the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Jun 2024
On the Estimation of Global Plant Water Requirement
Abstract. Water supply is the most critical constraint for vegetation growth and food security. The amount of water demand by plant growth is usually estimated by plant water requirement which unfortunately cannot be directly measured at any large scale in field conditions. Different estimation methods have been proposed in the past seven decades for estimating plant water requirements using the concept of reference evapotranspiration (ET0) methods or potential evapotranspiration (PET) methods. In addition, using PET or ET0 to estimate actual evapotranspiration (ETa) is a critical approach in hydrological and climate models. However, different PET or ET0 models provide diverse results for irrigation water requirement (IWR) that in turn may result in a huge waste of irrigation water. Here, we assess the suitability of six common methods for estimating PET at 170 eddy covariance flux sites and propose a practical approach for estimating the IWR using a physically consistent model STEMMUS-SCOPE.
Notably, the Priestley-Taylor and LSA_SAF method excels in providing reasonable approximations of daily PET. Consequently, in scenarios where net radiation data and ground heat flux are accessible, the Priestley-Taypor method emerges as the recommended choice. The LSA_SAF method is the better one when only net radiation data is available. Alternatively, in cases where only global radiation data is available, the Makkink and Hargreaves methods serve as viable substitutes. Although the FAO56 Penman-Monteith method is much better than the original Penman-Monteith method when wind speed and air humidity data are at hand, its suitability falls short of the preferred status. This study contributes to understanding and quantifying the applicability of different methods in estimating PET and IWR, based on input data availability and physical considerations.
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CC1: 'a few papers for reference', Joshua Fisher, 03 Jun 2024
This paper by Maes et al (2019) is very similar:
https://hess.copernicus.org/articles/23/925/2019/
Maes followed on preliminary work testing PET models at EC sites presented here:
Palmer, C., Fisher, J. B., Mallick, K., and Lee, J.: The Potential of Potential Evapotranspiration, Fall Meeting, 3–7 December 2012, American Geophysical Union, San Francisco, 2012.
Palmer followed on earlier work testing PET models at EC here:
Fisher, J.B., DeBiase, T.A., Qi, Y., Xu, M., Goldstein, A.H., 2005. Evapotranspiration models compared on a Sierra Nevada forest ecosystem. Environmental Modelling & Software 20(6): 783-796.
Also see for reference:
Fisher, J.B., Whittaker, R., Malhi, Y., 2011. ET Come Home: Potential evapotranspiration in geographical ecology. Global Ecology and Biogeography 20: 1-18.
Citation: https://doi.org/10.5194/egusphere-2024-1321-CC1 -
AC1: 'Reply on CC1', Yunfei Wang, 13 Jun 2024
Dear Prof. Joshua,
Many thanks for providing a series of very valuable references. It has given me a more systematic understanding of these studies. We will add further discussions in the revised version based on them.
Best, Yunfei
Citation: https://doi.org/10.5194/egusphere-2024-1321-AC1
-
AC1: 'Reply on CC1', Yunfei Wang, 13 Jun 2024
-
RC1: 'Comment on egusphere-2024-1321', Anonymous Referee #1, 06 Jul 2024
Reviewer Comments on "On the Estimation of Global Plant Water Requirement"
Decision: Reject and may resubmit
The manuscript presents an analysis of six different Potential Evapotranspiration (PET) methods using data from 170 flux sites, with an additional aim to link these analyses to irrigation water requirements (IWR). While the paper extends the dataset size compared to Wouter et al.'s 2019 study, there are significant issues that need addressing before this work can be considered for publication in the HESS journal.
- Clarity of research contribution: The manuscript claims to enhance the understanding and quantification of different PET and IWR estimation methods based on data availability and physical considerations (L23). However, the contribution in terms of IWR is not clearly demonstrated in the results or discussed in the conclusion. It would strengthen the paper to explicitly quantify and discuss the differences and implications of these estimation methods on IWR.
