Extratropical cyclones transport momentum, moisture and energy from subtropical to higher latitudes. They are responsible for most of the weather variability in the mid-latitudes and are often associated with meteorological hazards such as damaging winds and flooding events . Given these important societal impacts and in order to help shape practical adaptation responses to climate change, it is vital to improve our understanding of the likely changes that these phenomena will experience as the climate warms not only globally but at the regional and local levels.

Several studies have investigated how anthropogenic climate change will influence the behaviour of cyclones . The frequency, preferred pathways, and intensity of cyclones are expected to respond primarily to changes in the meridional temperature gradients in both the lower and upper troposphere . Additional influences include adjustments to the vertical temperature profile and diabatic heating rates . The multi-model mean of successive generations of the Coupled Model Intercomparison Project (CMIP) broadly agree on the large-scale spatial pattern of these changes in the North Atlantic ; however, substantial inter-model differences remain . A common signal is a summer reduction in cyclone activity, particularly across southern parts of Europe, and a winter tripole pattern marked by increased storminess over the British and Irish Isles but reduced activity in the Mediterranean and Norwegian Sea regions .

Evidence also suggests that the dynamical intensity, i.e. the cyclone intensity measured by a dynamical variable such as minimum sea-level pressure (SLP) or relative vorticity , of the most extreme cyclones will increase under climate change. Nevertheless, the magnitude of change remains uncertain and depends strongly on the choice of intensity metric used . The meteorological hazards associated with extreme cyclones are also projected to increase. Extreme wind speeds are projected to intensify, particularly along both cold and warm conveyor belt airstreams . Similarly, extreme precipitation associated with cyclones is expected to intensify, with projected increases of 20 %–50 % for the most intense events . However, considerable uncertainty remains in future projections of cyclone trends due to competing thermodynamic influences on North Atlantic baroclinicity , poor representation of mesoscale and diabatic processes in global climate models (GCMs) , distinguishing natural variability from the forced signal and scenario uncertainty .

Although examining general trends in this way is important for obtaining a broad appreciation of the likely changes cyclones will undergo in the future, there is a gap in understanding how specific types of impactful cyclones will be affected by climate change. This is because broad-scale trends in cyclone frequency and intensity cannot fully capture local variations or the unique combinations of processes that may shape individual cyclones. Specific cyclones, and specific impacts, often arise from complex and non-linear interactions between large-scale dynamics and mesoscale features, including local topography, ocean circulation, and diabatic feedbacks . As a result, general assessments of cyclone trends may mask divergent responses of different cyclone types, or driving mechanisms, to climate change.

To address this gap, in this study we investigate climate change effects on four contrasting extratropical cyclones that have impacted the UK, Ireland and France. These cyclones are contrasting in the sense that their paths exhibit characteristics that are different from each other and from the conceptual cyclone-development path, i.e. a cyclone developing in the central Atlantic and propagating eastwards with a northwards tilt. Our investigation is based on a recently developed approach, the cyclone analogue methodology , albeit with some adaptations to make it more suitable to the aims of this study. The method of cyclone track analogues involves finding cyclone events with comparable paths in climate simulations under present-day conditions and in projections of the future climate. These cyclones with similar paths are termed analogues . This approach simultaneously enables analysis of the impact of climate change on the frequency and intensity of cyclones with similar tracks, whilst providing an understanding of the meteorological conditions contributing to the event . applied the cyclone track analogues approach to the study of explosive European cyclones Alex, Xynthia and Eunice, finding a decline in the overall number of analogues in the future, alongside an increase in the number of explosive analogues. They also noted an increase in precipitation and wind severity over land, signalling increased meteorological hazards.

