Estimation of the Climate Change Impact on the Hydrological Balance in Basins of South-Central Chile

Round 1

Reviewer 1 Report

  This article examines the effects that would occur on hydrological variables in a given area of Chile when considering a scenario of climatic change. To do this, it has been necessary to calibrate the SWAT model with weather data recorded in the area. I think the article is a very instructive exercise although the resolution of the figures should be improved. you can hardly see the legends of the axes

Author Response

This article examines the effects that would occur on hydrological variables in a given area of Chile when considering a scenario of climatic change. To do this, it has been necessary to calibrate the SWAT model with weather data recorded in the area. I think the article is a very instructive exercise although the resolution of the figures should be improved. You can hardly see the legends of the axes

ANSWER: We appreciate the reviewer´s suggestion: In order to improve the paper´s quality, figures No 1 – 2 and figures 4 -10 were redesigned in the new manuscript with higher resolution and increasing the font sizes to allow the correct visualization of the legend axes and all the information contained.

Reviewer 2 Report

I have one major concern regarding the results of statistical analysis presented in this paper. For example, in lines 323, 341, 368 authors wrote: According to Student’s t test… but there is only short information in methods section that this test will be used.  Methods should answer for following questions:

• Why Student’s t test may be appropriate for this study?
• What are the assumption for this test?
• Were these assumptions fulfilling?
• And in the appendix section the results of Student’s t test are required.

Moreover, the following statements as those one in line 352: "significant decreasing trends” should be explained better. What significant means here?

In addition, I have several minor comments:

Line 19-20 should be moved to introduction section.

Line 28 should be removed from the abstract.

Lines 38-40 should be avoided in abstract.

Line 94-104. Goals   of the paper are too descriptive and should be more specific.

Lines 107-177 needs citation.

Line 123. The sentence should not start from abbreviation.

Line 125 needs citation.

In Fig. 2 (I) and (II) should be added to all subfigure.

In line 215 is lack of space.

Line 234. There is editorial mistake.

In line 325 there is lack of space.

Fig. 8. How runoff is calculated in “mm”. Is it correct?

There are only example of editorial mistake which should be corrected in the whole paper.

Author Response

1. I have one major concern regarding the results of statistical analysis presented in this paper. For example, in lines 323, 341, 368 authors wrote: According to Student’s t test… but there is only short information in methods section that this test will be used. Methods should answer for following questions:

• Why Student’s t test may be appropriate for this study?
• What are the assumption for this test?
• Were these assumptions fulfilling?
• And in the appendix section the results of Student’s t test are required.

 

ANSWER: We agree that information provided was not complete and thank the reviewer for pointing out this topic. To complete the information, the following sentences were included in the new manuscript in lines 290 – 298 answering the aforementioned question:

 

In order to determine the existence of significative differences for every component of the water cycle among simulation results for the historical, immediate and intermediate periods, a t-student statistic test for paired samples was applied. The test was performed once checked that every sample could be properly fitted to a normal distribution via the Kolmogorov-Smirnov test. Additionally, in order to comply the test requirements, all the simulations were performed under similar conditions but changing the climatic scenarios. In this way, the impact of climatic change over the water cycle components distribution was unveiled. This analysis was conducted on an annual scale, at the subbasin level, for 30 years periods with a 95% significance level.

 

2. Additionally, raw results of t-student test was included as appendix A, table A.1

Moreover, the following statements as those one in line 352: "significant decreasing trends” should be explained better. What significant means here?

 

ANSWER: Significative trend in the section 3.2 means p_values lesser than 0.05 for 95% confidence interval in the Mann Kendall test as referred in the materials and method section, lines 244-258 and in the results section 3.2, lines 347-349 in the new manuscript. The Mann-Kendall test tells us whether there is a trend in a time series. The p-value (<0,05) for 95% confidence interval shows that the null hypothesis (no significative trend) is rejected thus we may suggest that there is a significant trend in our time series.

However in the line 352 of the older manuscript it was not referred to a trend but a significant difference in the t student test. Then, “Significant trend” was omitted in this line in the new document.

