SAEM: Satellite Altimetry-based Extension of global-scale in situ river discharge Measurements

Accurate river discharge monitoring is essential for understanding hydrological processes, yet the availability of in situ measurements is increasingly limited due to a declining number of operational gauges and temporal gaps in gauge records. Satellite altimetry offers a robust alternative to address these limitations. Here, we introduce the Satellite Altimetry-based Extension of the global-scale in situ river discharge Measurements (SAEM) dataset, which integrates data from multiple satellite altimetry missions to estimate river discharge and enhance global hydrological monitoring networks. Our analysis evaluated 47,000 discharge gauges and successfully derived height-based discharge estimates for 8,730 gauges, expanding the coverage of current remote sensing datasets by a factor of three. These gauges collectively represent approximately 88% of the globally gauged discharge volume. The SAEM dataset achieves a median Kling-Gupta Efficiency (KGE) of 0.48, demonstrating superior performance compared to existing global datasets.

In addition to discharge time series, SAEM offers three supplementary products: (1) a catalog of Virtual Stations (VSs) with metadata, including geographic coordinates, altimetry mission details, distances to discharge gauges, and quality flags; (2) for VSs with quality-controlled discharges, we provide IDs from L3 databases such as Hydroweb.Next (formerly Hydroweb), the Database of Hydrological Time Series of Inland Waters (DAHITI), the Global River Radar Altimeter Time Series (GRRATS), and HydroSat, and for VSs without corresponding time series in these L3 products, we have generated water level time series (SAEM WL) as an additional product; (3) rating curves that map water levels to discharge using the Nonparametric Stochastic Quantile Mapping Function approach. The SAEM dataset can enhance hydrological research, support water resource management, and allow addressing complex water-related challenges in the context of a changing climate.