the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Jul 2026
Future scenarios of thunderstorm environments in Fennoscandia based on a regional climate model
Abstract. This study investigates how increasing greenhouse gas concentrations may affect environmental conditions favourable for thunderstorms over Fennoscandia. The future scenarios are based on data produced with the HARMONIE-Climate convection-permitting regional climate model forced by two global climate models at the lateral boundaries. The distribution of thunderstorm-favourable days, defined as days with co-occurring conditional instability and precipitation, in model data compares well with observed thunder days in May–September 2002–2018 across the study domain. By 2081–2100, the area-average frequency of favourable days is projected to increase by approximately 40–185 % in Finland, 30–185 % in Sweden, and 15–210 % in Norway relative to 1986–2005 under the RCP4.5 and RCP8.5 emission scenarios. Projected increases are largest over the northern Fennoscandia and in simulations exhibiting stronger warming. Thunderstorm-favourable conditions occurring simultaneously with strong vertical wind shear are also simulated to become more common, suggesting more frequent potential for severe organized convection in a future climate. More research is needed to understand how the changes in general storm-favourable environmental conditions may affect actual hazard occurrence. The results support the use of the HARMONIE-Climate model for convective storm scenario studies and offer valuable context for climate change adaptation in Fennoscandia.
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Status: open (until 06 Sep 2026)
- RC1: 'Comment on egusphere-2026-4247', Anonymous Referee #1, 24 Aug 2026 reply
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RC2: 'Comment on egusphere-2026-4247', Anonymous Referee #2, 26 Aug 2026
reply
In my understanding, this study aims to build on existing literature relating to proxies for thunderstorm activity in Europe by studying the Fennoscandia region specifically. The work demonstrates the value of locally tuned models, in this case HARMOIE. It also shows that thunderstorm environments are expected to increase in frequency in this region, but with wide uncertainty.
This is a good piece of work, but I believe the authors could go further in contextualising the results and addressing the underlying physical processes, and that there is value in doing so. That CAPE increases in Europe in climate models is fairly well known but the most interesting analysis would be to compare Fennoscandia with other regions.
Lines 71-73 raise an important point. What are 'processes relevant' and how are they different in the Fennoscandia region compared to continental Europe?
Lines 153-156 outline the thresholds used. From the literature, I believe the DLS threshold comes from Púčik, where sounding observations suggested that DLS above 15 m/s was likely to be indicative of supercells. Are we observing supercells in this more northerly region?
Lines 258-260, can you expand a bit on this and what may actually cause the differences observed? We expect some differences but are they due to noise and definitely not due to missing any of the physical processes.
Section 4.3, the discussion here is good but could benefit from greater depth. What causes a decrease in DLS environments and does this not reduce the number of severe storms given DLS was identified as necessary for severe convection likely to lead to greater hazards.
Line 410 onwards, aims to put the results in context of other studies. I think this paper needs to go further here. I believe other works such as Púčik predicted minimal change in Fennoscandia and I have seen others such as Battoglioli suggesting minimal thunderstorm activity in the Scandi region based on proxies developed in central Europe. I think it would be of great interest to assess in more detail whether the results from a local model are different to other works and if so why? If the background processes leading to thunderstorm days are not well captured by proxies based on continental Europe then this would be an interesting result.
Lines 474-476, this is an important limitation in the literature buried near the end of this paper.
Citation: https://doi.org/10.5194/egusphere-2026-4247-RC2
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- 1
Review of “Future scenarios of thunderstorm environments in Fennoscandia based on a regional climate model”
by Virman et al.
Summary:
This study investigates the change in thunderstorm occurrence in Fennoscandia in a warming climate. The HARMONIE convection-permitting climate simulations (3 km grid spacing) are used with boundary conditions from either EC-EARTH or GFDL. Furthermore, RCP scenarios 4.5 and 8.5, as well as mid and late century changes are compared to the historical period. Simple thresholds for combinations of CAPE, precipitation, and deep wind shear are used to assess the changes in thunderstorms, convective precipitation, and severe thunderstorms, respectively.
