A "complete rethink" of the UK's flood defences is required following widespread flooding across northern England, the Environment Agency says.
Deputy chief executive David Rooke said better waterproofing of homes and improved warning systems would be vital for tackling future weather extremes.
Parts of Yorkshire, Lancashire and Greater Manchester were flooded after downpours caused river banks to burst.
Prime Minister David Cameron defended government funding for flood defences.
He denied accusations - made by the leader of Leeds City Council - that there was a "north-south divide" in efforts to prevent flooding.
£2.3bn on defences
Judith Blake said flooding in Leeds was a "preventable disaster", saying the North had not received "anywhere near the support that we saw going into Somerset" - which flooded in 2014.
She said the government had cut funding for a flood defence project in Leeds in 2011, and there was now a "real anger growing across the North".
However, Mr Cameron - speaking as he visited flood-hit areas - said the UK had spent "more per head of the population on flood defences in the north than we do in the south".
"We are going to spend £2.3bn on flood defences in this parliament but we will look at what's happened here and see what needs to be done," he added.
The Environment Agency has nine severe flood warnings - meaning danger to life - in place in north-east and north-west England, and more than 100 other flood alerts across England and Wales.
It comes as more heavy rain and wind is forecast for late Tuesday into Wednesday. BBC Weather's Nick Miller says this next bout of bad weather has officially been named Storm Frank.
The Environment Agency's Mr Rooke told the BBC the UK was moving from a period of "known extremes" of weather to one of "unknown extremes".
"I think we will need to have that complete rethink and I think we will need to move from not just providing better defences... but also looking at increasing resilience," he said.
Improvements to flood warning systems and better building design would help, he added, so that "when properties do flood, they have solid floors, waterproof plaster, more electrics up the wall".
Many places in northern England have seen record river levels over the past 24 hours, including the River Aire in Leeds, and the rivers Calder and Ribble, affecting places such as Whalley, Hebden Bridge and Ribchester.
The River Ouse is now thought to have stabilised in York, where hundreds of people had to leave flooded homes following the torrential rain over Christmas, but water levels are still believed to be rising in the town of Selby.
Extra soldiers were deployed on Sunday to aid emergency services, and about 200 unpaid mountain rescue volunteers from Wales, Cornwall and the Lake District have also been helping in the city.
In other developments:
- The Scottish Environment Protection Agency (Sepa) says Storm Frank could bring further flooding to Scotland, while Wales is bracing itself for more rain
- Flooding has affected phone lines in York - including the non-emergency police number 101. People are advised to call 01609 768 182 instead
- York Council says plans for further evacuations will not go ahead, but it has opened a second rest centre for residents
- In Leeds, 1,000 homes have been flooded
- Electricity North West says about 850 properties remain without power in Greater Manchester and Lancashire
- Accountancy firm PwC says the cost of the flooding caused by Storms Eva and Desmond in December could exceed £1.5bn
Downing Street said emergency financial assistance would be available to homes and businesses in Yorkshire and Lancashire.
They will have access to the support package announced earlier in the month for people affected by Storm Desmond in Cumbria.
Shadow communities secretary Jon Trickett called for a major programme of public works and an end to cuts to local authorities in order to deal with the flooding.
Meanwhile, the Met Office has issued yellow (be aware) warnings for rain on Wednesday in areas of northern England, Wales and Northern Ireland, bringing the threat of further flooding.
Amber (be prepared) warnings for rain are also in place for parts of Scotland on Wednesday. There are currently no flood warnings in Scotland.
People can access information from council websites and the Environment Agency Floodline.
The agency is also operating a phone line - 0345 988 1188 - which will be staffed rather than offering recorded information.
Timeline: December flooding
5 December: Storm Desmond brings more than a month's rain to parts of Cumbria, leading to flooding in Carlisle and other areas
12 December: River levels remain high and more than 70 flood warnings are issued amid more heavy rain
22 December: Communities in Cumbria flood again - some for the third time in less than a month
25 December: More than 100 flood alerts and warnings are issued across England and Wales as torrential rain hits
26 December: Residents in West Yorkshire and Lancashire are evacuated from their homes and flooding hits Leeds, Greater Manchester and York
27 December: Police in York advise hundreds of people to evacuate their homes as severe flood warnings remain in place in northern England
Live flood warnings from the Environment Agency and the Scottish Environment Protection Agency.