Variability in evapotranspiration shifts from meteorological to biological control under wet versus drought conditions in an alpine meadow

The Tibetan Plateau is generally referred to as the Chinese water tower, and evapotranspiration (ET) affects the water budget and stability of alpine meadows on the Tibetan Plateau. However, its variability and controlling mechanisms have not been well documented under the drier conditions induced by global warming. Therefore, this study aimed to clarify whether meteorological or biological factors primarily affected the variability in ET under contrasting water conditions in the alpine meadow ecosystem on the Tibetan Plateau. Based on 6-year (2013–2018) eddy covariance observations and the corresponding meteorological and biological data, linear perturbation analyses were employed to isolate the contributions of meteorological and biological factors to the variability in evapotranspiration (δET). The results indicated that δET was mainly driven by meteorological factors in wet peak seasons (July and August) and was dominated by net radiation (Rn) and air temperature (Ta), indicating that the inadequate available energy was the factor limiting ET. However, the dominant factors affecting δET shifted from meteorological to biological in dry peak seasons when the canopy stomatal conductance (gs) and leaf area index (LAI) were dominant. At this point, the ecosystem was limited by the water conditions. This study provides empirical insights into how meteorological and biological factors regulate variability in ET under contrasting water conditions. This study can further improve our understanding of water cycle processes and can help effectively manage water resources in alpine meadow ecosystems under future climate change conditions.