the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Oct 2024
Influence of Floodplains and Groundwater Dynamics on the Present-Day Climate simulated by the CNRM Model
Abstract. The climate impacts of floodwater stored over large inundated areas and groundwater stored in large unconfined aquifers at the global-scale are not yet well-documented, despite their potential to affect the atmosphere through contributions to land surface evapotranspiration fluxes. To address these gaps in knowledge, the present study aims to assess the potential role of these processes on present-day climate using the CNRM-CM6-1 global climate model, the physical core of the Earth System Model (ESM) used by the French National Center for Meteorological Research for climate projections. This model includes a dynamic river flooding scheme and a groundwater scheme accounting for the 218 world's largest unconfined aquifer basins. The study consists of four experiments, each with five ensemble members driven by observed monthly sea surface temperature and sea ice cover for the 1980–2014 period. The experiments include configuration variations where both groundwater and floodplain processes were activated or deactivated, as well as configurations where each process was individually activated. The various forcings used in CNRM-CM6-1 adhere to the CMIP6 recommendations. The False Detection Rate test is employed to assess the significance of field differences. This study found that the impact of groundwater and floodplains on precipitation and 2-meter air temperature biases is predominantly positive in comparison to observations, although on a very regional scale. Additionally, the model's ability to simulate terrestrial water storage and river discharges is enhanced by these processes. The improvement in land hydrology with floodplains and groundwater is attributed to their ability to increase the hydrological memory of the model. Overall, the study highlights the importance of incorporating groundwater and floodplain processes into ESMs to improve the understanding of land surface-atmosphere interactions and the accuracy of climate simulations.
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Status: open (until 28 Dec 2024)
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RC1: 'Comment on egusphere-2024-3091', Dai Yamazaki, 09 Nov 2024
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This manuscript describes the results of the climate model experiment to discuss the potential impact of representing groundwater and floodplain. The experiment is well designed, and the simulation data are appropriately analyzed. The finding that the representing floodplains and groundwater improve the hydrological cycle and lower atmosphere status (precipitation and temperature) is interesting. I don’t find any critical errors in the manuscript, thus I feel the paper can be accepted after a minor revision.
Line 13: predominantly positive
This description is ambiguous, and I cannot get what changes were observed. Please include more easy-to-understand description. (e.g. “bias is reduced”).
Line 12: The study found:
I think it might be better to explain the finding that “the simulated hydrological cycle was improved by representing floodplain and groundwater (Fig 3 and 4)” also in the abstract.
L148: Figure 1b
Is the subgrid fraction “f_wtd” is variable in time or constant in time? From the sentence, it looks like the f_wtd is the parameter calculated by the topography. While in the figure, it is labelled as “All simulated annual mean f_wtd”, and I feel this is variable in time.
If f_wtd is a time-constant parameter, I think it’s better to show that in the model description section rather than the result.
L214: simulate bay ALL
“bay” should be “by”
Citation: https://doi.org/10.5194/egusphere-2024-3091-RC1 -
CC1: 'Reply on RC1', Jeanne Colin, 03 Dec 2024
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Thank you very much for your review and useful comments. We changed the manuscript to include your corrections and clarify the point regarding f_wtd.
Regarding your first two comments, we followed your suggestions and changed the sentences in the abstract (lines 10-15).
In the first version of the manuscript, it read : "This study found that the impact of groundwater and floodplains on precipitation and 2-meter air temperature biases is predominantly positive in comparison to observations, although on a very regional scale. Additionally, the model's ability to simulate terrestrial water storage and river discharges is enhanced by these processes. The improvement in land hydrology with floodplains and groundwater is attributed to their ability to increase the hydrological memory of the model."
It now reads : "The simulated hydrological cycle is improved by representing floodplains and groundwater, thanks to an increased hydrological memory which allows to better capture the seasonal cycle of the terrestrial water storage and river discharge. Additionally, the inclusion of groundwater and floodplains reduces precipitation and 2-meter air temperature biases at the regional scale."Yes, f_wtd is variable in time, as it depends on wtd. We clarified this point in the manuscript.
