the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Feb 2025
Anatomy of a Flash Flood in a Hyperarid Environment: From Atmospheric Masses to Sediment Dispersal in the Sea
Abstract. Flash floods in rivers near hyper-arid coastlines impact both land and marine environments, from recharging groundwater and supporting desert ecosystems to affecting marine water quality, organisms, and substrates. Few studies, however, have followed these events from atmospheric origins to marine effects. This study tracked a desert flash flood in October 2016 in Eilat, capturing stages from atmospheric conditions to sediment distribution at sea. Observations included satellite data, meteorological reports, floodwater discharge, and sediment levels from the Kinnet Canal outlet, alongside offshore turbidity and salinity data. Our findings indicate that a weakened polar vortex amplified a Rossby wave, triggering convective instability over the Eastern Mediterranean and northern Red Sea. In Eilat, 128 % of the average annual rainfall occurred within hours, with the flood reaching the sea approximately 50 hours later and lasting 27 hours. Around 25,000 tons of sediment were discharged, causing offshore salinity drops (up to 1.75 ‰ below the seawater background) and fluctuations of suspended sediment concentrations due to varying flow rates. In turn, particle dispersal in the sea switched several times between hypopycnal and hyperpycnal flows. These findings link the different stages of the flood and their cascading effects from air masses to sedimentary processes in the sea.
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RC1: 'Comment on egusphere-2024-3354', Anonymous Referee #1, 27 Feb 2025
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Review of "Anatomy of a Flash Flood in a Hyperarid Environment: From
Atmospheric Masses to Sediment Dispersal in the Sea"The study presents a comprehensive analysis of a flash flood event in the hyper-arid environment of Eilat, linking atmospheric conditions to sediment transport and dispersal in the Red Sea. While integrating multiple data sources is commendable, the study has several weaknesses, particularly in meteorological analysis and Dataset choices. Structural and presentation issues also detract from clarity.
Major Strengths:
1. Holistic Approach – The study links meteorological, hydrological, and marine processes, providing a broad view of the October 2016 flood in Eilat.
2. Data Integration – Including in-situ measurements, satellite data, and reanalysis datasets strengthens the study’s methodological rigor.
3. Marine Impact Analysis—Unlike many flood studies, this research follows sediment transport into the marine environment, which is valuable for understanding coastal ecosystems.Key Weaknesses:
1. Meteorological Analysis Issues
• Overinterpretation of Atmospheric Processes (Lines 338–357): The synoptic-scale discussion is overly detailed but does not provide sufficient context on how this event compares to other regional flash floods. A return period analysis or percentile ranking of rainfall intensity is missing.
• Lack of Anomaly Computation (Lines 338–349): No clear anomaly maps or statistical comparisons are provided to illustrate deviations from climatology.
• Choice of Data Sources (Lines 247–273): The study relies on NCEP/NCAR reanalysis, which has a coarse resolution (2.5° x 2.5°). A higher-resolution dataset such as ERA5 (0.25° x 0.25°) should have been used instead. Moreover, the temporal resolution used is not disclosed. You used daily information, whereas flooding in hyper-arid regions often requires data at sub-daily scales.
• Precipitation Data Validation (Lines 247–273): GPM-IMERG is used, but it is not compared with ground-based rain gauge data or CHIRPS, which might be more reliable in the region you are analyzing.
• Overly Complex Synoptic Discussion (Lines 338–410): The meteorological discussion does not add novel insights into Red Sea Trough (RST) events. The findings mostly reiterate known mechanisms of RST dynamics. If so, and I am not missing something, I would remove the meteorological analysis and instead focus on the hydrological and limnological analysis. Indeed, all the meteorological figures were placed in the supplementary information, which hints at its importance or the new insights this analysis provides.
• Misinterpretation of meteorological analysis (Line 349): Do you mean that something that had happened 37 days before contributed to the event’s development?
