the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Aug 2025
Hydroclimatic Variability and Weather-Type Characteristics in the Levant During the Last Interglacial
Abstract. Proxy-based reconstructions of the Last Interglacial peak indicate changes in precipitation characteristics in the Levant. These reconstructions suggest that precipitation occurred in brief and intense events, particularly in the region's southern parts. Some studies have offered conflicting paradigms for explaining hydroclimate variability. However, these have yet to be consistently tested in a modeling framework. Indeed, the modeling approach can undoubtedly enhance the combined interpretation of proxy records and our understanding of hydroclimate processes in the past. We used simulations from the Paleoclimate Model Intercomparison Project 4th phase (PMIP4) to evaluate and reconstruct the precipitation characteristics of the Levant. First, we identified the Alfred Wagner Institute Earth System Model to largely resemble proxy reconstructions. Then we used it to understand the variability of hydroclimate. We examined changes in the frequency, seasonality, and persistence of the Levant's rain-bearing weather types, including Cyprus Lows and Red Sea Troughs. We further decomposed the dynamic and thermodynamic contributions to changes in the water balance of precipitation minus evaporation, comparing the Last Interglacial peak with preindustrial time. Based on differences in daily mean precipitation, we provide evidence that the rain-bearing weather types yielded significantly more precipitation (≈ +20 %) during the Last Interglacial peak. This increase is most evident in the southern Levant, with higher precipitation during Red Sea Trough days, resulting primarily from thermodynamic changes. Minor differences in these weather types' characteristics were found. Our research provides insights into historical hydroclimate changes in the Levant, extending our perspective on future climate impacts driven by natural variability.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(6143 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-3088', Anonymous Referee #1, 28 Oct 2025
- AC1: 'Reply on RC1', Efraim Bril, 20 Nov 2025
- AC2: 'Reply on RC2', Efraim Bril, 20 Nov 2025
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RC2: 'Comment on egusphere-2025-3088', Anonymous Referee #2, 02 Nov 2025
This manuscript investigates hydroclimatic variability in the Levant during the Last Interglacial peak (MIS 5e) using PMIP4 paleoclimate model simulations in combination with a synoptic weather-type classification and moisture balance decomposition. The study mostly uses the AWI-ESM model to examine precipitation characteristics and the relative roles of thermodynamic and dynamic processes. Results indicate enhanced precipitation—particularly during Red Sea Trough and Cyprus Low events—driven largely by thermodynamic factors. The authors present integration of model and proxy data but the manuscript requires major revisions to address issues of clarity, internal consistency, and the robustness of methodological and interpretative claims. The manuscript is interesting and deseves publication in Climate of the Past, provided the authors address the comments and improve its quality.
Comments
Line 47-50:
First claim:
“The Levant experienced a relatively dry climate characterized by shorter, more intense rainfall events…”
This statement describes the entire Levant as relatively dry.Second claim:
“Proxy-based reconstructions have indicated that the southern Levant experienced relatively wet conditions during this period…”
This says that the southern Levant was relatively wet.Conflict:
These two statements describe opposite hydroclimatic conditions (dry vs. wet) for the same region and period, unless the author means to emphasize spatial variability within the Levant (north vs. south, for instance).So unless the text explicitly clarifies that the southern Levant differed from the rest of the Levant, the passage reads as internally inconsistent — the same time period is characterized both as relatively dry overall and relatively wet locally.
To fix it, you could clarify the regional contrast explicitly, for example:
“While the Levant as a whole experienced relatively dry conditions, proxy records suggest that the southern Levant may have been comparatively wetter during this period.”
Line 111: 'The analysis was based on 40-year model runs for each period.' Which period, please mention.
In Table 1, please mention spatial resolution of each model. Please also mention for what time period the simulations are available. In Table 1 you listed 9 models, and then you mostly use only two models for your analysis, what is the justification for this?
Line 122: 'Sharav Lows', is it Sahara Lows.
