Hundreds of people could perish in floods in parts of England, the Environment Agency has warned, as it urged the country to "adapt or die".
In a strongly worded report on the need to brace for climate change, the agency warned that floods which caused devastation in Germany this summer would soon happen here.
Chairwoman Emma Howard Boyd said the agency could not protect everyone from "inevitable" climate change.
"Some 200 people died in this summer’s flooding in Germany. That will happen in this country sooner or later, however high we build our flood defences, unless we also make the places where we live, work and travel resilient to the effects of the more violent weather the climate emergency is bringing. It is adapt or die," she said.
The agency added that floods and rising sea levels would "reshape" the natural world as changing weather means it "will not be technically, socially, and economically viable to protect every community".
"Instead, alongside constructing and maintaining defences, we must help communities learn to live with risk, minimise damage, and return to normal life quickly," it said.
The report warned that there is too much focus on trying to stop climate change and not enough on preparing for its effects, including flooding, coastal erosion and depleted drinking water supplies.
Population growth and climate change will also put more pressure on the water system, the agency said.
If no additional measures are introduced between 2025 and 2050, more than 3.4 billion extra litres of water per day will be needed to ensure public water supplies, its figures show.
Necessary improvements include restoring peat bogs and wetlands to improve water quality and availability, which is under pressure from growing demand, pollution and physical changes to rivers and the coast.
Sewer systems which allow raw sewage to be dumped in rivers and the sea will also have to be used more frequently, the agency said, causing more pollution.
The Environment Agency has pledged to spend £5.2bn on flood defences over the next six years, but has said it can’t protect all homes in its strongly-worded report.
The "burden of emergency response will increasingly divert our staff and resources from other activities", the report adds.
The agency has come under growing scrutiny amid concern about river pollution, as campaigners say concern about flooding is diverting attention from targeting polluters.
Not one of Britain’s rivers meets water quality standards, and last year Ms Howard Boyd wrote to George Eustice, the Environment Secretary, to say that the agency "no longer has the investment we need to protect and enhance the environment in all the ways asked of us", amid cuts to its enforcement budget.
Earlier this year international UN group the IPCC released a report warning that severe weather events such as flooding and heavy rain had already become more likely over recent decades because of a warming climate.