Assessing the Spatiotemporal Patterns and Impacts of Droughts in the Orinoco River Basin Using Earth Observations Data and Surface Observations

Round 1

Reviewer 1 Report

I have found the study interesting and worthy of discussion. There are minor issues to be considered.

1- I recommend providing a detailed discussion of Figure 1. Otherwise, it would not be necessary to give all of those details

2- Addressing the teleconnection between Large-scale oscillations and the drought time series is sometimes tricky. The large-scale oscillations sometimes need decades to affect the meteorological parameters. So, you can even address the lag operators or discuss them in the limitations of the study

3- Assumptions and limitations as well as recommendations for future studies missing

4- Please note that the linear trend analysis is not always an eye-opening method in detection of the serial trends

5- The conclusion can be summarized

Author Response

Dear Editor,

I hope this letter finds you well. I am writing to submit the revised version of our manuscript, entitled " Assessing the spatiotemporal patterns and impacts of droughts in the Orinoco River Basin using earth observations data and surface observations" for consideration in Hydrology. We appreciate the time and effort invested by the reviewers and the editor in evaluating our work, and we have carefully addressed each of their comments and suggestions. We believe these revisions have significantly improved the clarity and quality of our manuscript.

Below, I have outlined our point-by-point response to the referees' comments and detailed the revisions we have made in the manuscript:

Referee #1 [changes highlighted in cyan]:

1.1 Comment: I have found the study interesting and worthy of discussion. There are minor issues to be considered. I recommend providing a detailed discussion of Figure 1. Otherwise, it would not be necessary to give all of those details.

1.1 Response: We appreciate this comment and agree with the reviewer. To avoid confusion, we have specified in section 2.1 which panel of Figure 1 the reader should refer to in order to follow the narrative of the text.

1.1 Revision: please see lines 93, 97, 105 and 106.

1.2 Comment: Addressing the teleconnection between large-scale oscillations and the drought time series is sometimes tricky. The large-scale oscillations sometimes need decades to affect the meteorological parameters. So, you can even address the lag operators or discuss them in the limitations of the study.

1.2 Response: We are grateful for the suggestions. We appreciate the suggestions. We have performed a lagged correlation analysis to further examine the relationship between large-scale climate oscillations and drought variability using SPI-derived dry area as a proxy.

1.2 Revision: please see lines 202-208, 302-314, 416-420, and Table A2 (lines 542-548).

1.3 Comment: Assumptions and limitations as well as recommendations for future studies missing.

1.3 Response: We appreciate this insightful comment. In response, we have revised our manuscript to include the main assumptions and limitations of the methodological approaches that we employed in our study. We have also provided some suggestions for future research in this area.

1.3 Revision: please see lines 221-232, and 423-428.

1.4 Comment: Please note that the linear trend analysis is not always an eye-opening method in detection of the serial trends.

1.4 Response: Thank you for pointing this out. We appreciate your feedback. As a result, we have added a warning to inform the readers about these limitations.

1.4 Revision: please see lines 217-219, and 423-428.

1.5 Comment: The conclusion can be summarized.

1.5 Response: Thank you for pointing this out. We value your comment. To reflect this, we have revised our conclusions to highlight the most relevant findings that align better with our research objectives.   

1.5 Revision: please see lines 486-503, and 508-510.

Reviewer 2 Report

The work "Assessing the spatiotemporal patterns and impacts of droughts 2 in the Orinoco River Basin using earth observation data and 3 surface observations" presents the analysis of spatio-temporal patterns of droughts in the Orinoco basin. The study provides a comprehensive, multiaspect analysis. The structure of the article is good, and the reading flow is excellent. There are no major linguistic problems. The methods are clear and described in a sufficient way, with clear division into subsections. Results are presented in a sufficient way. There are only a few issues that need to be fixed before work can be accepted for publication:

Fig. 1 shows clearly all countries visible on the maps, as in the current version, labels are hard to read. Similarly, 1a presents "cities" for which names are impossible to read. I would also suggest adding suffixes for grid labels. In 1a, "hydrological divide" is not an appropriate term.

For links in methods (lines 126, 132, and 159), please use original links and not temporary shorteners, so the full structure and website address are visible.

L147-152. Please mark the location of these gauges on Figure 1.

L186-188. Explain to the reader why these exact numbers - if there is a citation, provide it; if this is your method, explain how you got to these exact numbers. Justification for this method and criteria must be provided.

