Exploring the influence of environmental factors in partitioning evapotranspiration along an elevation gradient on Mount Gongga, eastern edge of the Qinghai-Tibet Platea, China

Abstract

Evapotranspiration (ET) is a crucial part of the global hydrological cycle, and quantifying ET components is significant for understanding the global water cycle and energy balance. However, there is no consensus on the value of ET components, especially in topographic abrupt change zone, such as eastern margin of the Qinghai-Tibet Platea, where values of ET changes along the altitudinal gradients. Our aim is to explore the influencing factors in partitioning evapotranspiration and how ET components change with increasing elevations. A novel approach was proposed to estimate ET components by adding net solar radiation (Rn) instead of the vapor pressure deficit (VPD) into the underlying water use efficiency (uWUE) model based on one-year continuous measurements of flux data along the elevation gradient on Mount Gongga. Correlation analysis shows that the uWUE model’s performance can be improved significantly by considering Rn instead of VPD, with correlation coefficients increasing by 35%–64%. The ratios of transpiration (T) to ET (T/ET) were 0.47, 0.48, 0.50 and 0.35 for the deciduous broadleaf forest (BF), mixed coniferous and deciduous broadleaf forest (MF), evergreen needle forest (ENF) and shrub land (SL), respectively. Leaf area index (LAI) and air temperature (Ta) were the two main controlling factors in determining T/ET during the growing season and at an annual scale, while Rn and Ta played more important roles during the dormant season. This study highlights the importance of incorporating Rn in partitioning evapotranspiration by using the water use efficiency (WUE) method in a humid mountainous region, which can improve the estimation of T/ET on a global scale.