Abstract
Abstract. River discharge measurements have proven invaluable to monitor the global water cycle, assess flood risk, and guide water resource management. However, there is a delay, and ongoing decline, in the availability of gauging data and stations are highly unevenly distributed globally. While not a substitute for river discharge measurement, remote sensing is a cost-effective technology to acquire information on river dynamics in situations where ground-based measurements are unavailable. The general approach has been to relate satellite observation to discharge measured in situ, which prevents its use for ungauged rivers. Alternatively, hydrological models are now available that can be used to estimate river discharge globally. While subject to greater errors and biases than measurements, model estimates of river discharge do expand the options for applying satellite-based discharge monitoring in ungauged rivers. Our aim was to test whether satellite gauging reaches (SGRs), similar to virtual stations in satellite altimetry, can be constructed based on Moderate Resolution Imaging Spectroradiometer (MODIS) optical or Global Flood Detection System (GFDS) passive microwave-derived surface water extent fraction and simulated discharge from the World-Wide Water (W3) model version 2. We designed and tested two methods to develop SGRs across the Amazon Basin and found that the optimal grid cell selection method performed best for relating MODIS and GFDS water extent to simulated discharge. The number of potential river reaches to develop SGRs increases from upstream to downstream reaches as rivers widen. MODIS SGRs are feasible for more river reaches than GFDS SGRs due to its higher spatial resolution. However, where they could be constructed, GFDS SGRs predicted discharge more accurately as observations were less affected by cloud and vegetation. We conclude that SGRs are suitable for automated large-scale application and offer a possibility to predict river discharge variations from satellite observations alone, for both gauged and ungauged rivers.
Highlights
River discharge data are used to monitor the global water cycle, assess flood risk, and guide water resource management (Brakenridge et al, 2012)
The 10 experiments described in Sect. 2.3.1 for relating remotely sensed water extent to simulated river channel storage were compared, using Moderate Resolution Imaging Spectroradiometer (MODIS) and Global Flood Detection System (GFDS) water extent, respectively
We focused on flow pattern comparisons between predicted and observed discharges, so different vertical axes were chosen to bring them close to each other
Summary
River discharge data are used to monitor the global water cycle, assess flood risk, and guide water resource management (Brakenridge et al, 2012). Example applications include the assessment of the contribution of river flow to oceans and the distribution of river runoff on continents; the training of models to predict how water resources will be affected under climate change; the identification of where flood intensity and frequency is likely to increase; the provision of information for flood forecasting, monitoring, and warning systems; and the better formulation of water allocation plans for domestic, agricultural, and industrial uses (Van Dijk, 2015). Many ground-based gauging stations have been built to monitor river discharge across the world (Dai et al, 2009).
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