Lines: 126-127: 'We compared the average Euclidean distances for the different periods to assess if the weather types
during the Last Interglacial peak changed or were similar to today’s.' what do you mean here by different pereiods, please mention the periods to make it clear. What length of interglacial period you have compared with ERA5, and preindustrial.
Line 128: What preindustrial period you have chosen, please mention.
Line 140: the authors mention here the proxy data, the proxy data should be discussed in the data section before mentioning here. It is not clear which proxy is being used, and for what time period.Fig. 2: Explain how you have appllied the bootstrap test in methods section. In sub-figure titles write the complete model name not just AWI, or EC, othewise mention these abrevations in the main text before using in the figures. In method section for clarity to the reader, please justify why you subtract interglacial period from the preindsutrial. If possible please demarkate Levant basin in Fig. 2.
Line 172: 'First, we evaluated the PMIP4 models to assess their reliability compared to proxy-based reconstructions (see Sect. 1.3).' I do not see any evaluation of PMIP4 models in Sect. 1.3.
Lines 175-177: 'AWI-ESM suggests wetter winters in the
Levant basin compared to the Pre-Industrial period, consistent with speleothem evidence from the Negev [Vaks et al. (2007)].
In contrast, EC-ESM shows wetter winters confined to the northern Levant.' This statatemt is not consistent with Fig. 2b (winter) as I see similar wetter condtions for both models (AWI, and EC).Lines 180-182: 'Autumn
patterns also vary: AWI-ESM indicates drying in the northern Levant and increased precipitation in the south, while EC-ESM
suggests widespread precipitation increases across the northern region.' I do not find this statement consistent with Fig. 2A and 2E. Better demark Levant in the figure. It is not clear what you consider the Levant region, mention clearly in methods section.Fig. 3: What the y-axis shows? In the main text, please, elaborate the sub-figure that comes first, not just randomly. Not clear what periods you have chosen for ERA5, preindsutrial, and interglacial, mention them also in the main text in methods section.
Line 189: 'We evaluated weather-type frequencies to explore potential drivers of precipitation differences between periods'. Which periods, not clear?
Line 190-192: 'In AWI-ESM, the frequency of
Cyprus Lows increases during winter, occurring on about 50% of winter days. At the same time, no significant changes are
observed in other weather- types during autumn or spring (Fig. 3 B).' What do you mean by changes/inrease here, is it the change in frequency, if so, then compared to what, it is very confusing. While refering to results from the figures, please mention the sub-figure letter (e.g., Fig. 3A etc.) in the main text.Lines: 204-206: 'Analysis of precipitation by weather type suggests a 17.3% increase in the daily average precipitation during Cyprus Low days
in the AWI-ESM model compared to the Pre-Industrial period, with the most pronounced increase observed in the northern
Levant, particularly over Turkey (Fig. 4A).' Isnt there also significant increase over parts of Mediterreanean sea.Line 220:'At first glance, Figure 4 contrasts proxy-based findings,'. Which proxy based findings, it is not clear.
Lines 224-224: 'Proxy-based studies have
frequently highlighted increased precipitation from southern sources rather than Mediterranean ones.' Which proxy based studies highlighted this, please cite them here.Fig. 5 should be a table, not a figure. Further, the sub-figure numbers (e.g., 5A, 5C etc) are not marked.
In section 3.3 you are describing results with reference to the figure. please refer to the figure in the very first lines (236-239).Lines 237-239: 'During winter and spring,
the moisture balance remains largely unchanged across most of the Levant, with some localized decreases, particularly over
modern Israel.' I this statement realy consistent with the Fig. 6 (DJF, MAM) when you say that colored regions show sinificant changes at 5% level, thus what I understand from this the changes, even thoug small, are still significant.Line 280: 'Using proxy-based paleoclimate reconstructions and climate models ...' I do not see usage of proxy-based paleoclimate reconstructions in this manuscript, please clarify, how you used it.
