Evolution Characteristics And Risk Response Of Meteorological And Hydrological Drought In Yangtze River Basin

In recent years,under the environmental background of climate change and the increasing impact of human activities,the frequency and intensity of global drought have been increasing significantly.The study on the characteristics of drought evolution and its risk response can provide a reference for regional drought disaster prevention and control.Based on the meteorological data from 183 meteorological stations in the Yangtze River Basin and the monthly runoff data from 4 hydrological control stations in the main stream during1960-2016,standardized precipitation evapotranspiration index(SPEI)and standardized runoff index(SRI)were used to represent the meteorological drought and hydrological drought,respectively.The temporal and spatial evolution characteristics of meteorological drought and hydrological drought in the study area in recent 60 years and the response relationship of hydrological drought to meteorological drought were analyzed.Finally,a multivariable joint distribution model of meteorological drought and hydrological drought in the Yangtze River Basin was established based on Copula function.The main research results are as follows:(1)From 1960 to 2016,the 1,3,6 and 12-month time scales of SPEI in the Yangtze River Basin all showed a decreasing trend over time,among which SPEI3,SPEI6 and SPEI12 showed a significant decreasing trend over time,indicating an increasing trend of drought in the study area.The SPEI of the 1,3,6 and 12-month time scales in the Yangtze River Basin changed statistically in 1998.SPEI1 and SPEI3 had a significant period of 0.5-1 years,SPEI6 had a significant period of 1-2 years,and SPEI12 had a significant period of about 8 years.(2)From 1960 to 2016,SRI6 and SRI12 at Cuntan and Yichang stations and SRI1 at Hankou stations showed a significant decreasing trend.In the past 60 years,SRI12 at Cuntan,Yichang,Hankou and Datong stations had significant abrupt changes,and there were significant oscillation cycles of 4-16 years and 16-20 years.(3)The correlation between meteorological drought and hydrological drought is good,and the correlation coefficient of meteorological drought and hydrological drought at the12-month scale is the largest and the strongest.Taking the year 2003 before and after the operation of the Three Gorges Reservoir as the boundary,the variation of hydrological drought response to meteorological drought under the influence of the reservoir was discussed.The results show that the frequency and frequency of extreme drought in Yichang,Hankou and Datong stations are increasing compared with that before 2003,which may be related to the decrease of precipitation and the increase of temperature in the Yangtze River Basin in recent years.From the perspective of the correlation coefficients between SRI and SPEI at different time scales,the correlation coefficients between SRI and SPEI at Yichang,Hankou and Datong stations increased with the increase of time scales from 1960 to 2016,and at the12-month scale,the correlation coefficients of the three hydrological stations during2003-2016 were higher than that during 1960-2002.Compared with the period without the influence of reservoir,the time lag between hydrological drought and meteorological drought in Yichang,Hankou and Datong stations increased to a certain extent during the influence of reservoir,which may be related to the water impoundment of the Three Gorges Reservoir.(4)At the same level of return period,the return period of the univariate variable was between the joint return period of the two dimensional and three dimensional variables and the co-occurrence return period.The co-occurrence return periods of 2D and 3D variables are larger than the corresponding joint return periods.The co-occurrence recurrence periods of three dimensional variables are larger than those of the corresponding two dimensional variables,while the joint recurrence periods of three dimensional variables are smaller than those of the corresponding two dimensional variables.By studying the temporal and spatial evolution of meteorological and hydrological drought in the Yangtze River Basin,this paper discusses the response relationship of hydrological drought to meteorological drought,and analyzes the multivariable joint distribution model of meteorological and hydrological drought,in order to provide scientific support for water resources planning and drought prevention and drought resistance in the Yangtze River Basin.