Monitoring water discharge and floodplain connectivity for the Northern Andes utilizing satellite data: A tool for river planning and science-based decision-making

The river has witnessed rising trends in sediment transport during the last three decades, which correlate well with observed tendencies in land conversion and deforestation. An important part of the observed increasing sediment flux is being sequestered in riverbeds and along its adjacent floodplains, making these Andean rivers less resilient in regulating strong hydrologic pulses during extreme climate events. The northern Andean basins experience high rainfall rates and associated runoff excess over steep slopes, which are influenced by the El Niño Southern Oscillation (ENSO). River discharge inter-annual variability is in agreement with the El Niño-La Niña cycle at periods of 3-5 years. Between 2008 and 2011, strong La Niña conditions impacted the northern basins of Colombia, causing economic losses of over $US 7.2 billion. During this period, the Magdalena River experienced the strongest floods on record, flooding the country for almost three months. River authorities and the national disaster office lack consistent discharge data for drainage basin planning and flood hazard mitigation. In developing countries like Colombia, the flood alert system is based on records of hydrological gauging stations, which are often poorly calibrated and lack accuracy. River fluxes are underestimated when extreme discharges exceed bank-full discharge, and rating curves are not recalibrated after major floods during La Niña events, resulting in unreliable river discharge magnitudes. Satellite data have provided spatially and temporally dense river discharge mapping from space, offering a reliable alternative to ground-based gauging stations. The quasi-global coverage provided by satellite observations combined with open data policies can help avoid issues related to data access and continuity. For the Magdalena River, satellite-derived discharge estimates offer the only reliable data related to fluvial discharges and flood magnitudes, making them a valuable tool for river planning authorities. The study proposes a satellite-based technique to measure river discharge at selected sites for the Magdalena River, which has the advantage of back-calculating daily river discharges over a period of two decades. This method can be used to calculate return intervals of significant flood events and study river-floodplain connectivity. The derived discharges can form the base to study river-floodplain connectivity, providing environmental decision makers with a technique that makes it possible to better monitor river and ecosystem processes.