Increasing Tibetan Plateau terrestrial evapotranspiration primarily driven by precipitation

While terrestrial evapotranspiration (ET) from the Tibetan Plateau (TP) plays a key role in modulating water storage change in the Asian Water Tower, the magnitude, trend, and drivers of ET remain poorly understood in this region due partially to sparse ground measurements. This study used a water-carbon coupled biophysical model, Penman-Monteith-Leuning Version 2 (PML_V2), to characterize the variations in ET across TP during 1982-2016 and its drivers. Model parameters of PML_V2 were calibrated against ground-observed data from 14 eddy-covariance flux towers. Plot- and basin-scale validations demonstrate that the PML_V2 is robust enough in simulating both magnitude and trend in ET. The 35-year mean annual ET rates decrease from the southeastern to the northwestern TP, leading to a TP-averaged value of 353 +/- 24 mm yr(-1). Soil evaporation is the main component (64%) of ET, followed by plant transpiration (31%) and canopy evaporation (5%). From 1982 to 2016, TP-averaged ET increased significantly with a rate of 1.87 +/- 0.25 mm yr(-2) (p < 0.001) due primarily to precipitation enhancement. Spatially, precipitation is the dominant driver that controls ET trend over most parts of TP except certain regions in the southeastern and eastern TP, where net radiation and temperature do so instead, respectively. This is because 68% of the TP area is dryland with the aridity index < 0.65. While LAI appears less important than climate factors over much of TP, its relative contribution to ET trend exceeds 20% in many parts of eastern TP, indicating that vegetation change played a nonnegligible role in regulating annual ET variations over certain regions where LAI varied substantially. Our results are of vital importance for facilitating the understanding of hydrological processes over the Asian Water Tower.

Automated summary

This study investigates the terrestrial evapotranspiration (ET) from the Tibetan Plateau (TP) using a water-carbon coupled model. It finds that the TP-averaged ET has increased, primarily due to increased precipitation. However, the driving factors for ET vary across different regions of the TP.