Global satellite-based river gauging and the influence of river morphology on its application

Abstract

In the face of a sparse global river gauging station network in decline, new approaches are needed to reconstruct and monitor river discharge from satellite observations. Where in-situ river discharge measurements are not available, it may be possible to use discharge estimates from a hydrological model, provided the model simulations are of sufficient quality, to construct satellite-based discharge gauging. We tested this approach by developing model- and gauge-based satellite gauging reaches (SGRs) using 0.05° MODIS optical remote sensing at ~10,000 gauged and ~370,000 ungauged river reaches globally. Model-based SGRs are aimed to infer temporal flow patterns and reflect unusually high or low river discharge behavior (i.e. flood or drought conditions), if not necessarily absolute discharge volumes. The model-based SGRs achieved a discharge prediction skill that was often similar to gauge-based SGRs, and sometimes better than the model itself. Our results showed promising opportunities to develop model-based SGRs in sparsely gauged basins in South America, Africa, and Asia. We selected river reaches, with mean widths ranging from 67 to 3105 m, representing both poor and successful SGRs in different environments for case studies to analyze conditions for successful SGR development. River size and morphology were the main factors determining the performance of SGRs. Wide channels with strong temporal variations, broad floodplains and multiple braided or anastomosing channels provided the best conditions for SGRs. The probability of constructing a successful SGR could be predicted from high-resolution inundation summary data available globally, and can thus be predicted anywhere. Ongoing increases in the spatial and temporal resolution of remote sensing will further increase the number of river reaches for which satellite-based discharge gauging will become possible.