Preprints
https://doi.org/10.5194/hess-2020-548
https://doi.org/10.5194/hess-2020-548

  14 Dec 2020

14 Dec 2020

Review status: a revised version of this preprint is currently under review for the journal HESS.

Low and contrasting impacts of vegetation CO2 fertilization on terrestrial runoff over the past three decades: Accounting for above- and below-ground vegetation-CO2 effects

Yuting Yang1, Tim R. McVicar2,3, Dawen Yang1, Yongqiang Zhang4, Shilong Piao5, Shushi Peng5, and Hylke E. Beck6 Yuting Yang et al.
  • 1State Key Laboratory of Hydroscience and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing, China
  • 2CSIRO Land and Water, Black Mountain, Canberra, ACT 2601, Australia
  • 3Australian Research Council Centre of Excellence for Climate Extremes, The Australian National University, Canberra, Australia
  • 4Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China
  • 5Sino-French Institute for Earth System Science, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China
  • 6Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey, USA

Abstract. Elevation in atmospheric carbon dioxide concentration (eCO2) affects vegetation water use, with consequent impacts on terrestrial runoff (Q). However, the sign and magnitude of the eCO2 effect on Q is still contentious. This is partly due to the poor understanding of the opposing eCO2-induced water effects at different scales, being water-saving caused by partial stomatal closure at the leaf-level contrasting with increased water-consumption due to increase foliage cover at the canopy level, leading to highly debated findings among existing studies. None of the existing studies implicitly account for eCO2-induced changes to below-ground vegetation functioning. Here we develop an analytical eco-hydrological framework that includes the effects of eCO2 on plant leaf, canopy density, and rooting characteristics to attribute changes in Q and detect the eCO2 signal on Q over the past three decades. Globally, we detect a very small decrease of Q induced by eCO2 during 1982–2010 (−1.69 %). When assessed locally, along the resource availability (α) gradient, a positive trend (p < 0.01) in the Q-eCO2 response is found ranging from a negative response (i.e., eCO2 reduces Q) in low α regions (typically dry) to a positive response (i.e., eCO2 increases Q) in high α areas (typically warm and humid). Our findings suggest a minor role of eCO2 on changes in global Q over the past three decades, yet highlights the negative Q-eCO2 response in semi-arid and arid regions which may further reduce the limited water resource there.

Yuting Yang et al.

 
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Yuting Yang et al.

Yuting Yang et al.

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Short summary
This study developed an analytical eco-hydrological model that considers three aspects of vegetation response to eCO2 (i.e., stomatal response, LAI response and rooting depth response) to detect the impact of eCO2 on continental runoff over the past three decades globally. Our findings suggest a minor role of eCO2 on the global runoff changes, yet highlight the negative runoff-eCO2 response in semi-arid and arid regions which may further threaten the limited water resource there.