Increasing Trends of Heat Waves and Tropical Nights in Coastal Regions (The Case Study of Lithuania Seaside Cities)

Round 1

Reviewer 1 Report

The manuscript takes into account an important issue related to heat waves and tropical nights in coastal regions that could help several countries deal with global change. However, before publication, several modifications need to be implemented.

There is no main objective explanation in the Introduction section. In general, this section needs to be rewritten to include all required parts, such as objectives, methodology, etc. Although the authors explained in lines 152-154 "This study investigates heat waves (when Tmax ≥25 °C is present more than 3 days) and tropical nights (when Tmin ≥20 °C) in Lithuania seaside settlements on the Southeastern Baltic Sea.", the question is which variables have been investigated by the authors or from which perspective this issue has been assessed. If the objective is "The aim of this work is to study the trends in air heat wave changes during the day and night in the period 1993-2022.", this research study could be an appropriate report but not a scientific paper.  

Please use complete terms first and then; use abbreviations, such as "SST", in line 84. 

Some statements need to be referenced, such as "An air temperature of 20°C to 25°C can be the comfort limit for most of the inhabitants of middle latitudes, including the Baltic region."

Author Response

Dear reviewer,

Thanks for the review and advice. According to your recommendation, we implemented several modifications:

“There is no main objective explanation in the Introduction section. In general, this section needs to be rewritten to include all required parts, such as objectives, methodology, etc. Although the authors explained in lines 152-154 "This study investigates heat waves (when Tmax ≥25 °C is present more than 3 days) and tropical nights (when Tmin ≥20 °C) in Lithuania seaside settlements on the Southeastern Baltic Sea.", the question is which variables have been investigated by the authors or from which perspective this issue has been assessed. If the objective is "The aim of this work is to study the trends in air heat wave changes during the day and night in the period 1993-2022.", this research study could be an appropriate report but not a scientific paper”. 

• The introduction has been adjusted and rewritten based on your recommendation. The goal and aims descriptions of this research are formulated more objectively. The aim of the work, the variables to study, and the perspective of this study have been rewritten and presented in more detail (169- 195 lines):

“In this study, we examine heatwaves in Lithuania's coastal cities along the Baltic Sea, where the maritime climate is most pronounced. This area typically has cool, damp summers, a hallmark of mid-latitude maritime climates. With global climate change, we're seeing more irregular weather, including an increase in heatwaves. Yet, there's limited research on how these changes impact these coastal regions, known for their stable temperatures and frequent weather shifts. The likelihood of experiencing heat waves and extremely warm nights is rising along the Baltic Sea coast due to these climate changes. Heatwaves and tropical heat nights are indeed extreme weather events whose occurrence is becoming ever more likely on the Baltic Sea coast due to climate change.

This study examines changes and trends in air temperature, heat waves, and tropical nights as one of the main indicators of climate change. The aim of this work is to study the trends and changes in the frequency and intensity of heatwaves in the last 30 years (1993-2022) according to historical monitoring data in the Baltic Sea coastal areas. The results of this study present indicators of heatwaves according to the climate indices, such as the duration of heat waves and tropical nights in days, the number of heatwaves per year, and the length of the longest heatwave in days. Some of the heatwave indicators such as the intensity of severe heat waves in days were selected based on the national emergency management criteria.

This research is aimed at informing the public about the increasing number of cases of extreme events and raising awareness of the danger of heatwaves to human health in the resorts and urbanized areas of the Southeastern Baltic Sea. The studies of the trends in climate parameter variations are relevant not only for the knowledge of climate change processes but also for the development of strategies of adaptation to the consequences of the said processes. Extreme weather and climate events, such as heatwaves and tropical nights can lead to socio-economic and natural disasters. Therefore, information about the variability of heat waves statistics is of increasing importance for risk management and prevention.”

“Please use complete terms first and then; use abbreviations, such as "SST", in line 84.”

• Thank you for your advice. Abbreviations in the text have been explained, such as "SST" - Sea surface temperature (in line 18).

“Some statements need to be referenced, such as "An air temperature of 20°C to 25°C can be the comfort limit for most of the inhabitants of middle latitudes, including the Baltic region."

