The River Discharge Climate Change Initiative precursor project

The Global Climate Observing System (GCOS) identifies river discharge as an Essential Climate Variable (ECV), critical for understanding climate dynamics and managing water resources (GCOS, 2022). However, no satellite instrument currently exists to directly measure river discharge, which must instead be estimated indirectly. The ESA River Discharge Climate Change Initiative (CCI) precursor project (https://climate.esa.int/en/projects/river-discharge/) addresses this challenge by developing innovative methodologies based on satellite remote sensing data.Four complementary approaches are being explored: (1) the use of long-term satellite radar altimeter time series of water surface elevations, combined with rating curves to estimate discharge; (2) The use of satellite imagery data to obtain river width, combined with rating curves to estimate discharge; (3) multispectral sensor data in the near-infrared (NIR) band, used to analyze river flow variability through the reflectance ratio between wet and dry pixels; and (4) a hybrid approach combining these two techniques. Radar altimeters offer the advantage of weather-independent measurements, while multispectral sensors provide higher temporal resolution but are limited by cloud cover.This proof-of-concept study focuses on 54 locations across 18 river basins, spanning 2002–2022. The sites represent a variety of climatic zones, drainage areas (from 50,000 km² to the Amazon basin), levels of human activity, and availability of in situ data. The project showcases the potential for satellite-based global river discharge estimation, validated through comparisons with on-the-ground measurements.This presentation will outline the methodologies employed, the computed discharge time series along with their validation during the first Phase of this precursor project (2023-2024), the objectives for the second phase, which has just started, and the progress achieved.