the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 02 Aug 2024
Assessing the different components of the water balance of Lake Titicaca
Abstract. This study estimates the water balance of a poorly-gauged large lake using an integrated modeling framework that accounts for natural hydrologic processes and net irrigation consumption. The modeling framework was tested on Lake Titicaca, located in the Altiplano of the Central Andes of South America. We used a conceptual approach based on the Water Evaluation and Planning System (WEAP) platform at a daily time step for the period 1982–2016, considering the following terms of the water balance: upstream inflows, direct precipitation and evaporation over the lake, and downstream outflows. To estimate upstream inflows, we evaluated the impact of snow and ice processes and net irrigation withdrawals on predicted streamflow and lake water levels. We also evaluated the role of heat storage change in evaporation from the lake. The results showed that the proposed modeling framework makes it possible to simulate lake water levels ranging from 3,808 to 3,812 m a.s.l. with good accuracy (RMSE = 0.32 m d-1) under a wide range of long-term hydroclimatic conditions. The estimated water balance of Lake Titicaca shows that upstream inflows account for 56 % (958 mm yr-1) and direct precipitation over the lake for 44 % (744 mm yr-1) of the total inflows, while 93 % (1,616 mm yr-1) of total outflows are due to evaporation and the remaining 7 % (121 mm yr-1) to downstream outflows. The water balance closure has an error of -15 mm yr-1. At the scale of the Lake Titicaca catchment, snow and ice processes, and net irrigation withdrawals had minimal impact on predicted upstream inflow. Thus, Lake Titicaca is primarily driven by variations in precipitation and high evaporation rates. The proposed modeling framework could be replicated in other poorly-gauged large lakes, as we demonstrate that a simple representation of natural hydrologic processes and irrigation enables accurate simulation of water levels.
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RC1: 'Comment on egusphere-2024-2370', Anonymous Referee #1, 21 Aug 2024
The manuscript presents a water balance modeling chain for Lake Titicaca, simulating various water balance components, including precipitation, evaporation, inflow (considering irrigation water abstraction and glacial contributions), and outflow. The model effectively closes the water balance and quantifies the contributions of these components. Notably, the authors find that glaciers and irrigation water abstraction have a minimal impact on the overall results.
The manuscript is interesting, well-written, detailed, and comprehensive and of interest for publication in HESS. However, the text is at times overly lengthy and repetitive, particularly in the methods and results sections. Condensing the content without sacrificing critical information and possibly moving some material to supplementary sections would enhance clarity and focus. In addition, the level to which the presented manuscript is build upon and novel to Lima-Quispe et al., 2021 in terms of methods applied can be made a bit more explicit. To aid the authors with this, detailed comments and suggestions are provided below.
Major Comments
- The manuscript concludes that glaciers and irrigation have a minor impact on the water balance. Given this finding, the detailed analysis of these components could be relocated to the appendix to streamline the manuscript.
- The manuscript builds on the model presented by Lima-Quispe et al., 2021. For example, the climatological data used (from the GMET tool) are very similar. This should be more clearly described in the manuscript, taking Lima-Quispe et al., 2021 as a starting point and not presenting already published methods as novel. The authors should more explicitly differentiate their work from the previous study, highlighting the findings of the former, and showcasing how the current study builds upon it. The novelty is already highlighted to some extent, for example by articulating the contribution of a detailed glacier method. However, the direct contributions from this have very little impact on the final results. Seen both studies are authored by the same first author, a direct comparison between the results of both studies, possibly through a figure, would further clarify the advancements made in the current study (for example, figure 6 of Lima-Quispe et al., 2021 is very similar to Fig 10 of the current paper).
- The manuscript would benefit from a more concise presentation. Repetitions, and lengthy wordings in the introduction, methods and results should be reduced.
- Abstract and Introduction: The introduction currently provides a broad overview of large, poorly gauged lakes, but since the focus is on Lake Titicaca, it should be emphasized from the outset. The introduction would benefit from a revision to prioritize the unique aspects of Lake Titicaca, with general information on lakes serving as background rather than the main focus. The description in the introduction of lakes in general terms could be condensed, with more specific examples of how different lakes' conditions can vary. This will help contextualize the study’s focus on Lake Titicaca.
Specific comments:
L42: Specify which lakes are being referred to as "many lakes."
