Climate-induced trends in global riverine water discharge and suspended sediment dynamics in the 21st century

Abstract

Anthropogenic climate change, particularly through increased greenhouse gas (GHG) emissions, is projected to considerably impact 21st century precipitation distribution, altering fluvial processes such as sediment dynamics and riverine water discharge, worldwide. Changes in the magnitude of fluvial water and sediment fluxes can have profound impacts on the functioning and connectivity of earth’s natural systems. This study is focused on isolating the impacts of GHG-induced future climate change on riverine water discharge and suspended sediment fluxes in the 21st century at a global scale. A global-scale hydro-geomorphic model (WBMsed) was forced with precipitation and temperature projections generated from five General Circulation Models (GCMs), each driven by four Representative Concentration Pathways (RCPs). The results, based on an ensemble of model outputs, revealed that global river discharge and sediment dynamics are considerably impacted by anthropogenic climate change in the 21st century. Despite substantial regional heterogeneity, a global net increase is projected for both river discharge and sediment flux in the 21st century under all RCP scenarios. Increases are larger and more variable with increasing levels of GHG concentrations in the atmosphere. At the end of this century, climate change under RCP 2.6 is projected to cause approximately 1% increase in global river discharge and 5% increase in global suspended sediment flux. Under RCP 4.5 emission scenario, climate change will lead to a 5.6% increase in river discharge and 7% increase in sediment flux at a global scale. Approximately 5% and 9% increases are projected under RCP 6.0 in global river discharge and sediment flux respectively. Climate changes projected under RCP 8.5 will lead to the largest increases in river discharge and sediment flux (7.3% and 14.7% respectively) at the end of the 21st century. With increased warming, more extreme changes (increasing or decreasing) can be expected in both discharge and sediment flux. Also, the number of rivers with statistically significant trends in either direction increases with warming. In addition to magnitudes, inter-annual variability in both global river discharge and sediment fluxes also increase with increasing RCPs. Changes in sediment flux closely follow the patterns predicted for discharge, and are mostly driven by climate warming induced spatial and temporal variation in precipitation. However, the relationship between discharge and sediment flux was found to be non-linear both in space and time, demonstrating the utility of explicit modeling of both hydrology and geomorphology.