The Effects of Land Use and Climate Change on the Water Yield of a Watershed in Colombia
Round 1
Reviewer 1 Report
This manuscript presents an interesting work on hydrological modelling of a watershed in a region where modelling efforts are scarce. I had reviewed an earlier version of this manuscript in a prior submission and I’m happy to see that the authors have improved the manuscript based on previous comments. There are still few points that I believe that must be addressed, which can be decisive for the publication of this manuscript.
1. There is a bit of lack of character of the manuscript. This is a dry and direct application of the SWAT model, but the authors still fail (last paragraph of the introduction) to describe scientific and convincing objectives and a hypothesis of this study. It is stated that “this study aims at motivating scientists to work with water managers on strategies to improve their watershed management”, but I do not see how this is a motivational manuscript. At the same time, in the first paragraph of the conclusions, the authors state a hypothesis that hasn’t been revealed beforehand. I suggest the authors' review and rewrite the last paragraph of the introduction to address direct aspects of their research;
2. The discussion still lacks some consistent arguments. The low R2 for the best results still demands a better discussion on uncertainty by not only qualifying it but quantifying it with numerical analysis (which can be automatically given by SWAT in some cases);
3. Still, concerning the discussion, it would be very handy to contextualize your work with the results of Siqueira et al. (2018, DOI: 10.5194/hess-22-4815-2018) for the region of your watershed in Colombia;
These are short comments, but in my opinion, they need to be thoroughly addressed and may results in a few more paragraphs in the final manuscript version. Although I’m very positive about this work, I also would like to let the authors know that if I’m requested to review this manuscript again I would recommend for publication only if the authors take these comments very seriously. Otherwise, it still looks like a technical report.
Author Response
Following on the recommendations provided by the academic editor and the reviewers to manuscript water-422361, we are pleased to send the revised version of the article. We had a native speaker person (Fulbright visitor to the UPB campus) revise the manuscript. We introduced two new references to the article. This required to generate a new bibliography. All the changes in style and technical were tracked using the “Track changes tool” of Microsoft Word, and the responses to each of the comments provided by the reviewers follow:
Reviewer #1
This manuscript presents an interesting work on hydrological modelling of a watershed in a region where modelling efforts are scarce. I had reviewed an earlier version of this manuscript in a prior submission and I’m happy to see that the authors have improved the manuscript based on previous comments. There are still few points that I believe that must be addressed, which can be decisive for the publication of this manuscript.
1. There is a bit of lack of character of the manuscript. This is a dry and direct application of the SWAT model, but the authors still fail (last paragraph of the introduction) to describe scientific and convincing objectives and a hypothesis of this study. It is stated that “this study aims at motivating scientists to work with water managers on strategies to improve their watershed management”, but I do not see how this is a motivational manuscript. At the same time, in the first paragraph of the conclusions, the authors state a hypothesis that hasn’t been revealed beforehand. I suggest the authors' review and rewrite the last paragraph of the introduction to address direct aspects of their research;
Answer: Adopted. We completely redefined the last paragraph of the introduction according to the comments given by the reviewer. We also modified the last section of paragraph four within this section to add a new reference and improve its ending.
2. The discussion still lacks some consistent arguments. The low R2 for the best results still demands a better discussion on uncertainty by not only qualifying it but quantifying it with numerical analysis (which can be automatically given by SWAT in some cases);
Answer: The version submitted on December, 2018, included a supplementary Figure (Figure S7) showing the statistics for the automatic calibration process and the final ranges for each of the parameters involved in the calibration process. Due to the low NSE obtained for the final automatic iteration (NSE = 0.31), we moved to a manual calibration process in which we applied multipliers to the different parameters by subwatershed (see supplementary Table S7). Because these changes in the manual calibration were applied one-by-one on a sequential order, there are no statistics associated to the uncertainty of the parameters. The calibrated model (final iteration) is supported with the performance ratings (R2, NSE, PBIAS) reported in the results. To incorporate a quantitative component to the discussion, we added to its first paragraph the results of a T-test that confirms no difference between means of distributions for observed vs. modeled data (1990-1997 period). This is not the case, however, for the validation period (1999-2001) and future work (as established on the second paragraph of the discussion) needs to address the different current challenges for this Colombian site.
3. Still, concerning the discussion, it would be very handy to contextualize your work with the results of Siqueira et al. (2018, DOI: 10.5194/hess-22-4815-2018) for the region of your watershed in Colombia
Answer: Adopted. Please, see the last section of the first paragraph of the discussion.
These are short comments, but in my opinion, they need to be thoroughly addressed and may result in a few more paragraphs in the final manuscript version. Although I’m very positive about this work, I also would like to let the authors know that if I’m requested to review this manuscript again I would recommend for publication only if the authors take these comments very seriously. Otherwise, it still looks like a technical report.
Reviewer 2 Report
The authors organize scenario-based projections for evaluating the impact of land use and climate change on water yield simulated in SWAT in the Tona watershed (192.5 km2), located in north-eastern Colombia. The authors calibrate and validate SWAT by using monthly values of discharge and reach acceptable accuracy. The results highlight that potential afforestation program will likely reduce water yield by increasing evapotranspiration demand.
