Sediment load responses to climate variation and cascade reservoirs in the Yangtze River: A case study of the Jinsha River

Climate change and human activities have substantially changed hydrological and geomorphologic processes, particularly in upper mountainous catchments. The Jinsha River Basin (JRB), the uppermost region of the Yangtze River and the largest hydropower production region in China, was chosen to investigate the sediment load responses to climate variations and human activities. The non-parametric Mann-Kendall test and double mass curve were used to explore the spatial-temporal variations of hydro-meteorological variables and quantify the contributions of climate variation and human activities to changes in discharge and sediment load in the JRB from the 1950s to 2015. The results indicate that human activities, in particular cascade damming, were the governing factor for sediment load changes, while climate variations (increasing precipitation and snow and glacier melt) dominated the discharge changes in the JRB. The average annual sediment load at the Panzhihua (PZH) station increased by 42.4% from 1966-1984 to 1985-2010, mainly due to mineral extraction and deforestation, followed by a decrease of 75.9% in 2011-2015 because of the operation of the cascade reservoirs in the middle JRB since 2010. The construction of new dams like the Xiangjiaba Reservoir (2012) and the Xiluodu Reservoir (2013) in the lower JRB and many other cascade reservoirs since 2010 in the middle JRB further decreased the sediment load by 58.5% (BHT) and 83.8% (XJB) in the recent five years from 2011 to 2015. Although channel erosion downstream of the XJB Dam can provide new sediment to the Three Gorges Reservoir (TGR), the sedimentation rate of the TGR has decreased rapidly and will continue to be reduced due to the construction of more dams in the future.