| The drought index is the basis of drought monitoring,evaluation and management.The construction of a comprehensive drought index and research on the spatio-temporal characteristics of drought evolution can provide a basis for regional drought prevention and drought management.In view of the shortage of data in alpine mountainous areas and the difficulty of a single drought index to reflect all the characteristics of drought,this paper takes the five major watersheds of the upper Shiyang River in Gansu Province as an example,and constructs a watershed SWAT hydrological model based on hydrometeorological data from1981 to 2017.Combine simulated evapotranspiration,soil moisture,runoff with measured rainfall data,use parameterized or non-parametric methods to construct univariate drought indices,such as the Standardized Precipitation Evapotranspiration Index(SPEI),the Standardized Soil Moisture Index(SSI)and the Standardized Runoff Index(SRI).Use Mann-Kendall test and R/S analysis method and other methods to analyze the temporal and spatial characteristics of meteorological,agricultural,and hydrological drought in the study area.The nested Archimedean construction method is used to construct the meteorological-agricultural-hydrological comprehensive drought index(CDI)to discuss the applicability of the comprehensive drought index by using historical drought events and univariate drought indexes and analyze the temporal and spatial characteristics of the comprehensive drought.The following main results were obtained:(1)Based on the meteorological and hydrological data of five river systems(Xida River,Dongda River,Xiying River,Jinta River,and Zamu River)in the upper reaches of Shiyang River,SWAT hydrological model is established,and the model parameters are calibrated and validated by the SUFI2 algorithm in SWAT-CUP.The rates of Xida River,Dongda River,Xiying River and Jinta River all meet the uncertainty requirements of P-factor(29)0.7 and R-factor(27)1.5 during the calibration and validation period.The uncertainty of the calibration period of Zamu River Basin is relatively large,while the uncertainty of the validation period is within an acceptable range.The accuracy in calibration period is generally higher than the simulation accuracy of the verification period.Both the R2 and ENS of the Xiying River and Jinta River basins were above 0.7 during the calibration and validation period.The R2 and ENSin calibration period of the Xida River,Dongda River and Zamu River basins are all above0.7,and the R2 and ENS during the validation period are concentrated between 0.68 and 0.69.The results show that the uncertainty and simulation accuracy of the constructed hydrological model meet the requirements and can be used to describe the hydrological process of the basin.(2)The volatility of the drought degree represented by the univariate drought index SPEI,SSI,SRI gradually decreased with the increase of time scale.The time evolution of the same drought index in each basin in the study area is consistent.The meteorological drought intensity in the study area was mostly concentrated in 0.30?1.40,and the years with heavier drought intensity were mostly concentrated in 1991 and 1984.The agricultural drought intensity is mostly concentrated in 0.20?1.50,and the years with heavier drought intensity are mostly concentrated in 1991 and 1992.The hydrological drought intensity is mostly concentrated in 0.10?1.50,and most of the years with heavier drought intensity occurred in1991.During the study period,various droughts in the study area mainly show an insignificant weakening trend.Among them,only the meteorological drought in the Xida River Basin and the hydrological drought in the Xida River and the Xiying River Basin have significant weakening trend.Both meteorological and agricultural droughts may show an insignificant weakening trend in the future.Hydrological drought may also show a weakening trend.Among them,the Xida River and Xiying River Basin have significant changes,while the Dongda River,Jinta River and Zamu River Basin have insignificant changes.(3)The comprehensive drought index CDI was constructed based on the nested Archimedean construction method,and its applicability was analyzed.The extreme drought months of comprehensive drought are mostly concentrated in 1984.08?1985.01,1991.08?1992.03 and 2013.03?2014.05.The months with the lowest CDI value of each basin are also concentrated in 1991.08?1992.02,which is consistent with historical drought events,indicating that CDI has certain accuracy.CDI can monitor arid areas not monitored by SPEI,SSI or SRI,indicating that the index can simultaneously characterize meteorological drought,agricultural drought and hydrological drought,and can describe the drought characteristics of the region from multiple angles,and has a certain comprehensiveness.The correlations of the sub-watersheds on the monthly,seasonal and annual scales all pass the significance test of?=0.1,indicating that CDI at different time scales can be used to describe the comprehensive drought characteristics of the study area,and the index has certain reliability.(4)The comprehensive drought intensity is mostly concentrated in the range of 1.00 to2.00,and the years with heavier drought intensity are mostly concentrated in 1991 and 2013.From the seasonal perspective,in general,the drought in the entire basin has shown an insignificantly weakening trend.Only the Xiying River and Jinta River in the summer,and the Xiying River and the Dongda River in winter showed an insignificant increase trend.In particular,there will be a significant drought weakening trend for the Xida River and Xiying River in autumn.From the perspective of interannual change,the comprehensive drought degree of Xida River,Dongda River,Xiying River,and Jinta River basin may decrease in the future,while the comprehensive drought degree of Zamu River Basin may increase in the future,but the changing trend is not significant.Based on the simulation results of the SWAT hydrological model,this study can provide the study area with the shortage of evaporation,soil moisture and other hydrological element sequence data,and the constructed comprehensive drought index can be used for drought monitoring in the study area.The construction method of the comprehensive drought index can also be used in similar areas with lack of data. |
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