ABSTRACT                        

Study region: Hainan Island, China, focusing on three major rivers: the Nandu, Changhua, and Wanquan River basins. Study focus: Tropical cyclones (TCs) are key drivers of episodic riverine material fluxes in coastal mountainous regions. However, their quantitative role in regulating water discharge and suspended sediment discharge (SSD) in tropical island basins remains poorly constrained. Based on 64 years (1960–2023) of daily hydrological records, this study quantifies TC-associated contributions to water discharge and SSD and examines how TCs modify water–sediment transport. New hydrological insights for the region: Quantitative analysis indicates that TCs exert a substantial influence on water discharge and SSD, contributing 4 ± 4% to 8 ± 6% of annual water discharge and 11 ± 10% to 30 ± 27% of annual SSD on average, with contributions reaching 91–95% of SSD in extreme years. Their influence on SSD is markedly stronger than on water discharge, indicating a pronounced sediment-routing enhancement. Sensitivity to TC forcing varies substantially across basins and these inter-basin differences are jointly regulated by TC characteristics, basin geomorphology (such as area and slope), and reservoir regulation. The identified water–sediment response regimes further highlight the nonlinear nature of sediment transport under TC forcing. These findings refine the understanding of extreme-event-driven material fluxes and provide a critical basis for managing flood risks, reservoir operations, and soil conservation in tropical island river systems.