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https://doi.org/10.5194/egusphere-2025-2560
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2025-2560
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
16 Jul 2025
| 16 Jul 2025
Enhancing Evapotranspiration Estimates Under Climate Change: The Role of CO2 Physiological Feedback and CMIP6 Scenarios
Abstract. The future state of global evapotranspiration (ET) estimation under climate change remains uncertain. Current formulations primarily developed based on the high emission CMIP5 scenario, have been widely used to represent conditions under elevated greenhouse gas pathways. However, these formulations may not adequately capture the enhanced vegetation–climate interactions projected under the lower-emission scenarios of CMIP6. Without updates to account for evolving plant physiological responses to rising CO2, projections may overlook critical feedbacks between atmospheric CO2 concentrations, vegetation behavior, and hydrological processes.
To address this, developing CMIP6-specific formulations is essential to leverage its improved datasets and reduce uncertainties in future ET simulations. In this study, we update the Penman-Monteith evapotranspiration (PM-ET) model by incorporating the CO2-vegetation coupling effect. This is achieved using outputs from four Coupled Model Intercomparison Project Phase 6 (CMIP6) global climate models (GCMs) under four Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5).
Results indicate a sustained historical increase in potential evapotranspiration (Ep). Compared to earlier frameworks based on Coupled Model Intercomparison Project Phase (CMIP5) data, the inclusion of CO2 physiological effects reduces the deviation in projected ET trends by approximately 15–20 %, accounting for the increase in stomatal resistance driven by CO2 concentrations rising from ~284 ppm to ~935 ppm. Furthermore, our model predicts an increasing dependence of ET projections on emission scenario, highlighting the growing influence of pathway-specific feedbacks.
Overall, our approach demonstrates greater compatibility with CMIP6 simulations, allowing for more accurate representation of ET responses to future CO2 increases. These findings provide valuable insights for advancing the analysis of nonlinear vegetation-atmosphere interactions and hydrological uncertainty under climate and physiological forcings.
How to cite. Yang, X., Chen, Y., Qiu, H., Bento, V. A., Song, H., Shui, W., Zeng, J., and Wang, Q.: Enhancing Evapotranspiration Estimates Under Climate Change: The Role of CO2 Physiological Feedback and CMIP6 Scenarios, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-2560, 2025.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
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RC1: 'Comment on egusphere-2025-2560', Anonymous Referee #1, 06 Aug 2025
- AC1: 'Reply on RC1', Qianfeng Wang, 29 Aug 2025
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RC2: 'Comment on egusphere-2025-2560', Anonymous Referee #2, 18 Aug 2025
Publisher’s note: this comment was edited on 22 August 2025. The following text is not identical to the original comment, but the adjustments were minor without effect on the scientific meaning.This manuscript (EGUSPHERE-2025-2560, Enhancing Evapotranspiration Estimates Under Climate Change: The Role of CO2 Physiological Feedback and CMIP6 Scenarios) addresses a critical gap in evapotranspiration (ET) estimation under climate change by integrating CO2 physiological feedbacks with CMIP6 multi-scenario projections to update the Penman-Monteith (PM) model. The focus on nonlinear vegetation-atmosphere interactions also provides valuable insights for hydrological uncertainty analysis under global change. In general, this is a well-written manuscript, and it could be improved by polishing the analysis and figures. I recommend the publication of this work once a series of revisions have been carried out.1.Abstract Graph: The abstract diagram is too simple. Flow charts can be added to show the experimental ideas and writing background (such as how to derive new indicators, how to analyze, etc.) to enrich the content of abstract graph.2.Figure 5-8: There are different colors in the background. Unify their background colors (e.g., light gray/white) to avoid visual distraction and ensure coherence.3.In Section 2.1, the manuscript does not clearly explain the specific details of the time range division for CMIP6 data, such as whether the connection logic between the "historical period" (1861-2100) and the "future period" (2015-2100) are uniformly applicable to all GCMs. It is recommended to supplement the clear definition of the data time range to avoid confusion among readers regarding the analysis period.In Section 2.3.2(Line 194), the description part uses ET0 to refer to evaporation, but the corresponding formula does not have this variable, only Ep. It is suggested to unify the implied evaporation reference in this description and the formula.In Section 2.3.4, the specific steps of how this the updated PM-RC-CO2 model coefficient was derived from the four selected GCMs are not detailed. It is recommended to add a brief description of the calibration process, such as whether the coefficient is an ensemble mean of GCM-specific results or derived from a specific GCM to improve method reproducibility.6.The part 3.3 of the results is relatively single. It is recommended to enrich the analysis content and add some charts, such as the proportion of different land use types. This can more intuitively reflect the characteristics of underlying surface and provide more comprehensive background support for evapotranspiration (Ep) related results.7.Discussion(Line 427): Is the EP here the same as Ep in the previous paragraph? If so, it is recommended to change it to Ep to avoid misunderstanding.8. Section 5 (conclusion) mentions that "regional uncertainty stems from the heterogeneity of vegetation response", but does not specify which regions are more significant. It is suggested to add an explanatory sentence corresponding to recommendation and opinion 4 to make the conclusion more specific.Citation: https://doi.org/
10.5194/egusphere-2025-2560-RC2 - AC2: 'Reply on RC2', Qianfeng Wang, 29 Aug 2025
Status: closed
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
-
RC1: 'Comment on egusphere-2025-2560', Anonymous Referee #1, 06 Aug 2025
Reviewer Comments
This is a valuable paper that enhances evapotranspiration estimates by incorporating CO₂ physiological feedback and CMIP6 scenarios, which is of great significance for understanding hydrological processes under climate change. The study contributes to improving the accuracy of future ET projections and provides insights for related research.
