Inter-Annual And Intra-Annual Evolution Of Runoff And Its Attribution Analysis In Juhe River Basin

With climate change in recent years,global crises such as climate warming,sea level rise,acid rain and flooding are seriously affecting the earth’s natural resources and the normal living conditions of human beings.The Loess Plateau,as an extremely fragile ecological region,is suffering from water shortage,ecological pollution,land desertification and severe soil erosion,which,together with rapid population growth and urbanisation,are seriously damaging the fragile ecological environment,especially the issue of water resources,which needs to be settled urgently.Under the joint impact of climate variation and human activities,the regional hydrological cycle has changed,the consistency of runoff time series has been disrupted and hydrological variability has emerged,which poses considerable problems for the allocation and rational use of regional water resources.Therefore,it is important to study the hydro-meteorological elements and runoff evolution characteristics of the basin under the changing environment,and to quantitatively identify the response of runoff to climate variation and human activities,which can provide a basis for exploring the driving mechanism of the hydrological cycle under the changing environment,and also has significant theoretical and practical implications for the management,development and use of water resources and the healthy development of the ecosystem in the basin.In this paper,the inter-and intra-annual trends and abrupt changes in hydro-meteorological factors of the Juhe River basin,a first-order tributary of the Bei Luo River,are studied.The effects of precipitation,potential evaporation and human activities on the annual runoff depth of the Juhe River basin are quantified using the complementary relationship approach based on Budyko’s hypothesis and the cumulative slope rate of change method.The abcd hydrological model was used to quantify the impacts of climate variation and human activities on the annual runoff depth of the Juhe River basin and the runoff depth during the flood and non-flood periods.The key research results achieved are as follows:(1)The interannual trends and abrupt change years of the main hydro-meteorological element series in the Juhe River Basin were revealed.The linear regression and 5-year sliding average methods were used to analyse the trends of annual precipitation,annual potential evapotranspiration and annual runoff depth in the Juhe River Basin from 1967 to 2019,and the results showed that the annual runoff depth and annual potential evapotranspiration in the Juhe River Basin generally showed a decreasing trend during 1967-2019,while the annual precipitation showed an increasing trend.The Mann-Kendall mutation test and the ordered clustering method were used to determine the mutation years of the annual runoff depth series,the annual potential evapotranspiration series and the annual precipitation series in the Juhe River Basin,and the results showed that the mutation year of the annual runoff depth series in the Juhe River Basin was 1985,the mutation year of the annual precipitation series was 2002,and the mutation year of the annual potential evapotranspiration series was 1982.(2)The continuity of the main hydro-meteorological elements and the periodicity of the annual runoff depth series in the Juhe River Basin were clarified.The results of the R/S analysis showed that the Hurst indices of the annual runoff depth series,annual precipitation series and annual potential evapotranspiration series all ranged from 0.5 to 1,so the trends of these three series have some continuity in the future.The results of the wavelet analysis-based periodic analysis of the annual runoff depth series in the Juhe River basin show that the annual runoff depth series in the Juhe River basin from 1967 to 2019 exhibits a periodic evolution of multiple time scales,with major cycles of 6a,14a and 29a,among which the 14a cycle is the most oscillatory,followed by 29a and 6a.The annual runoff depth series of the Juhe River Basin has a large scale of alternating abundance and depletion.(3)The characteristics of land use change and vegetation cover change in the basin were revealed.The results show that the land use types in the Juhe River Basin from 1980 to 2015 were mainly forested,grassland and arable land,and that different land use types underwent some transformation during this period;the inter-annual variation of vegetation cover in the Juhe River Basin from 1980 to 2015 was large and the spatial variation was small.(4)The impacts of climate variation and human activities on the annual runoff depth change in the Juhe River Basin was quantified.According to the results of the complementary relationship method based on Budyko’s hypothesis,the contributions of annual precipitation,potential annual evapotranspiration and changes in the basin substrate conditions to the annual runoff depth variation in the Juhe River Basin were 39.22%,15.18%and 75.96%,respectively;according to the results of the cumulative slope rate of change method,the contributions of annual precipitation,potential annual evapotranspiration and human activities to the annual runoff depth variation in the Juhe River Basin were 19.29%,-15.18%and 75.96%,respectively.The contribution of annual precipitation,annual potential evapotranspiration and human activities to the change of annual runoff depth in the Juhe River basin were 19.29%,-10.12%and 90.83%respectively.The results of both methods show that human activities are the main factors affecting the annual runoff depth variation in the Juhe River Basin.(5)The impacts of climate variation and human activities on the annual runoff depth of the Juhe River Basin at different time scales were quantified based on the abcd hydrological model.The contribution of climate change and human activities to the annual runoff depth variation is 35.77%and 64.23%respectively;the contribution of climate variation and human activities to the flood runoff depth variation is 43.63%and 56.37%respectively;the contribution of climate variation and human activities to the non-flood runoff depth variation is 23.35%and 76.65%respectively.Human activities have always been the main factor influencing runoff depth in the Juhe River basin,both at inter-and intra-annual scales.