L81: Replace "water uses" with "water management" to include aspects like dam management, which could lead to differences in flow magnitude and seasonality.
L84-86: Clarify and reformulate the example given.
L124: Clarify whether "net water withdrawals" refer to the lake itself.
Section 1.4: Explain why Lake Titicaca was chosen for this study and what value the water balance study brings to lake managers.
L155: Introduce Lima-Quispe et al., 2021 earlier in the introduction, detailing its findings and limitations.
L161: why is this an “integrated” water balance approach and what is the difference with a normal water balance approach?
L169: Include the lake's surface area.
Section 2.2: Acknowledge the methodological overlap with Lima-Quispe et al., 2021.
Figure 2, panel b: Adjust the color bar to ensure white corresponds to zero or use a sequential color bar.
L252: Explain "Crop coefficient Kc" when first introduced; consider moving this to the methods section.
L347: Clarify what is meant by "production."
L445: Specify if LSWT time series availability is meant here.
L475: Replace "assessment" with "evaluation."
Models A, B, C: Consider renaming these to something more descriptive (e.g., IRR+GLAC) to avoid repetitive explanations and ease the figure interpretations.
L568-573: Rewrite these sentences to be more concise.
L595: Indicate in the figure caption that it deals with “glacier” mass balance; same for Table 4.
Figure 8: Highlight in the text that variability between glaciers for simulated mass balance is greater than for geodetic mass balance. What would be a possible explanation?
L614-615: Remove or shorten this sentence, as it is likely repeated later. There is no need to refer to the next section in the last sentence of the current section.
Fig. 12: add the “mm/year and mm/month” to the numbers in the legend, or alternatively, put the numbers in a separate table would allow to compare them more clearly.
Section 4.2.2: It would be useful to incllude the relative contributions of different water balance terms in the main text, as referred to in the abstract.
Section 5.1: This section contains significant repetition and should be condensed.
L736-740: the direct comparison and description of the added value of the present study with Hosseini-Moghari et al., 2020 is a repetition from the intro, and possibly redundant as they treat very different lake system (Urmia), moreover, there are more water balance studies of large lakes, such as Vanderkelen et al., 2020 and other studies included in the introduction.
L744-750: These lines contrast the following paragraph: here, the point is made the current study includes more detailed representation of snow and ice, and irrigation in the upstream catchments. In the next paragraph there is discussed that these components are of little importance to the water balance of the lake. While the manuscript proves its value of uncovering this, it should not be highlighted this clear in the text that it is an added value.
L878-880: Is it really necessary to refine the glacier simulations as they are not important in the water level simulations?
Section 5.3: how feasible is it to translate this modelling chain to another large lake? Also, what are the implications for Lake Titicaca of the presented results? This would be interesting to include in the papers abstract. Appendix: Ensure all figures in the appendix are referenced in the main manuscript.
Appendix: make sure that all appendix figures are referenced in the main manuscript.
Citation: https://doi.org/10.5194/egusphere-2024-2370-RC1 -
AC1: 'Reply on RC1', Nilo Lima-Quispe, 26 Sep 2024
We sincerely thank the referee for the time and effort she/he spent reviewing the initial manuscript and for providing clear, pertinent, and constructive suggestions for improvement. These have been invaluable in rewriting the paper. Please, find our responses in a supplement file as a detailed point-by-point reply to the referee comments.
We hope the revisions made to the manuscript have enhanced its scientific quality.
Nilo Lima on behalf of the co-authors
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RC2: 'Comment on egusphere-2024-2370', Benjamin Kraemer, 03 Sep 2024
Lima-Quispe et al present a valuable contribution to the field of hydrology by addressing the challenging task of assessing the water balance of a poorly-gauged large lake, Lake Titicaca. The integrated modeling framework proposed in the study is novel and addresses limitations in existing methods, particularly for large lakes with sparse data availability. The study's findings on the dominant role of precipitation and evaporation in Lake Titicaca's water balance are substantial and have broader implications for water resource management in similar regions. The scientific methods and assumptions are generally sound, and the results are comprehensive and well-supported. The most important areas of feedback are:
- Clarity and Focus: The introduction could benefit from a more research question-driven approach. Clearly stating the main research question at the outset would improve focus and engagement. Additionally, consider streamlining the methods section by moving some of the detailed discussions (e.g., glaciological and hydrological control data) to the appendix.
