Channel adjustments over 50 years in response to climate change and human activities in the Parlung Zangbo River, Tibetan Plateau, China

Rivers change the morphology and pattern of their channels in response to environmental changes, a central theme in fluvial geomorphology. However, short-term changes in channel morphology on the Tibetan Plateau, particularly in response to significant climate change and human activities in recent decades, remain poorly understood. This study examines five reaches of the Parlung Zangbo River, a major tributary of the Yarlung Zangbo River, integrating Landsat remote sensing imagery with hydrological records to analyse changes in channel morphology—including channel width, channel area, braided index and the number and area of mid-channel bars—between 1973 and 2020. The results indicate that all five sub-reaches of the Parlung Zangbo River underwent expansion, with significant increases in channel width, channel area, braided index, and both the number and area of mid-channel bars during this period. However, these changes occurred in distinct phases: an overall expansion of river channels from 1973 to 2000, followed by channel narrowing in the reaches of the Parlung Zangbo River trunk stream between 2000 and 2020. The initial expansion of river channels was likely driven by increased precipitation, meltwater and discharge associated with climate change. In contrast, the decline in precipitation over the southern Tibetan Plateau since 2000 has led to reduced discharge, contributing to channel narrowing. Additionally, upstream of hydroelectric stations, human activities may have altered the riverbed gradient and reduced sediment transport capacity, promoting channel expansion and the deposition of side bars. Among these factors, climate-related influences, particularly changes in precipitation and temperature, exert the most profound and long-term effects on river hydrology and channel morphology in the Parlung Zangbo catchment, surpassing the impact of human activities.