Atmospheric Rivers Feeding Terrestrial Floods in the Senyar 2025 Event: A Conceptual Review

Before Cyclone Senyar made landfall on Sumatra in November 2025, it drew moisture from across the South China Sea, the Gulf of Thailand, and the Indian Ocean. The substantial damage its heavy rainfall caused on the NE and W coasts of Sumatra urges us to rethink the relationships between climate, forests, hydrology, land use, human presence, and vulnerability. Cyclones will recur, but flood damage does not have to be repeated. The simple narrative that “deforestation causes floods” is not adequate for guiding a “building back better” strategy. To account for the space-time pattern of Senyar effects with its multiple landfalls, we reviewed key concepts and framing of the links between ocean temperature, atmospheric moisture transport, rainfall extremes, saturation of existing buffers (“sponges”), river flow, and flooding. We hypothesize how atmospheric roughness slowing down rivers in the sky can induce congestion and precipitation. Surface infiltration and water retention in the soil profile matter. Mid- and downstream flow delays due to sponge effects depend on land cover beyond what a simple forest–non-forest terminology can represent. Rather than indiscriminate tree planting, adaptation efforts to avoid future disasters should balance reductions in human exposure (effective land use planning) and efforts to reduce hazards by restoring and managing vegetation and drainage systems.