- Novelty and Contributions: While the novelty of the integrated modeling framework is evident, it could be further emphasized in the abstract and introduction. Clearly articulating how this approach differs from traditional models and highlighting its unique advantages would strengthen the manuscript's impact.
- Assumptions and Limitations: The discussion of assumptions, particularly regarding the fixed glacier area and the exclusion of groundwater exchanges, could be expanded. Addressing the potential limitations of these assumptions and their implications for the study's findings would add depth to the analysis.
- Incorporating relevant data sources: Several key data sources were not included but could strengthen the manuscript substantially especially data on irrigated versus non-irrigated agriculture and LSWT.
- Reproducibility: Providing the modeling code or a detailed description of the algorithms as supplementary material would significantly enhance the reproducibility of the study and its value to the research community.
- Presentation: The manuscript is well-written and organized. However, the discussion section could be condensed to avoid repetition and improve clarity. Additionally, minor revisions to figures and captions could enhance their visual appeal and informativeness.
I have organized my feedback below according to the HESS review criteria.
1. Relevance to HESS Scope:
The manuscript addresses topics that are highly relevant within the scope of Hydrology and Earth System Sciences (HESS). It focuses on assessing the water balance of Lake Titicaca using an integrated modeling framework, which is particularly valuable given the challenges of studying poorly gauged large lakes. This research is of significant interest to the hydrology community due to its emphasis on understanding the impacts of climate variability and human activities on lake water levels.
Suggestions for Improvement:
- Lines 123-129: Consider enhancing the discussion on the relevance of the study by providing specific examples of how the integrated modeling framework addresses gaps in existing research. For example, you could highlight how this study overcomes certain limitations faced by previous research on poorly gauged large lakes. This would help position the manuscript more clearly within the broader context of current literature.
2. Novelty:
The manuscript introduces novel concepts, particularly in the integration of various hydrological processes, such as snow and ice melt, heat storage changes in evaporation, and irrigation impacts, within a single modeling framework. However, the manuscript would benefit from a clearer differentiation from previous work.
Suggestions for Improvement:
- Abstract and Introduction: The abstract and introduction could be more research question-driven. Clearly identifying the main research question in the first few sentences would improve focus. Consider whether there is uncertainty or disagreement over the dominant drivers of Lake Titicaca’s water budget and clarify if this manuscript aims to resolve such questions.
- Lines 155-163: The introduction mentions several research questions. It would be beneficial to identify the most important one and focus on it throughout the introduction, rather than on data sourcing details, which might detract from the main narrative.
- Lines 161-163: Please clarify what is meant by an "integrated" water balance approach and how it differs from traditional models. This will help readers better appreciate the novelty of your approach.
3. Substantial Conclusions:
The conclusions presented in the manuscript are well-supported by the results. The inclusion of snow and ice processes and heat storage changes in evaporation is particularly important for modeling lake water levels.
Suggestions for Improvement:
- Lines 744-750: While it is important to highlight that snow, ice, and irrigation have minimal impacts, ensure this does not detract from the value of including these processes in the model. Emphasizing that understanding the minimal impact is itself a valuable finding could strengthen this point.
- Lines 377-378: Elaborate on the potential impact of assuming a fixed glacier area on long-term simulations. Discuss how this assumption might influence the results under different climate scenarios or with ongoing glacier retreat.
4. Scientific Methods and Assumptions:
The scientific methods and assumptions are clearly outlined and valid. However, the methods section could be made more concise, as it currently includes a level of detail that may be repetitive.
Suggestions for Improvement:
- Lines 258-259: The difference between rainfed and irrigated agriculture can also be captured by other land cover datasets, such as those produced by the ESA Land Cover CCI, which offers annual datasets.
- Lines 445-446: Consider using Lake Surface Water Temperature (LSWT) data available from remote sensing sources, such as the ESA Lakes Climate Change Initiative, which might provide more accurate results in a hydrosystem driven by net radiation and evaporation.
- Lines 295-315: Consider moving the detailed discussion of glaciological and hydrological control data to the appendix. This would streamline the methods section and enhance readability.
- Lines 469-474: Discuss the implications of excluding groundwater exchanges, especially in light of observed discrepancies in the water balance. Including a brief sensitivity analysis or discussion on the potential significance of this exclusion under different hydrological conditions could add depth to the analysis.