- AC2: 'Reply on RC2', Efraim Bril, 20 Nov 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-3088', Anonymous Referee #1, 28 Oct 2025
This study by Bril et al. presents an in-depth analysis of hydroclimate variability and weather regimes in the Levant during the Last Interglacial. The authors use PMIP4 model simulations under Last Interglacial forcing and compare them to pre-industrial conditions representing the current interglacial without anthropogenic influence. Their results indicate distinctly wetter conditions during the Last Interglacial, driven by an increase of approximately 20% in precipitation associated with rain-bearing weather regimes due to thermodynamic changes.
The methods are generally appropriate, the study region and time period are of high scientific relevance (e.g., implications for human migration during MIS5e), and the conclusions are supported by strong modelling evidence. The use of weather-regime clustering to differentiate hydroclimatic drivers is particularly valuable and insightful. The eddy/thermodynamic/dynamic decomposition is also an elegant and insightful analysis. However, the experimental setup and data/methods descriptions are at times unclear, making it difficult for the reader to fully follow the workflow. With revisions to improve clarity, this study is suitable for publication in Climate of the Past. Below, I outline two (moderate) major comments and several minor comments.
Major Comments
- Clustering methodology
The clustering approach-referred to briefly as a "semi-synoptic classification algorithm" is insufficiently described. It is not clear whether this is a specific established method or an adaptation of previous approaches. Given that this clustering strategy is central to the study and is not widely used (to my knowledge), a more detailed methods description is necessary. The authors should explain how the clustering is performed, provide references for the algorithm, and justify its selection over more commonly used approaches (e.g., k-means, DBSCAN, self-organizing maps).
- Model selection and usage
The current presentation of the climate models is confusing: multiple models are listed and none of them is mentioned in the text. Meanwhile, the text emphasizes the use of only two models, and the analysis in section 2.3 appears to use only AWI-ESM. It is unclear whether this choice is motivated by model performance, data availability, or other practical considerations.
Together, it is hard to tell when and where the authors use which model. Additionally, Table 1 lists models that are not discussed in the main text. The authors should clearly state which models are used for which analyses, why certain models are prioritized, and how these decisions affect interpretation.
Minor Comments
- L94-95: The phrasing is unclear. Suggest: "This study aims to characterize the mechanisms underlying hydroclimatic changes during the Last Interglacial using PMIP4 simulations, a weather-type classification, and dynamic-thermodynamic decomposition."
- L105: Replace "from" with "contributing to." Note that GCM stands for General Circulation Model, not Global.
- L111: Clarify the data usage rationale. For example: "Due to data availability at daily resolution, only AWI-ESM and EC-ESM are used for daily-scale analyses, while all PMIP4 models are used for monthly-scale analyses."
- L114: Should read "We evaluated each model's ability".
- Table 1: Consider unifying naming conventions (e.g., EC-ESM vs. EC-Earth3-LR) to avoid confusion.]
- L123-125: Explicitly state the temporal resolution (daily).
- L140: Why is AWI-ESM used instead of EC-ESM, given EC-ESM's higher resolution? Clarify the reasoning.
- L140: Clarify "alignment with proxy data". Does this mean precipitation, evaporation, circulation patterns, or simply temperatures?
- L186: Clarify whether "increased rainfall intensity" refers to the Last Interglacial relative to present.
- L187: Expand explanation of EC-ESM's behavior. If this discrepancy informs its exclusion from later analysis, state this explicitly earlier.
- L193: Specify "90% of summer days".
- When introducing section 2.3, keep the description general and explain model selection later to avoid confusion.
- Add a reference for "enhanced contributions from the south."
- Clarify whether the reported 4-7°C temperature rise is based on Table 1 model outputs or previous literature, and cite accordingly.
- L262-263: Provide a reference for moisture intrusions during MIS5e.