• Citations have been arranged (125 lines):

“People's sensitivity to the weather is not the same: weather-liable people react sensitively to weather changes, while meteo-stable people may not feel it at all (Liukaityte 2011). According to the same source an air temperature of 20°C to 25°C can be the comfort limit for most of the inhabitants of middle latitudes, including the Baltic region.”

With sincere respect,

Authors

Author Response File: Author Response.pdf

Reviewer 2 Report

This is a review of the MPDI Sustainability Oceans [manuscript id 2527090] entitled  “Increasing trends of heat waves and tropical nights in coastal regions (the case study of Lithuania Seaside cities)”.

– General review and comments –

There is very little background information in the introduction. Between lines 27 and 66, several important details are provided without specifying their sources (especially the regional climate characterization). Additionally, I believe the informative purpose between lines 160-163 is not accurately presented. It is unlikely that the general public will read a scientific article, so strategies for dissemination or suggestions on how to make the information more accessible to the general population should be included.

Another important aspect is that the data used in the article is referenced as sourced from the "Lithuanian Hydrometeorological Service under the Ministry of Environment," and at the end, it states, "Data Availability Statement: The data presented in this study are available on request from the corresponding author," which hinders independent evaluation. This needs to be addressed. The authors have access to various public databases (e.g., Zenodo) where they can upload the data and enable independent evaluation. Data quality must be ensured here.

In the methodology of the article, there is an issue regarding the use of linear regression to show a trend. The cons of using linear regression with climatological normals from 1993 to 2022 includes potential limitations in capturing non-linear relationships and seasonal variation in the data. Stationarity assumptions may not hold for climatological variables affected by climate variability. Outliers and data availability can also impact the accuracy and reliability of the results. The authors have explored this aspect very little. The application of other methods here, such as moving averages or seasonal decomposition, would be more applicable than simply plotting a linear line that does not represent a "trend" in any way.

In the Results section, they are presented with low quality. There are simpler and visually more interesting methods to present results like these (e.g., number of heat waves presented as symbols instead of bars). Similarly, a regression line here makes no sense (see my other comments). For example, Figure 4 is quite confusing, along with its explanation and discussion. The same applies to Figure 5. I understand that the onset and progression of the heat wave are important for this analysis, but there are other articles in the literature that present better figures for these same questions. It does not seem to me that the authors conducted a very in-depth survey. The IPCC documents themselves present graphical forms that could be used here. The discussion becomes relatively lost when connected to Tropical Nights (TNs) from line 400. Another example, in Figure 8, Atm press and relative humidity have the same color on the graph. There is confusion in the way the data is presented. Here, the authors should dedicate more effort to the graphical production of the results, so that the discussion becomes more objective and clear (consequently, the connection with EHW and Figure 9 should also be improved).

The discussion section, between lines 454 and 531, seems to be a repetition of the results, but with a superficial connection. The fact presented by the authors, that specific warming started in the Baltic Sea region from the 1970s-1980s, and that the projected changes until 2100 range between 1.5 and 4.5°C, is poorly explored here. The manuscript could better explore the fact that its results are showing a greater warming than the global average. Between lines 505 and 512, the urban heat island effect is superficially discussed, and the authors mention very superficially about the urban evolution and occupation of the Baltic Sea, aspects that are also included in the IPCC report and BACC. Therefore, at this point, there is a disconnect between the heatwaves and the actual causes, when in fact, the manuscript should reinforce precisely this aspect of the anthropogenic climate change process.

And finally, the conclusions must necessarily accompany the overall improvement in the manuscript. Based on these comments and review, I do not recommend the article for publication without a profound change in the manuscript. Note that this change does not invalidate the presented results, but the way they are presented here falls short of what could be achieved.

— specific comments 

It would be highly beneficial to have a Figure 1 with a regional map displaying the regional configuration and climate characterization described between lines 46-52. The Figure 1 presented on page 5 is only a basic map with very low resolution (note that the scale is incorrectly positioned) and lacks any climatic features. It should be placed closer to the introduction. Similarly, a schematic diagram of summer circulation around lines 190-210 is necessary to help readers understand the ocean's role in the region and its connection to the article's objective.