- Structure and cohesion: The paper is structured around two main objectives: validating various PET methods and proposing a model for IWR calculation. However, the connection between these objectives is not well articulated, leaving the reader unclear on how they interrelate and support a cohesive thesis. The introduction fails to link these sections logically, and the conclusion briefly mentions IWR without integrating it into the key findings. Further, the description and justification of the STEMMUS-SCOPE model used are insufficiently detailed. This model is very important as the PET calculated by this model is used as a reference to assess the 6 PET formulas. Then I am curious about how this model works, if it works better than 6 PET formulas, and how accurate/uncertain this model is. However, this information is largely ignored in this paper.
- Terminology and definitions: What is the meaning and definition of plant water requirement? It appears once in the title and twice in the abstract, and then disappears in the rest of the text. Is plant water requirement equal to PET, ET0, or IWR? A precise definition of each term at the outset, and consistent usage throughout the paper, are necessary to ensure clarity and professionalism.
- Introduction: The introduction is not well-organized with convincing logical lines, which leads to your research questions. In the whole paragraph from L44 to Line L52, there is no one reference to support your description, which is not a professional way of academic writing. For example, in the sentence “Across various research endeavors, semi-empirical methods and process-based models have demonstrated noteworthy prolificacy in ET0 estimation by leveraging the limited climatic variables as inputs.”, references are needed to demonstrate “Across various research endeavors”.
- Figures: The figure 1 and 3 suffer from low resolution. The width of the bars in Figure 3 should be the same.
Summary: The manuscript could have potential but requires significant revisions for research questions, narrative flow, and overall manuscript presentation, particularly in defining and integrating its key components—PET and IWR estimation. I recommend a thorough restructuring to better align this journal's expectations.
Citation: https://doi.org/10.5194/egusphere-2024-1321-RC1 - AC2: 'Reply on RC1', Yunfei Wang, 29 Jul 2024
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RC2: 'Comment on egusphere-2024-1321', Anonymous Referee #2, 07 Jul 2024
This paper evaluates methods to calculate Potential Evapotranspiration (PET) by comparing them with PET simulated by STEMMUS-SCOPE model at 170 sites. It calculates Irrigation Water Requirement (IWR) as the difference between PET and Actual Evapotranspiration (ETa) simulated by STEMMUS-SCOPE. It seems that these two objectives are not well connected as the results of PET methods does not add any information to the calculation of IWR. If the authors aim to use STEMMUS-SCOPE ETa and ET0 to calculate IWR, why needs to validate other 6 methods considering simulated ET0 as the reference? What is the relevance or significance of calculating IWR for natural land covers (i.e., forest, shrubland)? Why do we need to (know how much to) irrigate these natural vegetations and wetlands?
The paper seems to assume that FAOPM ET0 and PET (of other 5 methods) estimate the same quantity, which is inaccurate by definition. FAOPM is not comparable to other PET methods. It is the only of the 6 methods that calculates PET for a hypothetical reference crop, hence called Reference ET. Even Allen et al. (1998, chapter 1) strongly discouraged using the term PET due to its definition ambiguities, which distinguishes this method from other PET methods. Raza et al. (2022) also showed the difference in definition and purpose of RET (ET0) and PET through a systematic review. Indeed, hydrologists should not use FAOPM RET as a reference to compare with PET by other methods (also mentioned in L58). Then why is FAOPM RET compared with other PET methods here?
This difference in definition might also be the reason for FAOPM to differ greatly from other methods, except when the authors compare them over a vegetation surface with closer characteristics to the FAOPM hypothetical reference crop (e.g., GRA, CRO in Figure S2.1-4). It would make more sense to compare PET methods with FAOPM ETc which is closer to PET definition: the crop evapotranspiration under well-watered and optimal agronomic conditions.
Figure 2: Why does the distribution of ET0s look remarkably lower than ETas for DBF, ENF, GRA, and MF? Can WSF be greater than 1? By definition, ETa should never be higher than ET0 (Fisher et al., 2010). This makes the method to derive ET0 by using STEMMUS-SCOPE simulated ETa and WSF seem not reliable. If so, it should not be used as a reference to evaluate the other PET methods.