L201-202. You did not discuss the normality of all your data but are using a method that requires it. Provide justification for why Pearson r is used and proof that your dataset meets the criteria for the method.

L367-368. I disagree; chronology here matters; it's your findings that confirm earlier studies, not the other way around.

L444-448. Your study is not about water quality, and no results of your study confirm this statement. Please limit your conclusions to your true results and observations. This should include "dry facts" that come from your work.

Author Response

Dear Editor,

I hope this letter finds you well. I am writing to submit the revised version of our manuscript, entitled " Assessing the spatiotemporal patterns and impacts of droughts in the Orinoco River Basin using earth observations data and surface observations" for consideration in Hydrology. We appreciate the time and effort invested by the reviewers and the editor in evaluating our work, and we have carefully addressed each of their comments and suggestions. We believe these revisions have significantly improved the clarity and quality of our manuscript.

Below, I have outlined our point-by-point response to the referees' comments and detailed the revisions we have made in the manuscript:

Referee #2 [changes highlighted in grey]:

2.1 Comment: The work "Assessing the spatiotemporal patterns and impacts of droughts in the Orinoco River Basin using earth observation data and surface observations" presents the analysis of spatio-temporal patterns of droughts in the Orinoco basin. The study provides a comprehensive, multiaspect analysis. The structure of the article is good, and the reading flow is excellent. There are no major linguistic problems. The methods are clear and described in a sufficient way, with clear division into subsections. Results are presented in a sufficient way. There are only a few issues that need to be fixed before work can be accepted for publication. Fig. 1 shows clearly all countries visible on the maps, as in the current version, labels are hard to read. Similarly, 1a presents "cities" for which names are impossible to read. I would also suggest adding suffixes for grid labels. In 1a, "hydrological divide" is not an appropriate term.

2.1 Response: We are grateful for your insightful feedback. Based on your suggestion, we have enhanced the readability of Figure 1 by enlarging the labels in all panels, adding units to the grid labels, and using a more accurate term than ‘hydrological divide’.

2.1 Revision: please see line 112 (Figure 1).

2.2 Comment: For links in methods (lines 126, 132, and 159), please use original links and not temporary shorteners, so the full structure and website address are visible.

2.2 Response: We are grateful for your useful recommendations. We have replaced the temporary shortened links with native links.  

2.2 Revision: please see lines 126, 133, 141, 146 and 165.

2.3 Comment: L147-152. Please mark the location of these gauges on Figure 1.

2.3 Response: We appreciate your valuable suggestion and have implemented it accordingly. To enhance the clarity, we have included Figure 2.

2.3 Revision: please see lines 265-267.

2.4 Comment: L186-188. Explain to the reader why these exact numbers - if there is a citation, provide it; if this is your method, explain how you got to these exact numbers. Justification for this method and criteria must be provided. 

2.4 Response: Your feedback and suggestions are highly appreciated. We have clarified the reasoning behind this method and criteria.

2.4 Revision: please see lines 194-198.

2.5 Comment: L201-202. You did not discuss the normality of all your data but are using a method that requires it. Provide justification for why Pearson r is used and proof that your dataset meets the criteria for the method.

2.5 Response: Thank you for recommendation. We have added more details about the assumptions and limitations of the statistical methods we used. 

2.5 Revision: please see lines 221-234.

2.6 Comment: L367-368. I disagree; chronology here matters; it's your findings that confirm earlier studies, not the other way around.

2.6 Response: Thank you for recommendation. We have enhanced the coherence of the narrative at this point.

2.6 Revision: please see lines 420-422.

2.7 Comment: L444-448. Your study is not about water quality, and no results of your study confirm this statement. Please limit your conclusions to your true results and observations. This should include "dry facts" that come from your work.

2.7 Response: We appreciate this comment and agree with the reviewer. To prevent confusion, we restricted our conclusions to facts derived from our results.

2.7 Revision: please see lines 486-503.

Reviewer 3 Report

The authors present an assessment of the use of different indices to assess drought duration, intensity and severity within a large river basin in South America using earth observation data and surface observations. The paper provides an interesting evaluation of different indices and metrics which can be used to assess drought conditions. I would like to acknowledge the good work done by the authors, but there are still some improvements that can be made. I find that the paper is quite well written, but more global contexts can be added to improve its relevance to the readership and to make the paper more citable. I have made some additional recommendations for the conclusion as it reads more ‘thesis’ like and can be more streamline.

