Spatiotemporal Changes On The Critical Factors Of The Water Cycle And Their Impacts On The Mainstream Runoff In The Yellow River Basin

The intensification of the impacts of climate change and human activities will cause runoff changes,then affect the water cycle.The runoff changes will undoubtedly affect the formation,utilization,and management of water resources in the basin and determine the development of the social economy and human society.Therefore,it is significant to reveal the changes in critical factors which affect the water cycle,like the runoff,temperature,precipitation,evapotranspiration,and land use/cover change,and to quantitatively explore the impact of climate change and human activities on runoff change for regional water resources utilization and adaptive management based on a detailed and in-depth understanding of regional hydrological conditions.As one of China’s critical areas,the Yellow River Basin(YRB)plays a vital strategic and social development role.However,the YRB water resources are in extreme shortage,facing a sharp contradiction between supply and demand and many environmental problems.Meanwhile,the runoff of the YRB faced many issues like excessive cutoff and reduction due to the co-impact of climate change and human activities.Therefore,this paper took the Yellow River basin as an example and divided the research into upper YRB(UYRB),middle YRB(MYRB),and lower YRB(LYRB)according to the topography,geomorphology,and hydrological characteristics.Based on meteorological and runoff data,the linear regression,Mann-Kendall trend test,cumulative anomaly,sliding t-test,and Budyko elastic coefficient were used to reveal the spatiotemporal changes of the critical factors of the water cycle and explore the correlation between the mainstream runoff changes of the YRB and the water cycle critical factors,to quantify the contribution rate of climate change and human activities to the mainstream runoff changes in the UYRB,MYRB,and LYRB,and to put forward adaptive management strategies and suggestions.The main conclusions are as follows.(1)The temperature of the YRB,UYRB,MYRB,and LYRB increased significantly from 1960 to 2020.The precipitation increased insignificantly in the YRB and the upper YRB(UYRB),while it decreased insignificantly in the middle YRB(MYRB)and lower YRB(LYRB).The potential evapotranspiration decreased insignificantly in the YRB,UYRB,and LYRB while increasing insignificantly in the MYRB.The temperature,precipitation,and potential evapotranspiration in the YRB have periodic changes and apparent spatial heterogeneity.(2)Land use types include cultivated land,forestland,and grassland in the YRB and MYRB,cultivated land,grassland,unused land in the UYRB,and cultivated land in the LYRB.The areas of these land use types changed in different dynamic degrees and transferred in and out to varying degrees in the YRB,UYRB,MYRB,and LYRB from 1980 to 2020.(3)The runoff in the UYRB,MYRB,and LYRB decreased significantly.The runoff had periodic change characteristics from 1960 to 2020 and wet and dry changes.According to the runoff change characteristics,there are three sections,including1960-1968,1969-1985,and 1986-2020.(4)There was a significant resonance period between temperature and runoff in the UYRB and MYRB in the high-energy and low-energy subareas and a significant negative correlation with a lag time of about 1.5 months.There was no considerable resonance period between temperature and runoff in the UYRB.There was a significant resonance period between precipitation and runoff in the UYRB,MYRB,and LYRB in the high-energy and low-energy subareas and a significant positive correlation with a lag time of about 1.5 months.There was a considerable resonance period between potential evapotranspiration and runoff in the UYRB,MYRB,and LYRB in the high-energy and low-energy subareas and a significant negative correlation with a lag time of about 1.5 months.(5)Different land use types have various effects on runoff formation,and multiple land use types closely determine the runoff change.The adverse effects of climate change and human activities on runoff change can be reduced by rational optimization of land use structure and pattern to enhance runoff formation and reasonably allocate water resources.(6)Runoff change sensitivity to precipitation,potential evapotranspiration,and land surface elements gradually increased in the UYRB,MYRB,and LYRB.The largest runoff change sensitivity to various factors was the LYRB,followed by the MYRB and the UYRB.Runoff change was the most sensitive to precipitation changes in the UYRB,MYRB,and LYRB in 1960-1968,1969-1985,and 1986-2020,respectively.(7)Climate change in the MYRB and the UYRB significantly influenced runoff change from 1969 to 1985,and human activities had a considerably affected runoff change from 1986 to 2020.In the LYRB,human activities especially involved runoff change in both periods.In addition,the impact of human activities on the LYRB was more significant than that of the MYRB and UYRB in 1969-1985.The effect of human activities on the UYRB was more important than that of the MYRB and LYRB in 1986-2020,and the impact of human activities was enhanced in the UYRB,MYRB,and LYRB.Based on the research results,suggestions for adaptive management have been proposed regarding climate change adaptation,human activity management,and scientific research investment.These can provide a reference and scientific basis for regional water resource utilization.