2. Flood Event Characterization Issues
• Flood Return Period Not Established: The study does not quantify how rare this event was in a historical context.
• Rainfall Distribution Analysis is Weak (Lines 425–450): While the authors describe spatially uneven rainfall, they do not analyze how this variability influenced runoff and flood formation.
3. Structural and Presentation Issues
• Redundant Sections (Lines 267-270): Some sections repeat information unnecessarily.
• Terminology Confusion (Lines 410–413): The study misuses the term “mesoscale” for features such as the Polar Jet and Subtropical Jet, which are large-scale systems, and the Red Sea Trough, which is a synoptic-scale system.
• Poorly Labeled Supplementary Figures (Lines 399–403): The supplementary figures lack detailed captions, making it difficult to verify claims. Please provide a document that includes all supporting information figures with captions.• Missing references related to the Red Sea Trough: Alpert, P., Osetinsky, I., Ziv, B. and Shafir, H. (2004), A new seasons definition based on classified daily synoptic systems: an example for the eastern Mediterranean. Int. J. Climatol., 24: 1013-1021. https://doi.org/10.1002/joc.1037
Awad, A.M. and Almazroui, M., 2016. Climatology of the winter Red Sea trough. Atmospheric Research, 182, pp.20-29.
El‐Fandy, M.G., 1948. The effect of the sudan monsoon low on the development of thundery conditions in Egpyt, Palestine and Syria. Quarterly Journal of the Royal Meteorological Society, 74(319), pp.31-38.
Hochman, A., Rostkier-Edelstein, D., Kunin, P. et al. Changes in the characteristics of ‘wet’ and ‘dry’ Red Sea Trough over the Eastern Mediterranean in CMIP5 climate projections. Theor Appl Climatol 143, 781–794 (2021).
Hochman A, Plotnik T, Marra F, Shehter ER, Raveh-Rubin S, Magaritz-Ronen L. 2023. The sources of extreme precipitation predictability; the case of the ‘Wet’ Red Sea Trough. Weather and Climate Extremes 100564.Conclusion: This study presents an interesting dataset linking atmospheric events to sediment transport, but it requires substantial revisions in methodology, interpretation, and presentation. Addressing these concerns will significantly improve its scientific robustness and clarity.
Citation: https://doi.org/10.5194/egusphere-2024-3354-RC1 -
AC1: 'Reply on RC1', Akos Kalman, 06 Mar 2025
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We thank the reviewer’s recognition of the major strengths of the paper. And similarly, we sincerely appreciate the reviewer’s thoughtful comments and suggestions regarding weaknesses. We’ve assessed the manuscript with these important remarks and have made changes that we think address those issues and have improved the presentation of the study. We made changes related to all the comments, and also provide an explanation.
Below, we provide detailed responses to each point.
- Meteorological Analysis Issues
R1C1 (Reviewer 1, Comment 1): Overinterpretation of Atmospheric Processes (Lines 338–357): The synoptic-scale discussion is overly detailed but does not provide sufficient context on how this event compares to other regional flash floods. A return period analysis or percentile ranking of rainfall intensity is missing.
Author Response (R1C1): This part of the manuscript was intended to lack interpretation whatsoever, and instead describe the atmospheric conditions that corresponded with different stages of the sequence, similarly as described in Dayan et al., (2001). Therefore, we have reviewed the section (previously 338-357) and made corrections to be certain that this is the case.
Regarding the second comment related to this section, because it was reporting rather than interpretation or discussion, we did not include comparative examples. However, we agree that it should contain more quantitative language which also allows for comparative values. Also, the aim of the study was to follow the full sequence of any flashflood, and we were fortunate to catch and quantify one in more detail than is typically available, and therefore the scale of the flood was not emphasized. There are now more comparatives included in the discussion (see below for additional changes within R1C2, R1C6, R1C7).