The data and methodology are generally sound, and the manuscript is well-structured and comprehensive. This study extends previous research by updating the Penman-Monteith model based on CMIP6 data, and it fits within the scope of relevant journals, which will be of interest to readers.
I recommend this work for publication after some minor revisions.
Comments
- In the Abstract, the phrase "reduces the deviation in projected ET trends by approximately 15–20%" should be revised to "reduces the deviation in projected ET trends by approximately 15–20% compared to CMIP5-based frameworks" for improved clarity.
- The keywords are relevant, but it is suggested to add "Penman-Monteith model" to better reflect the methodological core.
- In the Introduction, when describing "Yang et al. (2019) model", it is recommended to supplement a brief note on its key parameter (e.g., original coefficient 2.4×10⁻⁴) to lay a clearer foundation for the subsequent update to 1.9×10⁻⁴.
- In Section 2.1, when mentioning "resampled to a uniform spatial resolution of 0.25° × 0.25°", it is suggested to specify the resampling method (e.g., bilinear interpolation) for reproducibility.
- In Section 2.2, the criteria for "non-water-limited regions" (e.g., "ET/P ratio < 2.0") are clear, but it is recommended to add a brief explanation of why this threshold is chosen (e.g., based on previous studies) to improve rigor.
- The formulas in Sections 2.3.2–2.3.4 use symbols like "s", "γ", and "u". It is suggested to add a unified list of symbols at the end of the paper or in an appendix to avoid confusion for readers.
- Figure 1 (Taylor diagrams) lacks explicit units for variables (e.g., relative humidity in %). It is recommended to add units in the figure caption to enhance clarity.
- In Section 3.2, "Ep intensification rates vary by scenario: under SSP5-8.5, the decadal increase is approximately 2.1%" – it is suggested to specify the reference period (e.g., relative to 2015–2025) for this rate.
- Figure 5 (time series decomposition) has subplots labeled (a)–(d) corresponding to SSP scenarios, but the caption does not explicitly link each subplot to the scenario (e.g., "(a) SSP1-2.6, (b) SSP2-4.5..."). It is recommended to add this correspondence to help readers.
- In Section 4.1, "low-emission scenarios exhibit more dispersed distribution across models", but it is suggested to briefly cite 1–2 relevant studies (e.g., Pan et al., 2020) to support this observation and strengthen the discussion.
- The limitations section (4.2) notes that the model "assumes fixed vegetation responses to CO₂". It is suggested to add a short sentence on how future work could relax this assumption (e.g., integrating species-specific parameters) to make the prospects more concrete.
- In the Conclusion, "improved consistency with CMIP6 data" is suggested to be rephrased as "improved consistency with CMIP6 simulations" to align with terminology used in the main text.
