Changes in river morphology and influencing factors in the upper Yellow River over the past 25 years

Changes to the morphology of the upper Yellow River (UYR) had various impacts on the surrounding ecology and society, as well as the entire basin. However, low-spatial-resolution imagery (e.g., MODIS, AVHRR) cannot capture sufficient spatial details for monitoring complex water bodies, while high-spatial-resolution imagery (e. g., SPOT, Quickbird, Ikonos) lacks spatial coverage and the revisit frequency necessary for large-scale water body monitoring. To address these limitations, this study utilized the Google Earth Engine (GEE) and ArcGIS spatial analysis tools, applied pan-sharpening to downscale Landsat imagery of the study area from 1999 to 2023, performed river extraction, and calculated the spatiotemporal changes in river morphology in the UYR using river morphological parameters (i.e. area, channel width, centerline length, sinuosity index, lateral migration rate, channel stability). The Automated Water Extraction Index (AWEIsh) effectively characterized the study area, and pan-sharpening technology improved the extraction accuracy of small water bodies. Finally, the overall accuracy and Kappa coefficient were 0.993 and 0.985, respectively. Over the past 25 years, the area and average width of the entire reach of the UYR changed significantly, with the maximum value being 1.3 times the minimum value, whereas the centerline length and sinuosity index showed no apparent changes, and the lateral migration rate varied minimally, with the average annual movement ranging from 4.67 m to 10.18 m. In typical river segments without human activity, although single-channel reaches exhibited stronger stability than multichannel reaches, natural factors (i.e. annual precipitation, annual runoff, annual sediment discharge) had a noticeable impact on the morphology of both single-channel and multi-channel reaches. Large-scale cascade hydropower development in the UYR has significantly impacted river morphology over a short period. Meanwhile, in river sections unaffected by human activities, the changes occurred gradually. This study provides support for better understanding complex river morphologies at large regional and long-term scales and a scientific basis for water resource management and sustainable development in the UYR.