This study is situated within the CANARI (Climate Change in the Arctic–North Atlantic Region and Impacts on the UK) research programme aimed at improving our understanding of the impacts on the UK due to changes in the Arctic–North Atlantic region as the climate warms . As part of CANARI a new large ensemble of climate simulations, the CANARI Large Ensemble (hereafter CANARI LE), has been produced . This study utilises the CANARI LE to examine the influence of climate change on four contrasting historical high-impact cyclones impacting the UK, Ireland and France, assessed through the following research questions:

How well does the CANARI LE simulate analogues of the four case study cyclones?

The rest of the paper is organised as follows: Sect.  summarises each of the four historical cyclones examined, highlighting their contrasting characteristics. Section  describes the data and methods used, emphasising the differences between our methodology and that of . Section  provides a general assessment of the representation of extratropical cyclones in the CANARI LE. Section  analyses biases and future changes in the frequency of cyclone analogues in the CANARI LE. Section  provides a comparative composite analysis for key intensity metrics and dynamical drivers in the present-day and future simulations. Section  summarises the projected changes for each case-study cyclone, highlighting the implications of cyclone-specific responses for adaptation and mitigation strategies.

In this section, the four historical cyclones under investigation are described together with a brief overview of their impacts and synoptic conditions.

To provide confidence in the results of the track analogue methodology, we first briefly examine the representation of North Atlantic extra-tropical cyclones in the CANARI LE. Since the track analogue methodology focusses on cyclone tracks at the time of maximum intensity, we examine how closely the statistics of such points from the historical simulations resemble ERA5, and how they change in the future simulations. Figure a shows the spatial density of cyclone tracks at their time of maximum intensity. In ERA5, most cyclones reach peak intensity within a band extending from the east coast of North America to northern Europe, with a pronounced density maximum south of Greenland. The CANARI LE overestimates the total number of cyclones over the region by 2.9 %. The largest local biases, however, are 10 %–15 % and negative, to south of Greenland and to the north of the UK. This spatial pattern is broadly consistent with the cyclone-track density biases reported for other CMIP6 models relative to ERA5 . In contrast, the biases over the primary target regions of this study, namely around the UK, Ireland and France, are considerably smaller, providing confidence in the suitability of the CANARI LE for simulating analogues of the four historical cyclones.

Figure b shows the density of extreme cyclones at peak intensity, where extremes are defined as cyclones with a track-maximum relative vorticity exceeding 8.2×10-5s-1 (see Sect. ). Averaged over the region, the CANARI LE underestimates the number of extreme cyclones by 14.4 % relative to ERA5. The spatial pattern of extreme cyclone peaks broadly resembles that in Fig. a; however, the negative biases are larger south of Greenland and across much of the North Atlantic. This is consistent with the intensity biases identified across the sub-polar gyre in . In contrast, the target regions of this study exhibit only a modest negative bias, of the order of 1–4 cyclones per decade, indicating that the representation of extreme cyclone activity in these areas is considerably closer to ERA5 than over the open ocean.

To examine the distributions of cyclone intensity in more detail, Fig.  compares quantiles of track-maximum RV for North Atlantic extratropical cyclones in ERA5 and the CANARI present (orange) and future simulations (blue). There is close agreement between the CANARI LE and ERA5, indicating that the CANARI LE simulates cyclone intensity distributions well. However, there is a slight tendency towards weaker intensities relative to ERA5 at the upper tail, indicating that the CANARI LE underestimates the strength of the most extreme cyclones. The target regions over southern UK and the North Sea exhibit similar intensity biases (not shown). This behaviour is consistent with the tendency of global climate models to underestimate the intensity of the most extreme cyclones , potentially arising from the misrepresentation of dynamical processes at cyclone scales, such as baroclinic energy conversion and diabatic heating . Large-scale circulation biases are also likely to contribute, as they shape the background environment in which cyclones develop; for example, linked cyclone intensity biases to the tilt of the North Atlantic jet stream.

Taken together, this comparative analysis and evaluations from and support the use of the CANARI LE for analysing the frequency of extreme cyclones affecting the UK, Ireland and France, particularly because biases associated with extreme cyclones are small over the target region.

