Comprehensive Assessment Of Drought In The Tarim River Basin Based On GLDAS And GRACE Data

Drought is one of the most widespread and frequent natural phenomena in the world.Under the combined effects of global climate change and human activities,the issue of drought has become increasingly prominent,and it has become a basic problem and an important challenge faced by various countries or regions.In China,especially the Tarim River Basin in the arid and semi-arid regions of the northwest,its status is extremely important,but the frequent occurrence of drought has brought great distress to the development of the basin.Some scholars have pointed out that the northwestern region of China has gradually tended to become warm and humid,but other scholars have raised doubts and given the opposite view.Then,under the controversial background of "the northwestern China gradually develops in the direction of warmth and humidity",what is the drought change in the Tarim River Basin,and how is the risk of drought disasters in different regions? The discussion of these issues is of great significance for understanding the drought problem in the basin.Based on this,this study takes the "four sources and one trunk"(four sources: Aksu Basin River,Kaikong Basin River,Hetian Basin River,Yarkant Basin River;one trunk: the main Stream Baisn of Tarim River Basin)in the Tarim River Basin as the specific research object,and the four sources are divided into mountainous and plain areas,and the one trunk is divided into upstream,middle and lower reaches,and the perspectives of different types of droughtsmeteorological drought and hydrological drought,respectively,and combines station measured data and earth product data to explore the drought variations in this basin during 1961-2010.First,the trend analysis,empirical mode decomposition(EEMD),empirical orthogonal function analysis(EOF),and rescaling range analysis method(R/S analysis method)were applied to meteorological drought and hydrological drought in the “four sources and one trunk” of the Tarim River Basin.This paper analyzes the spatiotemporal variations of meteorological drought and hydrological drought and explores whether the area has become drier or wetter in the past 50 years.Secondly,the lag correlation analysis and cross-wavelet analysis are used to analyze the response of hydrological drought to meteorological drought.Finally,based on the theory of the regional disaster system,it is believed that the regional disaster system is mainly composed of disaster-causing factors,disaster-pregnant environments,disaster bearers,and disaster prevention and mitigation capabilities.We evaluate the risk of meteorological drought disasters,hydrological drought disasters,and comprehensive meteorological-hydrological drought disaster risks in the "four sources and one trunk".The main conclusions are as follows:(1)From the perspective of time,the meteorological drought and hydrological drought in the "four sources and one trunk" have generally weakened during the study period,and there are multiple time-scale oscillation cycles in the meteorological drought index and hydrological drought index.In terms of the trend of drought changes in the past 50 years,the meteorological and hydrological droughts of the "four sources" are consistent and show a weakening trend.Among them,the weakening trend of the meteorological drought in summer was the most obvious.the weakening ternd of hydrological drought in winter is the most obvious.Meteorological droughts in the upper reaches of the mainstream have shown an increasing trend,while hydrological droughts have shown a weakening trend.Meteorological and hydrological droughts in the middle and lower reaches have the same changes,showing a decreasing trend.However,the meteorological and hydrological drought trends of the “four sources and one trunk” have obvious stages,that is,the dry and wet trends of “four sources and one trunk” vary in different years,among them,the 1970 s and 1990 s were the periods when meteorological drought and hydrological drought increased.In terms of average drought duration and intensity,the meteorological and hydrological drought durations of the "four sources and one trunk" all became shorter and the drought intensity showed a decreasing trend,among them,the average drought duration of hydrological drought is longer than the average drought duration of meteorological drought.The trends of shorter average drought duration and weaker average drought intensity in the Yarkant and Hetian river basins are not obvious,and the overall changes of the two are similar.However,the average duration and intensity of drought in the Aksu River Basin,Kaikong River Basin,and the mainstream river basins have obvious phase characteristics.In terms of drought intensity,the meteorological drought and hydrological drought intensity of the "four sources and one trunk" have no obvious phase characteristics,and the change process is relatively stable,showing only a slight weakening trend.The "four sources and one trunk" meteorological drought index and hydrological drought index all have cycles of monthly scale,interannual scale and interdecadal scale.Among them,the monthly scale cycle has obvious seasonality.The cycles of the meteorological drought index and hydrological drought index between the “four sources and one trunk” and between the respective internal mountainous and plain areas(or upstream,middle and lower reaches)are relatively close on a short time scale.As the time scale increases,the variability of cycles is also increasing.