Extreme Precipitation Events in Alaska: Historical Trends and Projected Changes

Round 1

Reviewer 1 Report

Thank you for the opportunity to review this paper. I found it well-written overall and worthy of publication. It covers a topic of high interest and relevance and the results are valuable to the scientific community. I suggest the following revisions, most of which are relatively minor and clarify the points made in the paper.

 

Hourly precipitation data from ERA5 – how accurate is this timescale? Are there any verification of hourly data when compared to observations?

 

Line 159: missing an ‘of’.

Line 282: Range is misspelled.

 

Line 192: The year 1975/76 is a known inflection point for trends in much of Alaska, corresponding to a shift in the PDO teleconnection pattern (Hartman and Wendler, 2005). Do the author’s feel that inclusion of the years 1970-74 might influence the results in any way?

 

A spatial scale and topography would be good to include on figure 3 panels for reference, since the author denote the precipitation events were widespread and topographic features. The figures could benefit from being zoomed in to the area of interest, rather than all covering the entire state (aside from the Aleutians).

 

For reference and comparison, it might be good to point out the highest precipitation ever reported for the state. Also, some language on the climate regions of the various flooding locations would be good to point out, ie. Bieniek et al. 2012.

 

What is the data source for figure 4?

 

The legend and pressure values for figure 5 are not readable.

 

It would be good to have the ERA grid pattern perhaps on one of the figures.

 

In Table 2, what would be the reasoning that the storm total exceedances (especially 3-day total at 86) at Nome are so high?  

 

The font in figure 10 appears to be off with the legend and axis titles overlapping.

Author Response

Responses to Review #1 (Responses in italics)

Thank you for the opportunity to review this paper. I found it well-written overall and worthy of publication. It covers a topic of high interest and relevance and the results are valuable to the scientific community. I suggest the following revisions, most of which are relatively minor and clarify the points made in the paper.

Thank you for the comments. In the following, we list our responses to the comments, nearly all of which we have incorporated into the revision of the manuscript. Our responses are in italics.

Hourly precipitation data from ERA5 – how accurate is this timescale? Are there any verification of hourly data when compared to observations?

We have added a new paragraph (L151-160), providing an assessment (with supporting references) of the ability of ERA5 to capture precipitation, especially heavy precipitation events. The new reference to Avila-Diaz et al. (2021) is especially relevant because it contains an evaluation of heavy precipitation events in various atmospheric reanalyses (including ERA5) over northern land areas. ERA5 is shown to perform well in this regard.

Line 159: missing an ‘of’

Corrected.

Line 282: Range is misspelled.

Corrected.

Line 192: The year 1975/76 is a known inflection point for trends in much of Alaska, corresponding to a shift in the PDO teleconnection pattern (Hartman and Wendler, 2005). Do the author’s feel that inclusion of the years 1970-74 might influence the results in any way?

We examined the time series in Figures 6 and 7 for discontinuities in the mid-1970s and were unable to find any of significance. We note (L495-519) that the time series of heavy precipitation events were characterized by an absence of trends over the 1950-2020 period, which is sufficiently long that the Pacific Decadal Oscillation should undergo several phase shifts, thereby reducing its impact on trends in the 70-year period.

A spatial scale and topography would be good to include on figure 3 panels for reference, since the author denote the precipitation events were widespread and topographic features. The figures could benefit from being zoomed in to the area of interest, rather than all covering the entire state (aside from the Aleutians).

We have redrafted Figure 3 to enhance the clarity of the maps of precipitation amounts. Since the purpose of this figure is to provide a comparative depiction of the five events, we prefer not to zoom in on the flood locations as that would eliminate the opportunity for “big picture” comparisons of the events. Inclusion of the topographic turns out to be incompatible with the color-scaled mapping of precipitation amounts (two sets of overlain color shades do not work), so we left the topography map in Figure 1.

For reference and comparison, it might be good to point out the highest precipitation ever reported for the state. Also, some language on the climate regions of the various flooding locations would be good to point out, ie. Bieniek et al. 2012.

(1) We added sentences in Sections 3.2 and 3.5 on record rainfall amounts, including the Alaska statewide record for a 24 hour period, and we note that this statewide record was indeed set during the Seward flood event included in this paper (Section 3.2). (2) In the next-to-last paragraph of Section 1 (L114-129), we have provided information on the climate divisions in which each flood event occurred; we have also added a reference [19] to the study by Bieniek et al. (2012) in which the construction of Alaska’s climate divisions is described.

What is the data source for figure 4?

In the caption of Figure 4, we have added the information on the source of the data and the plotting software.

The legend and pressure values for figure 5 are not readable.

Figure 5 has been redrafted with enlarged panels (conforming to the layout of Figures 3 and 4), and the legend has been removed. We have added H and L symbols to denote High and Low pressure centers so that the actual pressure values are not essential to the discussion, and we added a statement that the color scales vary among the panels.

