Abstract: Plateau urban wetlands, as an important component of plateau urban ecosystems, play a critical role in maintaining economic development and ecological environment construction in plateau cities, yet the understanding of vegetation dynamics and their influencing factors remains elusive. We employed various vegetation indices to assess vegetation conditions in plateau urban wetlands and investigated their responses to climate change. We calculated the normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), ratio vegetation index (RVI), and fractional vegetation cover (FVC) for the Lhalu Wetland National Nature Reserve in Qinghai-Tibet Plateau using Landsat multi-source image data during the vegetation growing season (May to September) between 2000 and 2020. Trend regression analysis was used to uncover the spatial-temporal variations of these indices and vegetation cover over the past two decades in Lhalu wetland, and their correlations with precipitation and temperature were explored. Our results showed that: (1) The FVC levels in the Lhalu wetland were relatively high, averaging at 0.57 from 2000 to 2020. Higher FVC values were observed in the central and southern regions. While the proportion of increasing FVC areas surpassed that of decreasing areas, the dominant trend (32.38% of areas) showed a non-significant increase. (2) NDVI and RVI displayed a strong correlation (R²=0.92, P<0.01), being more effective than EVI in monitoring FVC in Lhalu wetland. EVI exhibited high sensitivity to variations in vegetation growth, especially in areas characterized by dense vegetation coverage, while NDVI stood out as the most effective and adaptable index for accurately assessing and retrieving vegetation cover. (3) NDVI, EVI, and RVI indices displayed a negative correlation with temperature while showing a positive correlation with precipitation. Temperature exhibited a greater impact on vegetation indices. Our results highlight the relative stability and incremental improvement of FVC trends in Lhalu Wetland National Nature Reserve from 2000 to 2020. Spatially, vegetation indices showed higher values in the central and southern parts. Notably, NDVI was the most proficient index for vegetation assessment, surpassing RVI and EVI, with temperature showing a more pronounced influence on vegetation indices than precipitation. This research provides valuable scientific insights and empirical support for the conservation and restoration efforts in Lhalu Wetland National Nature Reserve.

Key words: Lhalu wetland, fractional vegetation cover, vegetation index, spatiotemporal variation, climate change