Propagation Characteristics Of Meteorological Drought To Hydrological Drought Based On Nonstationary Drought Index

Under the background of global warming,the issue of drought has attracted more and more attention.The drought index is one of the easiest ways to monitor drought conditions.With the increasing impact of climate change and human activities,the traditional drought index based on the assumption of stationarity will bring certain deviations in drought assessment.Therefore,it is particularly important to construct a new drought index that can characterize nonstationary characteristics.This paper uses GAMLSS model to construct a nonstationary standardized runoff index and applies it to the hydrological drought assessment in the upper reaches of the Heihe River Basin.On this basis,in order to provide assistance for drought monitoring and early warning in the basin,the Copula function,frequency analysis and other methods are used to explore the time characteristics and probability characteristics of the propagation of meteorological drought to hydrological drought.The results of the study are as follows:(1)The precipitation in the upper reache of the Heihe River Basin presents the characteristics of stability,while the runoff series are different.The runoff series of the QL has stable characteristic,and the runoff series of the ZMSK and YLX stations has a non-stationary characteristic.Nonstationary model constructed by the GAMLSS model is far better than the stationary model in fitting the runoff of ZMSK and YLX stations(nonstationary series),and the model with two covariates is better than the one or three covariates;the runoff in the study area is most affected by precipitation in the rainy season,the dry season is most affected by the previous runoff,and the drought conditions in our case are mainly affected by precipitation;the NSRI identifies more drought events than SRI does.(2)Multi-scale SPI and NSRI-1 are closely related,but not completely synchronized.The study found that SPI-9 has the strongest correlation with NSRI-1,that is,the propagation time from meteorological drought to hydrological drought in the study area is roughly 9 months.Analyzing the drought propagation characteristics in different months in the basin,it was found that from August to July of the following year,the propagation time increased from 1 month to12 months.From the season,it is found that the propagation time is the shortest in summer,which is roughly 3 months;followed by autumn,the propagation time is 4 months;and the propagation time is the longest in winter,reaching 10 months.(3)The probability of hydrological drought under different meteorological drought conditions showed an S-shaped curve.Under the condition of no drought in SPI,the probability value of hydrological drought is greater than 0,indicating that other factors may also cause hydrological drought in addition to meteorological drought;when SPI changes from no drought to light drought,the upward trend of the curve is obvious,that is,hydrological drought is Meteorological drought is more sensitive,and meteorological drought is more likely to cause mild and moderate hydrological drought,while severe and extreme hydrological drought are often the result of meteorological drought and other factors.By calculating the interval conditional probabilities of the four seasons,the response of hydrological drought in summer to meteorological drought is more sensitive,while this sensitivity is weaker in spring,which is related to the seasonal climate characteristics of the study area.