the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Sep 2024
Disentangling Atmospheric, Hydrological, and Coupling Uncertainties in Compound Flood Modeling within a Coupled Earth System Model
Abstract. Compound riverine and coastal flooding is usually driven by complex interactions among meteorological, hydrological, and ocean extremes. However, existing efforts of modeling this phenomenon often rely on models that do not integrate hydrological processes across atmosphere-land-river-ocean systems, leading to substantial uncertainties that have not been fully examined. To bridge the gap, we leverage the new capabilities of the Energy Exascale Earth System Model (E3SM) that enable a multi-component framework that integrates coastal-refined atmospheric, terrestrial, and oceanic components. We evaluate compound uncertainties arising from two-way land-river-ocean coupling in E3SM, and track the cascading meteorological and hydrological uncertainties through ensemble simulations over the Delaware River basin and estuary during Hurricane Irene (2011). Our findings highlight the importance of two-way river-ocean coupling to compound flood modeling and demonstrate E3SM’s effectiveness in handling multivariate flooding on the coast. Our study shows the growing uncertainties that transition from atmospheric forcings to flood distribution and severity. Furthermore, an Artificial Neural Network based analysis is used to assess the roles of some understudied hydrological drivers, such as infiltration and soil moisture, in the generation of compound flooding. The response of compound floods to tropical cyclones (TCs) is found to be susceptible to these often overlooked drivers. For instance, flood damage could be tripled if Hurricane Irene was preceded by an extreme antecedent soil moisture condition (AMC). The results not only support the use of a multi-component framework for interactive flooding processes, but also underscore the necessity of broader definitions of compound flooding that encompasses the simultaneous occurrence of intense precipitation, storm surge, and high AMC during TCs.
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RC1: 'Comment on egusphere-2024-2785', Anonymous Referee #1, 15 Oct 2024
Summary
This paper uses an earth systems modeling framework (1) to simulate compound flooding from Hurricane Irene with different processes represented (e.g., components activated) (2) to investigate the uncertainties that meteorological outputs from an atmospheric model introduce on flooding, and (3) to study the sensitivity of Hurricane Irene flooding under different hydrologic conditions. The authors find that coupling different model components (river, land, ocean) improve the model’s ability to generate flooded area from Hurricane Irene (compared to satellite imagery). However, the E3M tends to overestimate flooding overall and requires the use of a computationally expensive local ocean model to resolve the surge inundation. The authors show that the contribution of the uncertainty of the meteorological inputs (via an atmospheric model) is large and that antecedent soil moisture conditions impact the river discharge.
I commend the authors on their analysis and think there are interesting results that inform complexities that arise with modeling hurricane flooding. I particularly enjoyed the analysis of the hydrologic conditions/drivers. The article covers topics relevant to NHESS and could be considered for publication after major revisions. I have included some general and specific comments for the authors.
General Comments
The gaps are not clearly stated so it is hard to understand the novelty/contribution of this work in the context of existing literature. Overall, this paper seems to focus on how E3Ms new components can be used to study different things including model coupling uncertainty, meteorologic uncertainty, and the impact of different hydrologic conditions on river discharge. These analyses have been done more in-depth in previous studies which the authors could discuss and cite (e.g., Munoz et al. (2022); Gori et al. (2020); Eilander et al. (2023); Bermudez et al. (2021)). Is the focus of the study on improving modeling of compound riverine and coastal flooding compared to regional models (Line 11, 54)? Is it on uncertainties – model coupling, meteorological, and initial hydrologic conditions (Line 59, 91)? The layout of the introduction could be improved with more relevant citations for the issues the paper is addressing.
The methods section was unclear at times. This work refers to previous papers that describe the modeling framework, validation, and application. However, there is not enough information provided so that the paper is readable by someone in the field. For example, in Section 2.1, are these components 1D or 2D? What are the spatial and temporal resolutions? How have the different model components been used in previous studies and/or validated? By improving the description of the different model components in the paper, it would help readers understand the limitations of the different analysis. For example, if the river model uses a macroscale inundation scheme (Line 284) that should be stated earlier on.
The clarity of the manuscript could be improved. The authors should define terms and use them consistently throughout the paper including forcing, drivers, processes, components, responses, conditions, scenarios/experiments (for example Lines 78-81, Lines 210-220, Line 355, Line 371-380, Line 387). The authors should state in the abstract and early in the introduction that E3SM is global. It wasn’t until Line 109 that this is mentioned making it unclear in the introduction how/why “regional models” are mentioned in comparison (Line 55-57, Line 391).
