AbstractApproximately 40% of the Tibetan Plateau (TP) is underlain by continuous permafrost, yet its impact on fluvial water and sediment dynamics remains poorly investigated. Here we show that water and sediment dynamics in the permafrost-dominated Tuotuohe basin on the TP are driven by air temperature and permafrost thaw, based on 33-year daily in-situ observations (1985-2017). Air temperature regulates the seasonal patterns of discharge and suspended sediment concentration (SSC) by controlling the changes in active contributing drainage area (ACDA, the unfrozen erodible landscape that contributes hydrogeomorphic processes within a catchment) and governing multiple thermal processes such as glacier-snow melt and permafrost thaw. Rainstorms determine the short-lived fluvial extreme events by intensifying slope processes and channel erosion and likely also by enhancing thaw slumps. Furthermore, the SSCs at equal levels of discharges are lower in autumn (September-October) than in spring (May-June) and summer (July-August). This reduced sediment availability in autumn can possibly be attributed to the increased supra-permafrost groundwater runoff and the reduced surface runoff and erosion. Due to rapid climate warming, the ACDA has increased significantly from 1985 to 2017, implying expanding landscapes for hydrogeomorphic processes. As a result, the fluvial water and sediment fluxes have substantially increased. In a warmer and wetter future for the TP, the fluvial sediment fluxes of similar permafrost-underlain basins will continue to increase with expanding erodible landscapes and intensifying thermal and pluvial-driven geomorphic processes. Thus, permafrost thaw should be considered as an important driver of past and future water and sediment changes for the TP.This article is protected by copyright. All rights reserved.

Abstract Accelerated glacier-snow-permafrost erosion due to global warming amplifies the sediment availability in cold environments and affects the time-varying suspended sediment concentration (SSC) and discharge (Q) relationship. Here, the sediment-availability-transport (SAT) model is proposed to simulate dynamic SSC-Q relationships by integrating the sediment availability coupled by thermal processes, fluvial processes and long-term storage exhaustion into a sediment rating curve (SSC = a ? Qb with a and b as fitting parameters). In the SAT-model, increased sediment sources from glacier-snow-permafrost erosion are captured by changes in basin temperature, showing an exponential amplification of SSC when basin temperature increases. Enhanced fluvial erosion by the elevated water supply from rainfall and meltwater is captured by the factor of runoff surge, which results in a linear amplification of SSC. The SAT-model is validated for the permafrost-dominated Tuotuohe basin on Tibetan Plateau utilizing multi-decadal daily SSC/Q in-situ observations (1985?2017). Results show that sediment rating curves for Tuotuohe display significant inter-annual variations. The higher parameter-b in a warmer and wetter climate confirms the increased sediment availability due to the expanded erodible landscapes and gullying-enhanced connectivity between channels and slopes. Through capturing such time-varying sediment availability, the SAT-model can robustly reproduce the long-term evolution, seasonality, and various event-scale hysteresis of SSC, including clockwise, counter-clockwise, figure-eight, counter-figure-eight, and more complex hysteresis loops. Overall, the SAT-model can explain over 75% of long-term SSC variance with stable performance under hydroclimate abrupt changes, outperforming the conventional and static sediment rating curve approach by 20%. The SAT-model not only advances understanding of sediment transport mechanisms by integrating thermal- and fluvial-erosion processes, but also provides a model framework to simulate and project future sediment loads in other cold basins.