.