Section 2.5 mentions FAO for the calculation of IWR, but lack references. If the authors referred to the FAO-56 guideline, this method is inaccurate according to the definition in this guideline. Allen et al. (1998) defined IWR = CWR – Peffective, where CWR is ET0 * Kc and Peffective is calculated as detailed in Doorenbos et al. (1977). Therefore, IWR is not the same as ET0 – ETa, which is equal to (1-Kc)*ET0. The equation 9 and 10 seem to be authors’ own derivation based on Figure 4. I wonder why the sign of Percolation is negative on the right side of these equation. Shouldn’t it have the same sign as Runoff, since they are both ‘outflows’ from the crop root zone to groundwater storage? Why does Recharge have an upward arrow in Figure 4?
Introduction lacks a lot of references. The whole paragraph L44-L56, there’s not a single reference to any of the claims.
Minor comments
- L65: FAOPM does not use alfalfa as reference. Maybe you mean ASCE method?
- L66: references?
- L71-72: ETas and ET0s. I suggest explaining that ‘s’ means simulated
- L96 & Table 1: suggest to make it clearer which methods are considered radiation-based, resistance-based, global radiation & temperature-based
- Section 2.3.4: How was ga calculated?
- L123: even if with wet surface, the stomata cannot be as open as a water surface. Therefore, gs cannot be infinity.
- L145: references?
- Figure 3: some bars looks exceeding the maximum value of y-axis. It’s not easy to tell if these are much higher than ymax.
References
Allen, R.G., Pereira, L.S., Raes, D. and Smith, M., 1998. Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. Fao, Rome, 300(9), p.D05109.
Doorenbos, J., William O Pruitt, and A Aboukhaled. Guidelines for Predicting Crop Water Requirements. Rev. Rome: FAO, 1977.
Fisher, J.B., Whittaker, R.J. and Malhi, Y., 2011. ET come home: potential evapotranspiration in geographical ecology. Global Ecology and Biogeography, 20(1), pp.1-18.
Raza, A., Al-Ansari, N., Hu, Y., Acharki, S., Vishwakarma, D.K., Aghelpour, P., Zubair, M., Wandolo, C.A. and Elbeltagi, A., 2022. Misconceptions of reference and potential evapotranspiration: A PRISMA-guided comprehensive review. Hydrology, 9(9), p.153.
Citation: https://doi.org/10.5194/egusphere-2024-1321-RC2 - AC3: 'Reply on RC2', Yunfei Wang, 29 Jul 2024
Status: closed
-
CC1: 'a few papers for reference', Joshua Fisher, 03 Jun 2024
This paper by Maes et al (2019) is very similar:
https://hess.copernicus.org/articles/23/925/2019/
Maes followed on preliminary work testing PET models at EC sites presented here:
Palmer, C., Fisher, J. B., Mallick, K., and Lee, J.: The Potential of Potential Evapotranspiration, Fall Meeting, 3–7 December 2012, American Geophysical Union, San Francisco, 2012.
Palmer followed on earlier work testing PET models at EC here:
Fisher, J.B., DeBiase, T.A., Qi, Y., Xu, M., Goldstein, A.H., 2005. Evapotranspiration models compared on a Sierra Nevada forest ecosystem. Environmental Modelling & Software 20(6): 783-796.
Also see for reference:
Fisher, J.B., Whittaker, R., Malhi, Y., 2011. ET Come Home: Potential evapotranspiration in geographical ecology. Global Ecology and Biogeography 20: 1-18.
Citation: https://doi.org/10.5194/egusphere-2024-1321-CC1 -
AC1: 'Reply on CC1', Yunfei Wang, 13 Jun 2024
Dear Prof. Joshua,
Many thanks for providing a series of very valuable references. It has given me a more systematic understanding of these studies. We will add further discussions in the revised version based on them.
