Can high-resolution convection-permitting climate models improve flood simulation in southern Quebec watersheds?

Sabzipour, Behmard; Lucas-Picher, Philippe; Turcotte, Richard; Rondeau-Genesse, Gabriel

doi:10.5194/egusphere-2025-3436

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https://doi.org/10.5194/egusphere-2025-3436

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19 Aug 2025

| 19 Aug 2025

Can high-resolution convection-permitting climate models improve flood simulation in southern Quebec watersheds?

Behmard Sabzipour, Philippe Lucas-Picher, Richard Turcotte, and Gabriel Rondeau-Genesse

Abstract. In August 2024, Montreal and its surroundings, located in the south of the Quebec province, experienced one of its most destructive meteorological events in history, associated to the remnants of the tropical storm Debby, according to the Insurance Bureau of Canada (Published on 2024, September 13). With climate change, the frequency and intensity of extreme weather events are expected to increase, explaining why government and private sectors, particularly insurance companies, requires enhancing their preparedness.

Recent studies highlighted the potential of high-resolution climate models (with grid sizes smaller than 4 km) to improve precipitation extremes at sub-daily timescales. This study focuses on heavy rainfall events during the warm season, comparing outputs from the latest Canadian Regional Climate Model (CRCM6/GEM5) at 12 km and 2.5 km resolutions. For the first time, we estimated that the CRCM6/GEM5-2.5km better captured the intensity of extreme hourly rainfall events compared to the CRCM6/GEM5-12km, aligning more closely with weather station data.

To assess whether this added value extends to hydrological modeling, we used a lumped hydrological model to simulated water flows at an hourly time step for 11 basins located over southern Quebec for the period 2001–2018. For most basins, summer-fall peak flows simulated using the CRCM6/GEM5-2.5km had lower biases compared to those simulated with the CRCM6/GEM5-12km. These findings emphasize the importance of high-resolution climate models in improving extreme event simulations, which is essential for better risk assessment and adaptation strategies in a warming climate.

Received: 16 Jul 2025 – Discussion started: 19 Aug 2025

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Behmard Sabzipour, Philippe Lucas-Picher, Richard Turcotte, and Gabriel Rondeau-Genesse

Status: final response (author comments only)

RC1:
'Comment on egusphere-2025-3436', Anonymous Referee #1, 07 Oct 2025
The authors evaluate the perfomance of a 12-km RCM and a 2.5-km CPRCM with respect to reproduction of primarily observed precipitation (rainfall) and discharge extremes in Quebec. Is is found (claimed) that the CPRCM better reproduces both types of extremes. While the topic is relevant and interesting, the methods appear overall well selected and applied, the presentation is neat, I cannot recommend publication of the manuscript in its present form. In the following I will explain why.
General comments
The paper tries to argue that the CPRCM does a much better job than the RCM, but this is, in my view, not (well) supported by the results. Sometimes it is clear that the CPRCM greatly overestimates the extreme rainfall (Fig. 3a, Fig. 4a), but this is basically neglected. Sometimes argumentation is based on visual inspection (Figs. 6-9) or a few numbers (Table 3) but without testing whether differences are statistically significant (which is really important, especially as you sometimes work with very small data sets). OK, it may be that the CPRCM does a (significantly) better job than the RCM, but the current results do not prove that.

Some very important aspects are not taken into account, notably the impact of spatial resolution and the impact of climate model bias, both having a huge impact on both rainfall and discharge (extremes). They are briefly mentioned but without being investigated, which makes the significance of the results virtually impossible to judge, in my opinion.

The text is overall well written, but with far too much of superfluous information (things that one must assume is known to HESS readers) and repetition. To me it has the feel of a (good) student essay, but not on the level of a scientific paper in HESS. Some examples:
The description of GCMs and RCMs in the introduction (40-55) is known to readers.

Readers know how KGE works (248-250), what a CDF is (296-299), how box plots should be interpreted (447-451), and other similar examples.

Section 5 (Discussion) is in my view mainly a rather long summary of the study, mainly consisting of repetitions and with few real conclusions, other than general statements.

Specific comments:
164: Is this supposed to be a separate section?

270: 18 annual maxima is not much to work with, consider peak-over-threshold instead.

315: Should be (Fig. 3a, 3c, 3f), I think.

358-363: There is no need to repeat the figure caption in text, same happens also elsewhere. And how to visually interpret the match bewteen histograms is trivial. In addition, you do not need to explain the colour legends in the captions; we understand from the panels.

