UK Floods A car is submerged under flood waters in the city centre of Carlisle, north west England, December 7, 2015. REUTERS/Andrew Yates

Record rainfall in northwest England and Scotland has caused flooding on an unprecedented scale, submerging houses, leaving tens of thousands without power, and leading to at least one death.

The hardest-hit county, Cumbria, got 34 centimetres (13.4 inches) of rainfall in one day this past weekend — more rainfall than the area usually receives during the entire month of December.

While the UK government is now facing criticism for delaying funding of flood defence schemes, engineers highlight a worrying structural challenge for future planning.

"The worrying aspect of these floods is that they are causing such severe damage even after major steps had been taken to improve the flood defences in Carlisle and Cockermouth and to improve the resilience of the nation's electricity infrastructure," Jim Hall of the Royal Academy of Engineering told BBC News.

The region got so much rain, engineers don't even know how to build defence systems to handle these types of weather events anymore.

"Storm Desmond means that we will have to re-evaluate standards of flood defence and then think again about what needs to be done to reduce the risk of major damage and disruption to flood-prone communities," Hall said. 

David Balmforth, a former president of the Institution of Civil Engineers, expressed a similar concern when it comes to designing structures to defend against flooding. He told The Guardian: “We tend to design defences to a particular standard, to give an annual probability against flooding, which might be, say, a one-in-100- or one-in-200-year chance of the defence being overtopped. That would be a typical sort of figure that would be used. The question that now remains is: were the events that we’ve now seen in recent days so excessive that it’s reasonable to expect them to overtop defences?”

The British government has invested more than £45 million on flood defence systems since 2009, including £4.4 million on a scheme in Cumbria that involved self-closing barriers, according to the BBC.

More than 3,000 homes have been flooded in the recent storm, mostly in Cumbria, despite these preventative measures.

Floods Minister Rory Stewart says that government-built flood defences helped by slowing down the water from inundating streets.

"What the defences do do is they slow it [the flooding] down. It gives us more time, it's given people here more time to evacuate safely and it's meant that there's less water on the streets than there would have been if we hadn't had that defence in place," Stewart told the Associated Press.

But the barriers aren't failproof. "When you face, as we have now, probably the highest rainfall we have ever had in the United Kingdom, it is going to come over the top of defences," he said.