The corrected version reads as follows:
“By viewing the daily precipitation patterns retroactively from the time of the event, it was possible to recognize the first subtle expression of the Sudan Monsoon Low over the Red Sea (also known as the ‘Red Sea Trough’, RST) 37 days before heavy precipitation developed. This eventually led to the flash flood event in Eilat on October 28, 2016. The northward propagation of the RST towards the Eastern Mediterranean had already begun at that time, and its presence persisted. As a result, the RST was more of a retained formation of the inverted V-shaped low tongue, even though the pressure drop from north to south was significantly higher on the 24th (3mb over 9mb), three days before the onset of the massive rainfall in Eilat (Supplementary Fig. 1).”
R1C2: Lack of Anomaly Computation (Lines 338–349): No clear anomaly maps or statistical comparisons are provided to illustrate deviations from climatology.
Response: That is correct, we did not perform computations for modelling, instead, we used the widely accepted and applied NCEP/NCAR Reanalysis II, which uses a combination of observation data and fixed numerical weather model to create gridded dataset that represents the state of atmosphere over time.
Within the section in question (Lines 338-349), Supplementary Figure 1 shows the presence of the RST prior (1a) and on the flooding day (1b). For a proper comparison and deviation of the pressure values at sea level relative to flood producing conditions, we replaced Supplementary Figure 1a to a case, where RST was absent.
R1C3: Choice of Data Sources (Lines 247–273): The study relies on NCEP/NCAR reanalysis, which has a coarse resolution (2.5° x 2.5°). A higher-resolution dataset such as ERA5 (0.25° x 0.25°) should have been used instead. Moreover, the temporal resolution used is not disclosed. You used daily information, whereas flooding in hyper-arid regions often requires data at sub-daily scales.
Response: Thank you for pointing out this issue, which can be confusing, and we agree that such a coarse resolution would not be appropriate for analyzing the watershed area. Upon reviewing the dataset, we realized that we used the PERSIANN dataset, which has a resolution of 0.25° x 0.25° and provides half-hourly temporal resolution, rather than the NCEP/NCAR reanalysis. This dataset was applied at a regional scale only, which is more suitable for the analysis, and we have now corrected this in lines 248-245. When we considered the conditions in the watershed area of the Kinnet (in local scale), we used GPM-Imerg with (0.1° X 0.1°) resolution. To clarify this in the manuscript, we have added and changed the first paragraph in Section 2.1 ()Meteorological data) as follows (lines 248-255:):
“The synoptic analysis in this study, used to track precipitation centers, was based on two data sources. One of these in a regional scale was the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN) dataset (Nguyen et al., 2019), obtained via CHRS Data portal, with a 0.5° × 0.5° resolution. Additionally, in a local scale, NASA's Global Precipitation Measurement (GPM) Integrated Multi-Satellite Retrievals (IMERG), with a 0.1° × 0.1° resolution, were utilized to compensate for the lack of a dense meteorological network in the trans-national Kinnet watershed, located at the northernmost tip of the Gulf of Aqaba-Eilat. Given the region’s hyperarid conditions and limited gauging systems, satellite-derived precipitation data were essential for accurately estimating precipitated water.”
R1C4: Precipitation Data Validation (Lines 247–273): GPM-IMERG is used, but it is not compared with ground-based rain gauge data or CHIRPS, which might be more reliable in the region you are analyzing.
Response: We fully acknowledge that CHIRPS is a valuable dataset; however, its reliance on ground-based rain gauge data (see lines 253–255) is problematic in this region due to the limited availability of stations and the patchy nature of rain events at the northernmost tip of Gulf of Aqaba-Eilat. While CHIRPS offers a fine spatial resolution (0.05° × 0.05°), its daily temporal resolution is less suited for capturing short-lived convective storms and flash floods, which are characteristic of hyperarid environments. We selected GPM-IMERG because its half-hourly data allow for better tracking of these rapid and intense precipitation events.
