Spatio-temporal trends and causes of variations in runoff and sediment load of the Jinsha River in China

The Jinsha River Basin is an important basin for hydropower in China and it is also the main runoff and sediment source area for the Yangtze River, which greatly influence the runoff and sediment in the Three Gorges Reservoir. This study aims to characterize the spatial distribution, inter-annual variation of runoff and sediment load in the Jinsha River Basin, and to analyze the contribution of rainfall and human activities to the runoff and sediment load changes. The monitoring data on runoff, sediment load and precipitation were collected from 11 hydrological stations in the Jinsha River Basin from 1966 to 2016. The data observed at the outlet of the basin showed that 71.4% of the runoff is from the upper reaches of the Jinsha River Basin and the Yalong River, while 63.3% of the sediment is from the lower reaches (excluding the Yalong River). There is no significant increase in runoff on temporal scale in the Jinsha River Basin, while it has an abrupt change in runoff in both upstream and midstream in 1985, and an abrupt change in downstream in 1980 and 2013. The sediment load demonstrated a significant increasing trend in the upstream, no significant reducing trend in the midstream, but significant reducing trend in the downstream. The sediment load in upstream showed abrupt change in 1987, in midstream in 1978 and 2014, in downstream in 2012. Rainfall dominated runoff variation, contributing more than 59.0% of the total variation, while human activity, including reservoirs construction, the implementation of soil and water conservation projects, is the major factor to sediment load variation, contributing more than 87.0% of the total variation.