The framing of the results and conclusions could be improved. I wonder if it would be more effective to narrow the scope of the manuscript, especially because it addresses so many issues and methods (models, structural equation, ANN). Some of my confusion with the results and discussion relate back to the lack of clarity in the gap/objective of the study. For example, Figure 4. results show that the hit rate is very low when the ocean is not resolved. The large-scale river model is not reliable for event-scale riverine flooding (Line 285). However, discharge and surge are key processes in compound flooding from hurricanes (Lines 35-40) and this is the event the model is being evaluated against. Your results seem to support the need for resolving flood processes at finer resolutions (e.g., regional or smaller) (again Line 340-342) which E3M is not able to do efficiently due to computational constraints (Line 427). Why did you choose a hurricane to study? Would it be more interesting to look at the impacts of coupling, inputs, conditions, etc. on long-term simulations which the E3Ms seems more suited for (as the authors suggest in Line 435-438)?
Specific Comments
- Line 19: The findings in the abstract are not very specific and it would be beneficial to add more detail. For example, what is the measure of the “effectiveness” of the model framework? Is it reproducing the flood extent from Irene?
- Line 23: The authors state that flood damage could be tripled if Hurricane Irene was preceded by extreme AMC. I do not see this supported anywhere in the results. It would be more appropriate to state the results of changes in the flood hazard (e.g., discharge, flooded area) since these are modeled, not damages.
- Line 61: What are the “critical” impacts?
- Line 110: What is the scale of the coastal refined meshes? Are they comparable size and resolution to “regional models”?
- Lines 130-135: It would be helpful to include what a perfect score is for each metric (e.g., 0 or 1).
- Line 138: Why did you choose a small threshold of 0.02? I’m assuming meters is the units.
- Line 144-146: Why did you choose a depth of 1m to calculate the inundation fraction?
- Line 190: I think this should be flood hazards, not flood risks. I would check the use of risk throughout the paper as this is typically defined as the combination of hazard, exposure, and vulnerability.
- Line195: How did you select the 5 ensemble members? How do you define a reasonable spread?
- Lines195-200: What data did you use to get trends in historical soil moisture? To better help the reader understand the range you are looking at, can you state the basin averaged soil moisture range you are using in the simulations? From the supplemental, it looks like the range is 0.065 to 0.087.
- Line 200: Since these two parameters are reported in the results, you should provide more detail on what they represent in the text.
- Line 205: What do you mean by widely distributed impacts?
- Line 226-237: Some of the statements about the model performance (e.g., “effectively” and “successfully” simulates compound riverine and coastal inundation) might be better suited in the discussion or should be given after you have stated the results that can support these findings.
- Line230-231: Are these inundated cells in the upstream parts of the basin fluvial or pluvial flooding? It is hard to tell if they are located along the river network since that is not shown on Figure 4.
- Line 240: Is the predicted flooded area just an indicator of flooding from the model output or is this measurement used in the comparison with the satellite data?
- Figure 4. It would be helpful to spell out hit rate, false rate, and success index in the caption. It would also be helpful to include 1 sentence that lists what the Experiments are again based on the components land, river, ocean.
- Line 245: What is the error/uncertainty in the satellite data you are comparing to? Does it perform well in capturing pluvial, fluvial, and coastal flooding from Hurricanes which generally have significant cloud cover? It would be helpful to discuss this in the context of your model results.
- Figure 276: Do you mean the influence of the two-way coupling on flooded area (FA) is more significant… not discharge?
- Line 293-294: Are you saying that the small variations in the soil water storage is because it can’t exceed the maximum soil storage capacity? What are the ranges of capacity of the soil?
- Line 297: Do you consider sea level rise in this modeling framework?
- Figure 8: redefine all variables so caption can be understood standalone
- Figure 10: It would be helpful to have hyetograph and hydrographs of Hurricane Irene, even in the supplemental, to provide context on the results shown in Figure 10.
- Does flooded area shown in Figure 5 included the ocean model and then in Figure 9 it is only the river? I would explicitly state this because it is unclear.
- Line 355: Did you look at how the time-varying impacts of hydrological processes on compound flooding, not just river discharge?
- Figure S6: Where does the 625 number come from?
- Figure S7: What does the Irene color mean?
Citation: https://doi.org/10.5194/egusphere-2024-2785-RC1 - RC2: 'Comment on egusphere-2024-2785', Anonymous Referee #2, 20 Oct 2024
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