 

In addition, I have several minor comments:

 

3. Line 19-20 should be moved to introduction section.

ANSWER: The sentence was moved to introduction to lines 90-92.

4. Line 28 should be removed from the abstract.

ANSWER: The sentence was removed from the abstract as recommended.

5. Lines 38-40 should be avoided in abstract.

ANSWER: The sentence was removed as recommended.

6. Line 94-104. Goals of the paper are too descriptive and should be more specific.

ANSWER: The paragraph is now separated in two parts, first concerning the study scope lines 92-98 and then a second paragraph considering specific objectives lines 99-102

7. Lines 107-177 needs citation.

ANSWER: References were included in the text Olson et al. [1] and Myers et al. [2]

8. Line 123. The sentence should not start from abbreviation.

ANSWER: The sentence was re-written considering revision.

9. Line 125 needs citation.

ANSWER: Reference was included in the text Neitsch et al [3]

10. In Fig. 2 (I) and (II) should be added to all subfigure.

ANSWER: In figure 2, index (I) and (II) belongs to the gauging points of both basins, and are only represented on figure 2.d. However, the basins´ names were included in all the subfigures as “Quino basin” and “Muco basin”.

11. In line 215 is lack of space.

ANSWER: The space was included considering revision.

12. Line 234. There is editorial mistake.

ANSWER: The sentence was re-written according to revision to avoid the mistake

13. In line 325 there is lack of space.

ANSWER: Space omissions in the paragraph were corrected.

14. 8. How runoff is calculated in “mm”. Is it correct?

ANSWER: It is correct, every parameter was reported as calculated by SWAT in mm. SWAT calculate all these parameters in water mm to help understanding and comparing the water cycle components Arnold et al [4]

15. There are only example of editorial mistake which should be corrected in the whole paper.

ANSWER: Some other editorial mistakes were corrected in the new manuscript version.

REFERENCES

1. Olson, D.M.; Dinerstein, E. The global 200: Priority ecoregions for global conservation. Ann. Missouri Bot. Gard. 2002, 89, 199–224.

 

2. Myers, N. Biodiversity Hotspots Revisited. Bioscience 2003, 53, 916–917.

 

3. Neitsch, S.L.; Arnold, J.G.; Kiniry, J.R.; Williams, J.R. Soil and Water Assessment Tool. Theoretical Documentation.; Soil and Water Research Laboratory: Temple, TX, 2005;

 

4. Arnold, J.G.; Kiniry, J.R.; Srinivasan, R.; Williams, J.R.; Haney, E.B.; Neitsch, S.L. SWAT 2012 Input/Output Documentation 2012, 30.

 

Author Response File: Author Response.docx

Reviewer 3 Report

Although the manuscript presented used standard approaches and methods, some rather interesting conclusions were drawn regarding climatic and hydrological changes in the river basins of south-central Chile. In this regard, the findings of the work are of practical interest to local authorities. Indeed, the content of the manuscript deserves publication in the journal Water. Nevertheless, before publishing, I have several comments and suggestions to the authors.

1. You mentioned in your work that the current climate scenarios for the coastal Southeast Pacific and the land of Chile are not identical. The authors should further justify why they used the RCP 8.5 climate scenario for modeling. This is an important point in the work that authors should take more responsibly.
2. If the forecasts obtained are correct, they will come true (in terms of hydrological changes), provided that the land cover (land use) does not undergo significant changes. But as temperatures rise and precipitation decreases, even without human intervention, the earth's cover is unlikely to remain unchanged until 2080. These scenarios should also be covered in the work, even if at a qualitative level.
3. Line 114 and Figure 1. What does the height interval from 27 to 1724 m above sea level mean for the two basins? Please write the highest and lowest height for each basin studied. Are you sure that the lowest point (hydrological post) of one of the basins is located 27 m above sea level, given the distance from the Pacific coast of several tens of kilometers? It would be ideal if you additionally plot hypsographic curves for each basin.
4. Figure 1. Which of the two maps does the scale at the bottom frame refer to?
5. Figure 2. The soil cover map. Is it just enough to know only the types of soils for modeling but not their granulometric composition, which determines many important soils' hydrological properties? You do not say anything about this in your work!
6. Figure 2. How do you explain the choice of the collection points' location for climate information in the two basins? Please give more explanation in the work.
7. Line 202. “ … using the cover land/use corresponding to 1986 …” cover land/use?
8. Figure 4 needs to be redone. It is poorly readable.
9. Line 315-316. 79 mm (LAT_Q). What is LAT_Q? There was no information about it in the text above.
10. It would be beneficial to provide a single summary table of changes in the water balance structure for different periods, including periods of calibration and/or validation.
11. Line 469-472. Why modeling in the BioBio River basin resulted in predictions with more dramatic reductions in precipitation and runoff than your study? Some discussion of these differences would be helpful. Have there been any other forecast studies for other river basins in the central Chile region?
12. Slight improvement in English is required.

