Rivers Aspot

Global River Discharge

 

Rivers Aspot
Rivers Aspot

The GLOBAL RIVER DISCHARGE study aims to develop a high-resolution, daily global river discharge dataset by combining optical and radar altimetry satellite observations. This work will deliver a novel, pre-operational solution to support hydrological monitoring.

Last Updated

06 January 2026

Published on

06 January 2026

About

Freshwater is a vital yet limited resource, and monitoring river discharge is essential for managing water availability, detecting climate trends, and supporting a wide range of hydrological applications. However, traditional in-situ monitoring networks are in decline, especially in remote and data-scarce regions. To address this gap, the GLOBAL RIVER DISCHARGE study explores the combined use of satellite altimetry and multispectral optical observations to estimate river discharge at a global scale. Building on previous research and recent advances in satellite technology, the study aims to deliver a pre-operational product with daily temporal resolution across more than 300 globally distributed river sites.

Objectives

The main objective of the GLOBAL RIVER DISCHARGE study is to generate a global, high-resolution river discharge product using multi-mission satellite data. Specifically, the study aims to:

  • develop a satellite-based algorithm that integrates radar altimetry and optical reflectance indices to estimate daily river discharge;
  • apply the algorithm to more than 300 river sites worldwide, covering a diverse range of hydrological and climatic conditions;
  • validate the discharge estimates against in-situ and modelled data to assess their accuracy and reliability;
  • evaluate the utility of the dataset for hydrological applications, including water resource management and climate analysis, particularly in ungauged basins;
  • provide a roadmap for the future development of Fiducial Reference Measurements (FRMs) to support long-term monitoring of river discharge from space.

Overview

Introduction

Monitoring river discharge is critical for understanding hydrological processes, managing freshwater resources, and assessing climate variability. However, the decline of in-situ gauging networks and the limited availability of data in remote or conflict-prone regions have created significant observational gaps. Satellite remote sensing offers a unique opportunity to address these challenges by providing consistent, wide-area measurements of inland water bodies. The GLOBAL RIVER DISCHARGE study responds to the need for an operational, high-resolution global river discharge dataset. It leverages the complementary capabilities of radar altimetry (e.g., Sentinel-3, Sentinel-6, SWOT) and optical sensors (e.g., Sentinel-2, Sentinel-3 OLCI, MODIS) to estimate discharge with improved temporal resolution and spatial coverage.

Methodology

The study follows a multi-step approach that considers the selection of over 300 global river sites representing diverse climatic and morphological regimes. Over these sites, altimetry data are pre-processed and integrated in a multi-mission framework to derive temporally densified water level time series (L2 ALT). Reflectance indices from multispectral imagery are then extracted from multiple satellite missions to serve as proxies for surface flow conditions (L2 REFL).

Finally, the river discharge algorithms are implemented using single-sensor inputs ((L3 QALT, L3 QREFL) and multi-sensor integration (L4 QCOMB), which combines water level and reflectance-based flow proxies. A validation process against ground based and modelled discharge data is carried out using standard hydrological performance metrics.

Figure 1. Overview of (a) sensor integration approach and (b) the study workflow

Results

Although the study is still ongoing, preliminary results from pilot sites demonstrate the following:

  • Multi-mission altimetry significantly improves the temporal coverage of water level time series, particularly when combining nadir and SWOT observations;
  • Reflectance-based proxies capture seasonal and event-scale variability in discharge, although they remain sensitive to cloud cover and snow conditions;
  • Integrated discharge estimates show promising agreement with in-situ measurements, particularly in medium-to-large basins.
  • Early validation at approximately 20% of the sites confirms the feasibility of producing daily discharge estimates with reasonable accuracy.
Figure 2. Example time series of discharge estimated by (top) only satellite, (centre) only multispectral, (bottom) from the combination of altimetry and multispectral against ground truth for the Po River
Figure 3. Example time series of discharge estimated by (top) only satellite, (centre) only multispectral, (bottom) from the combination of altimetry and multispectral against ground truth for the Niger River

Conclusions

The GLOBAL RIVER DISCHARGE study demonstrates the technical and scientific feasibility of producing a global-scale river discharge product using satellite observations. Key conclusions include:

  • Multi-sensor integration is essential for overcoming the limitations of individual satellite missions (e.g., revisit time, cloud cover).
  • Satellite-derived discharge estimates can provide a valuable complement to in-situ networks, particularly in data-sparse regions.
  • The methodology is scalable and adaptable to a wide range of river conditions, supporting potential pre-operational deployment in cloud environments such as the European Weather Cloud (EWC).
  • The development of dedicated Fiducial Reference Measurements (FRMs) is strongly recommended to ensure long-term validation and data continuity.

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