the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Feb 2024
The role of citizen science to assess the spatiotemporal pattern of rainfall events in urban areas: a case study in the city of Genoa, Italy
Abstract. Climate change in the Mediterranean region is evidenced by an increase in average air temperature and a variation in rainfall regime: the value of cumulated annual rainfall seems to be basically constant, however, rainfall of maximum intensity and short duration, between 1 and 24 hours, is increasing, especially in the period between late summer and early autumn. The associated ground effects in urban areas consist of flash floods and pluvial floods, often in very small areas, depending on the physical-geographical layout of the region. In the context of global warming, it follows that it is important to have an adequate monitoring network for these rain events, which are highly concentrated in space and time.
This research analyzes the meteo-hydrological features of August 27th and 28th 2023 event that occurred in Genoa, just 4 days after the record maximum air temperature recorded: between 19 UTC and 02 UTC nearly 400 mm of rainfall was recorded in the eastern sector of Genoa’s historic center, with significant ground effects such as flooding and overflowing in pressurized culverted waterways. Rainfall observations and estimates were taken using both official or “authoritative” networks (rain gauges and meteorological radar) as well as rain gauge networks inspired by citizen science principles.
The combined analysis of the observations by authoritative and "citizen science" networks highlights, for the analyzed event, a spatial variability of the precipitation field for the hourly and sub-hourly duration, which cannot be captured by the current spatial density of the authoritative measurement stations (which it is also among the highest in Italy). Monthly total rainfalls and maximum intensity and short duration annual maxima time series recorded by the authoritative rain gauge network of the Genoa area are then analyzed. Results show that at distances even less than 2 km the variations in average rainfall depth cumulated over sub-hourly duration are very significant. Thus, extreme weather monitoring activity is confirmed as one of the most important aspects in terms of flood prevention and protection in urban areas. The integration between authoritative and citizen science networks can prove to be a valid contribution for monitoring this type of extreme events.
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RC1: 'Comment on nhess-2024-24', Mingze Ding, 25 Feb 2024
This study analyzed the role of citizen scientist stations in an extreme rainfall event, which can be beneficial for promoting the utilization of citizen station data for precipitation research. However, there are several concerns that need to be addressed before considering this manuscript for publication.
Major Comment：
- It is suggested to increase the Data This section focuses on station information, especially the accuracy of the rain gauges used. And the meteorological and remote sensing data source and access was not mentioned in this paper. The missing part can also be added into Data section.
- The station datasets are often considered as the true value. Thus, the assessment of station datasets is pretty difficult. This paper combined many meteorological and remote sensing datasets to evaluate the station datasets. The precise representation of spatial distribution is crucial here. However, the coverage ranges of many figures in the manuscript appear inconsistent, and there is a lack of information within the figures to indicate their coverage ranges. This is detrimental to the analysis of assessment results. I will provide specific details in minor comments.
Minor Comment:
- Shen (2015) also investigated that adding more station as fusion data can enhance the accuracy of the precipitation data. Is the necessity of a denser network of station data for urban-scale precipitation research? I recommend expanding the discussion on this point.
- Line 88-106: Is this hydrological introduction merely serving as background information? Because it seems that the subsequent results do not involve hydrological models.
- Please provide more detail information for DDF curve. And the full name of DDF appears twice in the text, please delete it.
- Table 2: Please provide the formula expression of e of different return period.
- Line 95: what is a.m.s.l? please provide the full name (above sea level?).
- Line 199-201: Many values do not seem to be obtained from this research, please provide citations or Figure num.
- Line 185 – 195: This section also appears to lack citations support.
- Line 288: which fusion method is used in this study? Please provide the detail information of the fusion method or citations.
- Latitude and longitude range is missing in some figures.
- It is suggested to indicate the profile direction in Fig.13,14.
Shen Y, Xiong A. Validation and comparison of a new gauge‐based precipitation analysis over mainland China[J]. International journal of climatology, 2016, 36(1): 252-265.
Citation: https://doi.org/10.5194/nhess-2024-24-RC1 -
AC1: 'Reply on RC1', Francesco Faccini, 05 Mar 2024
1: Thanks for the comment. Indeed, a more detailed description of the source and reliability of the radar observations is missing, which we will add to the final version of the paper in the DATA section, as suggested. However, it should be noted that the radar data is used not so much to quantify the intensity or cumulative precipitation but to extract information regarding the space-time extension of the phenomena. S see the reply to comment #2 for more details
2: From the comment emerges a possible misunderstanding on the use and interpretation of the observation data, which probably arises from an unclear explanation in the text.