Author Response

Although the manuscript presented used standard approaches and methods, some rather interesting conclusions were drawn regarding climatic and hydrological changes in the river basins of south-central Chile. In this regard, the findings of the work are of practical interest to local authorities. Indeed, the content of the manuscript deserves publication in the journal Water. Nevertheless, before publishing, I have several comments and suggestions to the authors.

1. You mentioned in your work that the current climate scenarios for the coastal Southeast Pacific and the land of Chile are not identical. The authors should further justify why they used the RCP 8.5 climate scenario for modeling. This is an important point in the work that authors should take more responsibly.

 

ANSWER: During the IPCC fifth Assessment Report, four new emission scenarios were defined; known as the Representative Concentration Pathways (RCP). These pathways are characterized by the total Radiative Forcing for the year 2100 oscillating between 2.6 and 8.5 W/m²; comprising one scenario in which mitigation efforts conduct to a very low radiative forcing (RCP 2.6), two stabilization scenarios (RCP 4.5 and RCP 6.0 ) and one last scenario with the higher emissions of greenhouse gasses (RCP 8.5) [1].

According to the IPCC [2], it has been considered that the climate change would be an important stressing factor for terrestrial and fresh water ecosystems for the second half of XXI century, especially for scenarios considering high warming such as RCP 6.0 and RCP 8.5. Additionally it has been projected than even after 2100 the global warming will continue in all the RCP scenarios, except in RCP2.6 [2].

On one hand, the RCP 2.6 scenario could only be possible if greenhouse gas emissions become extremely controlled [3]. Even while the climate system is in a constant change state, achieving RCP2.6 would certainly present the smallest impacts to natural ecosystems and human activities [4]. Considering this scenario, the radiative forcing will reach approximately 3.1 W/m² in the first half of XXI century and then will decrease, reaching 2.6 W/m² during 2100. To reach such radiation levels, greenhouse gas emissions should be significantly reduced [5]. On the other hand, the other scenarios consider the increase of greenhouse gas emisions and radiative forcing in different tendencies, been RCP 8.5 the most critical scenario [4].

However, the database supplied by CR2 used in this work as the only available product for the study area, have only modeled up to the date two scenarios: RCP2.6 and RCP8.5 [6].That´s why, considering RCP 8.5 as a critical change scenario, it was selected for the study conducted. Nevertheless, future works could consider the remaining RCP scenarios if available.

Part of this information is included in the new manuscript: lines 165- 176

2. If the forecasts obtained are correct, they will come true (in terms of hydrological changes), provided that the land cover (land use) does not undergo significant changes. But as temperatures rise and precipitation decreases, even without human intervention, the earth's cover is unlikely to remain unchanged until 2080. These scenarios should also be covered in the work, even if at a qualitative level.

 

ANSWER: The study group that subscribes this article appreciates the suggestion made by the reviewer. In the information consulted for the present report, we observed that previous results have been obtained regarding the importance of analyzing the individual and combined effects of land use change and climate change. This could help on the one hand understanding the effect of these two stressors on the components of the hydrological cycle and, on the other hand, to address most probable future scenarios. The importance of treating the data in this way is to determine which of the alterations can affect the hydrological components to a greater and lesser extent to determine their individual and combined effect. Different studies have reported the importance of this analysis because the response of the basins could be also affected by the climatic region, the geographical physical characteristics, the scale and the land use/cover changes levels [7,8,9]. The results of these studies can help to understand the cause of changes in hydrology and to understand the relevant impacts for local actors, farmers and decision makers.