Best, Yunfei
Citation: https://doi.org/10.5194/egusphere-2024-1321-AC1
-
AC1: 'Reply on CC1', Yunfei Wang, 13 Jun 2024
-
RC1: 'Comment on egusphere-2024-1321', Anonymous Referee #1, 06 Jul 2024
Reviewer Comments on "On the Estimation of Global Plant Water Requirement"
Decision: Reject and may resubmit
The manuscript presents an analysis of six different Potential Evapotranspiration (PET) methods using data from 170 flux sites, with an additional aim to link these analyses to irrigation water requirements (IWR). While the paper extends the dataset size compared to Wouter et al.'s 2019 study, there are significant issues that need addressing before this work can be considered for publication in the HESS journal.
- Clarity of research contribution: The manuscript claims to enhance the understanding and quantification of different PET and IWR estimation methods based on data availability and physical considerations (L23). However, the contribution in terms of IWR is not clearly demonstrated in the results or discussed in the conclusion. It would strengthen the paper to explicitly quantify and discuss the differences and implications of these estimation methods on IWR.
- Structure and cohesion: The paper is structured around two main objectives: validating various PET methods and proposing a model for IWR calculation. However, the connection between these objectives is not well articulated, leaving the reader unclear on how they interrelate and support a cohesive thesis. The introduction fails to link these sections logically, and the conclusion briefly mentions IWR without integrating it into the key findings. Further, the description and justification of the STEMMUS-SCOPE model used are insufficiently detailed. This model is very important as the PET calculated by this model is used as a reference to assess the 6 PET formulas. Then I am curious about how this model works, if it works better than 6 PET formulas, and how accurate/uncertain this model is. However, this information is largely ignored in this paper.
- Terminology and definitions: What is the meaning and definition of plant water requirement? It appears once in the title and twice in the abstract, and then disappears in the rest of the text. Is plant water requirement equal to PET, ET0, or IWR? A precise definition of each term at the outset, and consistent usage throughout the paper, are necessary to ensure clarity and professionalism.
- Introduction: The introduction is not well-organized with convincing logical lines, which leads to your research questions. In the whole paragraph from L44 to Line L52, there is no one reference to support your description, which is not a professional way of academic writing. For example, in the sentence “Across various research endeavors, semi-empirical methods and process-based models have demonstrated noteworthy prolificacy in ET0 estimation by leveraging the limited climatic variables as inputs.”, references are needed to demonstrate “Across various research endeavors”.
- Figures: The figure 1 and 3 suffer from low resolution. The width of the bars in Figure 3 should be the same.
Summary: The manuscript could have potential but requires significant revisions for research questions, narrative flow, and overall manuscript presentation, particularly in defining and integrating its key components—PET and IWR estimation. I recommend a thorough restructuring to better align this journal's expectations.
Citation: https://doi.org/10.5194/egusphere-2024-1321-RC1 - AC2: 'Reply on RC1', Yunfei Wang, 29 Jul 2024
-
RC2: 'Comment on egusphere-2024-1321', Anonymous Referee #2, 07 Jul 2024
This paper evaluates methods to calculate Potential Evapotranspiration (PET) by comparing them with PET simulated by STEMMUS-SCOPE model at 170 sites. It calculates Irrigation Water Requirement (IWR) as the difference between PET and Actual Evapotranspiration (ETa) simulated by STEMMUS-SCOPE. It seems that these two objectives are not well connected as the results of PET methods does not add any information to the calculation of IWR. If the authors aim to use STEMMUS-SCOPE ETa and ET0 to calculate IWR, why needs to validate other 6 methods considering simulated ET0 as the reference? What is the relevance or significance of calculating IWR for natural land covers (i.e., forest, shrubland)? Why do we need to (know how much to) irrigate these natural vegetations and wetlands?