Citation: https://doi.org/10.5194/egusphere-2025-3088-RC1 - AC1: 'Reply on RC1', Efraim Bril, 20 Nov 2025
- AC2: 'Reply on RC2', Efraim Bril, 20 Nov 2025
-
RC2: 'Comment on egusphere-2025-3088', Anonymous Referee #2, 02 Nov 2025
This manuscript investigates hydroclimatic variability in the Levant during the Last Interglacial peak (MIS 5e) using PMIP4 paleoclimate model simulations in combination with a synoptic weather-type classification and moisture balance decomposition. The study mostly uses the AWI-ESM model to examine precipitation characteristics and the relative roles of thermodynamic and dynamic processes. Results indicate enhanced precipitation—particularly during Red Sea Trough and Cyprus Low events—driven largely by thermodynamic factors. The authors present integration of model and proxy data but the manuscript requires major revisions to address issues of clarity, internal consistency, and the robustness of methodological and interpretative claims. The manuscript is interesting and deseves publication in Climate of the Past, provided the authors address the comments and improve its quality.
Comments
Line 47-50:
First claim:
“The Levant experienced a relatively dry climate characterized by shorter, more intense rainfall events…”
This statement describes the entire Levant as relatively dry.Second claim:
“Proxy-based reconstructions have indicated that the southern Levant experienced relatively wet conditions during this period…”
This says that the southern Levant was relatively wet.Conflict:
These two statements describe opposite hydroclimatic conditions (dry vs. wet) for the same region and period, unless the author means to emphasize spatial variability within the Levant (north vs. south, for instance).So unless the text explicitly clarifies that the southern Levant differed from the rest of the Levant, the passage reads as internally inconsistent — the same time period is characterized both as relatively dry overall and relatively wet locally.
To fix it, you could clarify the regional contrast explicitly, for example:
“While the Levant as a whole experienced relatively dry conditions, proxy records suggest that the southern Levant may have been comparatively wetter during this period.”
Line 111: 'The analysis was based on 40-year model runs for each period.' Which period, please mention.
In Table 1, please mention spatial resolution of each model. Please also mention for what time period the simulations are available. In Table 1 you listed 9 models, and then you mostly use only two models for your analysis, what is the justification for this?
Line 122: 'Sharav Lows', is it Sahara Lows.
Lines: 126-127: 'We compared the average Euclidean distances for the different periods to assess if the weather types
during the Last Interglacial peak changed or were similar to today’s.' what do you mean here by different pereiods, please mention the periods to make it clear. What length of interglacial period you have compared with ERA5, and preindustrial.
Line 128: What preindustrial period you have chosen, please mention.
Line 140: the authors mention here the proxy data, the proxy data should be discussed in the data section before mentioning here. It is not clear which proxy is being used, and for what time period.Fig. 2: Explain how you have appllied the bootstrap test in methods section. In sub-figure titles write the complete model name not just AWI, or EC, othewise mention these abrevations in the main text before using in the figures. In method section for clarity to the reader, please justify why you subtract interglacial period from the preindsutrial. If possible please demarkate Levant basin in Fig. 2.
Line 172: 'First, we evaluated the PMIP4 models to assess their reliability compared to proxy-based reconstructions (see Sect. 1.3).' I do not see any evaluation of PMIP4 models in Sect. 1.3.
Lines 175-177: 'AWI-ESM suggests wetter winters in the
Levant basin compared to the Pre-Industrial period, consistent with speleothem evidence from the Negev [Vaks et al. (2007)].
In contrast, EC-ESM shows wetter winters confined to the northern Levant.' This statatemt is not consistent with Fig. 2b (winter) as I see similar wetter condtions for both models (AWI, and EC).Lines 180-182: 'Autumn
patterns also vary: AWI-ESM indicates drying in the northern Levant and increased precipitation in the south, while EC-ESM
suggests widespread precipitation increases across the northern region.' I do not find this statement consistent with Fig. 2A and 2E. Better demark Levant in the figure. It is not clear what you consider the Levant region, mention clearly in methods section.Fig. 3: What the y-axis shows? In the main text, please, elaborate the sub-figure that comes first, not just randomly. Not clear what periods you have chosen for ERA5, preindsutrial, and interglacial, mention them also in the main text in methods section.
Line 189: 'We evaluated weather-type frequencies to explore potential drivers of precipitation differences between periods'. Which periods, not clear?