Lines 32-33: "The number of heatwaves (HWs)..." should contain references here, although a quick search in current databases reveals that there are not many studies on this subject in this region. If so, the authors should highlight this.

Lines 38-40: It appears too superficial. It could be made more concise.

Lines 42-44: I believe this section should start with this paragraph, as it is the central theme of this manuscript.

Line 46: "young" refers to what? to the fact that it is a region formed mainly since the last glacial period by sea-level rise?

Line 146: "reached7.4°C (LHMS 2021)" - space missing between reached and 7.4.

Lines 223-228: The origin of the data is not presented. The reference to the Lithuanian Hydrometeorological Service under the Ministry of Environment is extremely vague. How were these data processed? Are they observations? Are they daily averages or hourly observations (or whatever) ? Better description here is a must.

Lines 259-261: The authors mention here for the first time the meteorological stations of Klaipeda, Nida, and Palanga, and I noticed that despite being cities too, in Figure 1, the legend should indicate the meteorological stations that are mentioned. Note that they have a WMO number (see on the WMO website). This information is important for replicating the work.

Lines 262-266: The use of linear regression in these cases is not the best option, as the authors assume a linearity that is not characteristic of climate change. The cons of using linear regression with climatological normals from 1993 to 2022 include potential limitations in capturing non-linear relationships and seasonal variation in the data. Stationarity assumptions may not hold for climatological variables affected by climate variability. Outliers and data availability can also impact the accuracy and reliability of the results. There is no discussion on this.

Lines 283-284: It seems that SKN is SNC, or would it be CSN? Review. This should be reviewed throughout the text (for example, also in table 2 and in the legend of figure 2). Figure 2, in particular, could be presented differently (for example, a box plot for each decade) with the correct legends (name of the month instead of number). The graph is poorly presented. The interpretation of the months with the greatest differences is not convincing.

Figure 7: What is the source of this data? How was it produced?

Author Response

Dear reviewer,

Thank you very much for your review, remarks, and advice to improve the work.

Corrections made the following:

There is very little background information in the introduction. Between lines 27 and 66, several important details are provided without specifying their sources (especially the regional climate characterization). Additionally, I believe the informative purpose between lines 160-163 is not accurately presented. It is unlikely that the general public will read a scientific article, so strategies for dissemination or suggestions on how to make the information more accessible to the general population should be included.

• The introduction has been adjusted and rewritten based on your recommendation.

Specifying source – 41-57 (was 27-66),

The aim of the work – 169-195.

Another important aspect is that the data used in the article is referenced as sourced from the "Lithuanian Hydrometeorological Service under the Ministry of Environment," and at the end, it states, "Data Availability Statement: The data presented in this study are available on request from the corresponding author," which hinders independent evaluation. This needs to be addressed. The authors have access to various public databases (e.g., Zenodo) where they can upload the data and enable independent evaluation. Data quality must be ensured here.

• The data are reliable and obtained from the state monitoring service (Lithuanian Hydrometeorological Service). Also, a scientist of this service is a co-author of this publication. Therefore "Data Availability Statement: The data presented in this study are available on request from the corresponding author."

In the methodology of the article, there is an issue regarding the use of linear regression to show a trend. The cons of using linear regression with climatological normals from 1993 to 2022 includes potential limitations in capturing non-linear relationships and seasonal variation in the data. Stationarity assumptions may not hold for climatological variables affected by climate variability. Outliers and data availability can also impact the accuracy and reliability of the results. The authors have explored this aspect very little. The application of other methods here, such as moving averages or seasonal decomposition, would be more applicable than simply plotting a linear line that does not represent a "trend" in any way.

• Thanks for this note. Line regression is the popular technique in climatology used for predictions. Added information to make it more understandable for the reader who is not a climatologist.

309-334 lines.

