Spatial And Temporal Variation Characteristics Of Drought In The Yangtze River Basin In Recent56 Years

Drought are the world's most damaging and pressing natural disaster.The effects of drought,a devastating natural disaster,have expanded due to intense global warming.Therefore,studying the spatio-temporal evolution and formation mechanism of drought is urgent and important.In this paper,the spatial and temporal characteristics of drought in the Yangtze River Basin are analyzed from 1960 to 2015 by using 0.5°×0.5°standardized precipitation evapotranspiration index(SPEI)data.Based on the monthly SPEI at a 3-month time scale,various characteristics of drought across the Yangtze River Basin were examined including:percentage of area affected,intensity,duration,and drought frequency.The Modified Mann-Kendall(MMK)trend test and Sen's slop estimate method were used to study the temporal trends of SPEI at a 3-month time scale.The principal component analysis(PCA)was applied to assess the spatial pattern of drought based on the monthly SPEI at a 12-month time scale and the Complete Empirical Mode Decomposition with Adaptive Noise method(CEEMDAN)was utilized to reveal the periodical features of drought condition in each sub-region.The wavelet coherence analysis(WTC)was used to explore the potential relationship between drought conditions and large-scale climate factors.The results are as follows:(1)In the past 56 years,there have been 21 global drought events in the Yangtze River Basin and there were 1352 drought events per year in the Yangtze River Basin.The most frequent drought occurred in 2011.From the seasonal point of view,except autumn showed a weak upward trend,the other three seasons showed a weak downward trend.The average drought station number ratio is in the order of autumn,summer,spring and winter.(2)Compared to upper and lower region,the middle reaches of the Yangtze River Basin had a more significant drought trend,especially in the intersection of Sichuan,Yunnan and Guizhou provinces and the intersection of Chongqing and Hubei provinces.Drought frequency presents spatial distribution characteristics of west high and low east.Drought occurs most frequently in the Ulan Moron which is the western source of the Yangtze River Basin.Consecutive drought events seem to prefer to appear in the Jinsha River Basin.(3)Six distinctive sub-regions with different temporal evolutions of drought are well identified,respectively,representing the southeast(R1),northeast(R2),southwest(R3),northwest(R4),central-south(R5)and central-north(R6)of the Yangtze River Basin.The drought variability in the basin include the intra-annual shocks which are mainly in 3 and 7months and inter-annual shocks which are mainly in 1 and 6 years.inter-decadal fluctuations are quite different.(4)The teleconnections of Atlantic Multidecadal Oscillation(AMO)and North Atlantic Oscillation(NAO)show significant influences on the regional droughts principally concentrated in the 1-to 4-year period,maybe responsible for the physical causes of the cyclical behavior of drought occurrences.Especially,AMO show strong influences on drought in two sub-regions(northeast and central-north of research area)over6-year cycle;NAO show obviously influences on drought in the central-north of research area over 6-year cycle.These results provide useful information for evaluating drought changes in the study area,early warning of drought,and water resource management.