the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Jan 2025
Brief communication: Hydrological and hydraulic investigation of the extreme September 2024 flood on the Lamone River in Emilia-Romagna, Italy
Abstract. In September 2024, several European countries experienced extreme and prolonged record-breaking rainfalls that induced severe flooding and caused widespread damage, casualties and disruptions. In this context, the Emilia-Romagna Region in Northern Italy suffered heavy precipitation primarily affecting the Lamone River basin, where a levee breach occurred near the village of Traversara causing the flooding of urban settlements, vineyards, orchards and crops. Since the same area was severely impacted by devastating floods no later than May 2023, it is relevant to understand whether this area indeed faced extreme precipitation events in two consecutive years and to explore how the hydrological-hydraulic modelling can support the preparedness against these recurring events.
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RC1: 'Comment on egusphere-2025-216', Gordon Woo, 06 Mar 2025
This is an interesting and important brief communication on flooding in the Lamone River Basin. The closing remarks section includes the following statement:
As a matter of fact, over the last two years, this region has been affected by two rainfall events that, at least for the considered
stations, exceeded the 500-years return period, despite they occurred in different seasons (Spring and Autumn) and presented
different characteristics (two consecutive events in May 2023 and a unique event in September 2024).The authors should provide some interpretive explanation for these exceedances. To what extent have the high return periods been exaggerated because they have not taken adequate account of climate change? Maybe in the current climate, they are not so rare.
For two independent rare events to occur in consecutive years is, a priori, very unlikely. To what extent are the extreme rainfall events in 2023 and 2034 actually connected, i.e. through antecedent conditions etc.?
Citation: https://doi.org/10.5194/egusphere-2025-216-RC1 -
AC1: 'Reply on RC1', Alessia Ferrari, 14 Mar 2025
Dear Dr. Gordon Woo,
Thank you for your insightful and positive feedback on our manuscript.
We agree that the statement you have highlighted would benefit from more explanation. We acknowledge that the statistical analysis we carried out to associate a return period to the considered event relies on the assumption of stationarity, which is commonly adopted to define future hydrologic information based only on historical data. However, while quantifying the effects of climate change on small river basins is still challenging, recent evaluations at the European scale highlight the role of climate projections in increasing the severity and frequency of present and future rainfall events. We will discuss this aspect in the revised paper.
We also appreciate the suggestion to provide more information about the 2023 and 2024 rainfall events. First, we confirm that these two events can be considered independent since the 2024 event occurred 16 months after the 2023 one. Moreover, we will revise the mentioned statement to include a deeper analysis of the similarities and differences between the 2023 and 2024 events (e.g. the number of rainfall days in the month before the events).
We hope that these comments, which we will develop during the manuscript revision, will address your suggestions effectively.
Once again, thank you for your appreciated feedback.
Citation: https://doi.org/10.5194/egusphere-2025-216-AC1
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AC1: 'Reply on RC1', Alessia Ferrari, 14 Mar 2025
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RC2: 'Comment on egusphere-2025-216', Anonymous Referee #2, 07 Apr 2025
This first reconstruction presents valuable insights and thoroughly addresses the multiple components typically required in a first analysis of a flood event—from the use of statistical rainfall data to hydrological modelling and the subsequent forcing of a hydrodynamic model. The manuscript is generally well structured, clear, and pleasant to read. The overall simulation strategy also appears coherent.
Based on the analysis of this brief communication, several questions and comments arise. Points 1 and 2 are deemed essential for ensuring methodological transparency and simulation reproducibility. Points 3 to 5 raise global questions for potential further analysis or clarification, and points 6 and 7 pertain to minor remarks and suggestions for additional clarification or enhancement.
- The rainfall-runoff model employed (‘Rhyme’) is not sufficiently described. The citation of Rinaldo et al. (1996) does not provide enough information to allow readers to understand or reproduce the model. Although temperature and evapotranspiration data are mentioned as model inputs, the manner in which they are used, and whether they are coupled or treated independently, remains unclear. It would be beneficial to include a conceptual schematic of the model to illustrate the interaction between storage reservoirs and their spatial configuration (e.g. whether all reservoirs are used per sub-catchment or if some of them are shared across the domain). If further references or documentation exist, they should be cited explicitly.