To identify future changes in cyclone statistics, Fig. c and d show the change in density of cyclones at peak intensity between the present and future simulations, for all and extreme cyclones respectively. Over the entire region, the number of cyclones decreases by 10.7 % [95 % confidence interval from ensemble bootstrap resampling: -11.1 % to -10.2 %]. There is an increase in cyclone density south and downstream of Greenland, consistent with a poleward expansion of the tropical circulation, strengthened jet speeds, and interactions with regional orography . A slight positive signal of 1 %–2 % appears over parts of the North Sea, plausibly linked to an extension of cyclone tracks and enhanced baroclinicity associated with changes in sea surface currents . In contrast, the British and Irish Isles exhibit a 3 %–5 % reduction in cyclone density, similar to much of the surrounding region. This is likely caused by reductions in lower-tropospheric temperature gradients under amplified high-latitude warming .

Extreme cyclones show a contrasting response, with reductions in cyclone density over the western North Atlantic but increased cyclone density over Ireland, the UK and much of Europe of the order of 1–3 cyclones per decade (Fig. d). This likely reflects enhanced temperature gradients in the upper troposphere and/or stronger diabatic feedbacks in cyclone cores .

Similarly, Fig.  (blue line) shows that the intensity distribution shifts towards fewer weak-to-intermediate cyclones and a larger proportion of the most intense cyclones, consistent with broader projections of fewer cyclones overall but greater intensity among the strongest cyclones .

In this section, the ability of the CANARI LE to simulate analogues of the four historical study storms is assessed relative to the period 1950–2014 in ERA5. The influence of climate change on the frequency of simulated analogues is assessed by comparing analogue rates in present-day (1980–2010) and future (2070–2100) periods. Figure  shows the paths for all cyclone analogues and extreme analogue subsets for each historical cyclone in ERA5 reanalysis, CANARI LE present and CANARI LE future.

Analogue cyclones are identified throughout the year in both ERA5 and the CANARI LE. The seasonality in both sets is qualitatively similar with most analogue cyclones occurring in the DJF season. The exception is the Great Storm of 1987 for which ERA5 analogues appear evenly distributed throughout the year. The same behaviour is found in the CANARI LE present period, but not in the future period which exhibits a marked clustering towards DJF (not shown). However, the number of analogues is not sufficiently large to make a quantitative assessment and therefore this aspect is not investigated further.

In this section, future changes in analogue dynamical intensity and associated hazards are assessed via track statistics measuring maximum cyclone-associated hazards along each cyclone track, and composite maps generated by averaging gridded fields from all analogue tracks at their time of maximum intensity. Hazards are assessed using wind speed at 850 hPa and precipitation rate. Further, each cyclone set is examined via composites of EGR and jet speed to identify dynamical processes contributing to the future changes in cyclone analogues.

The influence of climate change on four impactful European cyclones with contrasting characteristics have been assessed. Storms exhibiting comparable tracks and stages of development were identified and classified as analogues for both the present-day climate (1980–2010) and the future SSP3-7.0 scenario (2070–2100) from the CANARI LE simulations, following the methodology of with adjustments. Within this set, cyclones exceeding the 90th percentile of track-maximum RV were further defined as extreme analogues. The findings indicate that in the future climate the frequency and intensity of these analogues will likely exhibit divergent responses to warming.

Storm Martin was an exceptional event forming under rare large-scale conditions with no other extreme cyclone of its kind with a comparable track in ERA5. In the future climate, analogues are projected to become even less frequent, but the number of extreme analogues increases. Furthermore, the intensity of future analogues are projected to increase significantly in terms of PR, and positive signals of RV and WS850. Changes in intensity are likely driven by increased wind speeds in the upper troposphere and increased baroclinicity over the central North Atlantic basin. These factors indicate that the occurrence of extreme analogue cyclones will not become less likely. When they do occur in future, they will be more intense and accompanied by significantly more precipitation, presenting a greater meteorological hazard.