In the Results section, they are presented with low quality. There are simpler and visually more interesting methods to present results like these (e.g., number of heat waves presented as symbols instead of bars). Similarly, a regression line here makes no sense (see my other comments). For example, Figure 4 is quite confusing, along with its explanation and discussion. The same applies to Figure 5. I understand that the onset and progression of the heat wave are important for this analysis, but there are other articles in the literature that present better figures for these same questions. It does not seem to me that the authors conducted a very in-depth survey. The IPCC documents themselves present graphical forms that could be used here. The discussion becomes relatively lost when connected to Tropical Nights (TNs) from line 400. Another example, in Figure 8, Atm press and relative humidity have the same color on the graph. There is confusion in the way the data is presented. Here, the authors should dedicate more effort to the graphical production of the results, so that the discussion becomes more objective and clear (consequently, the connection with EHW and Figure 9 should also be improved).

• Thank you. We've tweaked based on your essential suggestions.

The discussion section, between lines 454 and 531, seems to be a repetition of the results, but with a superficial connection. The fact presented by the authors, that specific warming started in the Baltic Sea region from the 1970s-1980s, and that the projected changes until 2100 range between 1.5 and 4.5°C, is poorly explored here. The manuscript could better explore the fact that its results are showing a greater warming than the global average. Between lines 505 and 512, the urban heat island effect is superficially discussed, and the authors mention very superficially about the urban evolution and occupation of the Baltic Sea, aspects that are also included in the IPCC report and BACC. Therefore, at this point, there is a disconnect between the heatwaves and the actual causes, when in fact, the manuscript should reinforce precisely this aspect of the anthropogenic climate change process.

• Thank you for your remarks. We added more research results and examples in the discussion section.

The former information between lines 454-531 is supplemented and newly formed between 557-583 lines.

Specific comments

It would be highly beneficial to have a Figure 1 with a regional map displaying the regional configuration and climate characterization described between lines 46-52. Figure 1 presented on page 5 is only a basic map with very low resolution (note that the scale is incorrectly positioned) and lacks any climatic features. It should be placed closer to the introduction. Similarly, a schematic diagram of summer circulation around lines 190-210 is necessary to help readers understand the ocean's role in the region and its connection to the article's objective.

• Figure 1 has been adjusted. Thank you for the necessary comments. 58-83 lines.

Lines 32-33: "The number of heatwaves (HWs)..." should contain references here, although a quick search in current databases reveals that there are not many studies on this subject in this region. If so, the authors should highlight this.

• Supplemented (lines 51-53).

Lines 38-40: It appears too superficial. It could be made more concise.

• Thank you. We tried to shorten it.

Lines 42-44: I believe this section should start with this paragraph, as it is the central theme of this manuscript.

• Thank you for your support. Moved to the main opening paragraph. 29-32 lines.

Line 46: "young" refers to what? to the fact that it is a region formed mainly since the last glacial period by sea-level rise?

• You are right. I removed the word "young sea" because, of course, a reader not from the Baltic countries might not understand.

Line 146: "reached7.4°C (LHMS 2021)" - space missing between reached and 7.4.

• Thank you.

Lines 223-228: The origin of the data is not presented. The reference to the Lithuanian Hydrometeorological Service under the Ministry of Environment is extremely vague. How were these data processed? Are they observations? Are they daily averages or hourly observations (or whatever)? Better description here is a must.

• Added explanations in the methodology section. 300-303 lines

Lines 259-261: The authors mention here for the first time the meteorological stations of Klaipeda, Nida, and Palanga, and I noticed that despite being cities too, in Figure 1, the legend should indicate the meteorological stations that are mentioned. Note that they have a WMO number (see on the WMO website). This information is important for replicating the work.

• Added explanations in the methodology section, and in Figures 1. Lines 70-72, 226-229.

Lines 262-266: The use of linear regression in these cases is not the best option, as the authors assume a linearity that is not characteristic of climate change. The cons of using linear regression with climatological normals from 1993 to 2022 include potential limitations in capturing non-linear relationships and seasonal variation in the data. Stationarity assumptions may not hold for climatological variables affected by climate variability. Outliers and data availability can also impact the accuracy and reliability of the results. There is no discussion on this.

• The trend data series consisted of variables during the warm period only, so seasonality was not discussed.

