Spatiotemporal refinement of hydro-sediment processes in small disturbed permafrost watershed during rainfall and snowmelt events

Abstract

Under climate change, the hydro-sediment processes in permafrost watersheds have been visibly changed, impacting the function of water conservation and ecological barrier of river source areas. However, the lack of observational data and understanding of underlying mechanisms limits the evaluation of hydro-sediment variation and its environmental response. Here, we selected a small permafrost watershed in the northern Tibetan Plateau and conducted daily and event scale observations at four cross-sections: sunny slope tributary, shady slope tributary, confluence, and watershed outlet. Results indicate that during spring, there is a stronger correlation between runoff and sediment concentration, alongside higher sediment transport efficiency per unit of runoff at the watershed outlet. The sunny slope tributary is characterized by rapid runoff generation, high peak flow and sediment load. It predominantly influences the outlet processes, contributing 83% runoff and 125% sediment load in summer rainfall events and 59% runoff and 52% sediment in spring snowmelt events. Thermokarst trench networks also contribute significantly during spring. Conversely, the shady slope tributary demonstrates a slow, sustained runoff release and low sediment concentrations, contributing minimally to the outlet. The lower mainstream channel functions as a dynamic interchange between sources and sinks of runoff and sediment. The temporal and spatial differences are discussed in relation to climate factors, soil properties, soil freeze–thaw dynamics, and land coverage. This study provides valuable insights into hydrological and sedimentary processes in high-altitude cold region and their responses to environmental changes.