Sensitivity of Ocean Processes to Changes and Uncertainties in Global River Discharge

Abstract:

Global river discharge is an important component of global hydrologic cycle, but is difficult to observe. Here, we provide remote sensing-based estimates of global river discharge using land and ocean mass balances using multiple precipitation, evaporation and reanalysis products as well as mass change estimates derived from GRACE and altimetry. Compared to estimates from in-situ observations and land surface models, the remote sensing-based estimates show significantly larger amplitude at annual as well as interannual scales. This suggests a range of uncertainty in current methods of discharge estimation. Global river discharge is expected to change as a part of the intensification of the hydrologic cycle due to climate change, and also due to increased anthropogenic management. To explore the influence of changes in river discharge on ocean and climate processes, we run simulations of ocean-sea ice model forced with varying amount of river discharge and analyze fields such as sea surface salinity, sea surface temperature, mixed layer depth, barrier layer thickness, upper ocean circulation, meridional overturning circulation, and sea ice thickness and extent. This analysis provides insights on the extent to which changes- likely anthropogenic- and uncertainties in continental freshwater forcing can affect ocean, and therefore climate, processes, and the regions where the effects are likely to be most pronounced.