Abstract: Studying the connections between drought/flood characteristics and monsoons in the Lancang River basin is of vital significance for understanding the causes, mechanisms and prediction of regional drought/flood disasters; yet the vast majority of existing studies are focused on the temporal and spatial evolution characteristics of drought/flood rather than on the connections between drought/flood characteristics and monsoons in the Lancang River basin. In this paper, the temporal and spatial changes in characteristics of drought/flood in 1957-2015 are investigated in terms of standard precipitation index (SPI12), monsoon index, and water vapor flux; the connections between drought/flood changes and monsoon index are examined, and the mechanism of drought/flood changes driven by monsoons and water vapor fluxes is further revealed. Results indicated that: (1) flood/drought has obvious regional difference, and the downstream area is prone to flood and drought; (2) the frequency of drought is superior to that of flood, showing an increasing trend in annual and seasonal time scales; (3) the frequencies of flood and drought mainly varied periodically at 3-5 years, 8-15 years, and 20-25 years; (4) in drought/flood period, indices of the South Asian monsoon and the Plateau monsoon have relatively strong correlations with the standard precipitation index (SPI12) in the Lancang River basin; such correlation varies in different regions due to the limited transportation distance of monsoons. The results are helpful in understanding the temporal and spatial change characteristics of drought/flood in the Lancang River basin, and also offer scientific basis for the decision-making of drought/flood prevention.

Key words: drought and flood, monsoon, standard precipitation index, water vapor flux, Lancang River basin