It would be good to have the ERA grid pattern perhaps on one of the figures.

We experimented with overlays of the ERA5 grid and found that it introduced a distraction that more than offset any value added. The overlay was further complicated by the fact that the candidate maps for the underlay (e.g., Figure 1, Figure 3) were color-shaded, making it difficult for visualizing the ERA5 grid across the entire map.

In Table 2, what would be the reasoning that the storm total exceedances (especially 3-day total at 86) at Nome are so high?

We have added a few new sentences (L460-473) explaining why the number of threshold exceedances was so large at Nome. The topography and coastal configuration provide the explanation.

The font in figure 10 appears to be off with the legend and axis titles overlapping

The mis-placed font was a result of the template layout process. We have remade the figure in a more rigid jpeg format so that the text cannot be separated. The template layout is now safe from this problem.

Reviewer 2 Report

The manuscript with the title Extreme Precipitation Events in Alaska: Historical Trends and Projected Changes in Journal Atmosphere after Minor Revision. 

The manuscript is overall good and very well written with scientific significance.

 

In my opinion, the subject of this work is relevant for the Journal Atmosphere of course after some revisions and reconstructions.

The topic of the paper is very interesting and important, especially because it very rare and not enough investigated. To analyze historical data and historical trends is very important scientific trends. The Atmosphere journal readers, and sufficiently interesting to warrant publication. Also, this Journal wants paper could be with high impact and with strong scientific innovations. First the paper has the next section and sub-section (i.e. Abstract, Introduction, Data and methods, Precipitation data, Climate model projections, Synopsis of events, Fairbanks, August 1967, Seward, October 1986, Kivalina, August 2012, Allakaket/Bettles, August 1994, Haines, December 2020, Results and discussion, Synoptic and historical perspectives, Future projections, Conclusion).

 

The main concern is the missing some parts of the manuscript and this parts must be immediately added.  

The section of Introduction must be extended with references that reflect Historical Trends and Projected Changes investigated across the world.

 

First the Figure 1,

Because this Figure has external data, please add the source and describe in a few sentences is this Figure belongs to you or not?

 

For the right mapping of Figures (drawing of maps), please read and cite this reference:

- Aleksandar Valjarević, Tatjana Djekić, Vladica Stevanović, Radomir Ivanović, Bojana Jandziković,GIS numerical and remote sensing analyses of forest changes in the Toplica region for the period of 1953–2013,Applied Geography,Volume 92,2018,Pages 131-139, https://doi.org/10.1016/j.apgeog.2018.01.016.

 

The authors used ERA5 data of 35 km of resolution, can the authors compare some another database of climate data and describe in a few sentences.

 

Figure 2, must include lines to describe better trends of precipitations changes. Please use different colors for signs on the Figure.

 

Figure 3. Must be drawn in better resolution. The letters on the maps must be written in a larger font.

Figure 10 must be drawn again; the letters are not enough recognizable.

In the section of Discussion, it is necessary to add and cite more references and compare this research with other similar research within the same topic.

I recommend in the section of Discussion the next reference:

Hewitt, B.A.; Lopez, L.S.; Gaibisels, K.M.; Murdoch, A.; Higgins, S.N.; Magnuson, J.J.; Paterson, A.M.; Rusak, J.A.; Yao, H.; Sharma, S. Historical Trends, Drivers, and Future Projections of Ice Phenology in Small North Temperate Lakes in the Laurentian Great Lakes Region. Water 2018, 10, 70. https://doi.org/10.3390/w10010070. 

The authors must better describe the section of Conclusion. In this section it necessary to add why authors use to investigated this topic.  In the end, I recommend Minor Revision.

Good luck to the authors

The Reviewer#3

 

Author Response

Responses to Review #2  (Responses in italics)

The manuscript with the title Extreme Precipitation Events in Alaska: Historical Trends and Projected Changes in Journal Atmosphere after Minor Revision. 

The manuscript is overall good and very well written with scientific significance.

In my opinion, the subject of this work is relevant for the Journal Atmosphere of course after some revisions and reconstructions.

The topic of the paper is very interesting and important, especially because it very rare and not enough investigated. To analyze historical data and historical trends is very important scientific trends. The Atmosphere journal readers, and sufficiently interesting to warrant publication. Also, this Journal wants paper could be with high impact and with strong scientific innovations. First the paper has the next section and sub-section (i.e. Abstract, Introduction, Data and methods, Precipitation data, Climate model projections, Synopsis of events, Fairbanks, August 1967, Seward, October 1986, Kivalina, August 2012, Allakaket/Bettles, August 1994, Haines, December 2020, Results and discussion, Synoptic and historical perspectives, Future projections, Conclusion).

We thank the reviewer for the comments and suggestions.  In the following, we list our responses to the comments, nearly all of which we have incorporated into the revision of the manuscript. Our responses are in italics.

The main concern is the missing some parts of the manuscript and this parts must be immediately added.  