The paper seems to assume that FAOPM ET0 and PET (of other 5 methods) estimate the same quantity, which is inaccurate by definition. FAOPM is not comparable to other PET methods. It is the only of the 6 methods that calculates PET for a hypothetical reference crop, hence called Reference ET. Even Allen et al. (1998, chapter 1) strongly discouraged using the term PET due to its definition ambiguities, which distinguishes this method from other PET methods. Raza et al. (2022) also showed the difference in definition and purpose of RET (ET0) and PET through a systematic review. Indeed, hydrologists should not use FAOPM RET as a reference to compare with PET by other methods (also mentioned in L58). Then why is FAOPM RET compared with other PET methods here?
This difference in definition might also be the reason for FAOPM to differ greatly from other methods, except when the authors compare them over a vegetation surface with closer characteristics to the FAOPM hypothetical reference crop (e.g., GRA, CRO in Figure S2.1-4). It would make more sense to compare PET methods with FAOPM ETc which is closer to PET definition: the crop evapotranspiration under well-watered and optimal agronomic conditions.
Figure 2: Why does the distribution of ET0s look remarkably lower than ETas for DBF, ENF, GRA, and MF? Can WSF be greater than 1? By definition, ETa should never be higher than ET0 (Fisher et al., 2010). This makes the method to derive ET0 by using STEMMUS-SCOPE simulated ETa and WSF seem not reliable. If so, it should not be used as a reference to evaluate the other PET methods.
Section 2.5 mentions FAO for the calculation of IWR, but lack references. If the authors referred to the FAO-56 guideline, this method is inaccurate according to the definition in this guideline. Allen et al. (1998) defined IWR = CWR – Peffective, where CWR is ET0 * Kc and Peffective is calculated as detailed in Doorenbos et al. (1977). Therefore, IWR is not the same as ET0 – ETa, which is equal to (1-Kc)*ET0. The equation 9 and 10 seem to be authors’ own derivation based on Figure 4. I wonder why the sign of Percolation is negative on the right side of these equation. Shouldn’t it have the same sign as Runoff, since they are both ‘outflows’ from the crop root zone to groundwater storage? Why does Recharge have an upward arrow in Figure 4?
Introduction lacks a lot of references. The whole paragraph L44-L56, there’s not a single reference to any of the claims.
Minor comments
- L65: FAOPM does not use alfalfa as reference. Maybe you mean ASCE method?
- L66: references?
- L71-72: ETas and ET0s. I suggest explaining that ‘s’ means simulated
- L96 & Table 1: suggest to make it clearer which methods are considered radiation-based, resistance-based, global radiation & temperature-based
- Section 2.3.4: How was ga calculated?
- L123: even if with wet surface, the stomata cannot be as open as a water surface. Therefore, gs cannot be infinity.
- L145: references?
- Figure 3: some bars looks exceeding the maximum value of y-axis. It’s not easy to tell if these are much higher than ymax.
References
Allen, R.G., Pereira, L.S., Raes, D. and Smith, M., 1998. Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. Fao, Rome, 300(9), p.D05109.
Doorenbos, J., William O Pruitt, and A Aboukhaled. Guidelines for Predicting Crop Water Requirements. Rev. Rome: FAO, 1977.
Fisher, J.B., Whittaker, R.J. and Malhi, Y., 2011. ET come home: potential evapotranspiration in geographical ecology. Global Ecology and Biogeography, 20(1), pp.1-18.
Raza, A., Al-Ansari, N., Hu, Y., Acharki, S., Vishwakarma, D.K., Aghelpour, P., Zubair, M., Wandolo, C.A. and Elbeltagi, A., 2022. Misconceptions of reference and potential evapotranspiration: A PRISMA-guided comprehensive review. Hydrology, 9(9), p.153.
Citation: https://doi.org/10.5194/egusphere-2024-1321-RC2 - AC3: 'Reply on RC2', Yunfei Wang, 29 Jul 2024
Data sets
STEMMUS-SCOPE for PLUMBER2: A Physically Consistent Dataset Across the Soil-Plant-Atmosphere Continuum Yunfei Wang et al. https://zenodo.org/records/11057907
Model code and software
STEMMUS-SCOPE Yunfei Wang et al. https://github.com/EcoExtreML/STEMMUS_SCOPE
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