Contribution Of Climate Change And Human Activities To Runoff Variation In The Lower Yellow River

The impacts of climate change and human activities on runoff in river basins are hot topics in hydrology.In recent years,under the influence of climate change and human activities,especially the hydrological process in the Yellow River Basin has changed obviously,which is characteriszed by the decreased flow,and frequent drought and flood disasters.Therefore,it is of great significance to study the characteristics of runoff variation in the Yellow River Basin and to clarify the impacts of climate change and human activities on runoff variation.The spatial and temporal distribution of precipitation and air temperature in the Yellow River basin from 1961 to 2018 was analyzed by using the Mann-Kendall trend test method and empirical statistics method,the catastrophe time points of long time series runoff were detected based on the Mann-Kendall catastrophe analysis method and the double mess curve catastrophe test method,and the runoff variation of Huayuankou hydrological station in the Lower Yellow River was quantitatively analyzed by using the double mess curve method and sensitivity analysis method.The results can provide scientific basis for the sustainable utilization of water resources in the Yellow River Basin.The main conclusions are as follows:(1)The climate change in the Yellow River Basin from 1961 to 2018 is obvious,which mainly shows the decrease of precipitation and the increase of temperature.From 1961 to 2018,the annual,flood season,non-flood season precipitation are 489.71 mm,370.45 mm and 119.26 mm,respectively.And they all showed a decreasing trend,but they were all not significant;the precipitation was the most abundant in the 1960 s,then decreased gradually,reached the lowest level in the 1990 s,then recovered after the 21 st century.The annual average temperature in the Yellow River Basin showed a significant upward trend from 1961 to 2018(P < 0.01),the average annual temperature was 9.67°C.The temperature's rise rate in the basin was high to 0.29°C/10 a,which was higher than the average rise rate of 0.22°C/10 a in China.From 1961 to 2018,the annual,flood season and non-flood season potential evapotranspiration of the Yellow River basin were 908.67 mm,497.14 mm and 411.53 mm,respectively.(2)The runoff depth at Huayuankou Hydrological Station had obvious variation characteristics from1961 to 2018,and the abrupt change time occurred in the late 1980 s.The annual and non-flood season runoff depth of Huayuankou Hydrological Station showed a significant decreasing trend(P < 0.01),the average depth of runoff was 48.09 mm,28.13 mm and 19.96 mm,respectively.The abrupt change time of annual runoff and non-flood season runoff was in 1986,and that of flood season runoff was in 1989.(3)Human activities were the main controlling factor of runoff reduction in the Yellow River Basin from 1987 to 2018.The contribution rates to the change of runoff depth were higher than that of climate change on all time scales,and its contribution rate was high to 80%-90% The contribution rates of underlying surface contributes were 9.58%,3.25% and 12.25% to the annual,flood season and non-flood season runoff depth respectively.The precipitation was the main climate controlling factor of runoff change in the annual and flood-season,and their contribution rates were 23.39% and 16.54%,respectively;and evapotranspiration was the main climate controlling factor of runoff change in non-flood season,its contribution rate was 9.69%.The effect of precipitation on runoff was positive;the effects of evapotranspiration and underlying surface characteristic parameters on runoff were negative.(4)The contribution results were close between double cumulative curve method and sensitivity analysis method to the analysis of runoff depth change in the Yellow River Basin,but the sensitivity analysis method was more comprehensive when considering the factors of climate and human activities.(5)The Xiaolangdi Dam's regulation on the runoff at Huayuankou Hydrological Station reduced the annual,flood season and non-flood season runoff depth;and contribution was the highest in the non-flood season(51.57%),then was the contribution in the annual(51.52%),the lowest contribution was 32.13% to the flood season runoff depth.