At this moment, we are working on a manuscript that addresses the individual and combined effects of the land use/cover change and future climate change in basins of the south central zone of Chile. The present manuscript provides the first results to determine the importance of the individual effect of climate change in the south central zone of Chile. This combined to our previous report [9] that studied the individual effect of land cover/use change over the water cycle in other Chilean watersheds, have allowed us to address the study on the individual and combined effect of land use change and climate change together. Nevertheless, in the present manuscript, we have briefly incorporated the importance of considering both effects and the future perspectives of the investigation group (lines 536-547).

3. Line 114 and Figure 1. What does the height interval from 27 to 1724 m above sea level mean for the two basins? Please write the highest and lowest height for each basin studied. Are you sure that the lowest point (hydrological post) of one of the basins is located 27 m above sea level, given the distance from the Pacific coast of several tens of kilometers? It would be ideal if you additionally plot hypsographic curves for each basin.

 

ANSWER: The study basins were described again including the lowest and highest points of both watersheds (lines 112 - 116). The information is also included in figure No 1 in the new manuscript.

 

4. Figure 1. Which of the two maps does the scale at the bottom frame refer to?

 

ANSWER: The scale described the study basins, however, in the new manuscript this scale was relocated into the basins framework for a better understanding (figure 1).

 

5. Figure 2. The soil cover map. Is it just enough to know only the types of soils for modeling but not their granulometric composition, which determines many important soils' hydrological properties? You do not say anything about this in your work!

 

ANSWER: The information considering the soil type was obtained from the Agrological Studies of the IX Region of Chile as developed by the Natural Resources Information Center (CIREN) in 2002 [26]. This study provides information about the soil type present on the study area and their associated physical-chemical properties. This information was included in the database used in the SWAT model for the hydrological simulations. This information was included in the new manuscript lines 143 – 148

 

The database used by the model for the soil type consider the following parameters [10]:

 

SNAM: Soil name

HYDGRP: Soil hydrologic group (A, B, C, or D).

SOL_ZMX: Maximum rooting depth of soil profile (mm).

ANION_EXCL: Fraction of porosity (void space) from which anions are excluded.

SOL_CRK: Potential or maximum crack volume of the soil profile expressed as a fraction of the total soil volume.

TEXTURE: Texture of soil layer.

SOL_ Z: Depth from soil surface to bottom of layer (mm).

SOL_BD: Moist bulk density (mg/m³ or g/cm³).

SOL_AWC: Available water capacity of the soil layer (mm H₂O/mm soil).

SOL_K: Saturated hydraulic conductivity (mm/hr).

SOL_CBN: Organic carbon content (% soil weight).

SOL_CLAY: Clay content (% soil weight).

SOL_SILT: Silt content (% soil weight).

SOL_SAND: Sand content (% soil weight).

SOL_ROCK: Rock fragment content (% total weight).

SOL_ALB: Moist soil albedo.

USLE_K: USLE equation soil erodibility (K) factor (units: 0.013 (metric ton m² hr)/(m³-metric ton cm)).

 

6. Figure 2. How do you explain the choice of the collection points' location for climate information in the two basins? Please give more explanation in the work.

 

ANSWER: In order to select the gauging points, a consistency analysis was performed. For this purpose, the quality (percentage of days with acquired data), coherence (logic information) and the time extension of the databases were evaluated using the fluviometric data from CR2 [11]. According to results, in the study areas, only two hydrometric stations had a 95% of the information related to daily average flow. For Quino basin, there was obtained information from 1980-2012 and, in the case of Muco basin from 1980-2016; such information was used for the model calibration and validation procedures.

 

This information is included in the new manuscript lines 188 – 195

 

The available meteorological data from CR2MET database for past climate and data from RegCM4-MPI-ESM-MR used for future climate were extracted at the same geographical points (latitude-longitude). Point’s extraction was carried out to avoid possible biases induced by changes in the spatial positioning of the meteorological data provided to the SWAT model between calibration and projection. In this way a point to pixel extraction method was applied.

