the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Merits and Limits of SWAT-GL: Application in Contrasting Glaciated Catchments
Abstract. The recently released SWAT-GL aims to overcome multiple limitations of the traditional hydrological model SWAT (Soil Water Assessment Tool) in glaciated mountainous catchments. SWAT-GL intends to increase the applicability of SWAT in these catchments and to reduce misapplication when glaciers have a significant role in the catchment hydrology. It thereby relies on a mass balance module, based on a degree-day approach similar to SWAT’s snow melt module, extended by a glacier evolution component which is based on the delta-h (Δh) parameterization. The latter one is a mass conserving approach which enables the spatial distribution of ice thickness changes and thus dynamic glacier retreat. However, the extended SWAT version was not yet comprehensively assessed. Hence, our paper aims to evaluate SWAT-GL using four different benchmark glaciers which are part of the USGS (United States Geological Survey) Benchmark Glacier Project. The study considers a comprehensive evaluation procedure, where the routine is optimized on glacier mass balance and hypsometry as well as snow cover. Snow cover is included to consider snow-glacier feedbacks appropriately. Besides, a sensitivity analysis using Elementary Effects (or Method of Morris) is performed to give a detailed picture on the importance of the introduced glacier processes, as well as the relevance of the interactions with the already-existing snow routine. We intentionally did not include discharge in the optimization procedure to fully demonstrate the capabilities of SWAT-GL in terms of glacier and snow processes. Results demonstrate that SWAT-GL is able to perform reasonably well in contrasting glaciated catchments, which underlines SWAT-GL’s applicability and transferability. We could further show its strong (non-linear) interactions with the existing snow routine suggesting a simultaneous calibration of the snow components. While snow and glacier processes were adequately represented in the catchments, discharge was not necessarily represented sufficiently when excluded in the optimization procedure. However, SWAT-GL has been shown to be easily capable of reproducing discharge when used in a stand-alone optimization, although this may come at the expense of model consistency.
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RC1: 'Comment on hess-2024-89', Cyril Thébault, 09 Aug 2024
Dear authors,
Please find attached an annotated pdf with comments.
I found the document well presented with neat and informative figures. The quick methodological reminders at the beginning of each section are also useful for the flow of the reading. However, I found that the manuscript could be clarified here and there (see comments in the pdf) and that reading could sometimes be difficult due to the use of numerous acronyms. I also found that the document lacked a few methodological elements and a well-defined common thread to link the different elements presented (e.g. sensitivity analysis made but not used after, calibration on the streamflow variable in section 3.6. when it was previously only used for validation).
A main point of improvement I see is that the manuscript can (should?) benefit of a benchmark to compare the SWAT-GL model with a standard approach (e.g. SWAT-GL vs a simple degree-day glacier/snow module for glacier/snow variables and SWAT-GL vs SWAT for streamflow) in order to highlight the benefits and limits of SWAT-GL.
Kind regards,
Cyril Thébault
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RC2: 'Comment on hess-2024-89', Anonymous Referee #2, 20 Sep 2024
General comments
This paper presents a thorough sensitivity analysis and calibration for the newly developed SWAT-GL model, evaluated across four glaciated catchments. The findings are valuable for the broader scientific community, including those studying glaciers and using SWAT models. While the methodology and case study contents are clear, the results analysis are not well structured and disjoint. The manuscript needs improvements in writing. It is lengthy and difficult to read. I suggest the authors shorten it and consider using an English editing service. Below are detailed comments.
Major comments
- Section 2.4 (Line 240): It would be beneficial to explain why the analysis exhibits a monotonous pattern. Additionally, in Section 3.1, clarify why values of 0, 0.25, and 0.5 correspond to linear, monotonous, and nearly monotonous behavior, respectively. Please include references if applicable.
- Section 3: Numerous aspects of optimization are analyzed in this section. I recommend starting Section 3 with an overview of the different optimization aspects being investigated. Clearly state the goals of each aspect and explain how they complement each other in the results analysis. Without this context, the structure of the subsections appears disjointed.
Minor comments
- Figure 1: Could you add state/province names to the middle map? This would help readers identify regions, such as US states or Canadian provinces.
- Figures 2 and Onward: Please add abbreviations next to the glacier names in all figures and tables to help readers link the glacier names in the figures/tables with their abbreviations in the text.
- Figure 6: Clarify how the three blue symbols correspond to the best solutions for mass balance, snow cover, and discharge.
- Table 4: Please specify how KGE and PBIAS are calculated, or add references for these metrics.
- Line 370: Add the parameter symbol after its name to help readers link the parameter to Figure 6.
- Line 433: Use consistent formatting—should this be "Table 2" instead of "Tab. 2"?
- Line 437: Include references to support the statement "results often considered satisfactory in hydrological studies."
- Line 445: Is the "most significant" conclusion based on a statistical significance test? Please clarify.
- Lines 473-475: Please check the brackets in these lines for errors.
- Some sentences require grammar correction or rephrasing for clarity:
- Lines 360-361
- Lines 466-467
- Lines 500-501
- Lines 543-544 - Lines 299-322: Consider shortening or breaking this paragraph into smaller sections to improve readability and focus.
Citation: https://doi.org/10.5194/hess-2024-89-RC2 - RC3: 'Comment on hess-2024-89', Dipti Tiwari, 17 Oct 2024
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