Variation Character of Water and Sediment and Its Response to Rainfall and Human Activities in Longtong Region of the Middle Yellow River

To evaluate the benefits of soil and water conservation and adjust ecological and environmental policies in the middle reaches of the Yellow River,the relationships between precipitation and changes in vegetation index,and water and sediment flows were analyzed using precipitation,runoff,sediment transport and remote sensing data in the Longtong region from 1957 to 2019.The cumulative anomaly method and double cumulative curve were used to analyze the relationship between precipitation and changes in vegetation index,and water and sediment flows.The results showed that precipitation in the Longtong region did not exhibit an apparent decline with time,but runoff and sediment transport exhibited a significant decline with time.The abrupt change to runoff,from abundant to dry,occurred in 1985,and the abrupt change to sediment transport,from abundant to dry,occurred in 1985 and 2002.The normalized vegetation index (NDVI) exhibited a recovery,with an annual increase of 1.7%,and the spatial NDVI exhibited fluctuations in a generally increasing value.Vegetation cover in the southern part of the basin was the best.Compared with the reference period A(1957~1985),the contribution of precipitation to runoff in period B(1986-2019) was 26.21%,while the contribution of anthropogenic to runoff was 73.79%.Compared with the reference period A(1957~1985),the contribution of precipitation in periods B(1986~2019) and C(2003~2019) to sediment transport was 22.80% and 11.73%,respectively,while the contribution of anthropogenic sediment transport were 77.20% and 88.27%,respectively.