Under the chalk cliffs east of Folkestone sits the Warren, a coastal wilderness largely owned by the railway, hosting a nature trail for walkers, as well as the Victorian rail line that runs on to Dover.

It is also, problematically for Network Rail, an active landslide. “Our monitoring here,” says Derek Butcher, principal geotechnical engineer for the southern region, “shows we’re actually moving ever closer to France – despite Brexit.”

The geological combination of permeable chalk above gault clay means this has long been a known risk area: a massive landslide in 1915 moved the tracks about 50 metres towards the sea, and the line stayed closed for nearly four years because manpower had been diverted to the first world war trenches. Although numerous sea defences and drains have been built since, the line has taken a battering again as a run of the wettest winters on record piled up in the past 10 years.

The Warren is just one of many risk sites. Unprecedented rainfall in the last 18 months – hot on the heels of record-breaking summer heat – has in every sense shifted the ground for the railway. Resilience to extreme weather of all kinds is a preoccupation in planning.

The kind of money that not long ago would have electrified a railway line is now going, in large part, down the drains. Network Rail has dedicated £2.8bn in the next five years simply to bolster Britain’s tracks against the changing climate – and its leaders have warned that it may never be enough to save all the routes that exist today.

Recorded landslips on the British railway alone have almost doubled in frequency, from 475 to 848 in the five years either side of 2019. At the Warren, recent movement of the earth is clearly visible on a large fault line that runs from the rail tracks to the sea.

“It’s opened up quite significantly over the last two months or so,” Butcher points out: in the footpath through the shrub, 20cm to 30cm of fresh bare earth is visible against the green of weeds; at sea level, a concrete apron built half a century ago to protect the beachfront from erosion is ruptured again. “And trains don’t need a lot of track movement to derail.”

While the trackside has been re­inforced and fresh ballast laid, the undulation is clear on the line emerging between the tunnels here. For safety, a 20mph speed limit has been imposed and high-speed trains that reach 140mph a few miles north on their way to London now crawl along, the ends of the carriages visibly lifting and falling as they pass over the dip.

A 75-metre-deep inclinometer has been sunk into the earth and Network Rail engineers are out walking the tracks, checking for any further movement of the rails. More and more risk sites are now monitored remotely with sensors in the earth, but even large-scale mitigation work can only do so much.

Network Rail’s chief executive, Andrew Haines, says technology can help manage the effects, but adds bluntly: “We cannot infrastructure-build our way out of climate change. The price tag is too expensive and it’s too disruptive.”

Although the buckling rails seen in a sweltering July 2022 might become a more frequent concern as temperatures rise, the primary issue now is abnormally high rainfall. “It’s not a risk for a future – we are living climate change,” Haines says.

He commissioned a full review of the railway’s earthworks in the wake of the 2020 Stonehaven rail crash, where heavy rain and a faulty drain contributed to a fatal derailment. It suggested, as Haines puts it, that “you’ve got to start looking at what the Asian railways are doing, because they are used to dealing with much more torrential rain.

“We have to progressively invest in better drainage, drainage engineers. We probably can’t do that in a generation.”

Intense monitoring of the earth is supplemented at the Warren with a weather post that automatically relays readings to local control centres, to check how its microclimate matches the forecast. Staff across the railway are being trained in how to read such data more expertly, and understand the likely effects, in a “weather academy” staged at Network Rail’s Milton Keynes offices.

The academy hopes to bring more knowledge and confidence in decisions to keep the railway operating when possible, says Lisa Angus, Network Rail’s weather response director. “There’s a view that over the last few years, and particularly since the Stonehaven accident in 2020, that we have all become a little bit more risk averse,” she says.

“We don’t want people looking out of the window and thinking it’s raining today, that’s my bloody rail service scuppered … Our job is to minimise the disruption to give the best service we possibly can.”

Parallel work includes tests to see whether trains can run through more floodwater than had previously been deemed safe. But while the railway devises more ways to keep going through extreme weather, it may not be the longer-term answer.

Lisa Constable, who leads on climate change adaptation strategy at Network Rail, says future planning includes looking at regions where extreme weather and higher net rainfall is likely to cause more flooding or erosion – and how to respond when that occurs. “In some cases, that means abandoning the railway,” she says.

Long stretches of the UK’s railway hug the coastline – as vividly illustrated by the collapse of the seawall at Dawlish in Devon in 2014, which took 80 metres of track away from the mainline that connected Cornwall to the rest of the rail network.

That line was immediately restored in emergency works that took just six weeks. Whether the instinct to repair should always be followed everywhere in future is a moot point, Constable suggests, citing routes like the Cambrian and Cumbrian coast lines, or Holes Bay near Poole. “It may be that it’s just not feasible from a technical or a financial perspective to maintain the railway in that area.

“Do we decide we have to build out into the sea on reclaimed land? Or are we going to abandon the track, bring it inland, build a new one, put people on buses instead of the trains? What is best for communities and the economy, as well as the railway?”

Thinking beyond rail alone will be vital, says Juliet Mian, of the engineering firm Arup, co-author of a “resilience framework” for how railways around the world can address the climate crisis. “There’s not a silver bullet,” she says. “Because we’ve got a big Victorian railway, we absolutely don’t have the money to replace it. We need to find cross-sectoral solutions. Otherwise you have every organisation looking at the price tag alone and feeling daunted.”

Resilience, she says, also means thinking about the climate impact of the work itself. Higher concrete walls might resist flooding, but have a carbon cost; and electrification is “a necessary thing”, even though overhead wiring is susceptible to damage in storms, Mian says. “If we don’t get to net zero, those extremes will be much bigger and more difficult to navigate.”

The speed restrictions at Folkestone, reducing the number of trains that can run, are only temporary; Network Rail expects to spend millions to eventually repair the line, the fractured sea defences and footpaths it maintains. But with the cracks so visible, Butcher says: “Who knows what the future of the Warren is, with the extent of climate change?”