The section of Introduction must be extended with references that reflect Historical Trends and Projected Changes investigated across the world.

We have revised and expanded the Introduction in response to this comment. In the second paragraph of the Introduction, we have addressed worldwide trends by summarizing the relevant results in the IPCC’s recent AR6 report (2021), and we follow this large-scale picture down with a synthesis of previous work on northern high latitudes in the third paragraph of the Introduction, which then includes some Alaska-specific references. For future projections, we follow a similar approach by summarizing the worldwide studies in the fourth paragraph and then focusing on previous studies for the Arctic and Alaska in the fifth paragraph. The Introduction now includes 19 references.  

First the Figure 1,

Because this Figure has external data, please add the source and describe in a few sentences is this Figure belongs to you or not?

Figures 1, 2, 4 and 5 now include explicit sources of information in their captions.  We have also added to the captions the source information for the plotting software as well as for the data source.

For the right mapping of Figures (drawing of maps), please read and cite this reference:

- Aleksandar Valjarević, Tatjana Djekić, Vladica Stevanović, Radomir Ivanović, Bojana Jandziković,GIS numerical and remote sensing analyses of forest changes in the Toplica region for the period of 1953–2013,Applied Geography,Volume 92,2018,Pages 131-139, https://doi.org/10.1016/j.apgeog.2018.01.016.

At the reviewer’s suggestion, we have read this paper, and we have followed the practice in that paper of acknowledging sources of data and plotting software in the figure captions. As noted above, Figures 1, 2, 4 and 5 now include such information. In particular, for Figure 1 (a base map), we have taken pains to follow the source citation procedure used in the Valjarevic et al. paper. In subsequent figures (Figure 6 onward, the figure legends and text provide the information on data sources (described in Section 2) used in constructing the figures.

The authors used ERA5 data of 35 km of resolution, can the authors compare some another database of climate data and describe in a few sentences.

As noted in the response to Reviewer 1, we have added a new paragraph (L151-160), providing an assessment (with supporting references) of the ability of ERA5 to capture precipitation, especially heavy precipitation events. The referenced studies include comparisons of ERA5’s performance with that of other reanalyses. The new reference to Avila-Diaz et al. (2021) is especially relevant because it contains an evaluation of heavy precipitation events in various other atmospheric reanalyses (including ERA5) over northern land areas. ERA5 is shown to perform relatively well in this regard.

Figure 2, must include lines to describe better trends of precipitations changes. Please use different colors for signs on the Figure.

We have replaced Figure 2 with a higher-resolution version in which the grid lines (for the x- and y-axis values) are more visible. All data points have positive values on the x and y axes, so we are not sure how to interpret the request to “use different colors for signs on the Figure”.

Figure 3. Must be drawn in better resolution. The letters on the maps must be written in a larger font.

We have replaced Figure 3 with a higher-resolution version, using jpeg rather than ppt and ensuring that there are legible numbers on the color bars and in the latitude/longitude indicators.  There are no letters on the maps in Figure 5; rather, there are solid star and triangle symbols denoting the locations of the observing stations nearest to each flood site.

Figure 10 must be drawn again; the letters are not enough recognizable.

As noted in the reply to Reviewer 1, the mis-placed font was a result of the template layout process.  We have remade the figure in a more rigid jpeg format so that the text cannot be separated. The template layout is now safe from this problem.

In the section of Discussion, it is necessary to add and cite more references and compare this research with other similar research within the same topic.

I recommend in the section of Discussion the next reference:

Hewitt, B.A.; Lopez, L.S.; Gaibisels, K.M.; Murdoch, A.; Higgins, S.N.; Magnuson, J.J.; Paterson, A.M.; Rusak, J.A.; Yao, H.; Sharma, S. Historical Trends, Drivers, and Future Projections of Ice Phenology in Small North Temperate Lakes in the Laurentian Great Lakes Region. Water 2018, 10, 70. https://doi.org/10.3390/w10010070. 

We have added this reference ([37[in the revised manuscript) in Section 5, together with various other new references – see response to following comment.

The authors must better describe the section of Conclusion. In this section it necessary to add why authors use to investigated this topic.  In the end, I recommend Minor Revision.

We have revised and expanded the Conclusion (Section 5) in several ways. First, Section 5’s opening paragraph ((L600-605) now restates the objectives to set the stage for a mapping of the conclusions (bulleted points) to the objectives that motivated the study. This serves the purpose of not only saying why we investigated the topic, but also highlighting the outcome of the investigation. Second, in a new paragraph (L629-640) following the bullet points, we place our study’s findings into a broader context of Arctic environmental change. This paragraph contains several new (and previously cited) references, including the Hewitt study suggested by the reviewer. Finally, we added two additional new references [39,40] supporting our contention that changes in airflow trajectories such as “atmospheric river” events will be key determinants of any future changes in heavy precipitation events over Alaska.

Good luck to the authors.