Line 190-192: 'In AWI-ESM, the frequency of
Cyprus Lows increases during winter, occurring on about 50% of winter days. At the same time, no significant changes are
observed in other weather- types during autumn or spring (Fig. 3 B).' What do you mean by changes/inrease here, is it the change in frequency, if so, then compared to what, it is very confusing. While refering to results from the figures, please mention the sub-figure letter (e.g., Fig. 3A etc.) in the main text.Lines: 204-206: 'Analysis of precipitation by weather type suggests a 17.3% increase in the daily average precipitation during Cyprus Low days
in the AWI-ESM model compared to the Pre-Industrial period, with the most pronounced increase observed in the northern
Levant, particularly over Turkey (Fig. 4A).' Isnt there also significant increase over parts of Mediterreanean sea.Line 220:'At first glance, Figure 4 contrasts proxy-based findings,'. Which proxy based findings, it is not clear.
Lines 224-224: 'Proxy-based studies have
frequently highlighted increased precipitation from southern sources rather than Mediterranean ones.' Which proxy based studies highlighted this, please cite them here.Fig. 5 should be a table, not a figure. Further, the sub-figure numbers (e.g., 5A, 5C etc) are not marked.
In section 3.3 you are describing results with reference to the figure. please refer to the figure in the very first lines (236-239).Lines 237-239: 'During winter and spring,
the moisture balance remains largely unchanged across most of the Levant, with some localized decreases, particularly over
modern Israel.' I this statement realy consistent with the Fig. 6 (DJF, MAM) when you say that colored regions show sinificant changes at 5% level, thus what I understand from this the changes, even thoug small, are still significant.Line 280: 'Using proxy-based paleoclimate reconstructions and climate models ...' I do not see usage of proxy-based paleoclimate reconstructions in this manuscript, please clarify, how you used it.
- AC2: 'Reply on RC2', Efraim Bril, 20 Nov 2025
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- 1
Efraim Bril
Adi Torfstein
Roy Yaniv
Assaf Hochman
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(6143 KB) - Metadata XML
This study by Bril et al. presents an in-depth analysis of hydroclimate variability and weather regimes in the Levant during the Last Interglacial. The authors use PMIP4 model simulations under Last Interglacial forcing and compare them to pre-industrial conditions representing the current interglacial without anthropogenic influence. Their results indicate distinctly wetter conditions during the Last Interglacial, driven by an increase of approximately 20% in precipitation associated with rain-bearing weather regimes due to thermodynamic changes.
The methods are generally appropriate, the study region and time period are of high scientific relevance (e.g., implications for human migration during MIS5e), and the conclusions are supported by strong modelling evidence. The use of weather-regime clustering to differentiate hydroclimatic drivers is particularly valuable and insightful. The eddy/thermodynamic/dynamic decomposition is also an elegant and insightful analysis. However, the experimental setup and data/methods descriptions are at times unclear, making it difficult for the reader to fully follow the workflow. With revisions to improve clarity, this study is suitable for publication in Climate of the Past. Below, I outline two (moderate) major comments and several minor comments.
Major Comments
The clustering approach-referred to briefly as a "semi-synoptic classification algorithm" is insufficiently described. It is not clear whether this is a specific established method or an adaptation of previous approaches. Given that this clustering strategy is central to the study and is not widely used (to my knowledge), a more detailed methods description is necessary. The authors should explain how the clustering is performed, provide references for the algorithm, and justify its selection over more commonly used approaches (e.g., k-means, DBSCAN, self-organizing maps).
The current presentation of the climate models is confusing: multiple models are listed and none of them is mentioned in the text. Meanwhile, the text emphasizes the use of only two models, and the analysis in section 2.3 appears to use only AWI-ESM. It is unclear whether this choice is motivated by model performance, data availability, or other practical considerations.
Together, it is hard to tell when and where the authors use which model. Additionally, Table 1 lists models that are not discussed in the main text. The authors should clearly state which models are used for which analyses, why certain models are prioritized, and how these decisions affect interpretation.
Minor Comments