Asymmetric changes in diurnal lake temperature and their potential ecological impacts on the Tibetan plateau

The Tibetan Plateau (TP) hosts numerous lakes that are highly sensitive to climate change. While lake surface water temperature (LSWT) is a known indicator of the lake ecosystem, the long-term trends of its diurnal temperature differences (DTDs)-which influence lake physical mixing, biological processes, and the lake-atmosphere carbon exchange-remain under-explored. Using satellite land surface temperature data from 2000 to 2024, we reveal a decreasing trend in DTDs of TP lakes, with the annual mean dropping from 14.99 °C to 11.51 °C (rate: -0.073 °C per year, p < 0.01). This narrowing is associated with asymmetric diurnal changes: significant year-round nighttime warming, potentially driven by rising air temperature and longwave radiation, contrasted with slight daytime cooling in winter and spring, possibly due to reduced shortwave radiation. A lake area threshold (35.4 km²) was identified, below which DTD decreases were 3.9 times greater than in larger lakes, suggesting that smaller lakes are more sensitive to climatic forcing. Attribution analysis indicates a positive correlation between DTD and chlorophyll-a (Chl-a) variability. The continuous decrease in DTDs may have implications for lake productivity, potentially through altered metabolic balance and stronger thermal stratification. Our study highlights DTD as a potentially useful metric for monitoring thermal change in high-altitude lake ecosystems.