Greening-induced increase in evapotranspiration over Eurasia offset by CO 2 -induced vegetational stomatal closure

• Published in: Environmental research letters 2021-12, Vol.16 (12), p.124008
• Main Authors: Zhang, Xuanze, Zhang, Yongqiang, Ma, Ning, Kong, Dongdong, Tian, Jing, Shao, Xingmin, Tang, Qiuhong
• Format: Article
• Language: English
• ISSN: 1748-9326; 1748-9326
• DOI: 10.1088/1748-9326/ac3532

Evapotranspiration (ET), as a key exchanging component of the land energy, water and carbon cycles, is expected to increase in response to greening land under a warming climate. However, the relative importance of major drivers (e.g. leaf area index (LAI), climate forcing, atmospheric CO 2 , etc) to long-term ET change remain largely unclear. Focusing on the Eurasia which experienced the strong vegetational greening, we aim to estimate the long-term ET trend and its drivers’ relative contributions by applying a remote sensing-based water-carbon coupling model— Penman–Monteith–Leuning version 2 (PML-V2) driven by observational climate forcing and CO 2 records, and satellite-based LAI, albedo and emissivity. The PML-V2 estimated an increasing ET trend (6.20 ± 1.13 mm year −1 decade −1 , p < 0.01) over Eurasia during 1982–2014, which is close to the ensemble mean (6.51 ± 3.10 mm year −1 decade −1 ) from other three ET products (GLEAMv3.3a, ERA5 and CRv1.0). The PML-based ET overall agrees well with water-balance derived ET in detecting the trend directions. We find that the Eurasian ET increasing trend was mostly from vegetated regions over central and eastern Europe, Indian and southeast China where ET trends were larger than 20 mm year −1 decade −1 . Modeling sensitivity experiments indicate that the Eurasian ET trend was mainly dominated by positive contributions from climate forcing change (40%) and increased LAI (22%), but largely offset by a negative contribution of increased CO 2 (26%). Our results highlight the importance of the suppression effect of increasing CO 2 -induced stomatal closure on transpiration. This effect was rarely considered in diagnostic ET products but plays a key role to ensure that the long-term ET trend should not be overestimated by only accounting for greening-induced increases in transpiration and rainfall interception.