In general, the objective of the paper is not to validate ground observations nor to do a cross validation of multisensor observations.
The objective of the paper is to demonstrate first of all that the events that affect the highly urbanized coastal areas of the Mediterranean, with a morphology very similar to the city of Genoa, have typical space-time scales that are often lower than the resolutions of standard observations, whether ground-based or satellite or radar-derived.
Each data source is then used to prove this claim. In particular,
- radar observations, which usually have a resolution of 1 km or more, can be used to provide evidence of the very small scale of extreme events that create problems in urban environments. They cannot be used effectively to quantify precipitation in urban basins, due to the resolution which is coarse compared to needs.
- The ground-based observations of the authoritative networks provide observations with high temporal resolution, but, even in the best cases, the distance between the stations is usually greater than the spatial scale of variability of the critical precipitation for urban basins
- citizen scientist networks, thanks to their high spatial density, allow to highlight that the spatial scale of the aforementioned critical events is actually very small and lower than both the average distance between the authoritative stations and the resolution of the operational weather radars.
In this case, we do not want to derive precise quantitative information from these last observations, but information on the actual space-time scales of variation of the critical precipitation events for urban floods.
Differences such as those observed between citizen scientists' rain gauges are certainly higher than the average error of such measurements (which we will try to quantify in the next version of the paper) therefore it is considered reliable that such observations can be used to study the characteristics of critical events for urban floods, and make a contribution to the definition of design ietographs for hydraulic infrastructures and flood protections in small urban catchments
We will take care of illustrating clearly all this in the revised version of the paper
Citation: https://doi.org/10.5194/nhess-2024-24-AC1 -
AC2: 'Reply on RC1', Francesco Faccini, 05 Mar 2024
1: Thanks for the comment. Indeed, a more detailed description of the source and reliability of the radar observations is missing, which we will add to the final version of the paper in the DATA section, as suggested. However, it should be noted that the radar data is used not so much to quantify the intensity or cumulative precipitation but to extract information regarding the space-time extension of the phenomena. See the reply to comment #2 for more details
2: From the comment emerges a possible misunderstanding on the use and interpretation of the observation data, which probably arises from an unclear explanation in the text.
In general, the objective of the paper is not to validate ground observations nor to do a cross validation of multisensor observations.
The objective of the paper is to demonstrate first of all that the events that affect the highly urbanized coastal areas of the Mediterranean, with a morphology very similar to the city of Genoa, have typical space-time scales that are often lower than the resolutions of standard observations, whether ground-based or satellite or radar-derived.
Each data source is then used to prove this claim. In particular,
- radar observations, which usually have a resolution of 1 km or more, can be used to provide evidence of the very small scale of extreme events that create problems in urban environments. They cannot be used effectively to quantify precipitation in urban basins, due to the resolution which is coarse compared to needs.
- The ground-based observations of the authoritative networks provide observations with high temporal resolution, but, even in the best cases, the distance between the stations is usually greater than the spatial scale of variability of the critical precipitation for urban basins
- citizen scientist networks, thanks to their high spatial density, allow to highlight that the spatial scale of the aforementioned critical events is actually very small and lower than both the average distance between the authoritative stations and the resolution of the operational weather radars.
In this case, we do not want to derive precise quantitative information from these last observations, but information on the actual space-time scales of variation of the critical precipitation events for urban floods.
Differences such as those observed between citizen scientists' rain gauges are certainly higher than the average error of such measurements (which we will try to quantify in the next version of the paper) therefore it is considered reliable that such observations can be used to study the characteristics of critical events for urban floods, and make a contribution to the definition of design ietographs for hydraulic infrastructures and flood protections in small urban catchments
We will take care of illustrating clearly all this in the revised version of the paper
Citation: https://doi.org/10.5194/nhess-2024-24-AC2
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RC2: 'Comment on nhess-2024-24', Aaron Alexander, 07 Mar 2024
This manuscript attempts to study the importance of citizen science on urban rainfall and flooding. While the authors do have interesting results, there are several concerns that need to be addressed before this can be published. Much of these are focused on restructuring the manuscript so that there is a clearer narrative. Major comment 1 summarizes this, but many of my major concerns can be addressed through consideration of if this is helping this study, which to me is answering the question posed on line 286: "What would happen if data from citizen science stations were included in the process of acquisition and production of radar derived rainfall maps?”