 

This information is included in the new manuscript lines 177 –181

 

7. Line 202. “ … using the cover land/use corresponding to 1986 …” cover land/use?

 

ANSWER: The term “cover land/use” is a typing mistake. The term was corrected to “land cover/use” in the new manuscript.

 

8. Figure 4 needs to be redone. It is poorly readable.

 

ANSWER: Figure 4 was corrected according to suggestion. In order to provide a better manuscript understanding, figures 1, 2 and 5–10 were also improved in resolution and font size.

 

9. Line 315-316. 79 mm (LAT_Q). What is LAT_Q? There was no information about it in the text above.

ANSWER: The term LAT_Q correspond to a parameter that was not analyzed in the present work. This information was deleted from the manuscript.

 

10. It would be beneficial to provide a single summary table of changes in the water balance structure for different periods, including periods of calibration and/or validation

 

ANSWER: Table No 2 was modified to include the absolute change values for the comparison periods.

This table reports now the absolute and relative changes among the historical period (comprising the calibration and validation periods) and the simulated future scenarios.

 

11. Line 469-472. Why modeling in the BioBio River basin resulted in predictions with more dramatic reductions in precipitation and runoff than your study? Some discussion of these differences would be helpful. Have there been any other forecast studies for other river basins in the central Chile region?

 

ANSWER

In the study conducted by Stehr et al. [12] in the the BioBio river basin, the climatic scenarios considered differ from RCP 8.5 used in the present report for Quino and Muco rivers´ basins. In effect, Stehr et al considered the IPCC 2001 scenarios A2 and B2 for a far future scenario (2070-2100). On the other hand, the climatic conditions in the BioBio river basin (precipitation and temperature regimes), are also different from the Quino and Muco watersheds conditions in the foothills of the Andes in the Araucanía region. Specifically, the Vergara river basin (part of the BioBio watershed) located at the central depression in the BioBio region, have lesser yearly precipitations (up to 1650 mm) [16, 17] than Quino and Muco Basins (up to 2693 mm). Another important characteristic to consider is that the BioBio river basin presents a very marked seasonality, with dryer summers due to the mediterranean climate influence [16, 17]. By the contrary, in Quino and Muco basins, the stations are less marked in the precipitation with wet summers because of a lesser influence of the Mediterranean climate but a higher dominance of temperate humid conditions. However, the objective to present this result as comparison in our study in to show that they both present similar trends according to an increase in the temperatures and a decrease in the precipitation with consequently lesser basin flows. Few other articles have reported studies conducted in this Chilean zone, mainly because of the data accessibility lack, however Vicuña et al. [13] did reported similar trends using A2 and B2 scenarios from IPCC 2001 in cordilleran basins in the Atacama region. In addition, Barrientos et al. [14] recently reported an study also conducted in experimental subbasins of the BioBio river obtaining similar results in the trends. Generally, as it has been reported by the CR2 group studies [11] and as the aforementioned references suggests, the warming effects and its consequences seems to be greater for northern than for southern zones in Chile [11].

Part of this discussion was included in the new manuscript in section 4, lines 519-528

12. Slight improvement in English is required.

 

ANSWER: According to the comments of the three reviewers, several aspects were corrected in the manuscript.

 

REFERENCES

 

