the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Oct 2023
Anomalous variations in stable precipitation isotopes driven by high-temperature events
Abstract. Stable hydrogen and oxygen isotopes in atmospheric precipitation have the potential to identify abnormal weather events, and climate change will cause more intense and frequent high-temperature events, which already pose a threat to human health and the development of the global economy. Based on precipitation isotope data from 37 high-temperature events that occurred in various global regions between 2010 and 2022, this article examines the impacts of high-temperature events on stable precipitation isotopes. The results show that (1) stable precipitation isotopes are more enriched under the influence of high-temperature events than in the same month of previous years; the slope and intercept of the precipitation local meteoric water line (LMWL) are lower than in the same month of previous years and the global meteoric water line (GMWL); and the precipitation d-excess is lower than the global average. (2) Temperature is the primary meteorological factor that produces abnormal variations in precipitation isotopes under the influence of high-temperature events, and the impact of temperature on precipitation isotopes is significantly amplified (P<0.05). (3) Furthermore, variations in atmospheric circulation patterns, water vapor transport fluxes, regional water vapor background, and surface morphology can lead to regional differences in anomalous variations in precipitation isotopes. This study reveals the impact of high temperatures on precipitation isotopes and their mechanisms, which is instructive for disentangling the influence of high-temperature events on water cycle processes. It may also offer fresh perspectives for the reconstruction of paleo-high-temperature events based on isotopes.
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RC1: 'Comment on egusphere-2023-2058', Anonymous Referee #1, 18 Jan 2024
General comment
Lin et al. investigate how high-temperature events are recorded by the water isotopes in precipitation (d18O and secondary marker d-excess). Using measured isotope data in precipitation, GNIP dataset and high-temperature events data, they conclude that precipitations are more enriched during high-temperature events compared to non-high-temperature ones, with a change in local meteoric water line. They analyze the cause of these changes with respect to water vapor transport.
The analyses in this paper are way too simple and not convincing, and it is not clear what data have been used (no maps, no plots). Moreover, the aspect atmosphere, which is important for ACP, is not analysed in detail (only one unreadable figure). For this reason, the paper should be rejected. A complete rework of this paper is necessary before re-submission to ACP ore to another journal.
Major comments
- The readers cannot see clearly which data has been used, and the plot of the data themselves.
- What are high temperature events? How are they defined?
- High temperature events are usually on short-term time scale (one day to several weeks). To base the analyses on monthly mean only is maybe an issue. Moreover, the authors mixed the seasons/months, like there was no change in atmospheric transport between the months of a year.
- Analyses are made on very broad regions or even at global scale, while very different processes influence the isotopic composition of precipitation at these different places. Moreover, as said by the authors, the effects of temperature are mainly important in mid- to high-latitudes. Other effects due to global warming affect isotope precipitation too, like extreme precipitation events (that can be related to very high temperature in the lower latitudes).
- The figure 1, supposed to show the impact of HT events on isotope precipitation; is hard to understand and misleading. First, the colorbars are not symmetric (e.g., between -10 and +10 ‰). Second, if there is an effect on HT events, d18O_HT – d18_NHT should be positive. It’s not what I see from this plot. Moreover, it is not clear what is compared to what in which region. What are NHT1, NHT2…?
- The effects on LMWL is significant over Europe, but not for the other regions (very small difference or not enough data points like for North America).
- The effects on deuterium-excess are not so clear according to the figure 3.
- The analyses in section 4 are too simplistic. The differences between HT and NHT events for the isotope-climate parameters relationships are not so different, and the correlations are pretty low (maybe because there is not enough data).
- The figure 4 is unreadable and it does not show really the impact of high temperature events. The anomalies between HT and NHT should be shown instead.
- The paragraph on paleoclimate reconstructions is not very relevant for this journal, and moreover the statements of the authors are not so correct. Such short-term high temperature events would be smoothed in paleoproxy data, even at very high resolution (and without considering other numerous effects during the recording process).
- The references used are pretty strange.
Citation: https://doi.org/10.5194/egusphere-2023-2058-RC1 -
RC2: 'Comment on egusphere-2023-2058', Anonymous Referee #2, 07 Mar 2024
The study “Anomalous variations in stable precipitation isotopes driven by high-temperature events” by Lin, Zhu, Qiu, Chen, Si, Ye, Lu, Jiao, Liu, Li, Wang, Yang and Zhang presents GNIP data supplemented with isotopic data from 11 additional rain samplers. The data was presented as GMWL, box plot and difference matrix plot.
The manuscript was difficult to read and understand due to missing information, unclear assumptions, and the data analysis and presentation in figures. Precipitation events are independent events with different amounts, and isotopic compositions are likely. Therefore, the novelty of this study is not apparent.
Different issues:
L12-14 long and convoluted sentences
The term “high-temperature event” is not clear and needs to be defined already here.
In addition, it is not clear how isotopes allow to identify extreme precipitation.
L16 provide a definition of events
L18-20 “The results show that (1) stable precipitation isotopes are more enriched under the influence of high-temperature events than in the same month of previous years.” Are rainfall events not independent, by definition, by which the isotopic composition of rainfall is different each year?