R1C5: Overly Complex Synoptic Discussion (Lines 338–410): The meteorological discussion does not add novel insights into Red Sea Trough (RST) events. The findings mostly reiterate known mechanisms of RST dynamics. If so, and I am not missing something, I would remove the meteorological analysis and instead focus on the hydrological and limnological analysis. Indeed, all the meteorological figures were placed in the supplementary information, which hints at its importance or the new insights this analysis provides.
Response: The purpose of that description is not to provide novel insights, but rather report on the conditions that were present at the time of this specific sequence (see C1 as well). We agree that this is not adding novelty in terms of ‘new’ results, but we think for many readers less familiar with RST, especially in the field of sedimentology and flood dynamics research, including this may improve their comprehension of the study and our dataset. We are comfortable removing or shortening upon your recommendation. According to the first comment (R1C1), it was suggested that we show some comparison of how RST conditions differ from non-RST conditions. Perhaps with this change this criticism may have already been addressed (see R1C1 response above).
R1C6: Misinterpretation of meteorological analysis (Line 349 this is probably meant to be 339?): Do you mean that something that had happened 37 days before contributed to the event’s development?
Response: Reading your comment does make sense that 37 days seems somewhat arbitrary. Because we worked ‘backwards’ from the flood event to the past, each day was reviewed to determine whether the shape of the RST was present; and the first expression of the RST occurred 37 days prior to the flood. We will clarify this and also hope that the addition of the comparative non-RST case will make that clear. In the discussion we will also be certain to clarify that the presence of this subtle development of RST 37 days prior to the flood does not necessarily lead to full RST expression. In this case it did and we are reporting this observation. Please see revised version (R1C1).
- Flood Event Characterization Issues
R1C7: Flood Return Period Not Established:The study does not quantify how rare this event was in a historical context.
Response: We agree that this is not explained clearly enough. Modern flood records are available only from 1994, and records of most of these floods are limited to reports rather than precise measurements. Known historical events, mentioned in the introduction and discussion, only include extreme cases that had tragic outcomes, so it is difficult to place this flood comparatively. Where we could, we did compare these results to past recent events (example: Lines 631-641: sediment dispersal comparing flood of 2006, 2013, and this flood). We have also added more detail regarding what is known about the impact of this flood as well as others from the recent records (Discussion—first paragraph):
“This study followed the sequence of a storm that occurred on 28 October 2016 in Eilat from its initial phase to and through a flash flood that started depositing alluvium in the northern Red Sea a day later. The flood was the 13th flood recorded since records began in 1994 (Kalman et al. 2020). From 1994 to 2012, there was a drought period wherein flood occurrence was below one per year (0.17), followed by increased occurrence of 1.7 floods per year (2012-2020). With regard to the hazard level of the 28 October 2016 flood, no deaths occurred nor was property damage reported; and transportation infrastructure (roads and airport) were not affected.“
R1C8: Rainfall Distribution Analysis is Weak (Lines 425–450): While the authors describe spatially uneven rainfall, they do not analyze how this variability influenced runoff and flood formation.
Response: This is not discussed here because we separated the interpretation from the results. Section 4.2 (From precipitation to flow into the sea) details the specific run off and accumulation patterns related to the uneven rainfall leading to flood formation.
- Structural and Presentation Issues
R1C9: Redundant Sections (Lines 267-270): Some sections repeat information unnecessarily.
Response: Thank you for the useful remark, it is being corrected and suggested as follows:
“In the Kinnet watershed, where ground-based meteorological stations and gauging systems are scarce, IMERG datasets are indispensable for assessing precipitation patterns. The integration of this high-resolution satellite data with NCEP/NCAR reanalysis imagery provides a comprehensive view of the region’s hydrological dynamics, supporting advancements in hydrological studies and water resource management.”
R1C10: Terminology Confusion (Lines 410–413): The study misuses the term “mesoscale” for features such as the Polar Jet and Subtropical Jet, which are large-scale systems, and the Red Sea Trough, which is a synoptic-scale system.
