The response of the suspended sediment load of the headwaters of the Brahmaputra River to climate change: Quantitative attribution to the effects of hydrological, cryospheric and vegetation controls

Abstract

The response of suspended sediment load to climate change has important implications for downstream ecosystems and biogeochemical cycles. Glaciers, permafrost, vegetation and hydrological processes are rapidly changing in high-altitude regions. However, there is currently no consensus about how and to what extent these factors will affect interannual changes of fluvial sediment export. Here, we investigate the increasing trend of suspended sediment load in the headwaters of the Brahmaputra River from 1972 to 2008. The key influencing factors, including the hydrodynamic flux and erosivity of glacier runoff, precipitation, vegetation cover, and soil erodibility were quantified, and their changing trends were analyzed. Two methods were used to attribute the variation of sediment load; Partial Least Squares Path Modeling (PLS-PM) based on statistical regression and Sediment Identity (SI) based on algebraic equations. The results obtained by these two relatively independent methods were broadly consistent, and the error of the SI model was less than 8%. The sediment load showed a significant increasing trend at an average changing rate of 18.9%/10a, without any abrupt fluctuations. The increase in fluvial sediment load was primarily due to increases in both the amount (43%) and erosivity (55%) of precipitation, combined with minor influences from increased sediment supply due to earlier thawing (16%) and intensified glacier melting (14%). The increases in fluvial sediment load were partially buffered by a decrease in water yield capacity due to denser vegetation cover (−29%). This study provides valuable insights into the natural response of fluvial sediment loads to climatic and environmental change, and the findings are critical for soil and water conservation planning in cold and high-altitude regions.