The Propagation Process Of Meteorological Drought To Hydrological Drought In The Upper Reaches Of The Shiyang River Basin

In the case of droughts and floods,the effects of droughts on natural and social systems are significant.As the two most important factors affecting ecosystems and the water cycle during drought,the occurrence of complex events has become more widespread.This is extremely detrimental to the effective regional assessment of drought risk and the accurate provision of drought warnings,so a comprehensive understanding of the spreading characteristics of meteorological drought to hydrological drought and its influencing factors is particularly important.Based on this,this paper selects the upper Shiyang River as the study area,calculates its Standardized Precipitation Index separately(SPI)and Standardized Runoff Index(SRI),and constructs the drought propagation intensity index(DPI),from a static and dynamic perspective,The distribution characteristics of eight tributary meteorological droughts to hydrological droughts in eastern Qilianshan in the past 59 years under the linear and nonlinear relationship,Furthermore,the degree of influence of natural and human factors on the propagation of meteorological drought to hydrological drought is analyzed and the following main conclusions are obtained:(1)The eight tributaries showed a significant trend of hydrological dryness in summer and autumn,and a wetter trend in winter and spring.In terms of wet and dry mutations,the eight tributaries all changed from meteorological drought to meteorological wetness.The hydrological mutation years of the three western tributaries Xida River,Dongda River and Xiying River gradually advanced,and the hydrological mutation years of the three eastern tributaries Huangyang River,Gulang River and Dajing River gradually lagged behind.The hydrological abrupt change year of the three western tributaries,Xida River,Dongda River and Xiying River,is gradually advanced,while the hydrological abrupt change year of the three eastern tributaries,Huangyang River,Gulang River and Dajing River,is gradually delayed.In terms of spatial heterogeneity of drought,the duration and intensity of hydrological drought in the eight tributaries was significantly longer than that of meteorological drought.The total frequency of meteorological drought in the eight tributaries was much higher than that of hydrological drought.(2)Eight tributaries have a longer propagation time from meteorological drought to hydrological drought in winter and spring,and a shorter propagation time in summer and autumn.Overall,the drought propagation time changed from longer to shorter in spring and winter,while the opposite was true in summer and autumn.The drought propagation intensity of each tributary was weakest in autumn and strongest in winter.In spring and summer,the transmission intensity from meteorological drought to hydrological drought was close to equal,while that of other tributaries was weak.In autumn,the transmission intensity of the Dongda River,the Xida River and the Dajing River was strong,while that of the other tributaries was weak.In winter,except Gulang River,the drought spread intensity of other tributaries was strong.(3)The balance between descending water and evaporation in different seasons directly affects the source and composition of runoff.In summer,in the dry year where meteorological drought occurs,the continuous impact of spring meteorological drought and strong evaporation under high temperature conditions in summer will accelerate the occurrence of summer hydrological drought to a certain extent,thereby shortening the propagation time of meteorological drought to hydrological drought.In spring,the temperature gradually rises,and the source of runoff recharge is mainly groundwater recharge,which will delay the occurrence of hydrological drought,which in turn leads to longer propagation time and weaker transmission intensity from meteorological drought to hydrological drought.(4)The surface soil moisture in Qilian Mountains changes the production and confluence processes of the watershed.Summer is the highest temperature season in the region.Potential evapotranspiration of tributaries presents a significantly rising trend,and the confluence of underlying surface decreases,which will aggravate the loss of soil water on the surface,thereby accelerating the propagation of drought and making the response time of summer hydrological drought to meteorological drought shorter.In spring,due to less precipitation,soil moisture in spring will be affected by the melting of snow in winter of the previous year as the temperature gradually rises,which plays a certain role in replenishment of surface runoff and increases surface soil moisture.As a result,the response of hydrological drought to meteorological drought is relatively slow.The accumulation of soil moisture in the early stage extends the propagation time of meteorological drought to hydrological drought to a certain extent.(5)The land use structure of different tributaries is obviously different.Taking Huangyang River as the boundary,the forest and grass of the five western tributaries,which were less affected by human activities,accounted for more than that of the eastern tributaries,and had stronger water storage capacity and transpiration in spring and winter,thus increasing the propagation time and intensity of meteorological drought to hydrological drought.However,the three eastern tributaries,which are greatly affected by human activities,have a relatively high propagation intensity to hydrological drought and shorten the propagation time due to the large proportion of cultivated land,small area of natural vegetation and water consumption.(6)The construction of the reservoir and the change of irrigation area have a great influence on the characteristics of meteorological drought spreading to hydrological drought in eight tributaries.There is no reservoir above the hydrology station of Xiying River,and the proportion of construction land is the smallest among the eight tributaries,which is closest to the natural state.This indicates that the most important factor affecting the spread of drought in Xiying River is the climate change factor.The reservoir of Dongda River is located above the hydrological station,and the variation of dry and wet hydrology is affected to some extent by the regulation of the reservoir.However,human activities are more intense in the eastern tributaries,especially in the Huangyang River and Dajing River.