Impact of hydroclimatic extremes on suspended sediment dynamics in a tropical river basin, India

Study region Tapi River Basin, a 724 km-long tropical river in India. Study focus: Hydrological and sediment connectivity regulate sediment supply and channel morphology, while intensifying hydroclimatic extremes enhance flood-driven sediment mobilisation. Using observations and hydrological modelling, we investigated flood, sediment, and channel responses to extreme events and a 35-year assessment. We also developed a flood connectivity framework to evaluate hydrological connectivity during floods and infer potential sediment disconnectivity when observed sediment data are unavailable. New hydrological insights Flood-wave connectivity varies spatially due to heterogeneous rainfall and anthropogenic regulation. Extreme events increase sediment loads by ~200–300% relative to average conditions. Channel response is governed by spatial variations in unit stream power (USP) and sediment availability, with high upstream USP promoting erosion and a 3–4-fold reduction downstream favouring deposition, potentially reducing channel conveyance and increasing flood risk. Sediment mobilisation is strongly associated with daily rainfall > 50 mm and seasonal discharge, highlighting the role of extreme rainfall and hydrological conditions. Model simulations indicate a ~36% increase in sediment yield alongside ~8% and ~28% increases in annual mean and maximum rainfall, respectively, over 35 years, under constant land use. Although hydroclimatic variability appears to be a major driver, land-use change, channel processes, and longitudinal barriers may also influence sediment dynamics. These findings highlight the need to incorporate hydroclimatic extremes and connectivity into sediment and flood-risk management.