Discharge Estimation Using Hydro-Geodetic Approaches

Abstract:

The publicly available global discharge database is limited in spatial and temporal coverage. Although regional exceptions exist, the population of the database has declined over the past several years. When aiming for global scale discharge at a sufficient temporal resolution and with homogeneous accuracy, the choice to use spaceborne sensors is only a logical step. In this respect, we take water storage changes from GRACE and water level measurements from satellite altimetry and present a comprehensive assessment of 5 different hydro-geodetic approaches for river discharge prediction: hydrological balance equation, hydro-meteorological balance equation, least squares prediction using the covariance matrices out of available old in situ data, satellite altimetry with quantile function based stage-discharge relationships and a runoff-storage relationship that takes time-lag into account. As a common property these approaches do not rely on hydrological modeling; they are either purely data driven or make use of atmospheric reanalyses. The discharge estimation skill of these approaches are validated against in situ data. Our validation shows that satellite altimetry, runoff-storage and least squares prediction approaches are able to capture river discharge with an error range (relative RMSE) of less than 15% for most of the rivers under study. We are thus able to avoid the complexity of hydrological modeling for discharge estimation. Our results show that the mentioned three approaches clearly outperform the global methods (hydrological and hydro-meteorological approaches). However, the global methods have the potential to provide discharge over all landmasses ---gauged and ungauged basins alike, but are still limited due to inconsistencies in the global hydrological and hydro-meteorological datasets that they use.