Analysis Of Drought Characteristics Based On Multiple Indices In The Hexi Inland River Basin

Drought and the resulting droughts have been one of the major natural disasters facing mankind since ancient times.In recent years,the trend of drought has become an important issue of global concern.In the context of climate change,with the increase of population and economic development,arid regions are showing an increasing trend,and the degree of drought has also increased.Drought not only poses a huge threat to agricultural production and food security,it also has a huge impact on the ecosystem and human life.The inland river basin in Hexi is located in the arid region of northwestern China.The precipitation is unevenly distributed in time and space,and the drought situation is complex and changeablIe.It is of great significance to carry out drought research in this basin.This study chooses Standard Precipitation Index(SPI),China Z index(CZI),Modified Z index(MCZI),Zscore Index(Zscore),Decile Index(DI),Normal Percentage Index(PN),Rainfall Anomaly Index(RAI),through correlation analysis,trend feature analysis,and the method of extracting drought characteristic variables based on the theory of run-length,combine with actual drought disaster materials,to select the meteorological drought index with good applicability in the study area from the above seven indexes.And then based on the preferred index,combine with the spatial and temporal changes of precipitation in the basin,to assess the meteorological drought characteristics of the research area from the trend,the number,the intensity,the frequency of drought events.Finally,the Copula function is used to construct the Comprehensive Drought Assessment Index(CDAI)to comprehensively evaluate the drought situation in the study area from the perspectives of meteorology and hydrology.The main conclusions of this study are:(1)The seven types of drought indexes have different performances in the drought assessment of the inland river basins of Hexi.The CZI,MCZI,and Zscore indices have a phenomenon that the some of drought events cannot be identified in the middle and lower reaches.There is a The DI,PN,and RAI indices have the phenomenon of excessive drought recognitionat above the severe level.The SPI index is not affected by the difference in the spatial and temporal distribution of rainfall,the range,duration and severity of drought events are identified from the typical drought year are in good agreement with the actual drought disaster materials,which is most suitable for application in inland river basins of Hexi.(2)The SPI at a shorter time scale responds quickly to drought events and can capture the occurrence of drought events.The SPI index on a longer time scale has a better identification of the duration of the drought event,the trend of drought aggravation in the lower reaches of the Heihe river basin and Mazongshan station can be well identified in terms of space.Combine with the changes of precipitation and SPI values over the years,the drought trend decreases in the inland river basins of Hexi,and the Heihe River Basin and Shiyang River Basin will have a tendency to become humid in the future.The SPI index on a longer time scale can identify a wide range of drought mitigation trends.(3)Taking the upper reaches of the Heihe River Basin as an example,based on the SPI and SRI indexes with the best correlation,the Gringorten empirical marginal distribution of the two indexes is calculated,and then the Frank Copula joint function is selected to construct the CDAI.Based on the theory of run-length,the drought characteristic variables are extracted of the CDAI index for drought assessment in the study area.By comparing and analyzing drought events,drought intensity,drought intensity,and drought duration in typical drought years in the study area,the CDAI index has a keen ability to identify drought events in the study area.It can not only identify quickly identify the occurrence of watershed meteorological drought events,but also can better identify the duration and end time of hydrological drought events.It can be used to comprehensively evaluate the hydrological and meteorological drought conditions in the upper reaches of the Heihe River Basin.