Estimates of Freshwater Discharge from GRACE

Freshwater discharge from the continents is a key water cycle component with important implications for Earth system interactions and global environmental change. However, no comprehensive global streamflow observing network for the world's major continental watersheds currently exists. Moreover, there has been a decline in the number of existing stream gauges worldwide. Here we propose a method for estimating monthly discharge for a range of spatial scales, from large watershed to continents, based on the use of GRACE- derived terrestrial water storage change estimates in a coupled land-atmosphere water balance. The method has been previously tested on the Amazon and Mississippi river basins. Here we apply and test the approach in some of the largest river basins in Pan Arctic region, in an effort to improve understanding of, and better quantify, freshwater discharges into the Arctic Ocean. Furthermore we extend the methodology to estimate freshwater discharges at continental scales. Results and comparisons to observations indicate that the method has important potential for large-scale water balance studies and global-scale discharge monitoring of combined surface water and submarine groundwater discharge.