(2)From a spatial perspective,during the study period,there are differences in the spatial patterns of meteorological and hydrological droughts among the “four sources and one trunk” and within each.Among them,the meteorological drought in the "four sources and one trunk" all showed a weakening trend in the whole basin,while the hydrological drought in the area with dense human activities shows an increasing trend,and in the area with few human activities shows a decreasing trend.In terms of drought trends in the past 50 years,the "four sources and one trunk" meteorological drought has shown a significant weakening trend in space.The hydrological drought is also generally showing a weakening trend in space,but it is increasing in areas with dense human activities.In terms of the number of droughts,the number of meteorological droughts in the Aksu River Basin,Yerjing River Basin,Hetian River Basin,and the mainstream river basins was generally higher than that of the Kaikong River Basin,most of which are between 37-45,and it is between 25-32 in Kaikong River Basin.The number of occurrences of hydrological drought varies greatly within the basin,while the differences between basins are small,mostly between 29-45.In terms of drought duration,the relatively high-value areas of meteorological drought and hydrological drought in the Yarkant River Basin and Hetian River Basin are distributed in areas with high human activities.Both the meteorological drought and the hydrological drought in the mainstream river basin are mainly distributed downstream.The meteorological drought in the Aksu River Basin and the Kaikong River Basin are evenly distributed in space,while the hydrological drought duration is relatively high in the mountainous area in the Aksu River Basin,and the relatively high value area in the Kaikong River basin is in the mountainous area and the tail area of the basin.In terms of drought intensity,the "four sources and one dry" meteorological drought intensity distribution is relatively uniform,and is basically in a moderate drought state,while its hydrological drought intensity is slightly higher in the mountain region than in the plain region,and it is generally in a light drought state.Both the meteorological and hydrological drought fields in the Aksu and Yarkant river basins have two types of spatial distribution modes: full-watershed uniform type and mountainplain inversion.These two modes correspond to the four forms of drought: dry in the whole basin,wet in the whole basin,dry in the plain and wet in the mountain,and wet in the plain and dry in the mountain.There is also a southwest-northeast staggered spatial distribution pattern in the hydrological drought field of the Yarkant River Basin,corresponding to the forms of humid-arid-humid-drought and drought-humid-drought-humidity from southwest to northeast;The meteorological drought field in the Hetian River Basin has two spatial distribution modes: full-watershed uniform type and southwest-northeast staggered type,while the hydrological drought field has two spatial distribution modes: full-watershed uniform type and mountainplain area reverse type;The meteorological drought field in the Kaikong River Basin has three spatial distribution modes: full-watershed uniform type,mountain-plain inversion,and human activity sparse area-human activity dense area inversion,while the hydrological drought field has a southeast-northwest inversion and southeast-northwest staggered spatial distribution mode.Both the meteorological drought field and the hydrological drought field in the mainstream river basin have two spatial distribution modes: full-watershed uniform type and mid-upper-middle-downstream inversion.In addition,the hydrological arid field also has upmiddle-downstream staggered spatial distribution modes,corresponding to the two forms of drought: wet in the upstream and downstream and dry in the midstream drought,and dry in the upstream and downstream and wet in the midstream drought.(3)Multiple time-scale responses of hydrological drought to meteorological drought.From a time series perspective,the resonance changes between hydrological and meteorological droughts are more complex and frequent on a short time scale,while it is relatively stable on a long time scale.From a spatial perspective,on the monthly and interannual time scale,meteorological drought and hydrological drought in the "four sources and one trunk" are basically positively correlated.And the correlation between meteorological drought and hydrological drought in the plains in the "four sources" is generally stronger than that in the mountainous areas.On the decadal scale,there is a negative correlation between meteorological drought and hydrological drought in a large area of the unused land in the "four-source" plain area,but both are not significant.Both the meteorological drought and the hydrological drought in the mainstream of the mainstream still show positive correlation.Hydrological drought generally lags meteorological drought for a period of time,the lag time of hydrological drought to meteorological drought in mountain areas is longer than that of plain area.The average lag time of plain area is within 7 days in the four source basins,while the lag time in the mountainous areas of the Aksu and Kaikong River Basin is mainly within 151-365 days and the lag time in the mountainous areas of the Yarkand and the Hetain River Basin is as high as one year or more.The lag time of hydrological drought to meteorological drought in the mainstream of the Tarim River is also within 7 days.(4)The high-risk areas of meteorological drought disasters,hydrological drought disasters,and comprehensive drought disasters are all distributed in human-intensive areas.The risk patterns of meteorological drought disaster-causing factors,hydrological drought disaster-causing factors and meteorological-hydrological drought disaster-causing factors are quite different.There is no obvious regularity in the risk of the meteorological drought-causing factors of "four sources and one trunk",but the hydrological drought disaster-causing factors and meteorological-hydrological drought disaster-causing factors are more risky in areas with high human activity,and lower in areas with less human activity.In addition,in areas where human activities are intensive,the sensitivity of the drought-pregnant environment and the exposure of the drought disaster bearers are relatively high,and the ability to prevent and reduce drought disasters is relatively strong.In areas with little human activity,the sensitivity of the drought-pregnant environment and the exposure of the drought disaster bearers are low,and the ability to prevent and reduce drought disasters is weak.In terms of the risk of drought disasters,the spatial patterns of the risks of meteorological drought disasters,hydrological drought disaster,and meteorological-hydrological comprehensive drought disaster risk are all similar,that is,the high-risk areas of meteorological drought disaster risk,hydrological drought disaster risk,and meteorological-hydrological drought disaster risk are mostly distributed in plain areas with densely population,large arable land and relatively high socioeconomic levels,while low-risk areas are mostly located in mountainous areas or sparsely populated unused areas.