River-controlled permafrost dynamics are crucial for sediment transport, infrastructure stability, and carbon cycle, yet are not well understood under climate change. Leveraging remotely sensed datasets, in-situ hydrological observations, and physics-based models, we reveal overall warming and widening rivers across the Tibetan Plateau in recent decades, driving accelerated sub-river permafrost thaw. River temperature of a representative (Tuotuohe River) on the central Tibetan Plateau, has increased notably (0.39 degrees C/decade) from 1985 to 2017, facilitating heat transfer into the underlying permafrost via both convection and conduction. Consequently, the permafrost beneath rivers warms faster (0.37 degrees C-0.66 degrees C/decade) and has a similar to 0.5 m thicker active layer than non-inundated permafrost (0.17 degrees C-0.49 degrees C/decade). With increasing river discharge, the inundated area expands laterally along the riverbed (16.4 m/decade), further accelerating permafrost thaw for previously non-inundated bars. Under future warmer and wetter climate, the anticipated intensification of sub-river permafrost degradation will pose risks to riverine infrastructure and amplify permafrost carbon release.

This review article deals with bank erosion from the perspective of rivers affected by seasonal ice formation. These rivers drain half of the terrestrial land surface globally, and are mainly located in both periglacial and cold, non-periglacial environments across the Northern Hemisphere. This review is based on a literature survey of 126 publications (articles, technical reports, conference papers and book chapters) documenting case studies in temperate and polar climates. The first details the global issues of bank erosion and pinpoints concerns specific to northern environments. The second describes the dominant erosion processes (fluvial vs. terrestrial), mechanisms (mechanical vs. thermal) and typical landforms encountered in the literature. The third reviews the environmental factors (hydraulic vs. non-hydraulic) controlling bank erosion, with a focus on the different forms of river ice. The fourth deals with the spatial and temporal variability in bank-erosion processes, discussing the distribution of process dominance occurring at the reach scale and the catchment scale, and describing the temporal window in which each process dominates. The fifth reviews the expected impacts on bank erosion resulting from climate-induced disturbances on hydrological cycles and from increasing anthropogenic pressures along riverbanks in northern countries. The relationships among erosion processes, environmental factors, climate change, and human impacts are summarized in a sixth that introduces a new synthetic conceptual diagram of bank erosion. Research needs that should be investigated in the future are highlighted in the seventh while the final synthesizes all the aspects presented in this review.