Figure 7: What is the source of this data?

• Thank you for this note. Added explanations in the methodology section. Explained in the relevant lines 336-349.

Lines 283-284: It seems that SKN is SNC, or would it be CSN? Review. This should be reviewed throughout the text (for example, also in table 2 and in the legend of figure 2). Figure 2, in particular, could be presented differently (for example, a box plot for each decade) with the correct legends (name of the month instead of number). The graph is poorly presented. The interpretation of the months with the greatest differences is not convincing.

• Thank you. We corrected considering the observed name discrepancies. 352-372 lines.

Figure 7: What is the source of this data? How was it produced?

Data source - NASA GLDAS Project. The NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) provides access to LDAS datasets using multiple methods, including the ability to subset spatially, temporally, and/or by variable.

Once again, we sincerely thank you for your consistent review and advice.

With sincere respect,

Authors

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript "Increasing trends of heat waves and tropical nights in coastal regions (the case study of Lithuania Seaside cities)" clearly focuses the research on the two most evident climatic indicators in the ongoing changes. The content of the manuscript is understood right from the title and also the description of the area, albeit meager, makes it possible to discriminate the differences recorded in the sites. Probably there is no clear reference to the scenario of the general circulation of the atmosphere changed in recent decades, of which these climatic indicators are representative; in the discussion we talk about the anticyclonic pressure field: is this the main element that has changed? If the authors indicated it would be a useful reference to correlate this research globally. In order to further improve the quality of the research, it would have been useful to compare these results with other contexts, in addition to that of Finland and Ukraine, also to confirm some local situations. These two additions could increase the list of references. However, this appears broad and up-to-date, perhaps the use of references in Lithuanian should be avoided if we are dealing with descriptions of places or methodologies: they could hardly be read by a large audience. The figures and tables are useful and all necessary. As regards figure 4, a good coincidence is observed in the three sites between the increase in temperature and the years in which this increase occurred, the authors could highlight in the text if particular weather conditions were recorded in those years, not necessarily locally. The requests for these additions are functional to improve the manuscript and do not diminish the quality of the research already achieved, for this reason I ask the authors to add them to make publication possible.

Author Response

Dear reviewer,

Sincerely thank you for the review and advice.

Corrections made the following:

Probably there is no clear reference to the scenario of the general circulation of the atmosphere changed in recent decades, of which these climatic indicators are representative; in the discussion, we talk about the anticyclonic pressure field: is this the main element that has changed?

• Thanks for the advice. The anticyclonic circulation is not the only element that is changing as a result of climate change and affecting more frequent heat waves. Therefore, we added more information about blocking pressure field, and also air temperature and sea surface temperature changes in the Baltic Sea area.

575-584, 591-603 lines

If the authors indicated it would be a useful reference to correlate this research globally. In order to further improve the quality of the research, it would have been useful to compare these results with other contexts, in addition to that of Finland and Ukraine, also to confirm some local situations. These two additions could increase the list of references.

• According to your recommendations, we added more research results and examples in the introduction and discussion sections, and also to the list of references. The results in the discussion section are supplemented with comparisons at the global and regional levels.

97-107, 119-121, 127-135, 561-574, 615-633, 694-741 lines

However, this appears broad and up-to-date, perhaps the use of references in Lithuanian should be avoided if we are dealing with descriptions of places or methodologies: they could hardly be read by a large audience.

• Yes, we agree with you. Thank you for your advice. However, we did not manage to avoid Lithuanian names and methodologies. One of the reasons is that the local methodology is applicable to this region and more understandable to representatives of other specialties, who apply it to warn the population or develop measures to reduce the risks of climate change.

The figures and tables are useful and all necessary. As regards Figure 4, a good coincidence is observed in the three sites between the increase in temperature and the years in which this increase occurred, the authors could highlight in the text if particular weather conditions were recorded in those years, not necessarily locally.

• Thanks for the good insights on Figure 4. Added its description in the text, also a particular weather example in the last 2022-year summer.

422-438 lines

Thank you again for your advice, the implementation of which improves the quality of the draft.

With sincere respect,

Authors

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Good luck!