454: One “generally” too much here.
Citation: https://doi.org/10.5194/egusphere-2025-3436-RC1
- AC1: 'Reply on RC1', Behmard Sabzipour, 16 Jan 2026
  
  Thanks to both anonymous reviewers, Thanks for your time and attention for reading our paper carefully and thanks for your constructive comments for improving the paper. We added the response as an attached file
  Behmard Sabzipour on behalf of all authors
  
  Citation: https://doi.org/10.5194/egusphere-2025-3436-AC1
RC2:
'Comment on egusphere-2025-3436', Anonymous Referee #2, 22 Dec 2025

The manuscript entitled “Can high-resolution convection-permitting climate models improve flood simulation in southern Quebec watersheds?” investigates whether CPRCM simulations provide added value for flood simulation in southern Quebec, with focus on extreme summer and fall rainfall events. The topic is relevant and the objectives of the study are clear. The manuscript is also well organized and written. The comparison between the 12 km and 2.5 km CRCM6/GEM5 simulations, and try to link precipitation extremes to hydrological responses, are interesting to both the regional climate and hydrological communities. However, several important issues need to be addressed before the conclusions can be fully supported.

1. The study aims to assess the added value of CPRCM simulations. In this context, the choice of a lumped hydrological model raises concerns. The hydrological model used in this study (GR5dt) is a conceptual and lumped model with only elevation bands. Given that the main added value of CPRCMs lies in their improved representation of the spatial patterns of intense precipitation, the use of a lumped model may substantially limit the ability to assess this added value. For example, Figure 5 shows that for many basins the KGE driven by RCM-12 km is higher than that driven by CPRCM-2.5 km, which may partly reflect this modeling choice. While this limitation is mentioned in the discussion, the authors should better justify the choice of model and more clearly acknowledge the associated limitations when interpreting the improvements in flood simulations.

In addition, the manuscript states that “KGE values slightly increase as basin size increases”, whereas the figure shows substantial variability from left to right. Other factors may influence the results, such as elevation-related precipitation biases. An elevation-dependent analysis (e.g., bias or performance metrics versus basin mean elevation) could be very informative, especially given known elevation-dependent biases in precipitation.

2. Table 3 presents useful results. However, in Figure 7, several basins do not show a clear added value in the boxplots of peak flow bias (e.g., small basins such as Bras d’Henri, as well as larger basins such as Eaton, Au Saumon, and Etchemin). Additional explanation would be helpful here. In addition, it would be useful to clarify whether the peak flow bias reported in Table 3 is defined consistently with that shown in Figure 9.

3. Biases in simulated precipitation strongly affect hydrological model performance. I understand that no bias correction was applied to the climate model forcings before driving the hydrological model. However, the potential impact of precipitation biases on the flood simulation results, should be discussed more explicitly.

4. The manuscript suggests that CPRCM outputs improve flood simulations and can be useful for risk management strategies. It remains unclear whether the authors imply that CPRCM outputs can be used directly for hydrological applications. If so, under what conditions (e.g., bias correction, calibration)? A clearer discussion of the applicability and limitations of using CPRCM outputs for hydrological modeling would strengthen the paper.
Overall, the study addresses an important question, and provides useful information for hydroclimate research.

Citation: https://doi.org/10.5194/egusphere-2025-3436-RC2
- AC2: 'Reply on RC2', Behmard Sabzipour, 16 Jan 2026
  
  Thanks to both anonymous reviewers, Thanks for your time and attention for reading our paper carefully and thanks for your constructive comments for improving the paper. We added the response as an attached file
  Behmard Sabzipour on behalf of all authors
  
  Citation: https://doi.org/10.5194/egusphere-2025-3436-AC2

Behmard Sabzipour, Philippe Lucas-Picher, Richard Turcotte, and Gabriel Rondeau-Genesse

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Behmard Sabzipour, Philippe Lucas-Picher, Richard Turcotte, and Gabriel Rondeau-Genesse

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Short summary

Quebec, Canada is experiencing more frequent and intense rainfall events during the warm seasons, a trend expected to increase due to climate change. This raises the risk of more frequent and severe flooding in urban areas. To better understand extreme rainfall and the resulting floods, this study evaluates, for the first time in Canada, the advantages of using high-resolution climate model outputs. We then assess whether these data can improve peak flow simulations using a hydrological model.


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