Analyzing mass balance estimates of global continental discharge from remote sensing and reanalysis

Total continental freshwater discharge into the oceans is a key feature of the global water cycle, but is currently impossible to observe using ground-based methods alone. To characterize the uncertainty across existing modeling and satellite approaches, we present an ensemble of historic monthly global continental discharge estimates that enforce water mass balance over land and ocean. We combine independent measurements of ocean/land mass change from altimetry and GRACE with multiple estimates of evaporation (E), precipitation (P) from remote sensing, and E-P from atmospheric moisture budget from five state-of-the-art reanalysis products, to compute a 25-member ensemble time series of global discharge. Results reveal excellent agreement in mass budget across approaches, but a large spread in satellite-based global E-P estimates that propagates into discharge estimates. We find that discharges with moisture convergences-based E-P provide a closer comparison with current observation-based estimates in terms of the mean, seasonal and interannual variability.