the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Aug 2022
The extremely hot and dry 2018 summer in central and northern Europe from a multi-faceted weather and climate perspective
Lauren S. Andersen
Florian N. Becker
Goratz Beobide-Arsuaga
Marcus Breil
Giacomo Cozzi
Jens Heinke
Lisa Jach
Deborah Niermann
Dragan Petrovic
Andy Richling
Johannes Riebold
Stella Steidl
Laura Suarez-Gutierrez
Jordis Tradowsky
Dim Coumou
André Düsterhus
Florian Ellsäßer
Georgios Fragkoulidis
Daniel Gliksman
Dörthe Handorf
Karsten Haustein
Kai Kornhuber
Harald Kunstmann
Joaquim G. Pinto
Kirsten Warrach-Sagi
Elena Xoplaki
Abstract. The summer of 2018 was an extraordinary season in climatological terms for northern and central Europe, bringing simultaneous, widespread, and concurrent heat and drought extremes in large parts of the continent with extensive impacts on agriculture, forests, water supply, and socio-economic sector. We present a comprehensive, multi-faceted analysis of the 2018 extreme summer in terms of heat and drought in central and northern Europe with a particular focus on Germany. The heatwave first affected Scandinavia by mid-July, shifted towards central Europe in late July, while Iberia was primarily affected in early August. The atmospheric circulation was characterized by strongly positive blocking anomalies over Europe, in combination with a positive summer North Atlantic Oscillation and a double jet stream configuration before the initiation of the heatwave. In terms of possible precursors common to previous European heatwaves, the Eurasian double jet structure and a tripolar sea-surface temperature anomaly over the North Atlantic were identified already in spring. While in the early stages over Scandinavia the air masses at mid- and upper-levels were often of remote, maritime origin, at later stages over Iberia the air masses had primarily a local to regional origin. The drought affected Germany the most, starting with warmer than average conditions in spring, associated with enhanced latent heat release that initiated a severe depletion of soil moisture. During summer, a continued precipitation deficit exacerbated the problem, leading to hydrological and agricultural drought. A probabilistic attribution assessment of the heatwave in Germany showed that the prolonged heat has become more likely due to global warming. Regarding future projections, an extreme summer such as this of 2018 is expected to occur every two out of three years in Europe under a 1.5 °C warmer world and virtually every single year under 2 °C of global warming. With such large-scale and impactful extreme events becoming more frequent and intense under anthropogenic climate change, comprehensive and multi-faceted studies like the one presented here quantify the multitude of effects and provide valuable information as basis for adaptation and mitigation strategies.
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Notice on discussion status
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
(4682 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.
- Preprint
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- Final revised paper
Journal article(s) based on this preprint
Efi Rousi et al.
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2022-813', Anonymous Referee #1, 16 Sep 2022
The purpose of this article is to present the multi-aspect study led by the ClimXtreme research network of a dry and hot compound event: the European summer of 2018, with a special focus on Germany. The authors succeed in showing the importance of such a multi-faceted analysis in understanding the drivers and dynamics of such dry and hot compound events. The science presented here is sound, and the article is well written.
However, I believe that the authors should have presented another case study (even if more local). Indeed, this is a long and dense article, as the authors look at different aspects of this compound event, for a case study that has already been intensively documented on different aspects by various publications: exceptionality (e.g. NOAA Global climate report and Met Office report for summer 2018), predictability and drivers (e.g. Dunstone et al. 2019; McCarthy et al., 2019), drought (e.g. Toreti et al. 2019; Peters et al. 2020), dynamics (e.g. Kornhuber et al. 2019; Drouard et al. 2019; Sousa et al. 2019; Li et al., 2020; Spensberger et al. 2020), attribution (e.g. World Weather Attribution Project, 2018; Vogel et al., 2019, Hari et al., 2020). In addition, it has already been regarded as a compound event by previous studies (e.g. Bastos et al., 2021). As the authors point out along the text, most of the findings shown by the authors were already evidenced in previous scientific papers. I understand the argument of the authors on the exceptionality of such a large-scale, persistent, and intense compound event, but I find the paper very long and dense and to me it does not show any substantial new insight on this widely documented compound event. The authors should reduce the length of the paper or better justify the necessity of such a study for the 2018 compound dry and hot event and its added value.
Additional specific comments:
- The data sub-section is very dense and long. Maybe it would benefit of an italic title for each paragraph to quickly find the piece of information needed.
- Lines 190-197: the computation of the 90th percentile differs for the two heatwave indices?
