Climate change is happening – you only have to switch on the news and see reports of heatwaves across Europe and North America to recognise that more extreme weather patterns are emerging globally. Although in Britain we’ve had a wet July and early August, in the last few years we’ve seen a more obvious sign of climate change on these shores: hot summers with a significant number of days in July and August at temperatures reaching and exceeding the low 30s°C and occasionally even touching the high 30s°C.

It can often be frustrating for customers that in hot weather their rail services may be delayed or cancelled – but why is this? Why is Britain’s railway so impacted by hot weather, particularly when it is possible to design and operate railways in very hot conditions, such as in Africa, Australia, and parts of Asia?

Legacy infrastructure

What is locally challenging for us is that our largely Victorian legacy railway infrastructure was never designed or expected to operate under repeated, and extended periods of such high temperatures. Also, some of the climate conditions the railway was intended to operate under during summer, autumn, and winter, like high rainfall and high winds, are occurring more regularly, and to greater extremes, than was expected even 30 years ago.

Heat is not the only consideration for our infrastructure during the summer. ‘Convective rainfall’ where very localised, high intensity rainfall takes place, often with several centimetres or inches of rain falling over a very short time period, is also challenging to mitigate. The nature of this type of rainfall means it can pose a risk of railway embankment or cutting damage, or washout of the ballast underpinning rails and sleepers.

A further legacy of our often 150-year-old railway infrastructure is that detailed design records may have been lost, or never have existed. Design records that are still available may only capture design intent, not construction reality. Also, incomplete documentation of maintenance and repairs, taking place multiple times over the intervening decades, may have changed the in-place built reality significantly from any original design.

Reducing the risk associated with extreme weather

Challenges for operating the railways during high temperatures include buckled rails and drooping overhead power lines, both of which can occur as a result of metal expansion as temperatures rise – as can overheating of the electronics controlling lineside signalling, electrification, communications systems, and full, or partial, failures of on-train air conditioning and engine or electronics cooling systems.

Short term railway measures to reduce the safety risk associated with high temperatures and rainfall-related effects include temporary and localised speed reductions, temporary line closures, and amended timetables. Once it is confirmed that no damage has been caused, subsequent temperature reductions and flood water drainage often mean speed reductions, closed lines and amended timetables can revert to normal within a matter of some hours, or a day or two. However, if, for instance, track, overhead power lines, embankment, or cutting damage has been caused, it may take several days to many weeks before normal services can be restored, depending on the type and severity of damage.

Long term measures to reduce both the safety and performance risk associated with high temperatures include being able to predict in advance where infrastructure or trains may fail or degrade. Doing this can allow engineers to design, and put in place, train or infrastructure repairs, or modifications, in advance of extreme weather conditions. They also include designing, and placing into service, new or enhanced infrastructure or trains that can cope better with high temperatures, high winds and heavier rainfall.

Making climate mitigation a priority

Given that the typical life of a train is over 30 years, and that new railway infrastructure can last from 40 to over 100 years, it will take some decades before our trains and railway infrastructure are resilient to climate change.

However, climate adaptation is increasingly recognised as a priority by the rail industry and its funders, which is leading to positive change. For example, we now have a much better understanding of climate-related risks on each part of the rail network, there is greater investment from Network Rail in track drainage systems, we have more accurate weather forecasts, and new trains are able to cope with wide temperature variations. There remains a lot more to be done, but we are making good progress.