It is found that both thunderstorm days and severe thunderstorm days significantly increase by mid-century, with only secondary differences across the ensemble. The northern half of Fennoscandia is most affected. The driver of this increase is more frequent occurrence of CAPE above the threshold despite the relative frequency of precipitation and shear on days with CAPE showing slight decreases.
General comments:
I agree that the topic is worth studying given the large expected impact of climate change on thunderstorm occurrence. Overall, the article is in good shape, with clear structure, scientific writing and illustrations. However, the novelty of the study is a bit unclear to me. The approach of using simple convective parameters to study thunderstorm trends has been used in many studies. It is perhaps worth looking into regional trends in a specific area like Fennoscandia in detail (I agree that Fennoscandia is left out in too many studies), but the analysis is fairly shallow for such a regional focus. The impact of the study could be increased with a more sophisticated analysis (comment 2 below), more comparison with the literature (comment 1), and a clearer justification for the novelty of the study (comment 3).
Specific major comments:
Thurnherr, I., Cui, R., Velasquez, P., Wernli, H., & Schär, C. (2025). The effect of 3°C global warming on hail over Europe. GRL. https://doi.org/https://doi.org/10.22541/au.173809555.59545480/v1
Battaglioli, F., Taszarek, M., Groenemeijer, P., Púčik, T., & Rädler, A. (2026). Contrasting trends in very large hail events and related economic losses across the globe. Nature Geoscience, 19(January), 52–59. https://doi.org/10.1038/s41561-025-01868-0
Raupach, T.H., Portmann, R., Siderius, C. et al.Shifting hail hazard under global warming and effects on crop hail risk. Clim. Chang. 16, 696–703 (2026). https://doi.org/10.1038/s41558-026-02660-7
Zhang, S., Zhang, Q., Allen, J. T., & Lin, X. (2026). Rising global hail damage potential in a warming world. Nature, 653(8116), 1069–1077. https://doi.org/10.1038/s41586-026-10543-2
Connected to this, if I didn't miss it, there is no explanation how convective parameters such as CAPE are calculated from the model fields. If I interpret it correctly, it's a standard model output that is being used? Taszarek et al (2021) suggest calculating e.g., CAPE from the model levels, which is not done in the standard ERA5 and ERA-Interim output as far as I know. Also see e.g., Taszarek et al. (2018) for some of the potential downsides of using Reanalysis data.
Taszarek, M., H. E. Brooks, B. Czernecki, P. Szuster, and K. Fortuniak, 2018: Climatological Aspects of Convective Parameters over Europe: A Comparison of ERA-Interim and Sounding Data. J. Climate, 31, 4281–4308, https://doi.org/10.1175/JCLI-D-17-0596.1.
Taszarek, M., Pilguj, N., Allen, J. T., Gensini, V., Brooks, H. E., & Szuster, P. (2021). Comparison of Convective Parameters Derived from ERA5 and MERRA-2 with Rawinsonde Data over Europe and North America. Journal of Climate, 34(8), 3211–3237. https://doi.org/10.1175/JCLI-D-20-0484.1
Other minor comments and suggestions:
Line 28: what observations are you referring to? Based on the references probably severe weather reports? The phrasing might be misleading because there are other more indirect observations like satellite or radar? Perhaps specify to "observations in form of direct reports"?
Line 38: Shouldn’t it be „convective available potential energy“
Lines 71-73: Related to comment 3 above, can you be a bit more specific here? Isn't the main problem with these studies that the statistical model was trained mainly for different climatological regions than Fennoscandia? Or is is this what you meant?
Fig. 2: thunderstorm days determined from environmental parameters are typically higher than observed lightning days because there are at least a few days where no storms are forming, e.g., due to too much CIN (Fig. 3 in Taszarek et al. 2019). Here you show the opposite, which I'm a bit confused about given that the analysis is also partly based on ERA Interim and similar thresholds are used as in Taszarek's study. Or am I missing something? Perhaps connected to this, the numbers in Fig 2a seem a bit higher than in Taszareks anaylsis. Do you have an explanation for this?