A Comprehensive Evaluation of Evapotranspiration in Mainland Portugal Based on Climate Reanalysis Data
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsReview report for ‘A comprehensive comparative study on evapotranspiration in mainland Portugal based on Climate reanalysis data’
The authors present an evaluation of different reference ET estimates calculated with different datasets and models to investigate the spatial and temporal patterns for mainland Portugal. The study found that the reference ET has increased over the last 40 years with an accelerated rate in the recent two decades. Those are important findings and will help to better understand the challenges in the coming decades and provide inside for policy makers and researchers alike to work on solutions.
The introduction is providing insight and context to the importance of study and what research already has been done by others to support the need of this study. The study area is well described with a nice map. The data, result and discussion sections are well written and describe the process undertaken, as well as the results very well. While reading through those sections I noticed that certain paragraphs were reading like results but were for example in the data sections, etc. Another example is that there are equations in the results section, usually all equations are in the methods sections.
I would recommend you reorganize the manuscript, so the different sections have only content in it that is more in line with the section. For example, in the results section you usually only report on the findings of the calculations YOU did with text and maps. Then in the discussion section you explain your results and what they mean in the context to other studies. You have all the pieces already beautifully written in the manuscript, just some reorganization would make the paper even stronger.
Some specific examples which paragraphs I suggest along with text edits and additional comments are provided in the text itself (in-line). Thank you for working on this important topic.
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
I have carefully reviewed the manuscript _ A Comprehensive Comparative Study on Evapotranspiration in Mainland Portugal Based on Climate Reanalysis Data.
Overall, the manuscript is scientifically sound, methodologically robust, and well aligned with the scope of Atmosphere. The methodological approach is appropriate and clearly described. The figures and maps are informative, well designed, and effectively support the results.
- Points Requiring Minor Revision
While the manuscript is of high quality, a few points should be addressed to further strengthen clarity and atmospheric framing, these are:
- Conceptual clarification (Ep vs. ETo) - Although technically correct, the manuscript would benefit from more explicitly stating, particularly in the Abstract and Introduction, that ETo is interpreted as a measure of atmospheric evaporative demand rather than an agronomic variable.
- Atmospheric framing in the Discussion - Some parts of the Discussion and Conclusion place strong emphasis on hydrological management aspects (e.g., reservoirs, irrigation, water planning). These aspects are relevant but should remain secondary and clearly framed as consequences of atmospheric processes, to maintain a strong atmospheric/climatological focus.
- Physical interpretation of trends - The observed strengthening of ETo trends, particularly in summer and early autumn during the recent period (2002–2023), would benefit from a slightly deeper discussion of potential atmospheric drivers (e.g., increased net radiation, rising temperatures, persistence of summer circulation patterns).
Addressing these minor comments will further strengthen the manuscript and enhance its contribution to the literature on atmospheric evaporative demand.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Authors and Editors,
This manuscript investigates the spatial patterns and trends of potential/reference evapotranspiration (Ep/ETo) over mainland Portugal from 1980 to 2023. It compares multiple data sources (GLEAM, ERA5-Land, and Bristol-derived ETo) and three common estimation models (Thornthwaite, Hargreaves–Samani, Penman–Monteith), employing the Mann–Kendall test and Sen's slope estimator to identify trends at monthly and annual scales. The topic holds regional hydro-climatological significance, the research framework is clear, and the figures are abundant, indicating potential publication value. However, several methodological and presentational issues require attention. My detailed comments are as follows:
Major Points:
- Introduction Section: The rationale for selecting Portugal as the study area could be strengthened. Briefly highlighting specific regional characteristics (e.g., pronounced climatic gradients, significant water resource pressure, strong agricultural dependency) would enhance the contextual relevance and motivation for the study.
- Trend Analysis Section: The methodology section for trend detection does not sufficiently address whether an autocorrelation-corrected version of the Mann–Kendall test was used, how seasonal cycles were handled in the monthly series analysis, or if any control for multiple testing was applied. These omissions could lead to an overestimation of significant trends. The authors should review and clarify these aspects.
- Result Comparison Section: The manuscript discusses both Ep (potential evapotranspiration) and ETo (reference evapotranspiration). However, subsequently using the Penman–Monteith derived ETo as the "reference" or benchmark to evaluate Ep products/models raises concerns regarding comparability and definitional biases. If the intention is to assess the substitutability of Ep models for ETo estimation, the authors should clearly articulate the purpose and justify the feasibility of this approach in the Methods or Discussion section.
Minor Points:
- In the literature review, reference numbers should not be inserted directly into the text. Please reformat citations to use the author(s) name(s) followed by the citation. For example, change "As such, the work of [16] compared..." to "As such, the work of XXXet al. [16] compared...". Please check and revise this throughout the manuscript.
- Although in the abstract, the first time an abbreviation was used, it was presented in the form of "full name + abbreviation". However, when they first appear in the text, they should also be presented in full form, followed by the abbreviated form, such as "Ep", "Eto". Please have the author check and make the necessary revisions.
- The time period for the Bristol dataset in Figure 2 and its caption (1981–2024) differs from the core study period (1980–2023). This discrepancy should be reconciled, or a clear explanation for the difference should be provided.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsThe manuscript entitled “A Comprehensive Comparative Study on Evapotranspiration in Mainland Portugal Based on Climate Reanalysis Data” presents an intercomparison of methods for estimating potential evapotranspiration (Ep) and reference evapotranspiration (Eto) for Portugal using different methods. It is well written and organized, with legible figures and the quality required for a good publication.
However, the biggest problem, in my opinion, is assuming data sources based primarily on satellite data (GLEAM) and a gridded analysis based on ERA5-Land reanalysis (Bristol) as the surface truth.
The study should have been conducted by comparing the results of the methods with evapotranspiration values ​​obtained from meteorological stations. The evapotranspiration values ​​then calculated with stations would be compared to those obtained from GLEAM and ERA5Land, via the different methods, with the values ​​obtained by the Penman-Monteith method serving as a reference for the comparisons.
This observational limitation introduces uncertainty into the analyses and would need to be very well justified and proven based on observations, which can be used as primary sources for intercomparison.
I recommend that the authors consider the above arguments for resubmitting the manuscript.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsLooks good now! Thank you for addressing the review comments.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
Thank you for submitting the revised version of your manuscript entitled A Comprehensive Comparative Study on Evapotranspiration in Mainland Portugal Based on Climate Reanalysis Data.
I have carefully reviewed the revised manuscript and the responses provided to the previous comments. I am satisfied that all the issues raised during the review process have been adequately addressed. I think the revisions have improved conceptual clarity, strengthened the interpretation of the results, and enhanced the overall methodological transparency of the study.
Thank you for your careful revisions.
Kind regards.
Comments for author File: Comments.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsI have reviewed the revised manuscript submitted by the authors and their response letter. The major points raised in the previous review round have been largely addressed. Now I have no further comments.