The evaluation of this manuscript is based on the following questions:
1) Is it a novel work based on a reliable scientific technique?
2) Is it clearly structured and well-written?
3) Are the experimental design and analysis of data adequate and appropriate to the investigation?
The manuscript is well-written, well-presented and is potentially ready for publication in WATER. To my opinion, it needs only minor revision before acceptance.
Regarding the calibration procedure, I would invite the authors to show the descriptive statistics of discharge monthly values in the calibration and validation period for both observed and simulated values. I would also try to use log-values of discharge in case of “poor” performance. Anyway a t-test (Student’s t-distribution) would objectively assess if the simulated and observed values have at least the same (in this case they belong to the same statistical population) mean of their distributions.
Another advice regarding the presentation of the results: the scenario-based framework is well-organized, but it would be useful to run the three land use change scenarios (A, B, C in Table 4) also under historic rainfall regime. This way the authors can evaluate and isolate the impact of LULC under both historic and projected rainfall scenarios. This comparison would be interesting in absolute and relative (%WY/P) terms. Again, comparisons should be made within a probabilistic framework, therefore we should visualize the statistical distributions of WY under different scenarios.
MINOR COMMENTS:
1) Avoid contractions of the negative form throughout the paper. For example “don’t” (line 368), “didn’t” (line 428), “wasn’t” (line 454) and so on.
2) I never heard about “moist bulk density” (line 164). Please, specify and provide citation
3) Line 472: replace “parameters” with “controls” or else
Author Response
Following on the recommendations provided by the academic editor and the reviewers to manuscript water-422361, we are pleased to send the revised version of the article. We had a native speaker person (Fulbright visitor to the UPB campus) revise the manuscript. We introduced two new references to the article. This required to generate a new bibliography. All the changes in style and technical were tracked using the “Track changes tool” of Microsoft Word, and the responses to each of the comments provided by the reviewers follow:
The manuscript is well-written, well-presented and is potentially ready for publication in WATER. To my opinion, it needs only minor revision before acceptance.
Regarding the calibration procedure, I would invite the authors to show the descriptive statistics of discharge monthly values in the calibration and validation period for both observed and simulated values. I would also try to use log-values of discharge in case of “poor” performance. Anyway, a t-test (Student’s t-distribution) would objectively assess if the simulated and observed values have at least the same (in this case they belong to the same statistical population) mean of their distributions.
Answer: Adopted. We developed t-tests to determine whether sample means of observed and modeled flow distributions were the same, for calibration and validation periods. As expected, we obtained positive results (same mean of distributions) for the calibration period, but not for the validation period (see following tables with test results). We complemented the first paragraph of the discussion section by including the results of the t-tests.
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Another advice regarding the presentation of the results: the scenario-based framework is well-organized, but it would be useful to run the three land use change scenarios (A, B, C in Table 4) also under historic rainfall regime. This way the authors can evaluate and isolate the impact of LULC under both historic and projected rainfall scenarios. This comparison would be interesting in absolute and relative (%WY/P) terms. Again, comparisons should be made within a probabilistic framework, therefore we should visualize the statistical distributions of WY under different scenarios.
Answer: The reviewer suggests that running the model with the historic rainfall regime and LULC scenarios would isolate the impact of LULC. We conscientiously evaluated his/her suggestion but concluded that adding those results would not add a significant improvement to the manuscript as we are already doing that by running each of the three LULC scenarios (A, B, C) for each of the future climates. Adding the suggested component would not allow comparisons between present and future conditions due to the very different spatial resolution between the two climate inputs (historic and future) for the model.
MINOR COMMENTS:
1) Avoid contractions of the negative form throughout the paper. For example “don’t” (line 368), “didn’t” (line 428), “wasn’t” (line 454) and so on. Adopted.
2) I never heard about “moist bulk density” (line 164). Please, specify and provide citation
Answer: NRCS defines moist bulk density as “the weight of soil (ovendry) per unit volume. Volume is measured when the soil is at field moisture capacity, that is, the moisture content at 1/3- or 1/10-bar (33kPa or 10kPa) moisture tension. Weight is determined after the soil is dried at 105 degrees C” [1–3]. This definition coincides with the one used by SWAT in its input/output documentation. Another name for this term is “bulk density, 1/3 bar”.
1. United State Department of Agriculture, Natural Resources Conservation Service National soil survey handbook, title 430-VI - https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs141p2_016186.pdf 2009.
2. Heuscher, S.A.; Brandt, C.C.; Jardine, P.M. Using Soil Physical and Chemical Properties to Estimate Bulk Density. SOIL SCI. SOC. AM. J. 2005, 69, 7.
3. Guides for Editing Soil Properties | NRCS Soils Available online: https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/office/ssr10/tr/?cid=nrcs144p2_074841 (accessed on Jan 15, 2019).
3) Line 472: replace “parameters” with “controls” or else
Answer: Adopted.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
I'm very happy to see the authors taking seriously all suggestions and making substantial improvements in the manuscript. Well done! Please keep improving hydrological predictions and parameterization in Colombia :)
Reviewer 2 Report
I am in general happy with the modifications provided by the authors and appreciated the effort they put in revising the material. Therefore I consider the manuscript publishable in the present form
