ESA CCI River Discharge precursor project: current status and challenges

River discharge is an Essential Climate Variable (Global Climate Observing System, 2022) which has been included in the ESA Climate Change Initiative (CCI) program since 2023, through a precursor project (https://climate.esa.int/en/projects/river-discharge/, CCI RD). Currently, no satellite instrument can directly measure river discharge, this project is a proof-of-concept and aims at estimating river discharge using Earth Observation and ancillary data. The objective is to deliver consistent discharge estimates from 2002 to 2025, at 50 locations across 18 selected river basins around the world. The CCI RD extends in situ discharge time series, using four robust methods: (1) estimating discharge through a rating curve approach using ancillary in situ discharge data and multiple satellite radar altimeter long time series of water surface elevation, (2) exploiting near-infrared (NIR) multispectral data, to compute the dry/wet pixel reflectance ratio linked to the river flow variations, (3) computing discharge from river width derived from optical images and ancillary discharge data using nonparametric stochastic quantile mapping approach, and (4) combination of these 3 approaches. These products are already available online: https://catalogue.ceda.ac.uk/uuid/dbba9cfe8d104648b19e39f4c2da1a27/. This presentation provides a general overview of the generated discharge products, their validation against ground observations, and their assimilation into basin-scale hydrology models . Furthermore, we will presents preliminary climate assessment based on these products.