Major Comments
- I believe that the most important portion of this paper is the question that is posed on line 286: “What would happen if data from citizen science stations were included in the process of acquisition and production of radar derived rainfall maps?” It took a long time to get to this point as the manuscript currently stands, and much of the framing done for this paper does not help move this question forward. I appreciate the effort that has gone into the diverse amount of analysis showcased, but I do think that some restructuring needs to be done. For example, moving data descriptions to one central location. Further, one could image a figure where information from Figure 4 is compiled with Figure 11 to further push forward the idea that using more data sources is imperative, especially in urban scales. I think that a careful look at what the authors intended purpose of this paper is, and whether the current structure of the paper serves that purpose. I believe that there is very useful work here, but clarification and a better structure is needed!
- The first paragraph in section 3 should be reworked into a more readable form. I think that using something like a “data” section would be useful. Right now, much of the paper is focused on these rainfall gauges, but there were other data sources used. Having these listed in once place would be better. Then, one could just jump directly into the meat of the analysis presented (which I believe is great) starting at line 150. This would also help with removing some of the continuity errors that I am having while reading through the paper (section 5.3 with the information about the sensors that were used).
- As it stands, section 4 doesn’t add much to the study. I think that there is a need to contextualize the flooding events that are a result of the rainfall, but this could be better integrated into the analysis of the August 27th and 28th Storm in section 5.
- As currently presented, you are missing a panel in Figure 7.
- The first mention of any citizen science based platform is on line 255. I would suggest either bringing this forward, reworking some parts of the introduction to be more of a focus on the importance of these data, or remove the emphasis of citizen science in the title of this study.
- The method of how Figure 12 is important enough to be included and not just referenced. Please add a brief section talking about this.
Minor Comments (in order throughout the document):
- Authors could consider adding the following citations to their outline of sub-daily extremes, especially as these papers are focused on urban areas and heatwaves leading to extreme rainfall (and this seems like a very key point of this study)
- Intensification of sub-daily rainfall extremes in a low-rise urban area (https://doi.org/10.1016/j.uclim.2022.101124)
- Compound Extreme hourly rainfall preconditioned by heatwaves most likely in mid-latitudes (https://doi.org/10.1016/j.wace.2023.100563)
- I am unsure if you need the end paragraph of the introduction. I think that there could be a stronger way of ending this section, with a bit more about “to this end, we investigate an intense rainfall event that occurred in the genoa urban center. We present a comprehensive analysis of XYZ…” Etc.
- Line 69: This could be combined with the paragraph below. It would help tie together that there are complex interactions between the synoptic and regional meteorology, while also pointing out that the complex terrain is a major contribution to rainfall extremes.
- Not a comment in a bad way at all. I love the use of morphological amphitheatre on line 91!
- I think that the hydrologic background is useful, but a bit long. Consider consolidating a bit.
- Consider showing the locations of the rain gauges on figure 1 if possible. Getting a feel of where these stations are in addition to information in Table 1 would be useful.
- On Figure 3&4: instead of the mean and median being a ‘thick and thin’ line, consider using a dashed like for one to help differentiate.
- In Table 2 description, please include what is the reference station ( I am assuming it is the GU station in Figure 3).
- On Figure 5: I suggest demarcating the location of interest to help draw readers attention to the region. You also could consider zooming into the Mediterranean area a bit more.
- Please consider making the color bar larger on Figures 8 & 9.
Citation: https://doi.org/10.5194/nhess-2024-24-RC2 -
AC3: 'Reply on RC2', Francesco Faccini, 13 Mar 2024
We are grateful to the reviewer for the comments and suggestions that will certainly help to improve the paper. More specifically, in the revised version of the manuscript dataset description will be enriched with all the data sources adopted and it will be moved to a more central location. Additionally, the text about the historical flood events in the Genoa region will be integrated into section 5 focused on the actual description of the event of 27 and 28 august 2023.
Furthermore, as correctly highlighted by the reviewer, the importance of citizen science data for the study of severe hydro-meteorological events will be highlighted in a clearer and more effective manner since the beginning of the paper in the introduction part.
Finally, the methodology to produce figure 12 will described in the paper including the reference paper (Bruno et al. 2021)
Bruno, G., Pignone, F., Silvestro, F., Gabellani, S., Schiavi, F., Rebora, N., ... & Falzacappa, M. (2021). Performing hydrological monitoring at a national scale by exploiting rain-gauge and radar networks: the Italian case. Atmosphere, 12(6), 771Citation: https://doi.org/10.5194/nhess-2024-24-AC3
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