Landsat observations reveal increasing trend in lake clarity on the Qinghai-Tibetan Plateau: Insights into the lake optical response to climate change

Lakes across the Qinghai-Tibetan Plateau (TP) have undergone substantial environmental changes in recent decades, under the influence of climate warming and enhanced precipitation. But the long-term changes in lake optical properties and their responses to climate change on the TP remain less explored. This study utilizes Landsat series datasets from 1986 to 2024 to estimate a fundamental lake optical property—the Secchi disk depth ( Z SD ) in TP lakes, for tracking the long-term shifts in TP lake ecosystems. To accommodate the limited spectral information of Landsat 5/TM imagery, an improved semi-analytical QAARGB model was proposed to enhance the applicability of the semi-analytical model on lakes with relatively low Z SD (<1 m). To maintain the consistency of Z SD retrieval across Landsat series datasets, MODIS data were also employed for cross-calibration. The results unveil a noteworthy upward trend of Z SD across TP lakes over the nearly 40 years (with average Sen's slope of 0.019 m/yr, P < 0.05), with more pronounced improvements observed in the western and central TP regions. Analysis of long-term lake Z SD and meteorological factors revealed three distinct response patterns of lake Z SD to climate change on the TP. These patterns were predominantly associated with NDVI (33.0% of lakes), lake area (31.0%), and air temperature (4.9%), unveiling clear spatial heterogeneity in the dominant meteorological factors associated with interannual Z SD variations. These findings highlight the cascading impacts of climate change on TP lakes—mediated by hydrological expansion, watershed vegetation, and thermal regime—ultimately reshaping their optical and ecological characteristics. • A new framework harmonizing Landsat sensors for consistent long-term Z SD estimation. • Employed MODIS to cross-calibrate Z SD derived from Landsat 5/TM and Landsat 8/OLI. • 53.0% of the TP lakes showed significant increases in Z SD during 1986–2024. • Revealed three response patterns of lake clarity to climate change on TP.