The UK has experienced its "weirdest" weather on record in the past few months, scientists say.
The driest spring for over a century gave way to the wettest recorded April to June in a dramatic turnaround never documented before.
The scientists said there was no evidence that the weather changes were a result of Man-made climate change.
But experts from three bodies warned the UK must plan for periodic swings of drought conditions and flooding.
The warning came from the Environment Agency, Met Office and Centre for Ecology & Hydrology (CEH) at a joint briefing in London.
Terry Marsh, from the CEH, said there was no close modern precedent for the extraordinary switch in river flows. The nearest comparison was 1903 but this year was, he said, truly remarkable.
What was also remarkable - and also fortunate - was that more people did not suffer from flooding. Indeed, one major message of the briefing was that society has been steadily increasing its resilience to floods.
Paul Mustow, head of flood management at the Environment Agency, told BBC News that 4,500 properties had been flooded this year.
"But if you look back to 2007 when over 55,000 properties were flooded, we were relatively lucky - if lucky is the right word - for the impacts we saw this summer," he said.
"The rainfall patterns affected different areas - and also there were periods of respite between the rain which lessened the impact."
He said 53,000 properties would have been flooded this year without flood defences. In total, he said, 190,000 properties had received flood protection in recent years.
Mr Mustow claimed that flood defences repaid their investment by a factor of 8-1 but admitted that continuing to invest would be a "challenge", after government cuts to planned projects.
But he said that new streams of joint funding from local authorities and private developers had allowed 60 schemes to happen that otherwise would not have gone ahead.
He said: "We have to get our heads round the possibility now that we're going to have to move very quickly from drought to flood - with river levels very high and very low over a short period of time.
"We used to say we had a traditional flood season in winter - now often it's in summer. This is an integrated problem - there's no one thing that's going to solve it. The situation is changing all the time."
But scientists present from the Met Office and CEH said not much could be read into the weird weather. Terry Marsh from CEH said: "Rainfall charts show no compelling long-term trend - the annual precipitation table shows lots of variability."
Sarah Jackson from the Met Office confirmed that it did not discern any pattern that suggested Man-made climate change was at play in UK rainfall - although if temperatures rise as projected in future, that would lead to warmer air being able to carry more moisture to fall as rain.
She said that this year's conditions were partly caused by a move to a negative phase of the North Atlantic Oscillation which would be likely to lead to more frequent cold, drier winters - like the 1960s - and also wetter summers for 10-20 years.
"Longer term we will see a trend to drier summers but superimposed on that we will always see natural variability," she said.
Whatever happens with the weather, the Environment Agency expects that more and more people will be protected from floods and droughts thanks to water sharing between farmers, water transfer between water companies, and better management of leaks and demand.
But Mr Mustow admitted that much more needed to be done to ensure that farmers did not increase flood risk with land drainage schemes and that developers and builders ensured that new developments allowed water to drain into the soil rather than flushing into the sewers.
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