- It is unclear which objective function(s) were used in the MCMC calibration algorithm. Please specify the criteria used to assess the model fit during calibration.
- The model includes linear reservoirs, suggesting that the recession time parameter may depend on sub-catchment area. As their surface can strongly vary and all parameters are un, this might have a significant impact. Was this parameter treated in a dimensionless way, for instance, scaled by surface area or other global catchment characteristics?
- The good performance of the hydrological model in 2024 and the overestimation of discharges in Reda during 2023, is somewhat surprising. Given that the model was calibrated on historical series dominated by moderate and low flows, one might have expected peak underestimation rather than overestimation. Could the authors provide possible causes for these results?
- Was the contribution of the downstream portion of the catchment (between Reda and the river mouth) included in the hydraulic model? If so, how was this inflow injected (e.g. at punctual cells as inlets located in another hydrological estimation point or spatially distributed throughout the river)? If not, would it be feasible to assess its impact on peak water levels near the levee breach, or conduct a sensitivity analysis to evaluate its influence on the simulated flood extent?
- From Figure 3, it appears that sub-catchments were defined based on tributary confluences. A short clarification in the text would help confirm this assumption.
- It would be useful to include a performance indicator (e.g. NSE, KGE, etc) for the hydrological model during both the calibration period and for the two extreme events. While the latter might be subject to higher uncertainty, such metrics would still provide useful insights into the model’s overall behaviour.
Technical Corrections:
- Lines 22–23: Please consider adding the publication year to the ARPAE reference, e.g., (ARPAE, 2024).
- Lines 43–45: Consider expressing rainfall amounts only in [mm] and specify the associated catchment area. This would improve readability and reduce the need for conversions between [mm] and [m³].
- Line 96: The phrase "spatially explicit" might be misleading. If the intention was to describe the numerical scheme, perhaps "explicit temporal scheme" was meant instead?
- Line 153: The phrase "fairly agree" should be revised for clarity. Consider alternatives such as giving an actual number or performance indicator.
- Line 153: Missing 's' in ' ... three gauge stations fairly agrees'.
- Line 167: Missing 's' in '... two intense and consecutive rainfalls'.
- Figure 3 : The sub-catchment subdivision should be realised in another colour and clearer. On a print version of the paper, the contours are barely visible.
Citation: https://doi.org/10.5194/egusphere-2025-216-RC2 -
AC2: 'Reply on RC2', Alessia Ferrari, 15 Apr 2025
Dear Referee,
Thank you for your thorough and positive feedback on our manuscript and for providing detailed comments and suggestions. We address your points below:
1. 2. 3. We appreciate the suggestion to provide more information about the rainfall-runoff model adopted here and about the calibration algorithm. In the revised manuscript, we will describe the main features of the model, add further references, and we will clarify the details of the MCMC calibration algorithm.
4. In the revision step, we will better clarify that the discharges estimated for the May 2023 event depend on the rating curves applied to convert the water levels measured at the Reda station and to extensive flooding occurred along this river stretch.
5. The downstream portion of the catchment was not included in the hydraulic model since neither minor channels nor tributaries flow into the Lamone River. We will specify this in the revised manuscript.
6. The sub-catchments were delineated using a digital elevation model. The hydrologic analysis tools available in ArcGisPro software were used to determine flow direction, calculate flow accumulation, delineate watersheds, and create stream networks. We will clarify this in the revised text.
7. We agree on the importance of quantitatively assessing the model performance. To this end, the Nash-Sutcliffe Efficiency indicator was evaluated for the calibration of the hydrological model. We will specify this in the revised manuscript.
We will check typos and introduce the suggested technical corrections.
We hope that these points, which we will develop during the manuscript revision, will effectively address your suggestions.
Once again, thank you for your appreciated feedback.
Citation: https://doi.org/10.5194/egusphere-2025-216-AC2
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