Recent stepwise sediment flux increase with climate change in the Tuotuo River in the central Tibetan Plateau.

The riverine sediment flux (SF) is an essential pathway for nutrients and pollutants delivery and considered as an important indicator of land degradation and environment changes. With growing interest in environmental changes over the Tibetan Plateau (TP), this work investigated the variation of the SF in response to climate change in the headwater of the Yangtze River over the past 30 years. Annual time series of hydro-meteorological variables during 1986-2014 indicate significantly increasing trends of air temperature, precipitation, ground temperature, river discharge, suspended sediment concentration and SF. Stepwise changes were identified with significantly higher values of the above variables in 1998-2014 compared with 1986-1997, which could potentially be attributed to the strong 1997 El Niño event. Double-mass plots indicated that both meltwater and rainfall contributed to the increased river discharge while the increased SF mostly resulted from enhanced erosive power and transport capacities of the increased discharge. However, it was buffered by a decrease in sediment source due to the shift of maximum monthly rainfall from June/July to July/August during which period a denser vegetation cover prevents soil erosion. Partial least squares structural equation modeling analysis confirmed the dominance of warming on the increase of discharge amplified by increased precipitation. It also confirmed that the increased precipitation drives the increase in suspended sediment concentration. Both processes conspire and equally contribute to the stepwise increase of SF. This study provides important insights into the controlling processes for recent SF changes and gives guidance for water and soil conservation on the TP.