Vb-cyclones and associated North-Western Mediterranean Sea state in regional coupled climate simulations: evaluation and projection
Abstract. Vb-cyclones propagating from the North-Western Mediterranean Sea (NWMS) into central Europe are often associated with extreme precipitation. This study explores the state and process chain linking the NWMS state and the Vb-cyclone precipitation in the Danube, Elbe, and Odra catchments in regional coupled atmosphere-ocean climate simulations with COSMO-CLM+NEMO. Two high-resolution simulations, an evaluation simulation (1951–2005) downscaling the centennial ERA-20C reanalysis and a continuous simulation (historical 1951–2005 + RCP8.5 future scenario 2006–2099) downscaling the EC-EARTH global climate data set are used for this purpose. The results show a good agreement in mean annual Vb-cyclone frequency between the evaluation (9.7 events/year) and the historical (10.1 events/year) simulations. But, there are significant discrepancies in the seasonal cycle. The mean cyclone intensity measured with minimum central pressure, track density, and precipitation rankings in the three catchments also show good agreement. The simulations for the future period show a basin-average SST warming of ≈ 2.5–3 K by the end of 21st century, but insignificant changes in Vb-cyclone frequency, mean intensity, and precipitation in the selected catchments. The NWMS sea surface temperature, evaporation, and wind speed anomalies corresponding to the Vb-cyclone precipitation rankings differ between the evaluation and historical simulations. In the evaluation simulation, Vb-cyclone precipitation rankings correspond with sea surface temperature, evaporation, and wind speed anomalies, while in the historical and the future simulation no such correspondence is seen. Especially the Adriatic and Ionian basins in the simulation driven by EC-EARTH show no sensitivity to the Vb-cyclone precipitation over the catchments. The change in the processes between evaluation and historical simulations might be due to the emergence of biases inherited from the driving EC-EARTH global simulation. The future simulation shows no significant process changes compared to the historical simulation.
This preprint has been withdrawn.
Praveen Kumar Pothapakula et al.
Praveen Kumar Pothapakula et al.
Vb-cyclones and associated North-Western Mediterranean Sea state in regional coupled climate simulations: evaluation and projection https://doi.org/10.5281/zenodo.6585342
Praveen Kumar Pothapakula et al.
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Review of «Vb-cyclones and associated North-Western Mediterranean Sea state in regional coupled climate simulations: evaluation and projection»
by Praveen Kumar Pothapakula, Amelie Hoff, Anika Obermann-Hellhund, Timo Keber and Bodo Ahrens
submitted to: Earth System Dynamics (esd-2022-24)
The submission tries to assess Vb-cyclones in a centennial simulation downscaled using a regional climate model coupled to an ocean module to investigate precipitation related to Vb-cyclones over three different catchments. The vast amount of data provided by such a simulation provides certainly an interesting and important basis to obtain a better understanding of Vb-cyclones under global warming, and to deepen the understanding during such events. This is important because these events are often related to extreme precipitation and flooding events in central Europe. Nevertheless, I don’t see how this study helps to foster or even increase the process understanding of Vb-cyclones with respect to the Mediterranean Sea:
First, the method is not well enough described, so that I find it hard to understand how variables (e.g., evaporation, wind speed and sea surface temperature) over the Mediterranean Sea are linked to the precipitation over the different catchments. How long are the Vb-cyclone events typically? What period is taken to accumulate precipitation? Is it daily and a four day lasting Vb-cyclone is counted as four events? How is it assured that the precipitation over the catchment is actually linked to the Vb-cyclone and not to another large-scale feature over northern Europe? The fact that half of the cyclones result in a negative anomaly with respect to the climatology (Figure 1) indicates that no real cyclone situation is present over the different catchments for these negative anomalies. What is the argument for negative precipitation anomalies while a Vb-cyclone is present in the vicinity of the catchment?
Second, I find the conclusions drawn for the future too strong (particularly in the abstract), particularly in the light of obvious missing processes in the GCM, for which the RCM cannot compensate for (e.g., evaporation and SST values and patterns) in the Mediterranean Sea. The chosen climate simulation does not very well represent the SSTs over the Mediterranean Sea during the historical period and some other CORDEX simulations do a much better job. Why did the authors not consider including these simulations in the analysis as well? This would certainly add value as it allows to estimate the robustness of the results and would give an indication of the sensitivity of the results with respect to the Mediterranean SSTs. Another option could be to correct the SSTs in the boundary conditions of the RCM by a delta change approach. These missing processes at least need to be better discussed in the conclusions and in the abstract.
Third, the results for the future are shown in figures, but are often mentioned in only one sentence in the text. In a climate study, it is valid to evaluate the historical period against a reference and point out misrepresentations or biases, but then the focus should be on the differences between the historical and the future period. These differences allow to reveal changes in processes, which should then be discussed with respect to the bias of the model. This is widely missing in this study. In addition, the results obtained in the evaluation period are often compared to the results in Krug et al. (2021 and 2022) and it is pointed out that the results of the two studies matches (e.g., L340ff). This is not surprising as the underlying data, the method and the analysis are identical, therefore also the figures are very similar to the Krug et al. (2022) study.
Fourth, a lot of the method is based on other studies. I agree that these methods do not need to be explained in detail, but it would be very helpful for the reader if the method is summarizes the main aspects, which is still lacking, particulalry if the methods have been further adapted. I do not think that a reader wants to read several other studies to understand the underlying method of the study (e.g., cyclone tracking, track density, regressions, etc.).
Fifth, for me it is unclear how the trendlines in the Figure 1 and S1 are calculated. I would suggest using a non-parametric approach, such as the Mann-Kendall test for a monotonic trend. The trend line could even be removed and just the statistical number about the trend (slope, p-value) could be given. Since the authors have a seamless simulation that connects the historical and the future period it could also help to use the full period for the trend analysis, rather than just the two 55-year periods. One could also think to show this analysis in terms of histograms, where the evaluation, historical and future periods are overlayed into one panel. In my opinion it seems as if particularly the variability of the Vb-cyclones is changing in the future, at least in some seasons.
Sixth, I think it would be more meaningful to restrict the whole analysis to the 50-100 most intense Vb-cyclones only. This might help to obtain more meaningful results. This would further allow to cover the systems that impact the different catchment areas a bit at least.
Seventh, the language of the paper is still not very fluent, and the grammar is not very good, rendering the manuscript difficult to understand.
Finally, I would like to point out that I have reviewed this manuscript before and most of the major comments have not been adressed or implemented into the new version. Reviewing publications is quite time consuming and I think it would be respectful to the reviewers to adress or include major comments from previous submissions. To submit a less sloppy manuscript, a final critical check of the spelling, citation style (usage of brackets, L35ff meaningless citation of “vol”) and the quality of the figures (aspect ratio of maps is not correct, axis labels overlay with labels of colour bar) before submission, is highly recommended.
Some further comments are (non exhaustive):
Vb-cyclones are rather mesoscale features (much smaller than other cyclones) and hence their impact radius is not very large.