I hope you find my comments useful. I have made some minor comments below.

Kind regards

Abstract:

Droughts affect Orinoco River basin Line 16.

Drought affects many river basins around the world. This statement is vague. But to mention the site within the first line narrows the papers scope and readership. I would advise to start with a global context about droughts. There were some great points made in the conclusion which could be linked up with.

The abstract does not contain any figures/numbers which are needed to give context to the material and add weight to some of the statements.

Introduction

Line 42 Dry periods over Cuba...etc

Line 57 Why agricultural and hydrological. SMDI often associated with agricultural while SSFI for hydrological.

Line 63 In most developing countries

Line 90 The heading says study area. I do not think its necessary to say this again. Join lines 91 and 92.

Line 106 significant figures

Line 114 Why the use of "for to Orinoco River basin" as the figure caption. Why not just "The Orinoco River basin with the spatial distribution of a)... etc.

Figure 1: The legends and text needs to be larger. The river line thickness could be reduced or only presented in one of the cut-outs to make it easier to read the rest of the information.

Line 147 please add in brackets m3/s. Is there a location of these gauges on the map?

Line 177 revise the scale of SPI. "not dry" and "close to normal" are not appropriate. Rather "wet" and "normal".

Line 221 Did you fit the streamflow data to a gamma distribution like SPI. If so, I would say standardized streamflow index was used (SSFI) this makes things clearer.

Figure 2: Nice figures! Caption "For the Orinoco River basin" please revise as per above. Write out all abbreviation in the captions (SPI).

Line 269 "Table 1 summarizes the main characteristics ...etc". The table caption does this role. It is therefore not recommended to repeat this in the text.

Line 284 These sentences read like method sentences.

Line 290 "Figure 3 summarizes ...etc" again the caption plays this role.

Figure 3 Nice figures, but they are too small to read.    

Figure 5. It is very difficult to see the station locations on the map. Maybe reduce the river networks to just the main sections and make the symbols larger for the gauges.

Line 416: But not just the Orinoco River basin, I am sure they can be translated to other basins globally.

Line 430 "we answer your research objectives as follows". Revise. These are not "your objectives". Maybe the study objectives but I would recommend not have a list like this as it comes across like a thesis. Starting from "our study" in line 449 would be a good idea. The conclusion is a bit long if these objectives were to be included.

Some minor comments have been suggested. 

Author Response

Referee #3 [changes highlighted in yellow]:

3.1 Comment: The authors present an assessment of the use of different indices to assess drought duration, intensity and severity within a large river basin in South America using earth observation data and surface observations. The paper provides an interesting evaluation of different indices and metrics which can be used to assess drought conditions. I would like to acknowledge the good work done by the authors, but there are still some improvements that can be made. I find that the paper is quite well written, but more global contexts can be added to improve its relevance to the readership and to make the paper more citable. I have made some additional recommendations for the conclusion as it reads more ‘thesis’ like and can be more streamline. I hope you find my comments useful. I have made some minor comments below.

3.1 Response: We are grateful for these recommendations and concur with the reviewer. We have revised the narrative of our conclusions to make them more concise and streamlined.

3.1 Revision: please see lines 498-502 and 510-518.

3.2 Comment: Abstract. Droughts affect Orinoco River basin Line 16. Drought affects many river basins around the world. This statement is vague. But to mention the site within the first line narrows the papers scope and readership. I would advise to start with a global context about droughts. There were some great points made in the conclusion which could be linked up with. The abstract does not contain any figures/numbers which are needed to give context to the material and add weight to some of the statements.

3.2 Response: We acknowledge the reviewers' helpful suggestions and have revised the abstract to introduce the regional focus more effectively. Additionally, we have included statistical metrics to support our main findings.

3.2 Revision: please see lines 16-19, 22-25, and 28-34.

3.3 Comment: Introduction. Line 42 Dry periods over Cuba...etc; Line 57 Why agricultural and hydrological. SMDI often associated with agricultural while SSFI for hydrological; Line 63 In most developing countries.

3.3 Response: Thank you for your valuable comment. We have corrected the typographical errors as suggested. Regarding the Soil Moisture Deficit Index (SMDI) and the Standardized Streamflow Index (SSFI), we agree with your description. SMDI measures the degree of water stress on the vegetation by the ratio of actual evapotranspiration (ET) to reference crop evapotranspiration (ET0), while SSFI is the standardized departure of streamflow following the same calculation applied to SPI, which reflects the hydrological drought status of a river basin. However, we did not use SMDI and SSFI in our study, because we considered that the soil surface moisture (SSM) anomalies from GLDAS and monthly flow anomalies from in situ records standardized by mean and its standard deviation provided us with an indicator of agricultural and hydrological drought conditions in the basin. We have clarified this point in the revised manuscript.     