Fewer cyclones reach peak intensity in a similar location to the Great Storm in the future climate. Despite this, the number of analogues increases significantly due to a large increase in the number of cyclones following a similar path. Moreover, all cyclone metrics investigated here (RV, WS850, PR) indicate a significant increase in intensity and associated meteorological hazards. Increases in PR are located along the cold front with increases in wind speed located in the warm sector. Significant increases in baroclinicity over the North Atlantic indicate that changing SST gradients may correspond with increases in intensity. The jet streak is also displaced southward and downstream in the future, potentially enhancing baroclinic growth due to upper-level forcing. This suggests that modifications of both the lower- and upper-level temperature gradients increase both the frequency and intensity of future analogues of the Great Storm in a warmer climate.

Storm Arwen was characterised by anomalously strong northerly winds associated with its distinct southward track, likely contributing to the severe impacts, as infrastructure and preparedness in the affected regions are primarily geared towards damaging westerly, rather than northerly, wind events . In the future period, both the number of analogues and extreme analogues of Arwen decrease significantly. On average, the future analogues are also weaker, with statistically significant reductions in WS850 and RV. In contrast, the subset of extreme analogues shows a robust increase in intensity: RV increases significantly, WS850 increases in the warm sector, and substantial increases in PR are projected. Large reductions in baroclinicity southwards and eastwards of Greenland, consistent with projected reductions in high-latitude lower-troposphere temperature gradient in a warmer climate, appear to suppress cyclogenesis and mean cyclone intensity. The increase in intensity of the extreme analogues which do occur likely reflects the downstream enhancement of the jet streak, enhancing air ascent and promoting increases in intensity. Together, these results suggest that future Arwen analogues, with damaging northerly winds, are likely to become less frequent in a warmer climate but that the most extreme analogues may be more intense, sensitive to the competing influences of weakened low-level and strengthened upper-level temperature gradients at high latitudes in the North Atlantic basin.

Finally, in the future climate, substantially fewer candidate cyclones reach peak intensity in a location comparable to Ophelia, and changes in analogue counts show only a weak positive signal. This likely reflects competing influences, with an overall reduction in TC frequency partially offset by increases in TC intensity, yielding only modest changes in the occurrence of PTCs. This is consistent with evidence that tropical cyclones are expected to intensify under warming , implying that when PTCs such as Ophelia occur they may be associated with more severe impacts. However, the low frequency of PTC occurrences limit the statistical significance of these projections. Further, tropical cyclones are typically poorly represented in GCMs , warranting cautious interpretation.

Since the storms investigated by and those included in this work are different, we do not attempt to perform a direct comparison between these two pieces of work. However, we can still contrast and compare the conclusions that are drawn from each study. There is a noticeable difference in the number of analogues identified in ERA5 in this work and by . The number of ERA5 analogues in range from about 5 (Xynthia) to about 18 analogues per decade (Eunice); the number of ERA5 analogues in this work range from less than 1 (Ophelia) to about 4 analogues per decade (Great Storm). However, the number of analogues identified in the present period of each large ensemble, namely the CESM-LE and the CANARI-LE, is very similar: The number of CESM-present analogues range from 1 (Xynthia) to about 7 analogues per decade (Eunice); the number of CANARI-LE analogues range from about 1 (Martin) to about 4 analogues per decade (Arwen). This results in a reduction in the assessed bias in the numbers of analogues between and the present study. The bias in the ratio of explosive cyclones, in , or extreme cyclones, in this work, to all analogues is similar in both the CESM-LE and the CANARI-LE at about 50 % mean absolute relative error. This lends confidence to the estimation of changes in extreme cyclones between the present and a future climate in both pieces of work. However, this is an aspect that highlights the value of the methodology being applied to contrasting storms: Alex, Eunice and Xynthia in the CESM-LE displayed a reduction in total analogue number but an increase in the proportion of explosive storms ; Martin in the CANARI-LE exhibits a similar behaviour; however, while both the Great Storm and Ophelia also display an increase in the proportion of extreme analogues, they also exhibit an increase in total analogue number, albeit weak in the case of Ophelia. Furthermore, Arwen represents a counterexample to the general trend in that it exhibits a reduction both in total analogue number and in the proportion of extreme analogues.

