Spatiotemporal Variability and Driving Factors of Tibetan Plateau Water Use Efficiency

摘要

Water use efficiency (WUE) provides vital information about the carbon-water coupling relationship of a terrestrial ecosystem. Understanding the spatiotemporal variability and driving factors of the Tibetan Plateau (TP) WUE can facilitate the prediction of the response of the carbon-water process in the TP to climate change. We used a land surface model to investigate spatiotemporal changes in WUE and the responses to environmental factors, such as atmospheric CO2 concentration and climate and land use change. Our results suggest that the average annual TP WUE was 0.38 g C kg(-1) H2O and that this variable tended to increase at a rate of 0.001 g C kg(-1) H2O year(-1) during the period of 1979-2010. Changes in atmospheric CO2 concentration caused a significant increase in the rate of WUE change (i.e., 0.00051 g C kg(-1) H2O year(-1)); these changes were also found to most significantly contribute to WUE increase in the TP and account for approximately 51 of the WUE fluctuation. Increasing temperature was found to result in a decreasing WUE (rate: -0.00028 g C kg(-1) H2O year(-1)). Regarding results on vegetation type, forested areas had the highest WUE (i.e., 0.88 g C kg(-1) H2O) and the highest rate of WUE change (i.e., 0.004 g C kg(-1) H2O year(-1)), whereas the lowest WUE (i.e., 0.26 g C kg(-1) H2O) was found in steppe and alpine vegetation areas. Although all other vegetation types were associated with increasing WUE, there was no significant change in the WUE of steppe areas. The main factors influencing WUE fluctuation for different vegetation types were found to be atmospheric CO2 concentration and temperature change.