In the model’s description section, lines 114-115, we changed the sentence « with vertical upward capillarity fluxes into the superficial unsaturated soil in a fraction of each grid cell defined by the actual distribution of the sub-grid topography » into « with vertical upward capillarity fluxes into the superficial unsaturated soil allowed over a fraction of each grid cell which varies with the water table head and its position with respects to the sub-grid topography distribution ».
Also, line 148, the sentence « Subgrid fractions, f_wtd, of each grid cell that allow z_wtd to rise into the superficial soil » was changed into « The temporal mean values of f_wtd the fraction of each grid cell over which z_wtd is allowed to rise into the superficial soil ».
We also corrected the typo line 214 ("bay" instead of "by").
Thank you again.Citation: https://doi.org/10.5194/egusphere-2024-3091-CC1
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CC1: 'Reply on RC1', Jeanne Colin, 03 Dec 2024
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RC2: 'Comment on egusphere-2024-3091', Anonymous Referee #2, 25 Nov 2024
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Thank you to ESD, the editor, and the authors for the opportunity to review this vital manuscript. Please see below for an article summary and detailed feedback.
SummaryIn their 2024 article “Influence of Floodplains and Groundwater Dynamics on the Present-Day Climate Simulated by the CNRM Model”, Decharme and Colin set out to assess whether and how globally significant groundwater and floodplains impact climate. To do this, they employ the Centre National de Recherche Météorologique model, which uses the Interaction Soil-Biosphere-Atmosphere (ISBA) land surface and CNRM Total Runoff Integrating Pathways (CTRIP) river routing models model to account for dynamic river flooding and horizontal and vertical groundwater flow. Four experiments with both, neither, or just one of the floodplains or groundwater modules turned on are used to investigate the impact of these earth system components on climate. The False Detection Rate test is used to determine whether the results are statistically significant compared to observations.
The floodplains and groundwater levels found in this study are in keeping with observations and previous studies. The ALL experiment, which uses the floodplains and groundwater modules shows greater skill across most seasons than the CTL experiment where both the floodplains and groundwater modules are turned off. The authors present the reasons behind the greater skill of ALL versus CTL region by region, as these reasons vary according to latitudinal band and topography. Decharme and Colin find that evaporable water increases where floodplains or shallow groundwater tables are present. However, while changes in evaporation in the ALL experiment are regionally significant (compared to CTL), they are not significant at a global scale. In addition, the authors find that including floodplains and groundwater decreases soil and air temperature compared to what is found in the CTL experiment.
Overall, CRNM-CM6-1’s inclusion of floodplain and groundwater processes improves hydrology and climate modelling in many regions due primarily to more accurate characterization of terrestrial water storage and river discharge. Model bias is reduced for soil moisture, near-surface air temperature, and precipitation. Incorporating floodplain and groundwater processes may also improve results for carbon cycle studies as soil moisture is a driver of the decomposition process.
General comments
This article is a fit for Earth System Dynamics given its focus on how the inclusion of floodplain and groundwater modules impact Earth System Model (ESM) results, linking improved hydrologic cycle representation to reduced bias in a number of land and atmosphere variables and usefulness in carbon cycle studies. The study is novel in the sense that the global scale interaction of the atmosphere with inundated areas has not been previously studied. Nor has a global study of the impact of realistically rendered groundwater aquifers been carried out with an ESM before.
The results of this comprehensive study are presented with clarity and sufficient detail overall. The experiment description is complete enough to allow for reproducibility. The title is also clear, but could potentially be revisited to include the term “Hydrology” as the impact of the floodplain and groundwater modules of land surface hydrology is a major part of this study. The supplement provides a useful deeper dive into the results and are referenced in a useful way within the main text.
Specific comments
- The methods used in this study are clearly outlined overall, with a small handful of requests for added clarity to be found within this section of the peer review.
