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|Title:||Calibration of Satellite Measurements of River Discharge Using a Global Hydrology Model|
|Authors:||BRAKENRIDGE Robert; COHEN Sagy; KETTNER Albert; DE GROEVE Tom; NGHIEM Son; SYVITSKI James; FEKETE Balazs|
|Citation:||JOURNAL OF HYDROLOGY vol. 475 p. 123-136|
|Publisher:||ELSEVIER SCIENCE BV|
|Type:||Articles in periodicals and books|
|Abstract:||Measurements of river discharge and watershed runoff are essential to water resources management, efficient hydropower generation, accurate flood prediction, and improved quantitative understanding of the global water cycle. Previous work demonstrates that orbital remote sensing can measure daily river discharge variation in a manner closely analogous to its measurement at ground stations, using reach flow surface area, instead of stage, as the discharge estimator. For international measurements, global hydrological modeling can be used to provide the needed calibration of incoming sensor data to discharge: our study tests this approach and investigates the accuracy of the results. We analyze 6 sites within the U.S. where co-located gauging station, satellite measurements, and model results are all available. Knowledge is thereby gained concerning how accurately satellite sensors can measure discharge, if the signal is calibrated only from global modeling results without any ground-based information. Calibration (rating) equations for the remote sensing signal are closely similar whether based on gauging station or model information; r2 correlation coefficients for least squares fits at one example site (#524; White River, Indiana) are both .66 (n = 144, monthly daily maxima, minima, and mean, 2003-2006). Space-based measurement of 4-day mean discharge at this site when using the model calibration is accurate to within +/- 67% on the average (n = 1824; largest percent error at low discharges), and annual total runoff is accurate to +/- 9 %, 2003-2008. Comparison of gauging station versus Water Balance Model (WBM) discharge indicates a small positive model bias; the observed errors of annual runoff values are also positive and are subject to improvement by bias removal. The results indicate that model-based rating curves can provide accurate calibration of remote sensing measurements of discharge. However, an analysis of an exceptional large flood event, along the Indus River in 2010, shows that WBM does not capture flood wave attenuation by overbank flow, and thus predicts faster flood wave celerity and higher peak discharge compared to remote sensing observations. Better modeling incorporating these and other processes will improve conversion of remote sensing measurements of rivers into accurate discharge, including for extreme events.|
|JRC Directorate:||Space, Security and Migration|
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