Partitioning global land evapotranspiration using CMIP5 models constrained by observations

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Abstract

The ratio of plant transpiration to total terrestrial evapotranspiration (T/ET) captures the role of vegetation in surface–atmosphere interactions. However, its magnitude remains highly uncertain at the global scale. Here we apply an emergent constraint approach that integrates CMIP5 Earth system models (ESMs) with 33 field T/ET measurements to re-estimate the global T/ET value. Our observational constraint strongly increases the original ESM estimates (0.41 ± 0.11) and greatly alleviates intermodel discrepancy, which leads to a new global T/ET estimate of 0.62 ± 0.06. For all the ESMs, the leaf area index is identified as the primary driver of spatial variations of T/ET, but to correct its bias generates a larger T/ET underestimation than the original ESM output. We present evidence that the ESM underestimation of T/ET is, instead, attributable to inaccurate representation of canopy light use, interception loss and root water uptake processes in the ESMs. These processes should be prioritized to reduce model uncertainties in the global hydrological cycle.

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Fig. 1: Simulated and observation-based estimates of T/ET at the global and stand levels.
Fig. 2: Emergent constraint on the model-simulated global T/ET.
Fig. 3: Contribution of environmental drivers to spatial variations of T/ET in ESMs.
Fig. 4: Implications for the model-derived T/ET of replacing dominant drivers with observations.
Fig. 5: Impact of modelled T/ET on the runoff responses to rising atmospheric CO2.

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Acknowledgements

This study was supported by the National Natural Science Foundation of China (41561134016 and 41530528), the 111 Project (B14001) and the National Youth Top-notch Talent Support Program in China. C.H. is grateful for funding from the Centre for Ecology and Hydrology National Capability fund in the UK.

Author information

S.P. designed the research; X.L. performed the analysis; X.L., S.P. and C.H. drafted the paper and all the authors contributed to the interpretation of the results and to the text.

Correspondence to Shilong Piao.

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Supplementary Text 1–4, Supplementary Tables 1–4, Supplementary Figures 1–7

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Lian, X., Piao, S., Huntingford, C. et al. Partitioning global land evapotranspiration using CMIP5 models constrained by observations. Nature Clim Change 8, 640–646 (2018) doi:10.1038/s41558-018-0207-9

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