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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Status: open (until 27 Sep 2024)
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RC1: 'Comment on egusphere-2024-2370', Anonymous Referee #1, 21 Aug 2024
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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
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