- Will the authors please add a description of GRACE and how it is used in the methods section? It would also help to know the rationale for selecting GRACE over other comparable products. And if other comparable products exist, it would also be good to learn why an observational ensemble is not being used. To be clear, I think it’s okay to use just one observational dataset, it would just be good to know why this choice has been made.
- Also related to the methods section, will the authors include a sentence to indicate why performing this set of experiments in offline mode is preferred?
- On line 174, skill scores are referenced. I assume this is related to the bias scores presented in Figure 3, but is it possible to state which test of skill is used and refer to the corresponding figure within the main text to make this more explicit?
- Could figure 11 be moved to before the discussion and conclusion section?
- Is it possible to include a model structure diagram to show how CRNM-CM6-1 incorporates the ISBA and CTRIP models, as well as sub-grid processes? This might help other ESM modelling teams envision how floodplain and groundwater processes could be incorporated into their own models.
- Figure 5b seems to appear before it is mentioned in the main text. Is it possible to move this figure (or the mention of it) so that this is no longer the case?
- Ask for confirmation of what the model uses as maximum rooting depth
- Please include a sentence on why the False Detection Rate test was used to test for statistical significance instead of other sign-based tests.
Technical corrections
Please consider the following technical corrections.
- Page 1: Consider capitalizing “S” in “simulated” for consistency with title case used throughout the rest of the title.
- Page 2, line 20: Delete “continental”.
- Page 2, line 22: Delete “front of” and replace with “the face of”.
- Page 2, line 30: Delete the “s” at the end of “represents”.
- Page 2, line 32: Add an “s” to the end of “term”.
- Page 2, line 33: Delete the “s” at the end of “discharges”.
- Page 2, line 40: Depending on the intended meaning, it may be clearer to say “potential evaporation” rather than just “potential”.
- Page 2, line 47: The word “partitioned” may be more accurate that “distributed” here.
- Page 3, line 53: Delete “the” after “North America, ”.
- Page 3, line 54: Replace “or” with “and” before “east Africa”.
- Page 3, line 54: Delete “these” before “water bodies”.
- Page 3, line 57: Delete “s” after “impacts”.
- Page 3, lines 57 and 58: Reverse the order of “enough documented” to read “documented enough”.
- Page 3, line 64: Delete “an” before “idealized”.
- Page 3, line 68: Delete the “s” at the end of “theirs”.
- Page 3, line 69: The word “capacity” may be preferred to “capability” in this context.
- Page 3, line 70: The word “role” may be more appropriate than “rule” in this sentence.
- Page 3, line 71: Consider including a comma after “rivers” to indicate that a phrase is being added to the main clause in this sentence.
- Page 3, line 72: Delete the “s” at the end of “others”.
- Page 3, line 76: Consider inserting the word “so” before “their potential”.
- Page 3, line 76: Add an “s” to the end of the word “remain”.
- Page 3, line 79: Add an “s” to the end of the word “account”.
- Page 3, line 84; Page 8, line 186: It’s possible that the word “assess” should be used instead of “access”.
- Page 3, line 84: It’s possible that the word “role” is intended instead of “rule”.
- Page 4, line 112; Page 5, line 143: Move “218” to after the word “world’s”.
- Page 4, line 114; Page 5, line 117; Page 7, line 149: This may be a matter of style, but it’s possible that the word “upper” is more precise in English than “superficial”, which would be preferred in some other languages, such as French (example: superficiel).
- Page 5, line 122: Replace “ed” at the end of “followed” with an “s”.
- Page 5, lines 123, 124, and 126: Delete the “s” at the end of the word “floodplains”.
- Page 5, line 129: Replace the “d” at the end of “build” with a “t”.
- Page 5, line 133: Delete the letters “es” from the end of the word “gases”.
- Page 5, line 134: Replace “are” with “is” after “forcing”.
- Page 5, line 137: Delete the “s” at the end of “differences”.
- Page 5, line 137: Change the uppercase “W” in “We” to a lowercase “w”.
