Application of Regionalized Health Assessment System for Rivers on Xizang Plateau

[Objective] Rivers on the Xizang Plateau are characterized by fragile ecosystems, high sensitivity to climate change, and significant regional differences. To ensure regional water security and ecosystem stability, it is crucial to conduct regionalized and multi-dimensional river health assessments. [Methods] A comprehensive river health assessment system comprising 12 indicators was developed based on the three criterion layers of natural structure, ecological environment, and social service functions. Based on the topographic and climatic characteristics of the Xizang Plateau, the study area was divided into three regions: Southern Xizang Valley, Northern Xizang Plateau Lake Basin, and Eastern Xizang Alpine Gorge. Differentiated assessment criteria were formulated for each region. The indicator weights were determined by combining the fuzzy analytic hierarchy process and an improved entropy weight method based on game theory to enhance the rationality and stability of the assessment. Three typical rivers from different regions—the Xizang section of the Jinsha River, the Nianchu River, and the Zagya Zangbo—were selected for comprehensive assessment through field investigation, remote sensing monitoring, and hydrological data collection. [Results] The health status of the three rivers exhibited significant regional differences: The Zagya Zangbo scored 95.51, indicating a “very healthy” status. Its natural structure and social service functions were in excellent condition. However, due to the high-altitude characteristics of the Northern Xizang Plateau, dissolved oxygen levels were slightly lower, and the self-purification capacity of rivers in this region was generally low. The Xizang section of the Jinsha River scored 91.85, classified as "healthy". Its natural structure and ecological environment were generally good. However, in the Eastern Xizang Alpine Gorge region, the riverbanks had significant elevation differences, resulting in poor riverbank stability and low flood control compliance rates. Additionally, the low branch sinuosity made the area prone to mountain flood disasters. The Nianchu River scored 81.57, barely reaching the “healthy” level. Rivers in the Southern Xizang Valley were heavily influenced by human activities. In the middle and lower reaches of the Nianchu River, soil erosion was severe, and the natural status of the riverbanks scored low. Furthermore, the ecological flow requirements were inadequately met, the integrity of zoobenthos and the water quality indicators in the downstream sections were poor, and some flood control facilities in certain river sections were aging, posing safety risks. [Conclusions] Based on the assessment results, this study proposes measures such as strengthening soil and water conservation,improving ecological flow release,and advancing flood control projects.