the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Groundwater in terrestrial systems modelling: a new climatology of extreme heat events in Europe
Liubov Poshyvailo-Strube
Niklas Wagner
Klaus Goergen
Carina Furusho-Percot
Carl Hartick
Stefan Kollet
Abstract. Due to climate change, years with positive temperature anomalies are becoming more frequent in Europe, requiring
high-resolution climate data to plan for climate change mitigation and adaptation. However, many regional climate models
(RCMs) simplify the representation of groundwater processes, leading to biases in simulated extreme heat events. Here, we
study the characteristics of summer heat events in a unique dataset from the regional Terrestrial Systems Modeling Platform
(TSMP) simulations, compared to an ensemble of EURO-CORDEX climate change scenario control simulations, for the historical
time period 1976–2005.
Our results show that in TSMP, the impact of groundwater coupling on the frequency of hot summer days depends on the
considered time period and the region, associated with respective evaporative regime. An increasing trend of the frequency
of hot summer days averaged across Europe is the lowest in TSMP compared to the other RCMs considered. Groundwater
coupling has a systematic effect on the duration and intensity of heat events: summer heat events with long duration and high
intensity are less frequent in TSMP compared to the CORDEX ensemble. In particular, extended heat events with a duration
exceeding 6 days, i.e. heat waves, occur on average in Europe about 1.5–8 times less often in TSMP, while single-day heat
events happen slightly more often in TSMP compared to the CORDEX ensemble. The frequency of high-intensity heat waves
in TSMP is up to 12 times lower on average in Europe compared to the CORDEX ensemble. Thus, an explicit groundwater
representation in RCMs may lead to rarer and weaker heat waves in Europe also in climate projections. The findings of this
work indicate an existing discrepancy in the ensemble of EURO-CORDEX climate change scenario control simulations and
emphasize the importance of groundwater representation in RCMs.
Liubov Poshyvailo-Strube et al.
Status: final response (author comments only)
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RC1: 'Comment on esd-2022-53', Anonymous Referee #1, 13 Jan 2023
The study aims to improve the understanding of how groundwater affects regional temperature anomalies by comparing the simulation results from TSMP and those from the other RCMs. Although the topic and method are of interest to the readership of Earth System Dynamics, several issues need to be addressed. First, the manuscript is poorly written because of many confusing and inaccurate sentences. Second, the results are not new since there already have been comparations in heat event analyses between TSMP and the other RCMs. For example, in line 60, “In fact, many RCMs overestimate the frequency, duration, and intensity of heat waves (e.g., Vautard et al., 2013; Lhotka et al., 2018)”, or in line 255, “Vautard et al. (2013), Plavcová and Kyselý (2016) have previously found a systematic tendency of most RCMs to overestimate the number and duration of long heat waves in comparison to observations”. Meanwhile, the key results showing characteristics of heat waves/events are not well organized for the readers to follow. Third, comparisons between the simulation results of TSMP and the ensemble of RCMs (Figure 5) are not convincing to conclude the influence of groundwater, since the different conceptualizations of physical processes among the models can also result in differences in temperature anomaly, let alone different forcing data (Table 1). Fourth, TSMP has the advantage of fully characterizing groundwater-soil moisture-temperature interactions. Still, the manuscript fails to analyze more variables of the model outputs rather than temperature anomalies. It fails to investigate why and how groundwater can affect the characteristics of extreme heat events. Please find the specific comments as follows:
- Title: Is that suitable to say “climatology of extreme heat events”? since this work is talking about the climatological characteristics/mechanisms of extreme heat events.
- Line 1: This sentence is not concise. Particularly, it seems unnecessary to talk about the requirements of high-resolution climate data, which is not the point of this study’s focus. The potential background might be why groundwater processes can affect extreme heat events for the second sentence.
- Line 4: What do you mean by a unique dataset? How unique?
- Line 5: Not all readers know what EURO-CORDEX is.