- Page 5, line 138: Revise “allows to reduce” to “reduces”.
- Page 5, line 144: the word “total” in “the total land surface” may not be necessary.
- Figure 1 caption: Delete the “s” at the end of “behaviours”.
- Page 7, line 149: The word “globally” may not be needed.
- Page 7, line 153: Revise “lowlands fraction” to “lowland fractions”.
- Figure 2 caption: Revise “Floodplains behaviours” to “Floodplain behaviour” and add the letter “s” to the end of “month” in “(c) Number of month”.
- Page 8, lines 159 and 161: Insert “at a” before “maximum”.
- Page 8, line 183: Add an “s” to the end of the words “return” and “lead”.
- Page 8, line 184: Delete the “s” at the end of “mid-latitudes” and insert the word “the” before “impact of”.
- Page 8, line 186: Revise “discharges are” to “discharge is”.
- Figure 3 caption: Delete the “s” at the end of the word “shows” in the sentence that begins “Bottom plots shows”. Add an “s” to “correspond”.
- Page 9, line 197: Replacing “Whatever” with “Regardless” may increase clarity.
- Page 9, line 198: Delete the “s” at the end of “floodplains”.
- Page 11, line 201: Replace the “s” at the end of “explains” with “ed”.
- Page 11, line 205: replace the word “of” with the word “for”.
- Page 11, line 214: Delete the “a” in “bay”.
- Page 11, line 215: Replace “in lesser extend” with “to a lesser extent”. Add an “s” to the end of the word “Gange”.
- Page 11, line 216: Change “plane” to “flattening”, “diminishing” or another word with a similar meaning that ends in “ing”. Consider replacing “due to the strong flooded” with “due to strong flood”.
- Page 11, line 218: Delete the word “to” after “allow”.
- Page 11, line 219: The meaning of the words “to dawn” is not clear in this context.
- Page 11, lines 220 to 225; Page 14, line 269: There is an extra space before a punctuation mark in these passages.
- Page 11, line 227: Delete the letter “s” at the ends of the words “floodplains”, “models”, and “performances”.
- Page 12, line 235: Replace the “ed” at the end of “showed” with the letter “n”.
- Page 12, line 238: Add an “s” to the end of the word “lead”.
- Page 12, line 239: Delete the word “a” after “rise and”.
- Page 12, line 240: Change “in” after “transported” to “to”. Delete the “s” at the end of “constitutes”.
- Page 12, Figure 5 subplot b title: Revise “Evapotranpiration” to “Evapotranspiration”.
- Page 13, line 243: Insert the word “in” between the words “increase” and “water”.
- Page 13, Figure 6 caption: Delete the “s” at the end of “grid-points”. Add a “.” at the end of the last sentence.
- Page 14, line 266: Add an “s” at the end of the word “floodplain”.
- Page 14, line 270: Move the word “respectively” to the end of the sentence and delete the “)”.
- Page 14, line 276: Delete the word “an” after “leads to”. Replace “enhancement” with “enhanced”. Delete the word “of” before “evapotranspiration”.
- Page 14, line 288: Insert a “)” after “FLD”.
- Page 15, Figure 7 caption: Consider inserting a space between “percentage” and “point” in “percentagepoint”.
- Page 16, line 304: Insert a “)” after “season”.
- Page 16, line 310: The term “downward surface solar heat flux” is a bit confusing.
- Page 16, line 322: replace “of” with “in” after “increase”.
- Page 18, line 328: Capitalize the first “a” in “amazonian”.
- Page 20, line 357: Add “‘s” to the end of the word “atmosphere”.
- Page 20, line 363: Replace the “s” at the end of “biases” with a “d”.
- Page 20, line 367: Revise “underestimations of these” to “underestimation of”.
- Page 21, Figure 10 caption: Note that “2m” is written as “2-meter” some of the time.
- Page 23, Figure 11 caption: Delete “s” at the end of “theirs”.
Citation: https://doi.org/10.5194/egusphere-2024-3091-RC2
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