Simulating climate-cryosphere-driven sediment transport dynamics in cold regions by Sediment-Availability-Transport Model

Sediment transport in cryospheric regions is characterized by distinct hydrogeomorphic processes and sediment sources from glacier retreat and permafrost disturbances. Ongoing atmospheric warming is melting glaciers and thawing permafrost at alarming rates. This rapid cryosphere degradation is expected to liberate unconsolidated sediment from previously frozen regions, expose glacially-conditioned sediment storage, and trigger more episodic events (e.g., floods and mass wasting). The substantial increases in readily transportable sediment and sensitive changes in hydrological conditions disturb suspended sediment concentration (SSC) and discharge (Q) relationships represented by sediment rating curves (SSC=a×Q^b with a and b as fitting parameters), creating complicated dynamics and various hysteretic patterns.

To constrain such dynamic SSC-Q relationships and reproduce the hysteresis effect, we propose a Sediment-Availability-Transport (SAT) model by extending traditional rating curves to incorporate the temperature-dependent sediment supply, pluvial processes, and sediment storage. Specifically, we highlight the sensitive response of SSC to discharge pulses triggered by rainstorms and intense melting, which can be attributed to enhanced fluvial erosion by flushing erodible hillslopes and scouring river channels.

Supported by multi-decadal daily discharge and SSC in-situ observations, the SAT-model can be parameterized, calibrated, and validated in various permafrost-dominated watersheds and glacierized watersheds. According to model validations in these pilot river basins, the SAT-model can robustly reproduce the long-term evolution, seasonal pattern, and various event-scale hysteresis in sediment transport, 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, outperforming the traditional sediment rating curve approach by 20%.

SAT-model proposed here not only advances the understanding of sediment transport dynamics driven by climate change and cryosphere degradation, but also provides a ready-to-use model and conceptual framework to simulate and project future sediment loads in worldwide cold regions. Parts of these results have been published in Water Resources Research: Zhang et al., 2021, Constraining dynamic sediment-discharge relationships in cold environments: The sediment-availability-transport (SAT) model. (https://doi.org/10.1029/2021WR030690)