What can we learn from existing satellites about Arctic river discharge: a new 30-year reanalysis

Abstract:

Arctic rivers drain 11.5-15.9% of the world’s landmass. As an integrative measure of continental water balance, river discharge documents changes in the Arctic hydrologic cycle, and conveys freshwater, heat, and terrigenous material to the Arctic Ocean. This significantly influences coastal ecosystem environments and thermocline circulation in the North Atlantic and consequently impacts global climate. In this study, we developed a discharge reanalysis dataset for the pan-Arctic region, and provide daily discharge for 414,256 river reaches with a median catchment area of 37 km² for 1984-2013. We generated this product by assimilating discharge observations derived from 148.47 Million width measurements made from 74,667 images from the Landsat 5, 7, 8 missions into a hydrologic model. We found that these satellite data can significantly improve the accuracy of simulated discharge: median KGE across our ~400,000 reaches increased by 0.15 compared to an ensemble of model simulations that do not assimilate satellite data. With this discharge reanalysis in hand, we found that total river discharge to the Arctic Ocean has a significant increasing trend (p-value = 0.036) during 1984-2013, with a slope of 15.1 km³/y/y. This is 2.7 times greater than previously reported. Our methodology also allows for explicit spatial analysis, and we found decreasing discharge through time in North America basins, whereas Eurasian basins show increasing discharge and drive the overall trend. The semi-desert, taiga, and continuous and isolated permafrost regions also tend to have a higher increased discharge than other regions. Finally, we note that our results are spatially explicit and represent vectorized river reaches as narrow as 6 m. We find a decrease in stream intermittency in some basins and increases in over-winter baseflow in others, and our methodology is ready to be expanded to all global rivers.