- Sub-section 2.2.2: I am not sure that three drought indicators are necessary as the purpose of the study is not to compare drought indices or to deeply evaluate the 2018 drought. Mentioning and showing only the SPEI is sufficient to evidence the occurrence and intensity of the drought, as the SPEI is a widely used drought index that considers both precipitation and evapo-transpiration. The SPI is not shown in the main body and does not bring any additional information. And the results shown with the climate network approach could be shown in another way with the SPEI. Showing only one drought indicator would contribute to lighten the text.
- Lines 230-232: The way the blocking index is computed is not clear. Is it a “hybrid” index that looks for an inversion of the Z500 meridional gradient and a strong Z500 anomaly? Are there any spatial and temporal constraints?
- Line 259: are the soil moisture LPJmL simulations absolutely necessary for the paper? It would also contribute to reduce the length of the paper.
- Figures 1d and 1e: you could plot the SPEI value only when it is below the drought threshold.
- Lines 364-365: could you show the thermopluviogram for the Scandinavian region as well?
- Figure 4: Could you show the NAO index for this season as you do for the blocking index?
- Lines 487-490: You should also cite Dunstone et al. 2019: they studied the predictability of this summer season and evidenced the role of this tripole.
- Lines 490-496: The lack of precipitation is also shown in Toreti et al. 2019.
- Lines 504-506: Add a citation.
- Sub-section 3.4: you should cite Vogel et al. 2019 in this sub-section
- Lines 655-656: Cite Dunstone et al. 2019.
Technical corrections:
- Line 468: the closing parenthesis is missing.
- Figure A2, line 702: should be “(b)” instead of “(c)”.
Reference:
Dunstone, N., Smith, D., Hardiman, S., Eade, R., Gordon, M., Hermanson, L., Kay, G. and Scaife, A., 2019. Skilful realâtime seasonal forecasts of the dry Northern European summer 2018. Geophysical Research Letters, 46(21), pp.12368-12376.
Citation: https://doi.org/10.5194/egusphere-2022-813-RC1 -
AC1: 'Reply on RC1', Efi Rousi, 04 Feb 2023
We thank the two anonymous reviewers for reading our article carefully and providing constructive criticism. We have done further work to account for their suggestions and to address their concerns. In summary, we reduced the length of the paper removing some, not strictly necessary, parts; we highlighted the advance of our paper compared to recent literature on the same case study; and we incorporated the reviewers’ suggestions to improve clarity in certain points. We believe that the Reviewer’s comments substantially improved the manuscript. The detailed responses are provided in the two attached pdf files. The reviewers’ comments appear in black font and our responses in red. All line numbers in the response documents refer to the lines in the revised manuscript without Track Changes (the manuscript is also provided with Track Changes).
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RC2: 'Comment on egusphere-2022-813', Anonymous Referee #2, 13 Dec 2022
General comments:
Firstly, I congratulate the authors for a very well organized and presented manuscript. It must be noted that it is not always easy to summarize and present such a multidisciplinary work, spanning different approaches, and the authors were able to provide this in a very clear and organized way, and furthermore, in a relatively concise way, which is also not easy. The quality of the writing is very good, thus very clear for the reader, and the text avoids being too “heavy”, so being easy to follow.
The manuscript is well structured, with the Abstract and Introduction stating in a clear way the motivation and objectives of the work. The same is valid for the Methods, which are presented in a sound way, providing, as said before, a clear structure of the work flow, despite the complexity of the multidisciplinary approach.
As a consequence, I believe the manuscript is very close to a format suitable to be published. Accordingly, I have just some small comments, which could enhance some small parts/sections. Besides that, I have only a few minor comments regarding one or two less clear sentences and/or typos.
Specific comments:
- L58-60: While I understand the idea in this sentence, I find it presented not in the best way. I would probably suggest the authors to be more specific regarding this specific event.
- L286: How did the authors estimate the impact and potential loss of confidence from regridding the ERA5 data?
-L309-311: Why this specific timeframe?
- Regarding feedbacks between soil moisture deficit and heatwave amplification, while the presented material and evidence is in my point of view more than sufficient for this multidisciplinary approach, I would probably appreciate some more discussion on the soil desiccation mechanisms, and the approaches/methodologies to address this relatively complex subject, which have for example been very well discussed (e.g. 2010 european HWs) in works such as the ones from Miralles et al. (2014), or Schumacher et al. (2019).
- L430-434: I understand the local/regional description, however this may be somehow slightly misleading. I am not sure if extreme heat and temperature records in NW Iberia related with the advection of a Saharan air mass could or not be completely defined as “regional”. In particular, the role of the advection of desertic air masses (associated with ridge activity) for Iberian heatwaves has been discussed in Sousa et al (2019).
