Britain must become more resilient to both drought and flooding, Environment Agency chairman Chris Smith has said.
New figures from the agency show that one in every five days saw flooding in 2012, but one in four days saw drought.
Rivers such as the Tyne, Ouse and Tone fell to their lowest and rose to their highest flows since records began, within a four-month period of the year.
Lord Smith said urgent action was vital to help "prepare and adapt" many aspects of Britain for such extremes.
Meteorologists fear that extremes of weather may increase as global temperatures slowly rise.
Met Office analysis has suggested that the UK could experience a severe short-term drought, similar to the drought experienced in 1976, once a decade.
With the population of the water-stressed south-east of England projected to grow by almost a quarter by 2035, Lord Smith argued that the number of smaller reservoirs needed to be increased immediately and that new ways of transferring water from areas where it is plentiful to areas where it is scarce must be established.
Lord Smith, whose agency covers England and Wales, insisted the reservoirs would be needed not just by farmers, but also by commercial turf growers, golf clubs, sport stadiums and race courses.
There are currently about 1,700 small-scale storage reservoirs across England and Wales, supplying 30% of total irrigation needs.
He also said more homes would need to be protected from flooding.
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. Interestingly 2007, which saw some of the most severe flooding in recent memory, also started the year with hosepipe bans.
"More of this extreme weather will exacerbate many of the problems that we already deal with including flooding and water scarcity, so taking action today to prepare and adapt homes, businesses, agricultural practices and infrastructure is vital."
He pointed out that modelling suggests that a changing climate could reduce some river flows by up to 80% during the summer in the next 40 years.
Part of the UK’s flooding problem is due to previous policies.
For decades, farmers were paid to drain boggy land in order to improve it for grazing. This caused water to rush off the fields into rivers, whereas previously it would have been held in the bogs to smooth out the flow into rivers throughout the year.
In addition, many flood plains have been built on.
Follow Roger Harrabin on Twitter @rharrabin