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

Abstract. River discharge is a crucial measurement, indicating the volume of water flowing through a river cross-section at any given time. However, the existing network of river discharge gauges faces significant issues, largely due to the declining number of active gauges and temporal gaps. Remote sensing, especially radar-based techniques, offers an effective means to this issue. This study introduces the Satellite Altimetry-based Extension of the global-scale in situ river discharge Measurements (SAEM) data set, which utilizes multiple satellite altimetry missions and estimates discharge using the existing worldwide networks of national and international gauges. In SAEM, we have explored 47 000 gauges and estimated height-based discharge for 8 730 of them which is approximately three times the number of gauges of the largest existing remote sensing-based data set. These gauges cover approximately 88 % of the total gauged discharge volume. The height-based discharge estimates in SAEM demonstrate a median Kling-Gupta Efficiency (KGE) of 0.48, outperforming current global data sets. In addition to the river discharge time series, the SAEMdata set comprises three more products, each contributing a unique facet to better usage of our data: (1) A catalog of Virtual Stations (VSs), defined by certain predefined criteria. In addition to each station’s coordinates, this catalog provides information on satellite altimetry missions, distance to the discharge gauge, and relevant quality flags.(2) The altimetric water level time series of those VSs are included, for which we ultimately obtained good-quality discharge data. These water level time series are sourced from both existing Level-3 water level time series and newly generated ones within this study. The Level-3 data are gathered from pre-existing data sets, including Hydroweb.Next (former Hydroweb), the Database of Hydrological Time Series of Inland Waters (DAHITI), the Global River Radar Altimeter Time Series (GRRATS), and HydroSat. (3) SAEM’s third product is rating curves for the defined VSs, which map water level values into discharge values, derived using a Nonparametric Stochastic Quantile Mapping Function approach. The SAEM data set can be used to improve hydrological models, inform water resource management, and address non-linear water-related challenges under climate change. The SAEM data set is available from (Saemian et al., 2024) https://doi.org/10.18419/darus-4475 during the review process.