Minor comments:
- L467 (and other instances): “warm conveyor belt”
- Fig.6 seems a bit too stretched vertically
- L547/551: I suggest adding here in brackets the period considered for ERA5 and “recent climate”
- L618: has warmed ~2ºC since when / compared to?
- L662: please put the mentioned UK record into context (very briefly of course, dates, etc.)
Citation: https://doi.org/10.5194/egusphere-2022-813-RC2 -
AC2: 'Reply on RC2', Efi Rousi, 04 Feb 2023
We thank the two anonymous reviewers for reading our article carefully and providing constructive criticism. We have done further work to account for their suggestions and to address their concerns. In summary, we reduced the length of the paper removing some, not strictly necessary, parts; we highlighted the advance of our paper compared to recent literature on the same case study; and we incorporated the reviewers’ suggestions to improve clarity in certain points. We believe that the Reviewer’s comments substantially improved the manuscript. The detailed responses are provided in the two attached pdf files. The reviewers’ comments appear in black font and our responses in red. All line numbers in the response documents refer to the lines in the revised manuscript without Track Changes (the manuscript is also provided with Track Changes).
-
AC2: 'Reply on RC2', Efi Rousi, 04 Feb 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2022-813', Anonymous Referee #1, 16 Sep 2022
The purpose of this article is to present the multi-aspect study led by the ClimXtreme research network of a dry and hot compound event: the European summer of 2018, with a special focus on Germany. The authors succeed in showing the importance of such a multi-faceted analysis in understanding the drivers and dynamics of such dry and hot compound events. The science presented here is sound, and the article is well written.
However, I believe that the authors should have presented another case study (even if more local). Indeed, this is a long and dense article, as the authors look at different aspects of this compound event, for a case study that has already been intensively documented on different aspects by various publications: exceptionality (e.g. NOAA Global climate report and Met Office report for summer 2018), predictability and drivers (e.g. Dunstone et al. 2019; McCarthy et al., 2019), drought (e.g. Toreti et al. 2019; Peters et al. 2020), dynamics (e.g. Kornhuber et al. 2019; Drouard et al. 2019; Sousa et al. 2019; Li et al., 2020; Spensberger et al. 2020), attribution (e.g. World Weather Attribution Project, 2018; Vogel et al., 2019, Hari et al., 2020). In addition, it has already been regarded as a compound event by previous studies (e.g. Bastos et al., 2021). As the authors point out along the text, most of the findings shown by the authors were already evidenced in previous scientific papers. I understand the argument of the authors on the exceptionality of such a large-scale, persistent, and intense compound event, but I find the paper very long and dense and to me it does not show any substantial new insight on this widely documented compound event. The authors should reduce the length of the paper or better justify the necessity of such a study for the 2018 compound dry and hot event and its added value.
Additional specific comments:
- The data sub-section is very dense and long. Maybe it would benefit of an italic title for each paragraph to quickly find the piece of information needed.
- Lines 190-197: the computation of the 90th percentile differs for the two heatwave indices?
- Sub-section 2.2.2: I am not sure that three drought indicators are necessary as the purpose of the study is not to compare drought indices or to deeply evaluate the 2018 drought. Mentioning and showing only the SPEI is sufficient to evidence the occurrence and intensity of the drought, as the SPEI is a widely used drought index that considers both precipitation and evapo-transpiration. The SPI is not shown in the main body and does not bring any additional information. And the results shown with the climate network approach could be shown in another way with the SPEI. Showing only one drought indicator would contribute to lighten the text.
- Lines 230-232: The way the blocking index is computed is not clear. Is it a “hybrid” index that looks for an inversion of the Z500 meridional gradient and a strong Z500 anomaly? Are there any spatial and temporal constraints?
- Line 259: are the soil moisture LPJmL simulations absolutely necessary for the paper? It would also contribute to reduce the length of the paper.
- Figures 1d and 1e: you could plot the SPEI value only when it is below the drought threshold.
- Lines 364-365: could you show the thermopluviogram for the Scandinavian region as well?
- Figure 4: Could you show the NAO index for this season as you do for the blocking index?
- Lines 487-490: You should also cite Dunstone et al. 2019: they studied the predictability of this summer season and evidenced the role of this tripole.
- Lines 490-496: The lack of precipitation is also shown in Toreti et al. 2019.
- Lines 504-506: Add a citation.
- Sub-section 3.4: you should cite Vogel et al. 2019 in this sub-section
- Lines 655-656: Cite Dunstone et al. 2019.
