Objective River runoff is an important water resource on the surface of the earth, and the analysis of the characteristics and causes of its change is a prerequisite for the scientific management and planning of water resources in the basin.
Method This study used Mann-Kendall trend test, Pettitt mutation test, Budyko elasticity coefficient method and other methods to analyze trends and causes of runoff variation in the upper and middle reaches of the Yellow River in recent 70 years (1951−2020).
Result (1) From 1951 to 2020, the annual precipitation in the upper reaches of the Yellow River increased 4.04 mm/(10 year) (P > 0.05) and decrease 4.90 mm/(10 year) (P > 0.05) in the middle reaches of the Yellow River. The potential evapotranspiration in the upper and middle reaches showed no significant increase trend (1.77 mm/(10 year), 2.23 mm/(10 year), P > 0.05). (2) From 1980 to 2020, the changes of landuse/cover in the upper and middle reaches of the Yellow River are obvious, mainly in the increase of forest and grass area, and the NDVI in the upper and middle reaches of the Yellow River increased significantly at the rates of 0.025/(10 year) (P < 0.01) and 0.042/(10 year) (P < 0.01), respectively. (3) From 1951 to 2020, the runoff of upper and middle reaches decreased at the rate of 3.46 mm/(10 year) (P < 0.01) and 7.46 mm/(10 year) (P < 0.01), respectively, and changed abruptly in 1986 and 1990, respectively. (4) Runoff in the upper and middle reaches is most sensitive to precipitation change, followed by land use/cover change and potential evapotranspiration change, and the sensitivity of runoff to each influencing factor increased year by year, which showed that the change of climate and land use will easily cause runoff change. (5) Land use/cover change was the main cause of runoff decrease in the upper and middle reaches of the Yellow River, followed by precipitation and potential evapotranspiration, but there were some differences in the nature and degree of influencing factors on runoff change in different regions of the upper and middle reaches. Among them, the nature and degree of influence of precipitation, potential evapotranspiration, and land use/cover change on runoff in the upstream area were −14.04%, 1.30%, and 112.73%, respectively; the midstream area was 21.54%, 3.63%, and 74.83%, respectively.
Conclusion The runoff change in the upper and middle reaches of the Yellow River from 1951 to 2020 is the result of climate change and land use/cover change, but the main influencing factor is land use/cover change dominated by human activities, and the influence of each factor on runoff is different in varied intervals. The results of this study can provide theoretical support for water resource management and comprehensive control in different sections of the upper and middle reaches of the Yellow River.
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