Abstract:

[Objective] This study focuses on morphodynamic evolution of braided rivers in the Source Region of the Yangtze River (SRYR), a representative high-altitude fluvial system on the Qinghai-Xizang Plateau. It aims to 1) systematically review recent advances in remote sensing monitoring, quantitative morphological characterization, and numerical simulation; 2) establish a unified morphological representation framework applicable across spatial scales; 3) analyze the response mechanisms of braided rivers to variations in water and sediment under climate change; 4) identify key process mechanisms and influencing factors to support the sustainable management and ecological protection of braided river systems on the plateau. [Methods] This study integrated multiple research approaches, including the extraction of morphological parameters at various scales from remote sensing imagery, UAV-based photogrammetry, and field surveys. Numerical models such as Delft3D were used to simulate morphological evolution under typical flood scenarios. A three-tier morphological representation system comprising whole-reach, sub-reach, and bar-channel unit levels was constructed. Indicators such as braiding intensity, channel density, and bar-to-channel area ratio were analyzed across different scales. Through literature review and empirical comparison, the climatic, hydrological, and geomorphic factors affecting the evolution of braided rivers on the Qinghai-Xizang Plateau were identified, and their evolutionary patterns were summarized. [Results] In recent years, research on the morphodynamics of braided rivers in the SRYR has made systematic progress. The focus has shifted from qualitative descriptions to quantitative analyses, covering spatial scales from bar-channel units to entire river reaches and temporal scales from individual flood events to interannual evolution. In terms of morphological characterization, a multi-scale index system incorporating indicators such as braiding intensity, channel density, and bar-to-channel area ratio has been developed, achieving a preliminary quantitative description of structural complexity. Regarding process mechanisms, explanatory frameworks such as “oblique bar cutting”,“dual driving by flow and sediment”, and “tectonic-geomorphic coupling” have been proposed. Concerning climatic responses, three typical response modes have been identified: Sediment-Increase Dominated Pattern, Water-Increase Dominated Pattern, and Sediment-Increase Constrained Pattern, which exhibit significant spatial differentiation. Methodologically, the integration of remote sensing, UAV photogrammetry, and numerical modeling has significantly improved the precision of fluvial dynamic process recognition. Despite these advancements, three major challenges remain: (1) the multi-scale quantitative characterization system lacks uniformity and transferability. Morphological parameters across different scales remain poorly integrated, and the coupling mechanism between bar-channel structures and overall stability has not been clearly understood. Existing indices, mostly derived from lowland alluvial river systems, are difficult to directly apply in high-altitude cold environments. Quantitative descriptions of three-dimensional riverbed structures remain inadequate, and topological network characteristics and flow direction information have not been systematically incorporated.(2) There is insufficient understanding of spatiotemporal response mechanisms, making cross-scale modeling difficult. A unified framework is still lacking to explain morphological evolution driven by both short-term flood events and long-term climate change. The absence of high-temporal-resolution data across multiple spatial scales hampers the parameterization and validation of dynamic evolution models, resulting in difficulties in scale conversion.(3) The bidirectional effects of climate change remain unclear. In the short term, glacier melt and permafrost degradation increase water and sediment fluxes, promoting the enhancement of braided structures. However, future glacier retreat may reverse the water and sediment processes, causing channel incision and transition toward single-thread morphology. There is currently no systematic method to predict the overall impacts of such bidirectional changes on braided river morphology, and research on threshold identification and irreversible responses remains lacking. [Conclusions] Overall, future research on braided rivers urgently needs to shift from qualitative understanding to quantitative prediction. An integrated research framework that combines process analysis, threshold identification, and evolutionary trend modeling should be established. By combining multi-source data and multi-scale models, this framework can provide scientific support for infrastructure planning and ecological conservation on the Qinghai-Xizang Plateau.

Key words: braided river, morphological characterization, multi-scale features, morphodynamics, water and sediment variations, climate change, source region of Yangtze River