More investment in flood defences and improved planning for future disasters are urgently needed, scientists have warned.

They predict that the number of extreme wet days – which have already increased this century – will continue to rise in the coming decades and will bring even greater devastation than that experienced this month after Storm Ciara and Storm Dennis swept across the country.

Ciara brought rain and wind gusts of up to 97mph, triggering more than 190 flood alerts. More than 500 properties were flooded and about 25,000 homes left without power. A week later Storm Dennis followed, which in some areas caused more than a month’s rain to fall within 24 hours.

Thousands of people had to be moved from their flooded homes, rivers – including the Wye in Hereford – rose to record levels, while the Environment Agency issued a record number of flood warnings and alerts, including more than 600 last weekend. Four people were killed during Storm Dennis.

“We are simply not prepared for the flooding coming our way in future,” said Prof Hannah Cloke, of Reading University. “We need to carry out a complete overhaul of our defences and be prepared to spend a lot more on them over a longer period of time.”

So far the government has committed to spending £4bn over the next five years on improving flood defences. But both the amount and timescale were criticised for being insufficient last week.

“Extremely wet days during UK winters are currently up by around 15% compared with previous decades,” said Dann Mitchell of Bristol University’s Cabot Institute for the Environment. “Wetter future winters is a consistent projection with some predicting a 30% to 35% increase in rain by 2070. Our government and town planners need to invest significantly in UK flood defences.”

Last week George Eustice, the environment secretary, said he wanted to see more nature-based solutions, such as the construction of dams made of natural materials and the planting of trees in upper catchment areas. These would hold on to water and prevent it from pouring too quickly into rivers and estuaries.

But this approach was dismissed as inadequate by Roger Falconer, professor of water management at Cardiff University. “It is like putting a small sticking plaster on a major open wound to control profuse bleeding. It would certainly be insufficient when dealing with the 30% increase in winter rainfall which the Met Office has predicted for some areas.”

Instead, Falconer called for the construction of a large number of flow-through or perforated dams above towns at high risk of flooding. “Such a dam fills during flooding in the upper parts of the river basin and is then emptied, under controlled conditions, after the flood,” Falconer said. “We need many more of these.”

Engineers and hydrologists also pointed out to modifications made to river channels, flood plains, land cover and drainage, and these often have serious impacts on water flow and bedevil attempts to predict how rivers will react to downpours.

For example, one recent study of the River Afan in Wales found 259 barriers had been erected along its course over the past 200 years, although only 33 had been officially recorded. Work on pinpointing barriers like these urgently needs to be carried out, scientists have said.

“Blame [for flooding] under these circumstances is misguided and unhelpful, and politicians should be very careful to ensure they understand the facts of flooding before seeking to champion any particular action,” said Prof David Sear, of Southampton University.

Bringing a halt to the construction of houses on flood plains has also emerged as a key issue. One in 10 new homes built in England since 2013 has been built on ground at high risk of flooding, official figures show. Prof Robert Wilby, of the University of Loughborough, told the Guardian that the government should review its housebuilding targets in view of the increased risks from floods.

This was backed by Mohammad Heidarzadeh, head of coastal engineering at Brunel University. “The UK’s flood defence systems were developed decades ago and are not fit to address the current climate situation,” he said. “While the interval for major floods was 15 to 20 years in the past century, it has shortened to two to five years in the past decade.

“The country needs further investment in its flood systems, but such investment should be within a holistic and integrated framework.”