3.3 Revision: please see lines 45, 65-67, 141-146, 155-156, and 159-160.

3.4 Comment: Line 90 The heading says study area. I do not think it’s necessary to say this again. Join lines 91 and 92; Line 106 significant figures; Line 114 Why the use of "for to Orinoco River basin" as the figure caption. Why not just "The Orinoco River basin with the spatial distribution of a) ... etc; Figure 1: The legends and text need to be larger. The river line thickness could be reduced or only presented in one of the cut-outs to make it easier to read the rest of the information; Line 147 please add in brackets m3/s. Is there a location of these gauges on the map? Line 177 revise the scale of SPI. "Not dry" and "close to normal" are not appropriate. Rather "wet" and "normal".; Line 221 Did you fit the streamflow data to a gamma distribution like SPI. If so, I would say standardized streamflow index was used (SSFI) this makes things clearer.

3.4 Response: Thank you for pointing this out. We appreciate your feedback. As a result, we have fixed all typos mistakes. We referred to the relevant subpanels 1a, 1b, 1c and 1d from Figure 1 to support the narrative in section 1.1. We modified the caption of Figure 1 for clarity. We also enhanced the resolution of Figure 1 and added a yellow buffer on the labels on Figure 1a to improve the contrast and visual quality. We retained the river network to support some of our arguments in the discussion and results sections, where it is important for the reader to compare the rainfall, land cover and elevation patterns at a finer level. We have included a new figure (Figure 2) that illustrates the spatial distribution of the fluviometric stations that we used in our study. Regarding the streamflow anomalies, we calculated them based on the mean and standard deviation of the streamflow values, using the formula (value – mean)/ SD. However, we did not follow the same procedure as the Standardized Precipitation Index (SPI), which applies a gamma function to normalize the residuals (i.e., value − mean). This means that our streamflow anomalies are not equivalent to the Standardized Streamflow Index (SSFI). We have clarified this point in the revised manuscript. Regarding the scale of SPI, we agree with the reviewer.           

3.4 Revision: please see lines 94-95, 100, 108, 109, 117 (the caption of Figure 1), 157, 159-161, 189-190, 205-209, and 258-261.

3.5 Comment: Figure 2: Nice figures! Caption "For the Orinoco River basin" please revise as per above. Write out all abbreviation in the captions (SPI); Line 269 "Table 1 summarizes the main characteristics ...etc". The table caption does this role. It is therefore not recommended to repeat this in the text; Line 284 These sentences read like method sentences; Line 290 "Figure 3 summarizes ...etc" again the caption plays this role; Figure 3 Nice figures, but they are too small to read; Figure 5. It is very difficult to see the station locations on the map. Maybe reduce the river networks to just the main sections and make the symbols larger for the gauges.

3.5 Response: Thank you for your feedback. We have modified the caption of Figure 2 (now Figure 3), rephrased lines 269 and 290, and moved line 284 to the methodology section. We have also improved Figures 3 and 5 (now Figures 4 and 6) for clarity.     

3.5 Revision: please see lines 295-297, 328-330, 343-344, line 350 (Figure 4), line 395 (Figure 5).

3.6 Comment: Line 416: But not just the Orinoco River basin, I am sure they can be translated to other basins globally. Line 430 "we answer your research objectives as follows". Revise. These are not "your objectives". Maybe the study objectives but I would recommend not have a list like this as it comes across like a thesis. Starting from "our study" in line 449 would be a good idea. The conclusion is a bit long if these objectives were to be included.

3.6 Response: We appreciate your feedback and have made the following changes to address it: We simplified our conclusions to highlight the main findings and implications of our study; we emphasized that our methodological approach can be applied to other basins that are vulnerable to drought as a consequence of climate change, and that it can provide valuable insights for water resources management and planning.  

3.6 Revision: please see lines 470-472, and 497-501.

Round 2

Reviewer 3 Report

Great work and well done to the authors! One final comment. Line 18. "The basin houses" maybe revise to the "the basin supports". 

My other comments have been fully addressed. 

N/A

Author Response

Thank you very much for the observation, the correction has been made.