1. Cambio Climático: Bases Físicas. GUÍA RESUMIDA GRUPO DE TRABAJO I DEL QUINTO INFORME DEL IPCC. Ministerio de Agricultura, Alimentación y Medio Ambiente, Madrid, España, 2015. Available in: http://www.magrama.gob.es/es/cambio-clima-tico/publicaciones.O The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Inter-governmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Bos-chung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, Uni-ted Kingdom and New York, NY, USA.
2. Climate Change 2014: Impacts, Adaptation, and  Vulnerability.  Part  B:  Regional  Aspects. In;  I to  the Fifth Assessment 525Report of the Intergovernmental Panel on Climate Change Barros, V.R., C.B. Field, D.J. Dokken, M.D. Mastrandrea, K.J. Mach, 526T.E.  Bilir, M.Chatterjee,  K.L.Ebi, Y.O.Estrada, R.C.Genova, B.Girma, E.S.Kissel, A.N.Levy,  S.Mac, and L.L.W.,  Ed.; 527Cambridge University Press: Cambridge, United Kingdom and New York, NY, USA, 2014; pp. 1133–1197.
3. Dash, S.S. et al. A hydrological modelling-based approach for vulnerable area identification under changing climate scenarios. Journal of Water and Climate Change, 2020. https://doi.org/10.2166/wcc.2020.202.
4. Araya-Osses, D.; Casanueva, A.; Román-Figueroa, C.; Uribe, J.M.; Paneque, M. Climate change projections of temperature and precipitation in Chile based on statistical downscaling. Clim. Dyn.2020, 54, 4309–4330.
5. Javaherian, M;Ebrahimi, H; Aminnejad, B. Prediction of changes in climatic parameters using CanESM2 model based on RCP scenarios (case study): Lar dam basin. Ain Shams Engineering Journal. 2020. https://doi.org/10.1016/j.asej.2020.04.012.
6. Centro de Ciencia del Clima y la Resiliencia (CR)2. Simulaciones climáticas regionales. 2018, 26.
7. Mwakalila, S.; Feyen, J.; Wyseure, G. The influence of physical catchment properties on baseflow in semi-arid environments. J. Arid Environ.2002, 52, 245–258.
8. Price, K. Effects of watershed topography, soils, land use, and climate on baseflow hydrology in humid regions: A review. Prog. Phys. Geogr. 2011, 35, 465–492.
9. Martínez-Retureta, R.; Aguayo, M.; Stehr, A.; Sauvage, S.; Echeverría, C.; Sánchez-Pérez, J.M. Effect of land use/cover change on the hydrological response of a southern center basin of Chile. Water (Switzerland) 2020, 12, 1–21.
10. Arnold, J.G.; Kiniry, J.R.; Srinivasan, R.; Williams, J.R.; Haney, E.B.; Neitsch, S.L. SWAT 2012 Input/Output Documentation 2012, 30.
11. Centro de Ciencia del Clima y la Resiliencia (CR)2. Simulaciones climáticas regionales. 2018, 26.
12. Stehr, A.; Debels, P.; Arumi, J.L.; Alcayaga, H.; Romero, F. Modelación de la respuesta hidrológica al cambio climático: Experiencias de dos cuencas de la zona centro-sur de Chile. y Ciencias del Agua 2010, 1, 37–58.
13. Barrientos, G.; Herrero, A.; Iroumé, A.; Mardones, O.; Batalla, R.J. Modelling the Effects of Changes in Forest Cover and Climate on Hydrology of Headwater Catchments in South-Central Chile. Water 2020, 1–22.
14. Vicuña, S.; Garreaud, R.D.; McPhee, J. Climate change impacts on the hydrology of a snowmelt driven basin in semiarid Chile. Clim. Change 2011, 105, 469–488.
15. Barrientos, G.; Herrero, A.; Iroumé, A.; Mardones, O.; Batalla, R.J. Modelling the Effects of Changes in Forest Cover and Climate on Hydrology of Headwater Catchments in South-Central Chile. Water 2020, 1–22.
16. Fustos, I., Abarca-Del-Rio, R., Ávila, A., Orrego, R. A simple logistic model to understand the occurrence of flood events into the Biobío River Basin in central Chile. Flood Risk Management. 2017, 10, 17–29.
17. Yevenes, M.A., Figueroa, R., Parra, O. Seasonal drought effects on the water quality of the Biobío River, Central Chile. Environ Sci Pollut Res (2018) 25:13844–13856. https://doi.org/10.1007/s11356-018-1415-6.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have made the changes suggested

Reviewer 2 Report

The paper has been significantly improved since the first time was reviewed. Authors followed and answered to all my comments. Now I can recommend paper for the publication.

Reviewer 3 Report

I thank the authors for the detailed revision of the manuscript.