Simulating the Potential Evapotranspiration of Egypt Using the RegCM4: Sensitivity to the Land Surface and Boundary Layer Parameterizations

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study investigates the sensitivity of potential evapotranspiration (PET) in Egypt to different land surface and boundary layer schemes using the RegCM4 regional climate model. The authors compared the Biosphere Atmosphere Transfer System (BATS) and the Community Land Model version 4.5 (CLM45) for land surface schemes, and HOLTSLAG (HOLT) and University of Washington (UW) for boundary layer schemes. The PET was evaluated against the high-resolution ERA5-land PET-based product (hPET) over a 32-year period (1979-2010), with bias correction applied using the linear-scaling (LS) method.

In my opinion the manuscript offers three main innovative contributions. Including, comparison of different land surface and boundary layer schemes using the RegCM4 model in an arid region, calibration of the Hargreaves-Samani (HS) equation for PET estimation in Egypt, and application and validation of the linear-scaling (LS) bias correction method to improve PET estimates.

Nevertheless, there are several caveats/questions that I listed below.

The ground truth data used for comparing the simulated evapotranspiration (ET) in the manuscript is the high-resolution ERA5-land PET-based product (hPET). While ERA5 is highly regarded, it is not free from biases. Studies have documented various biases in ERA5, particularly in specific regions and under certain climatic conditions. The biases in ERA5 could affect the evaluation of the simulated ET, leading to either overestimation or underestimation of the model's accuracy. Incorporating a discussion on these biases would strengthen the manuscript by providing a more nuanced interpretation of the results.

What criteria were used to determine the optimal coefficients for calibrating the Hargreaves-Samani (HS) equation? Were these criteria based solely on statistical performance, or were other factors considered?

How was the sensitivity analysis conducted to determine the impact of different land surface and boundary layer schemes on PET? Were there any specific statistical or computational techniques used?

How does the spatial variability of PET across different regions of Egypt influence the model's performance? Are there specific regions where the model performs significantly better or worse?

How does the model account for extreme weather events, such as heatwaves or droughts, which could significantly impact PET estimates?

Please make the abstract and some sections of the methodology and results more concise. (Additionally, please refer to the attached annotated PDF and make the necessary changes)

Improve figure labels and captions for better clarity and significance.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Author Response

Dear Sir,

Many thanks for your constructive comments to improve the manuscript quality. Our response is indicated in the attached file.

Best Regards

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

 

• Only in line 85 did the authors begin to write about the RegCM model, which is present in the paper title, so I think that this model should have been described earlier.

 

• There are many specific objectives, but this list does not necessarily contain scientific concerns, rather steps of the methodology. What is the main scientific aim of the paper?"

 

• 20 and 200 mm by year?

 

• p.216 – How can mm/day be converted into radiation units?

 

• The authors need to explain the difference (in terms of calibration methods) that allows Eq. 1 to be converted to Eq. 2.

 

• What is the reference for Equation 3?

 

• CRU and MODIS products can show bias when compared to in situ ET measurements. Thus, it is important for the authors to emphasize the uncertainties of these two datasets used as observations to assess the simulations

   

• Reading the results is exhaustive, as the authors basically perform the same analysis for the results presented in Figures 2-7. Could you possibly synthesize this information a bit more to make the text less tiring to read?

Comments on the Quality of English Language

I am not a native English speaker, but I did not have significant problems understanding the text completely.

Author Response

Dear Sir,

Many thanks for your constructive comments to improve the manuscript quality. Our response is indicated in the attached file.

Best Regards

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

TITLE: Simulating the Potential Evapotranspiration of Egypt Using the RegCM4: sensitivity to the land surface and boundary layer parameterizations

 

Reviewers' comments:

This article mainly studies the accurate calculation of PET and the application of LS correction method to reduce PET deviation. Although good results have been obtained in the research area of this article, what is the physical mechanism of the correction method? And I think that main physical factors that affect PET have not been considered, such as soil moisture.

I recommend publication of the paper in hydrology after revision.

 

Major comments,

 

1.     How is the empirical formula (1) obtained in this article? What is the physical mechanism? How applicable is it in other region?

2.     What is the applicability of ERA5 data in the research area? What is the accuracy rate?

 

Minor comments,

1.      Should the discussion of the Penman-Monteith (PM) method in chapter 4 be included in the introduction, and would it be desirable to compare it with the author's simulation results in the text?

2.      In chapter 2.1 please give the topography figure of study area.

3.      L.301 ‘TESSEL’ first time appeared should be given full name；

 

 

Comments on the Quality of English Language

minor revise

Author Response

Dear Sir,

Many thanks for your constructive comments to improve the manuscript quality. Our response is indicated in the attached file.

Best Regards

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

In my previous revision, I commented:

The ground truth data used for comparing the simulated evapotranspiration (ET) in the manuscript is the high-resolution ERA5-land PET-based product (hPET). While ERA5 is highly regarded, it is not free from biases. Various studies have documented biases in ERA5, particularly in specific regions and under certain climatic conditions. These biases could affect the evaluation of the simulated ET, leading to either overestimation or underestimation of the model's accuracy. Incorporating a discussion on these biases would strengthen the manuscript by providing a more nuanced interpretation of the results.

The authors acknowledge the potential biases in the ERA5 PET data, but it is unclear what measures they have taken to reduce this bias. If the ERA5 data is biased and the authors compare their scheme with ERA5 data, how can they conclude which of their schemes is more accurate? For example, the authors mention that their results showed the BATS scheme has a bias of up to -1.8 mm day-1, while the CLM45 scheme has a bias of up to -3 mm day-1. They conclude that BATS provides more accurate results. This conclusion holds true only if the ERA5 data are accurate and their ET product in the study region has less than 3 mm of bias. If the ERA5 PET product has a standard deviation of around 2 to 3 mm/day, how can the authors compare BATS and CLM45?

The changes made to the introduction have made this version worse. The introduction needs to be broken down into clear paragraphs with a coherent story and without redundancy. It seems like the authors glued paragraphs together without paying attention to coherence and conciseness.

The language also needs further editing.

 

Comments on the Quality of English Language

The language needs further editing.

Author Response

Dear Reviewer,

Many thanks for your concern. Please find the attached file to check our response to the suggested comments.

Best Regards

Samy

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

I accept the paper in the present form.

Author Response

Dear Reviewer,

Many thanks for your time. We appreciate your kind response.

Best Regards

Samy

Author Response File: Author Response.docx