To answer the research questions set out in the introduction:

How well does the CANARI LE simulate analogues of the four case study cyclones? The CANARI LE is capable of simulating analogues of the four case study cyclones, including those with atypical paths and post-tropical origins. However, in most cases the model underestimates analogue frequency compared with reanalysis, except for analogues of Arwen. Negative biases are more pronounced in winter, indicating that winter-time biases in the CANARI LE are a limiting factor in the representation of cyclone analogues.

How does the frequency of the cyclone analogues change in future? All candidate cyclones show a clear signal of decreased frequency and increased intensity. This aligns well with previous studies analysing future cyclone trends, typically projecting increases in intensity and associated meteorological hazards. However, there is substantial variation in the magnitudes of these changes between the four cyclone cases examined, highlighting significant regional changes in a warmer climate. This poses a challenge for policymakers to prepare for extreme cyclone events.

How do the intensity and meteorological hazards associated with the cyclone analogues change in future? Changes in the frequency and intensity of cyclone analogues exhibit greater inter-case variability than candidate cyclones, reflecting important changes of cyclone trajectories in a warmer climate. Of particular note is the significant change in the paths of cyclones reaching peak intensity in the North Sea. For example, both the Great Storm and Arwen reach peak intensity in this region, yet their analogue responses differ markedly: Arwen analogues show a robust decrease in both frequency and intensity, whereas Great Storm analogues show significant increases in intensity and a net increase in frequency. This arises because there are fewer candidate cyclones in the region overall, but a larger proportion follow the north-eastward path of the Great Storm and fewer follow the south-eastward path of Arwen. This is an important finding as each cyclone is associated with distinct meteorological hazards, requiring different adaptation measures. Arwen was associated with strong northerly winds, with the unusual direction exacerbating damages , while the Great Storm brought strong south westerly winds and the potential for heavy rain associated with the transport of warm, moist air from lower latitudes. This contrast highlights how aggregate cyclone-track trends alone may be insufficient to inform adaptation and risk-management strategies.

What are the underlying dynamical factors causing these projected changes? The strong correspondence between changes in EGR during the development stage of the analogue cyclones and changes in their frequency and intensity suggests that much of the inter-case variability is baroclinically driven. Composite analysis reveals a consistent dipole in baroclinicity, with reductions at higher latitudes (to the south and east of Greenland) and increases at lower latitudes (over the central North Atlantic). We propose that regional modifications to the lower-tropospheric temperature gradient, arising from Arctic amplification and evolving SST gradients in the central North Atlantic region increase the frequency and intensity of Great Storm analogues while reducing those of Arwen. Together, these results indicate that future UK-impacting cyclones may be accompanied by substantial changes in cyclone propagation direction linked to regional modifications of the lower-tropospheric temperature gradient.

These findings highlight marked regional variability and show that cyclone-specific responses can diverge from the aggregate signal under anthropogenic climate change. However, an aspect that has not been explored in the present analysis is that of the influence on analogue occurrence from large-scale modes of variability, such as El Niño–Southern Oscillation or the North Atlantic Oscillation, to determine whether there are any changes in these relationships attributable to climate change. Beyond this, further work is required, for example analysing a wider range of cyclones, to understand the full range of responses of specific cyclone types in the future climate and to understand the relative roles of different dynamical drivers, such as diabatic effects. Demonstrating how extreme events may recur under climate change, and with greater severity as indicated here, can strengthen the case for investing in protective and adaptive measures to reduce future risks . In this context, these cyclones provide useful reference points for guiding resilience planning and improving preparedness for similar events in the future.