Estimation of river discharge, propagation speed, and hydraulic geometry from space: Lena River, Siberia

Moderate Resolution Imaging Spectroradiometer (MODIS)-derived measurements of Lena River effective width (W-e) display a high predictive capacity (r(2) = 0.81, mean absolute error < 25%) to forecast downstream discharge conditions at Kusur station, some 8 d and similar to 700 km later. Satellite-derived mean flow propagation speed (88 km d(-1) or 1.01 m s(-1)) compares well with that estimated from ground data (84 km d(-1) or 0.97 m s(-1)). Scaling analysis of a similar to 300 km heavily braided study reach suggests that at length scales > 60-90 km (similar to 2-3 time valley width), satellite-derived W-e - Q rating curves and hydraulic geometry (b exponents) converge upon stable values (b = 0.48), indicating transferability of the discharge retrieval method between different locations. Put another way, at length scales exceeding similar to 60-90 km all subreaches display similar behavior everywhere. At finer reach length scales (e. g., 0.25-1 km), longitudinal extraction of b exponents represents the first continuous mapping of a classical hydraulic geometry parameter from space. While at least one gauging station is required for calibration, results suggest that multitemporal satellite data can powerfully enhance our understanding of water discharge and flow conveyance in remote river systems.