The major June 2023 flood event in Central Chile: Hydrometeorological characterization and rain-on-snow contribution

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Abstract In June 2023, an extreme hydrometeorological event caused widespread flooding across Central Chile (34–39°S), abruptly interrupting a 13-year dry period. This study provides a comprehensive analysis of the event, characterizing its atmospheric drivers, hydrological impacts, and the role of rain-on-snow (ROS) in a representative catchment. A Category 4 Zonal Atmospheric River persisted for 4 days in a warm environment, resulting in a steep orographic precipitation gradient over the foothills of the Andes with rainfall accumulations of up to 600 mm, and the freezing level above 3,000 m ASL. Many rivers reached their highest flows on record, with peak discharges associated with return periods ranging from 9 to 199 years, resulting in significant damage to critical infrastructure and the general population. We also present a quantitative diagnosis of a ROS event in the Andes Cordillera using a physically-based and semi-distributed hydrological model in a representative catchment. Simulations reveal that snowmelt plus rainfall from snow-covered areas contributed ~15% to the total flood volume, of which snowmelt was the secondary source driven by net longwave radiation and heat from the warm rainfall. This event serves as an example of a compound hydrometeorological extreme event, where intense and prolonged precipitation, combined with high temperatures, converged to produce a major flood in Central Chile. Our findings highlight the region's vulnerability to extreme events and underscore the need for future studies to assess the potential of an integrated hydrological forecasting system to mitigate the impacts of extreme events.

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