Precipitation Extremes and Trends over the Uruguay River Basin in Southern South America

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript analyzes the spatial distribution and trends in five extreme daily rainfall indices in the Uruguay River Basin.

Although the analysis is correctly performed, it is relevant only for water management in the analyzed region, and can be taken into account by the authorities to establish possible structural and non-structural measures for basin and regional management.

However, the manuscript does not bring new or improved scientific contributions regarding these types of analysis. The presented analysis applies a usual methodology, without bringing new elements.

The presented results and conclusions are relevant only for the analyzed area, they do not offer new elements and information to be used by other researchers in performing trend analyses.

Thus, my decision is to Reject the material, because it does not make new scientific contributions. Also, the authors do not mention and highlight the possible new elements presented in the manuscript.

Author Response

Thank you for taking the time to review our manuscript.

We understand and appreciate your concerns regarding the novelty and scientific contributions of our analysis. While we acknowledge that our study focuses on the specific region of the Uruguay River Basin, we believe that our findings hold significance within this domain.  

We agree that our methodology aligns with conventional approaches used in similar analyses of extreme rainfall indices and may not introduce new elements. However, we would like to emphasize that our study contributes to the existing body of knowledge by applying these methodologies to the unique context of the Uruguay River Basin. 

The impact of precipitation in the basin extends beyond its borders, given that the URB hosts hydropower plants that not only generate energy for the region but also for other parts of Brazil, Argentina, and Uruguay. Additionally, the basin plays a crucial role in the agricultural sector, contributing significantly to food production in these countries.

Furthermore, although the study inherently focuses on the regional scale, its results have implications beyond the Uruguay River Basin URB due to the multiscale interconnectedness of the climate system. The extreme precipitation patterns and trends observed in the basin not only impact the immediate region but also extend to areas, since the basin hosts several hydropower plants. These plants generate energy not only for the local region but also for other parts of Brazil, Argentina, and Uruguay. Moreover, the basin's strong agricultural sector plays a vital role in food production for these countries.

We have revised the manuscript to provide a more comprehensive discussion of our results. We emphasize the implications of our findings for water management, hydropower generation, and agricultural activities in the region. The reviewer will find a tracked-changes version of the manuscript with the revisions. In this version, removed text is marked in red-crossed format, while new discussions are highlighted in blue text. 

Please find attached the tracked-changes version of the manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Comments: 

The Authors did a beautiful analysis of precipitation trends covering different sub-basins of URB together, which is lacking in previous literature. However, there are significant issues in the manuscript that need to be taken care of before it can be recommended for publication. Below are point-wise comments.

1. It is noticed that there is a variation of URB region divisions in different studies. Some of the maps in published literature vary slightly. Authors are suggested to support their selection of boundaries with appropriate details.

2. The area of study is not so large, so it's suggested to find the exact no of hydropower, and storage reservoirs. Also putting them as points in the fig 1 if possible.

3. Is there a specific reason to consider data from 1993, whereas the CHIRPS data has been available since 1981?

4. Figure sub-names (a,b,c,d) are repeated in figure. I suggest removing one. and maintain consistency with other figures.

5. Line 179: It must be 350-400 mm, not 40 mm.

6. The Figure title of Fig 4-7, (N ° Day) confuses as N degree days, Suggested changing it to “No of “

7. The conclusion seems to repeat of same points as mentioned in the result section. Authors are suggested to link the amount and no of days of heavy and extreme rainfall to conclude the trend of extreme and heavy rainfall categories. 

8. The upper URB mostly has a negative trend for extreme and heavy rain, while it has a positive trend for CDD, what conclusion can be met considering these points combined?

9. “While the absence of statistical significance may hinder conclusive”: This line is mentioned ~6 times throughout the manuscript in different ways. Authors are suggested to limit the repetition.

10. The current state of manuscripts looks like a report of the five indices and its trend, Authors are suggested to add more discussion and conclusion concerning the usefulness of this result. Discuss more relating to the economic activities, settlements energy generation, agriculture, etc. 

11. Authors mentioned the importance of the URB region due to the presence of hydropower stations, and reservoirs, but the linkage of the result to the impact of this infrastructure is completely lacking. (For example by relating to the no of hydropower in different divisions with precipitation trend).

Author Response

The authors are very grateful for the additional comments and suggestions from the Reviewer. Find below our point-by-point responses. In addition to the point-by-point responses, the reviewer will find attached a tracked-changes version of the manuscript with the revisions. In this version, removed text is marked in red-crossed format, while new discussions are highlighted in blue text.

Replies to Reviewer:

1. It is noticed that there is a variation of URB region divisions in different studies. Some of the maps in published literature vary slightly. Authors are suggested to support their selection of boundaries with appropriate details.