5. Sufficiency of Results:
The results are sufficient to support the interpretations and conclusions. The comprehensive simulations and sensitivity analyses presented strengthen the validity of the findings.
6. Traceability and Reproducibility:
The manuscript provides detailed descriptions of datasets, model parameters, and calibration processes, which enhances the traceability of the results. However, reproducibility could be further improved.
Suggestions for Improvement:
- Lines 320-330: Consider providing the modeling code or at least a detailed description of the algorithms used as supplementary material. Alternatively, making the code available on a public repository would greatly enhance the reproducibility of the study and its usefulness to other researchers.
7. Credit to Related Work:
The manuscript appropriately credits related work and clearly indicates the authors' contributions. The review of relevant literature is comprehensive, situating the study within the broader context of hydrological research. However, in some areas, differentiation from previous work could be more explicit.
8. Title Accuracy:
The current title, "Assessing the Different Components of the Water Balance of Lake Titicaca," accurately reflects the contents of the paper. However, a more specific title that highlights the key findings could be more informative. Consider options like:
- "Modeling Lake Titicaca's Water Balance: The Dominant Roles of Precipitation and Evaporation."
- "Precipitation and Evaporation as Primary Drivers of Lake Titicaca’s Water Balance."
9. Abstract Quality:
The abstract effectively summarizes the key objectives, methods, and findings of the study. However, it could be slightly improved by emphasizing the study's contributions to existing knowledge and the novelty of the integrated modeling framework.
Suggestions for Improvement:
- First 3 Lines: A clear statement of the research question or gap in the first three lines would significantly improve the abstract’s clarity and focus.
10. Overall Presentation:
The manuscript is well-structured and clear, with a logical flow of information. The figures and tables are well-designed and contribute effectively to the presentation of results.
Suggestions for Improvement:
- Section 5.1 (Discussion): This section contains significant repetition. It could be condensed by focusing on summarizing key findings without reiterating points made earlier.
- Lines 568-573: These sentences could be made more concise by merging them into a single, impactful sentence.
11. Language Fluency and Precision:
The language used in the manuscript is fluent and precise, though it could be made more concise. The manuscript is generally well-written, with minimal grammatical errors or ambiguities, and the technical terminology is used appropriately.
Suggestions for Improvement:
- Lines 124-126: Clarify whether "net water withdrawals" refer specifically to the lake or the entire hydrological system. This could be rephrased for clarity: "net water withdrawals from both the lake and its contributing catchments."
- Lines 614-615: Consider removing or shortening this sentence, as it may be repetitive. There is no need to refer to the next section in the last sentence of the current section.
- Lines 745-747: To avoid redundancy, consider rephrasing to: "this study enhances the representation of snow and ice processes and irrigation impacts."
- Lines 807-808: Consider omitting this sentence as it might be unnecessary.
12. Mathematical Formulae and Symbols:
Mathematical formulae, symbols, abbreviations, and units appear to be correctly defined and used throughout the manuscript. The equations are clearly presented and appropriately referenced within the text.
13. Clarity of Figures and Tables:
The figures and tables are clear and informative. They effectively support the text and enhance the reader's understanding of the study's findings.
Suggestions for Improvement:
- Figure 2, Figure 8: Reverse the order of gradient legends so that low values are on the bottom and high values on the top.
- Figure 2, Right Panel: Adjust the color bar to ensure that white corresponds to zero, or use a sequential color bar to improve the visual interpretation of the data.
14. References:
The number and quality of references are appropriate. The manuscript cites a comprehensive range of relevant studies, including recent research, which strengthens the contextual foundation of the study.
Citation: https://doi.org/10.5194/egusphere-2024-2370-RC2 -
AC2: 'Reply on RC2', Nilo Lima-Quispe, 26 Sep 2024
We sincerely thank Dr. Benjamin Kraemer for the time and effort spent reviewing the initial manuscript and for providing clear, pertinent, and constructive suggestions for improvement. These have been invaluable in rewriting the paper. Please, find our responses in a supplement file as a detailed point-by-point reply to the referee comments.
We hope the revisions made to the manuscript have enhanced its scientific quality.
Nilo Lima on behalf of the co-authors
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