Remote sensing of lake chlorophyll-a in Qinghai-Tibet Plateau responding to climate factors: Implications for oligotrophic lakes

Plateau lake chlorophyll-a concentration [Chl-a] is one of the key water quality parameters to characterize trophic state responding to climate change. A total of 106 samples were collected in situ lake samples from 16 typical lakes in Qinghai-Tibet Plateau (QTP) from 2015 and 2019 to match Landsate series satellite imagery data. We developed a new empirical model of [Chl-a] and then analyze their relationships with climate factors, for oligotrophic lakes. The results show that the [Chl-a] model performed well with good fitting performance (R2 = 0.72) and few errors (RMSE = 0.49 ug L-1, and MAE = 0.38 ug L-1). The results further revealed that the amount of lakes with reduced [Chl-a] has gradually increased over the past 30 years (1990-2000: 50%; 2000-2010: 57.8 %; 2010-2020: 70%). Although the biochemical parameters of QTP lakes have been studied in more detail, this study found that[Chl-a] showed equilibrium with climate factors, e.g., averaged temperature and precipitation, from satellite long-term observations, as well as the lake area changes.The model could use available bands on Landsat sensors to generate historical[Chl-a] data for evaluating the water qualities changes and decision-making related to the Plateau's oligotrophic lakes and global climate change.