Based on the measured runoff and sediment data of six hydrologic stations (Pingshan

Zhutuo

Cuntan

Yichang

Hankou and Datong) situated at Yangtze River’s main stream

this study analyzed the inter- and intra- annual variation trends of runoff and sediment during 2001-2018 and their causes using statistical methods including linear regression

Mann-Kendall test

Sen’s estimation and accumulative anomaly. The results showed that since 2000

the annual sediment discharge of each hydrologic station significantly declined compared with that before 2000

with the decreasing amplitude higher than 56%

while annual runoff decreased insignificantly with the decreasing amplitude lower than 8%. The variability of sediment discharge

was higher than that of runoff. For the Yangtze River basin

from 2001 to 2018

the average monthly runoff and sediment discharge was 718×10

8

m

3

and 1 247×10

4

t

respectively

and mainly distributed between June and September. The trend analysis indicated that annual precipitation and runoff had no remarkable changes

however

annual sediment discharge showed a significantly decreasing trend. The change-points for Pingshan

Zhutuo and Cuntan station were in 2010 and 2012

and those for Yichang

Hankou

and Datong station were in 2005. Monthly runoff for Pingshan station had no obvious trends; for Datong station

runoff only increased significantly in January

that of the other four stations increased significantly between January and April. Monthly sediment discharge from June to October for the six stations showed significant decreasing trends. In this study

human activities such as water conservancy construction and soil and water conservation were the primary causes of sediment reduction in the Yangtze River basin.