Quantifying natural and anthropogenic impacts on runoff and sediment load: An investigation on the middle and lower reaches of the Jinsha River Basin

Abstract

The middle and lower reaches of the Jinsha River Basin (MLJRB). The main objective is to evaluate the impact of climate change and anthropogenic activities to the water and sediment resources of the studied region in 1960—2015. The variation of runoff and suspended sediment load is first analyzed with regard to their trends and abrupt change. Different factors attributable to the variation are then quantitatively separated. The annual runoff and sediment load across the MLJRB both decreased abruptly and coincidently in the recent two decades, with the transitional years detected to be 2006 and 2002, respectively. Comparing the post-transition period to the pre-transition period, runoff decreased 14.7% and sediment load decreased 63%. Climate change is the major contribution for the decrease in runoff, which explains 56.3% of the reduction, and impoundment of large reservoirs and water consumption contributed 18.6% and 2.7% respectively. The other 22.5% was ascribed to water-soil conservation and other factors. In contrast to water resources, human activities were dominant in sediment reduction, including 44.9% caused by large reservoirs, 1% from increased water consumption and 35% by conservation measures and other potential factors. Remarkably, almost 90% of the sediment load can be trapped as the direct consequence of the construction and operation of two huge dams, Xiluodu and Xiangjiaba, since 2013.