Response: Thank you for the correction, Figure 3 caption is corrected as follows:
“Composites on the heavy rainfall in Eilat (red dot) showing three mesoscale systems (Polar Jet, Subtropical Jet, upper-level trough) and a synoptic-scale system (Red Sea Trough) in which their fourfold contact zone narrowed down to ~200 km wide gap over the Eastern Mediterranean contributing to the formation of the historical flashflood.”
R1C11: Poorly Labeled Supplementary Figures (Lines 399–403): The supplementary figures lack detailed captions, making it difficult to verify claims. Please provide a document that includes all supporting information figures with captions.
Response: Thank you for your feedback.We have compiled a merged PDF document (please find it uploaded) containing all the supplementary figures and their corresponding detailed captions. This should provide a comprehensive overview and facilitate verification of the claims presented.
R1C12: Missing references related to the Red Sea Trough:
Response: Thank you for pointing these important sources out, it was certainly an oversight on our part and some may have been removed erroneously in phases of editing. All have been incorporated into the manuscript (detailed below)
Alpert, P., Osetinsky, I., Ziv, B. and Shafir, H. (2004), A new seasons definition based on classified daily synoptic systems: an example for the eastern Mediterranean. Int. J. Climatol., 24: 1013-1021. https://doi.org/10.1002/joc.1037
Lines 122-123: “At present, based on nearly 70 years of data reanalysis, the RST is 96% originated from Sudan (Almazroui et al., 2016), and is known to be the most active during the autumn and winter (Saaroni et al., 2020; Alpert et al., 2004).”
Awad, A.M. and Almazroui, M., 2016. Climatology of the winter Red Sea trough. Atmospheric Research, 182, pp.20-29.
Lines 122-123: “At present, based on nearly 70 years of data reanalysis, the RST is 96% originated from Sudan (Almazroui et al., 2016), and is known to be the most active during the autumn and winter (Saaroni et al., 2020; Alpert et al., 2004).”
El‐Fandy, M.G., 1948. The effect of the sudan monsoon low on the development of thundery conditions in Egpyt, Palestine and Syria. Quarterly Journal of the Royal Meteorological Society, 74(319), pp.31-38.
Lines: 116-117: “For decades, there has long been an interest in the linkages between meteorological conditions and resulting floods (El-Fandy, 1948).”
Hochman, A., Rostkier-Edelstein, D., Kunin, P. et al. Changes in the characteristics of ‘wet’ and ‘dry’ Red Sea Trough over the Eastern Mediterranean in CMIP5 climate projections. Theor Appl Climatol 143, 781–794 (2021).
Suggested to insert in Line: 514: “Hochman et al. (2021) used CMIP5 climate projections to categorize winter and dry Red Sea Troughs (RSTs) and analyze their characteristics and impact on the region. They found that rainfall associated with the wet Red Sea Trough (WRST) is projected to decline by 37% by the end of the 21st century due to shifts in atmospheric circulation patterns, increased temperatures, and a reduction in the frequency and intensity of WRST events.”
Hochman A, Plotnik T, Marra F, Shehter ER, Raveh-Rubin S, Magaritz-Ronen L. 2023. The sources of extreme precipitation predictability; the case of the ‘Wet’ Red Sea Trough. Weather and Climate Extremes 100564.
Suggested to insert in Line: 514: “Hochman et al. (2021) used CMIP5 climate projections to categorize winter and dry Red Sea Troughs (RSTs) and analyze their characteristics and impact on the region. They found that rainfall associated with the wet Red Sea Trough (WRST) is projected to decline by 37% by the end of the 21st century due to shifts in atmospheric circulation patterns, increased temperatures, and a reduction in the frequency and intensity of WRST events. Additionally, they found that extreme precipitation events related to the WRST show distinct atmospheric pattern differences when compared to lighter precipitation events within the same system (Hochman et al., 2023).”
- Meteorological Analysis Issues
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AC1: 'Reply on RC1', Akos Kalman, 06 Mar 2025
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