Flooding hit parts of England and Wales one in every five days last year, the Environment Agency said as it warned of the need to prepare for future extreme weather.
But one in four days were spent in drought, with hosepipe bans imposed for 20 million people across a swathe of England early in the year after two dry winters in a row.
Rivers such as the Tyne, Ouse and Tone went from record low levels to experiencing their highest flows since records began, in the space of four months, the Environment Agency said.
There was flooding on 78 days of the year, and for 95 days there was official drought declared for some areas, figures from the government agency show.
Met Office analysis suggests that the UK could experience a 1976-style drought every 10 years, and the Environment Agency said that with the population of London and the South East set to grow by 23% by 2035, action should be taken now.
Modelling suggests some river flows could be cut by up to 80% during the summer in the next 40 years as the climate changes, putting more pressure on businesses that rely on taking water from rivers for irrigation.
The Environment Agency called for an increase in small-scale water storage reservoirs, which can take advantage of wet times and help farmers, commercial turf growers, golf clubs, sports stadiums and race courses cope with dry periods.
There are currently around 1,700 such water storage reservoirs in England and Wales, supplying around 30% of irrigation needs, but they will need to increase as the UK faces more extreme weather as the climate changes, the agency said.
Environment Agency chairman Lord Smith said: "The extremes of weather that we saw last year highlight the urgent need to plan for a changing climate.
"In 2012 we saw environmental damage caused by rivers with significantly reduced flows, hosepipe bans affecting millions and farmers and businesses left unable to take water from rivers. But we also saw the wettest year on record in England, with around 8,000 homes flooded."