Citation: https://doi.org/10.5194/egusphere-2025-2560-RC1 - AC1: 'Reply on RC1', Qianfeng Wang, 29 Aug 2025
-
RC2: 'Comment on egusphere-2025-2560', Anonymous Referee #2, 18 Aug 2025
Publisher’s note: this comment was edited on 22 August 2025. The following text is not identical to the original comment, but the adjustments were minor without effect on the scientific meaning.This manuscript (EGUSPHERE-2025-2560, Enhancing Evapotranspiration Estimates Under Climate Change: The Role of CO2 Physiological Feedback and CMIP6 Scenarios) addresses a critical gap in evapotranspiration (ET) estimation under climate change by integrating CO2 physiological feedbacks with CMIP6 multi-scenario projections to update the Penman-Monteith (PM) model. The focus on nonlinear vegetation-atmosphere interactions also provides valuable insights for hydrological uncertainty analysis under global change. In general, this is a well-written manuscript, and it could be improved by polishing the analysis and figures. I recommend the publication of this work once a series of revisions have been carried out.1.Abstract Graph: The abstract diagram is too simple. Flow charts can be added to show the experimental ideas and writing background (such as how to derive new indicators, how to analyze, etc.) to enrich the content of abstract graph.2.Figure 5-8: There are different colors in the background. Unify their background colors (e.g., light gray/white) to avoid visual distraction and ensure coherence.3.In Section 2.1, the manuscript does not clearly explain the specific details of the time range division for CMIP6 data, such as whether the connection logic between the "historical period" (1861-2100) and the "future period" (2015-2100) are uniformly applicable to all GCMs. It is recommended to supplement the clear definition of the data time range to avoid confusion among readers regarding the analysis period.In Section 2.3.2(Line 194), the description part uses ET0 to refer to evaporation, but the corresponding formula does not have this variable, only Ep. It is suggested to unify the implied evaporation reference in this description and the formula.In Section 2.3.4, the specific steps of how this the updated PM-RC-CO2 model coefficient was derived from the four selected GCMs are not detailed. It is recommended to add a brief description of the calibration process, such as whether the coefficient is an ensemble mean of GCM-specific results or derived from a specific GCM to improve method reproducibility.6.The part 3.3 of the results is relatively single. It is recommended to enrich the analysis content and add some charts, such as the proportion of different land use types. This can more intuitively reflect the characteristics of underlying surface and provide more comprehensive background support for evapotranspiration (Ep) related results.7.Discussion(Line 427): Is the EP here the same as Ep in the previous paragraph? If so, it is recommended to change it to Ep to avoid misunderstanding.8. Section 5 (conclusion) mentions that "regional uncertainty stems from the heterogeneity of vegetation response", but does not specify which regions are more significant. It is suggested to add an explanatory sentence corresponding to recommendation and opinion 4 to make the conclusion more specific.Citation: https://doi.org/
10.5194/egusphere-2025-2560-RC2 - AC2: 'Reply on RC2', Qianfeng Wang, 29 Aug 2025
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Xiaofan Yang
College of Environment & Safety Engineering, Fuzhou University, Fuzhou, 350116, China
Yu Chen
School of Public Administration and Policy, RENMIN UNIVERSITY OF CHINA, Beijing, 100872, China
Department of Sustainable Earth System Sciences, University of Texas at Dallas, Richardson, TX, USA
Virgílio A. Bento
University of Lisbon, Faculty of Sciences, Instituto Dom Luiz, Lisbon, Portugal
Hongquan Song
College of Geography and Environmental Science, Henan University, 475004 Kaifeng, China
Wei Shui
College of Environment & Safety Engineering, Fuzhou University, Fuzhou, 350116, China
Jingyu Zeng
College of Environment & Safety Engineering, Fuzhou University, Fuzhou, 350116, China
College of Environment & Safety Engineering, Fuzhou University, Fuzhou, 350116, China
Short summary
The future of global evaporation under climate change remains uncertain. The current ET model relies primarily on high emission CMIP5 scenarios and does not fully represent the enhanced vegetation-climate interaction in CMIP6 low emission scenarios. Updated models using output of four CMIP6 GCMs under four SSPs show that ET projections will become increasingly dependent on emissions scenarios.
The future of global evaporation under climate change remains uncertain. The current ET model...
Reviewer Comments
This is a valuable paper that enhances evapotranspiration estimates by incorporating CO₂ physiological feedback and CMIP6 scenarios, which is of great significance for understanding hydrological processes under climate change. The study contributes to improving the accuracy of future ET projections and provides insights for related research.
The data and methodology are generally sound, and the manuscript is well-structured and comprehensive. This study extends previous research by updating the Penman-Monteith model based on CMIP6 data, and it fits within the scope of relevant journals, which will be of interest to readers.
I recommend this work for publication after some minor revisions.
Comments