Response 1: We analyzed the entire hydrographic region of the URB and divided the URB into three main areas to facilitate result discussions. We chose to use the Hydrographic Mesoregion division recommended by Brazilian Institute of Geography and Statistics (IBGE, acronym in Portuguese) and Brazilian National Water Agency (ANA, acronym in Portuguese), known as DHN25 (Divisão Hidrográfica Nacional), launched in 2021. This division, developed by a team of experts from both IBGE and ANA, was established based on the homogeneity of geomorphological, hydrographic, and hydrological factors, facilitating the planning and efficient utilization of water resources in the region. The southernmost part of the basin, mainly in Uruguay and a narrow strip of the easternmost extremity of the AR along the border with Uruguay, was designated as Low URB. The division between Mid and Low URB is similar to that usded by Armoa et al. in 2023 but expands the Low URB to include the entire hydrographic area south of the closing points of Salto Grande.

Additionally, this division allows us to analyze sub-regions with similar topography and precipitation patterns within the main URB area. The Upper URB has the steepest topography and receives the highest rainfall. The Mid URB transitions from steep terrain in the north to flat terrain in the Campanha Gaúcha region. The Low URB is characterized by flat terrain and slightly lower precipitation amounts.

We added this discussion in the revised version of the manuscript. 

2. The area of study is not so large, so it's suggested to find the exact no of hydropower, and storage reservoirs. Also putting them as points in the fig 1 if possible.

Response 2: Thank you for the suggestion, we added the hydropower locations in Figure 1 (study area).

3. Is there a specific reason to consider data from 1993, whereas the CHIRPS data has been available since 1981?

Response 3: Since the minimum period for climatological studies typically spans 30 years, we opted to use data only from 1993 to 2022. Additionally, due to the high resolution of CHIRPS data, we faced constraints regarding processing and trend calculation over a longer period. Instead of interpolating the data for a coarser resolution, we chose to use data from 1993 onwards and not from 1981. However, we acknowledge that using a longer time series could provide a more representative view of precipitation patterns, variability, and trends over time.

4. Figure sub-names (a,b,c,d) are repeated in figure. I suggest removing one. and maintain consistency with other figures.

Response 4: Thank you for pointing it out, the Figure 3 sub-names are corrected in the revised manuscript.

5. Line 179: It must be 350-400 mm, not 40 mm.

Response 5: Thank you for pointing out, it was a typing error and we have corrected it.

6. The Figure title of Fig 4-7, (N ° Day) confuses as N degree days, Suggested changing it to “No of “

Response 6: Thank you for the suggestion, we adjusted the Figures 4, 5, 6 and 7 titles in the revised version of the manuscript. 

7. The conclusion seems to repeat of same points as mentioned in the result section. Authors are suggested to link the amount and no of days of heavy and extreme rainfall to conclude the trend of extreme and heavy rainfall categories. 

Response 7: We agree with your comment, we rewrote the conclusion section. 

8. The upper URB mostly has a negative trend for extreme and heavy rain, while it has a positive trend for CDD, what conclusion can be met considering these points combined?

Response 8: This is an important result and we did not discuss it in the first version of the manuscript. The combination of a mostly negative trend in both heavy and extreme precipitation and a positive CDD in the upper URB suggests a shift towards drier conditions with less intense precipitation extremes but more prolonged dry periods.

9. “While the absence of statistical significance may hinder conclusive”: This line is mentioned ~6 times throughout the manuscript in different ways. Authors are suggested to limit the repetition.

Response 9: In the revised manuscript, we removed these phrases and tried to avoid repetition. Thank you.

10. The current state of manuscripts looks like a report of the five indices and its trend, Authors are suggested to add more discussion and conclusion concerning the usefulness of this result. Discuss more relating to the economic activities, settlements energy generation, agriculture, etc. 

Response 10: Thank you, we added more discussion of the results in the revised manuscript. 

11. Authors mentioned the importance of the URB region due to the presence of hydropower stations, and reservoirs, but the linkage of the result to the impact of this infrastructure is completely lacking. (For example by relating to the no of hydropower in different divisions with precipitation trend).

Response 11: In the result and conclusion sections we added more discussion linking the precipitation trends and hydropower plant locations and the impacts on energy generation in the basin. Thank you. 

Please find attached the tracked-changes version of the manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

As I pointed out in the first round of review, the analysis is correct, but unfortunately it does not have an approach that introduces at least a minimum of new elements, which I consider mandatory in scientific research.

I agree with the authors that the analysis has regional importance, but unfortunately it does not bring new elements and approaches so that the international community can use them in similar analyses.

Author Response

We appreciate your feedback.

Best regards.