Impacts of 21st Century Climate Change on Riverine Water Discharge and Suspended Sediment Fluxes at a Global Scale

Abstract:

Fluvial systems worldwide are experiencing substantial alterations due to anthropogenic climate change. Shifts in water and sediment regimes of large river systems can have considerable impacts on the functioning and connectivity of earth’s natural processes. This study is focused on simulating water discharge and suspended sediment fluxes in response to predicted climate change in the 21^st century at a global scale. Precipitation and temperature projections generated by five General Circulation Models (GCMs), based on the four Representative Concentration Pathways (RCPs), were used as inputs to a global-scale hydro-geomorphic model (WBMsed). Simulations were conducted under pristine environmental conditions without human impacts, in order to isolate the signal of 21^st century climate change on river fluxes. The results revealed that global water discharge and sediment dynamics are highly sensitive to anthropogenic climate change in the 21^st century. A global net increase is projected for both natural river discharge and sediment flux toward the end of the century under all climate change scenarios. Larger increases are observed with increasing levels of atmospheric warming. Projected climate changes under RCP 2.6, 4.5, 6.0 and 8.5 scenarios, will increase mean global river discharge by 2%, 6%, 7.5% and 11% respectively by the end of this century relative to the 1950–2005 period, while mean global suspended sediment flux will show 11%, 15%, 14% and 16.4% increases under pristine conditions. 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 precipitation, discharge and sediment flux was found to be non-linear both in space and time.