Recent trends and future projections of UK storm activity

Published May 2021.

Climate change is set to have a wide variety of impacts around the world, including altering the weather patterns we experience here in the UK. This article looks at what research currently tells us about storm activity in the UK, including recent observed trends and the changes we expect to see in the long-term future as a result of climate change. We will focus on low-pressure cyclones, most prevalent in the UK during autumn and winter, touching only briefly on the convective storms which tend to occur during summer.

Recent trends

When considering recent trends in storm activity in the UK it is useful to consider two major components of storms separately: wind and rainfall. Recent data and trends in these phenomena are detailed in the 2018 State of the UK Climate Report (Kendon et al., 2019). This report found that there is no compelling trend in maximum gust speeds recorded in the UK since 1969, measured as the number of days more than 20 weather stations recorded gust speeds above 40, 50 or 60 knots. Changes in observation methods and instruments mean the data can only be reliably assessed back to 1969, while changes to the wind measurement network and the way gusts are measured mean the data should still be interpreted with caution, but there is nothing to suggest maximum wind speeds have persistently changed in recent decades.

In contrast, the report does reveal a discernible trend in rainfall across the UK. Annual trends are small relative to variability between years, with the decade 2009-18 being on average 5% wetter than the 1961-90 average and 1% wetter than 1981-2010. Much larger increases are seen when summers and winters are assessed separately. UK summers during 2009-18 were on average 13% wetter than the 1961-90 average and 11% wetter than 1981-2010, while the figures for winters are 12% wetter and 5% wetter, respectively. These trends are sensitive to the start and end dates used owing to a great deal of inter-annual variability, while some historic data is subject to a degree of uncertainty, so the report advises caution when interpreting these trends. It is also unclear how or if these trends can be linked directly to climate change.

In summary, while there is no compelling evidence of trends in maximum wind gusts in the UK, the associated storm systems are likely to have brought more rain, being partly responsible for the observed increasing trend in rainfall. The following section will discuss how storms may change in the future.

Future projections

Predicting the effect of climate change on storm activity in the future is crucial to putting effective adaptation and mitigation plans in place to limit the impact of storm events. We are already able to predict periods of storminess at the seasonal scale up to 3 months in advance, as was done for the increased risk of storms and heavy rainfall during the winter of 2015/16 (Scaife et al, 2017) when Storm Desmond struck the UK in December. Climate change is also increasing the risks from these events (Otto et al., 2018).

Longer term predictions of storm activity, for instance on the decadal scale, are also possible but usually focus on broad trends. Various such projections of future storm activity, as well as wind speeds and rainfall, are made in the UK Climate Projections report (UKCP18, Lowe et al., 2018). Winter wind speeds are projected to increase in the second half of the 21st century, accompanied by an increase in the frequency of winter storms. The overall increases in wind speeds are small compared to the differences between individual years, however (Fung et al., 2018). Projected changes in future rainfall vary depending on which season you are looking at, with summers likely to become significantly drier while winters become wetter, along with an increase in the frequency and intensity of extreme temperature and rainfall events (Met Office, 2018; 2019a).

Variations in the North Atlantic Oscillation (NAO) are a key driver of changes in UK storm activity, but this varies strongly from year to year and decade to decade. For this reason, some past studies on future storm activity have returned mixed or inconclusive results (e.g. Catto et al., 2019). A more coherent picture has been suggested by other studies, including Zappa et al. (2013), using CMIP5 models to project an increase in the frequency and intensity of winter storms in the UK. These findings are supported by Met Office analyses (Senior et al., 2016; Met Office, 2019b). More winter storms, including disproportionately more severe storms, are projected to cross the UK in the future, with fewer to the north, over Iceland, and fewer to the south, over central and southern Europe. This pattern also appeared in previous generations of climate models, adding confidence to the projection. It is known to be linked to Atlantic sea surface temperatures (McDonald, 2011). This research indicates that the UK should expect to see storms more frequently than today, therefore additional adaptation and mitigation measures may be necessary to mitigate their impacts. Additional research using more advanced models, including those used in the CMIP6 project, should help us refine this projection and make more confident predictions about future storm activity.

These simulations also indicate that summer cyclones will become less frequent due to the jet stream being positioned further north during summer than today, owing to the increased temperature gradient between the tropics and the poles caused by a warming climate.

On potential future changes in the clustering of storms in the UK, Economou et al. (2015) found that typically these changes were small and inconsistent between CMIP5 models, but there was some evidence for a potential increase in clustering of extreme storms over northern Europe and Scandinavia.

While this article has predominantly focused on large-scale winter cyclones, smaller scale convective summer storm activity is also projected to increase over the UK in the future (Met Office, 2019a). In addition, tropical cyclone activity is set to change as well. These storms will become more intense as ocean temperatures increase, potentially enabling them to retain more strength as they move into subtropical and temperate areas, such as the UK, and have a greater effect here than they do currently.

Research gives us an indication of how storm activity may change in the UK in future, but these findings still demand further study. Additional research into long-term projections of winter storm activity and clustering will help provide deeper understanding and more confidence in these projections in the future. Efforts are also underway to further develop the ability to confidently attribute extreme weather events to climate change, allowing us to better understand how these effects may develop in the future. Continued development of forecast accuracy will increase confidence in our Met Office forecasts from seasonal forecasts, to decadal predictions and multi-decadal projections, giving the UK more time to prepare for the impacts of future storm events.



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