L43-48 2012). “One of the most common extreme temperature events, a high temperature, is not clearly defined and is measured using different standards across the world. However, depending on the criteria used, a high temperature can be broadly characterised as an extreme event in which the daily maximum temperature exceeds a specific threshold over a continuous period of time.”
I fully agree that the definition is not defined. The chosen threshold was not clear from the manuscript, which makes it unclear what is meant by high-temperature events and how these are different across the planet. Define the commonly used thresholds and which thresholds were used in this study. This will help compare high-temperature events in the Midwest US with events in southeast Asia, southern Argentina, or Greenland.
L79-80 The reasoning behind using stable isotopes as a tool to address the research gap is not clear. It seems something is missing here to support the knowledge gap.
L100 “37 high temperature”
Explain why only 37 and how where these events were defined and not more or not less.
“different regions” Explain which regions are meant here and why these regions were selected.
L106-109 The introduction shouldn’t end with a discussion/conclusion. Remove.
L116 “we chose 70 GNIP and 11 stations with data representing high-temperature events” It is not clear based on which criteria these 70 stations were chosen or what type and which data the 11 stations the authors refer to.
L125 Table 1. I suggest moving the four-page-long Table 1 to the appendix.
L141 What type of sampler was used, and which mechanisms were used to prevent evaporation? Clearly state.
L143-146 Since precipitation was normalised for rainfall amounts. Was this also done for solid precipitation e.g. how was this done for snow and hail? Provide this information.
L150 State the accuracy and precision of the analyser, standards and analysis scheme used.
L168 Results contain references and discussion elements. Rewrite the Result section to fit the journal's common format.
L176-180 “This enrichment may be related to the "temperature effect" of precipitation isotopes and the "below-cloud effects."
Temperature effects are commonly assumed to be related to the isotopic composition, with warmer temperatures closer to 0 permille and the colder it gets, the more depleted it is. However, it could also be that the isotopic composition is related to the amount of effect. Meanwhile, fractionation could be related to evaporation below the cloud or just evaporation from the water sampler. Even GNIP samplers can suffer from evaporation. Therefore, instead of hypothesising only which process could have affected the isotopic composition, additional analyses are needed to corroborate results and support observations.
“Specifically, stable precipitation isotopes are more enriched in the month of the high-temperature event than over the same period in previous years in different regions of the world.”
That today’s isotopic composition is different from last year's isotopic composition is likely since precipitation events are independent. In addition, this statement generalises by merging time and space. Rewriting of this section and adding additional analysis and information is needed to demonstrate the novelty.
L193 Figure 1 This figure is not clear. What do the numbers represent, and what do the axes represent?
L196-197 “the gray … represent isotope…” However, the grey rectangles are empty and confusing.
L264 Figure 3: Axes labels are missing, and the statistic table is not needed when using boxplots. In addition, a new term, “heat wave,” is introduced, but the context and definition are missing, which confuses. It seems that heat waves and non-heat waves are similar across the world. A significant difference test is needed.
L273-280 “correlations” Correlations are not explained in the method and are suddenly introduced here. It is unclear which type of correlations and how the data was treated. It seems that all data was “lumped” compared to separated for different parts of the world. Are there differences around the world? Explain and add additional analysis to support.
In addition, there are correlations stated with precipitation amount, but wasn’t the isotopic composition normalised for precipitation amounts affecting these results? Please discuss and adjust.
L330-333 “weather background” Not clear; rephrase the sentence.
L393 Figure 4 text is too small and low resolution. Not readable.
L431 “normal vs abnormal” A definition of normal is needed.
L436 “significantly enhanced” is not a commonly used stable isotope term and needs to be explained.
L453-455: “These findings also contribute.” This study did not show that it can contribute to paleo archives, and it needs to demonstrate and discuss this.
In general, what are the potential errors and uncertainties in the analysis? Include an analysis to support this.
Citation: https://doi.org/10.5194/egusphere-2023-2058-RC2 -
RC3: 'Comment on egusphere-2023-2058', Anonymous Referee #3, 10 Mar 2024
In this ms, the authors discuss the influence of high-temperature events on the stable isotopic composition of precipitation. This is a topic which could prove very attractive for, among others, the paleoclimate community as it would pave the way for reconstructions of past warm events using the stable isotope composition of precipitation “locked” in various sedimentary archives. However, this is the only positive message I can have regarding this manuscript. Thus, while the idea is worthwhile pursuing, the way this is being done here is problematic, to say the least. First, “high-temperature” events are not clearly identified? Do the authors mean long periods of high temperature? Short, but intense heat waves? These should be clearly identified and quantified, before moving into analyzing the links between their characteristics and the stable isotope composition of precipitation. Second, the authors use monthly isotope data and discuss these in relations with much shorter high-temperature events. This is more than problematic, it is plainly wrong – several factors influence the monthly isotope data, high-temperature events being only one of these. As it reads now, in some months it just happened that the influence of these events was stronger than that of others (moisture source changes, precipitation amount, post-depositional evaporation etc). Third, the long-term period over which data was collected (2010-2022) might include the influence of global warming and this is not discussed.
Overall, while I think the idea is worthwhile pursuing, the methodology employed in this ms. is problematic and the results are not correct. The entire study should be approached in a more systematic way to prevent usage of wrong assumption that would ruin the results.
Citation: https://doi.org/10.5194/egusphere-2023-2058-RC3
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