- Line 6: It should be “period of 1976-2005”
- Line 8: What is the respective evaporative regime? And in the following sentences, regional differences are not mentioned.
- Line 9: Are “the other RCMs considered” just the CORDEX ensemble?
- Line 13: Not rigorous for using “slightly more”
- Line 13: Although it has been explained that a heat event with a duration exceeding 6 days indicates a heat wave, what are high-intensity heat waves?
- Line 15: First, using simplified might be better than using “explicit”? Second, it seems hard to conclude “rarer and weaker heat waves” since the frequency of heat waves and high-intensity heat waves is higher for the CORDEX ensemble, where only single-day heat events happen less often. Third, as mentioned above, are the RCMs in this study mean the CORDEX ensemble?
- Line 15: what do you mean about “also in climate projections”?
- Lines 44-49: These are not informative or conclusive enough to be an independent paragraph.
- Introduction section: Overall, this section is relatively clear about the importance of soil moisture in groundwater-soil moisture-temperature coupling, which affects temperature anomaly, and the advantage of groundwater parameterizations in TSMP. However, it is not firmly linked to the manuscript’s aim to study the statistics of the heat event characteristics (frequency, duration, intensity).
- Model section: The introduction of TSMP could be simplified, while the setup of TSMP could be clearer for reproducibility.
- Line 105 and 108: It is unclear in which period the model was warmed up.
- Lines 112-115: Is the model calibrated by well observations of the water table or observation-based surface temperature datasets? And how accurate are the simulation results?
Citation: https://doi.org/10.5194/esd-2022-53-RC1 -
AC1: 'Reply on RC1', Liubov Poshyvailo-Strube, 18 Mar 2023
We thank the referee for the review and useful and detailed comments. Please see the attached .pdf file where we provide a point-by-point reply, with reviewer comments repeated in black, responses to the reviewer’s comments in blue, and the revised text in italics and in quotation marks.
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RC2: 'Comment on esd-2022-53', Anonymous Referee #2, 18 Jan 2023
Poshyvailo-Strube and colleagues investigated how the inclusion of groundwater modeling would affect heat wave characteristics in Europe. This is an important topic as groundwater plays a critical role in land-atmosphere interactions, but its modeling has been oversimplified or neglected in climate models. However, before I recommend publication, I have two major concerns that need to be addressed by the authors. Hope they will be useful to the authors.
1. The title seems to suggest that this paper will be providing and evaluating a new climatology of extreme heat events in Europe. I would expect the authors to compare their new climatology to observation-informed heat wave characteristics. However, I did not find any comparison with observations. The paper itself seems to discuss how groundwater modeling would affect heat waves just by comparing their model to other no-groundwater models. This seems not new to me as the authors have stated in line 60. An opportunity to improve probably is to add an observational perspective. Are the heat wave characteristics modeled by TSMP better agree with temperature observations than other models and by how much?
2. The current paper lacks an investigation of which process the groundwater had the influence to change the temperature anomalies. The intuitive processes are soil moisture and evapotranspiration. The comparison between TSMP and other RCMs may not be entirely due to groundwater. Other factors such as forcing, and structure differences (how they model vegetation) may also contribute to the difference. An opportunity to address this is to run the TSMP without the groundwater component and compare the affected processes within TSMP rather than across different RCM settings.
Citation: https://doi.org/10.5194/esd-2022-53-RC2 -
AC2: 'Reply on RC2', Liubov Poshyvailo-Strube, 18 Mar 2023
We thank the referee for the review and for the helpful comments and suggestions. Please see the attached .pdf file where we provide a point-by-point reply, with reviewer comments repeated in black, responses to the reviewer’s comments in blue, and the revised text in italics and in quotation marks.
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AC2: 'Reply on RC2', Liubov Poshyvailo-Strube, 18 Mar 2023
Liubov Poshyvailo-Strube et al.
Liubov Poshyvailo-Strube et al.
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