Attribution Of Runoff Change In Songhua River Basin Under The Background Of Climate Change

In the context of continuous global climate change(temperature rise,solar radiation decline,etc.),it has positive or negative effects on the ecosystem in different time and space.Songhua River Basin is located in the middle and high latitude region(Northeast of China)which is the most sensitive to climate change and human activities.It has the longest transboundary river and an important commodity grain base in China.Under the influence of human activities and climate,the Hydro-climatic process of the Songhua River Basin has also undergone correspondingly changes.Therefore,the analysis of the impacts of climate change and human activities on the runoff of the basin has become the basis of the research in the field of hydrology and water resources.Based on this,its background of climate change,quantitative analysis of the Songhua river basin hydrological-climate time changes(trend,cycle,mutation)and spatial variation characteristics,the result shows: the Songhua river basin from 1974 to 2018 total annual runoff and the annual evaporation have decreasing change.Annual precipitation have decreasing change in Nenjiang river basin,the second Songhua river basin and the Songhua river mainstream basin,in contrast to the Nenjiang river basin,annual precipitation has increased.From the trend change of total annual runoff,annual potential evapotranspiration and annual precipitation,annual potential evapotranspiration and annual runoff showed a negative change,that is,annual potential evapotranspiration gradually increased,and annual total runoff gradually decreased.Annual runoff and annual precipitation have approximately the same changing trend,that is,annual precipitation increases with the increase of annual runoff,and annual precipitation and annual runoff have a positive change,which reveals the change relationship between hydrological-climate process within the basin.Then,the elasticity coefficient method based on Budyko hypothesis was used to calculate the elasticity coefficient of the Songhua River Basin,which reflected the sensitivity of annual precipitation,annual potential evapotranspiration and underlying surface changes to annual runoff.The elastic coefficient of annual precipitation is greater than that of annual potential evapotranspiration and that of underlying surface in the Songhua River Basin.The annual precipitation has the most sensitive influence on annual runoff,followed by underlying surface changes,and finally annual potential evapotranspiration.On this basis,the contribution rates of climate factors to runoff change were calculated.In the Second Songhua River Basin,the contribution rate of annual precipitation to annual runoff depth is 30.5%,the contribution rate of annual potential evapotranspiration to annual runoff depth is 5.8%,and the contribution rate of underlying surface change to annual runoff depth is-63.7%.In the Nenjiang River Basin,the average contribution rate of annual precipitation to annual runoff depth is-2.2%,the average contribution rate of annual potential evapotranspiration to annual runoff depth is 1.3%,and the average contribution rate of underlying surface change to annual runoff depth is-96.5%.In the main watershed of Songhua River,the average contribution rate of annual precipitation and annual runoff depth is 3.1%,the average contribution rate of annual potential evapotranspiration is 0.8%,and the average contribution rate of underlying surface change to annual runoff depth is-96.1%.The results show that underlying surface change is the leading factor of runoff reduction in the Songhua River Basin,followed by annual precipitation and annual potential evapotranspiration.Parameter n is an important indicator to measure the change of underlying surface.We use the data of LUCC in the Songhua River Basin to represent the change of underlying surface.From the perspective of LUCC,the LUCC structure of different regions in the Songhua River Basin has great differences.In the Songhua River Basin,the vegetation increased gradually on the whole,with the most extensive increase of crop vegetation.According to the correlation analysis,the change of cultivated land,woodland and grassland is negatively correlated with the change of annual runoff in the basin,while the change of water area and urban construction land is positively correlated with the change of annual runoff in the basin.This result is consistent with the attribution of runoff change in the Songhua River Basin based on Budyko hypothesis.We further discuss the correlation between NDVI(Normalized Vegetation Index)and underlying surface parameter n,and the two are positively correlated,indicating that vegetation coverage is an important factor affecting underlying surface parameter n,which is consistent with the results of runoff attribution analysis in the Songhua River Basin.The Songhua river basin hydrology and water resources of the impact of climate change and the change of underlying surface(human activity),and quantify runoff composition changes driving factors,to study the driving mechanism of water cycle process to provide the reference theory in the regional environment change,the reasonable development,optimal allocation of water resources and the sustainable utilization is of great significance.