Technical corrections:
- Line 468: the closing parenthesis is missing.
- Figure A2, line 702: should be “(b)” instead of “(c)”.
Reference:
Dunstone, N., Smith, D., Hardiman, S., Eade, R., Gordon, M., Hermanson, L., Kay, G. and Scaife, A., 2019. Skilful realâtime seasonal forecasts of the dry Northern European summer 2018. Geophysical Research Letters, 46(21), pp.12368-12376.
Citation: https://doi.org/10.5194/egusphere-2022-813-RC1 -
AC1: 'Reply on RC1', Efi Rousi, 04 Feb 2023
We thank the two anonymous reviewers for reading our article carefully and providing constructive criticism. We have done further work to account for their suggestions and to address their concerns. In summary, we reduced the length of the paper removing some, not strictly necessary, parts; we highlighted the advance of our paper compared to recent literature on the same case study; and we incorporated the reviewers’ suggestions to improve clarity in certain points. We believe that the Reviewer’s comments substantially improved the manuscript. The detailed responses are provided in the two attached pdf files. The reviewers’ comments appear in black font and our responses in red. All line numbers in the response documents refer to the lines in the revised manuscript without Track Changes (the manuscript is also provided with Track Changes).
-
RC2: 'Comment on egusphere-2022-813', Anonymous Referee #2, 13 Dec 2022
General comments:
Firstly, I congratulate the authors for a very well organized and presented manuscript. It must be noted that it is not always easy to summarize and present such a multidisciplinary work, spanning different approaches, and the authors were able to provide this in a very clear and organized way, and furthermore, in a relatively concise way, which is also not easy. The quality of the writing is very good, thus very clear for the reader, and the text avoids being too “heavy”, so being easy to follow.
The manuscript is well structured, with the Abstract and Introduction stating in a clear way the motivation and objectives of the work. The same is valid for the Methods, which are presented in a sound way, providing, as said before, a clear structure of the work flow, despite the complexity of the multidisciplinary approach.
As a consequence, I believe the manuscript is very close to a format suitable to be published. Accordingly, I have just some small comments, which could enhance some small parts/sections. Besides that, I have only a few minor comments regarding one or two less clear sentences and/or typos.
Specific comments:
- L58-60: While I understand the idea in this sentence, I find it presented not in the best way. I would probably suggest the authors to be more specific regarding this specific event.
- L286: How did the authors estimate the impact and potential loss of confidence from regridding the ERA5 data?
-L309-311: Why this specific timeframe?
- Regarding feedbacks between soil moisture deficit and heatwave amplification, while the presented material and evidence is in my point of view more than sufficient for this multidisciplinary approach, I would probably appreciate some more discussion on the soil desiccation mechanisms, and the approaches/methodologies to address this relatively complex subject, which have for example been very well discussed (e.g. 2010 european HWs) in works such as the ones from Miralles et al. (2014), or Schumacher et al. (2019).
- L430-434: I understand the local/regional description, however this may be somehow slightly misleading. I am not sure if extreme heat and temperature records in NW Iberia related with the advection of a Saharan air mass could or not be completely defined as “regional”. In particular, the role of the advection of desertic air masses (associated with ridge activity) for Iberian heatwaves has been discussed in Sousa et al (2019).
Minor comments:
- L467 (and other instances): “warm conveyor belt”
- Fig.6 seems a bit too stretched vertically
- L547/551: I suggest adding here in brackets the period considered for ERA5 and “recent climate”
- L618: has warmed ~2ºC since when / compared to?
- L662: please put the mentioned UK record into context (very briefly of course, dates, etc.)
Citation: https://doi.org/10.5194/egusphere-2022-813-RC2 -
AC2: 'Reply on RC2', Efi Rousi, 04 Feb 2023
We thank the two anonymous reviewers for reading our article carefully and providing constructive criticism. We have done further work to account for their suggestions and to address their concerns. In summary, we reduced the length of the paper removing some, not strictly necessary, parts; we highlighted the advance of our paper compared to recent literature on the same case study; and we incorporated the reviewers’ suggestions to improve clarity in certain points. We believe that the Reviewer’s comments substantially improved the manuscript. The detailed responses are provided in the two attached pdf files. The reviewers’ comments appear in black font and our responses in red. All line numbers in the response documents refer to the lines in the revised manuscript without Track Changes (the manuscript is also provided with Track Changes).
-
AC2: 'Reply on RC2', Efi Rousi, 04 Feb 2023
Peer review completion
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Efi Rousi et al.
Efi Rousi et al.
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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.
- Preprint
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