Why hasn't April's rain been enough to tackle the drought?

People shelter from the rain in Greenwich Park this week (Getty Images)

A hosepipe ban for 20 million people in south and east England in the face of widespread drought has been followed by the wettest April on record.

But experts and water companies are still warning that the drought has not gone away - so why hasn't all the rain we have had been enough to tackle the problem?

According to the Environment Agency, the rainfall has eased the situation for farmers, gardeners and wildlife, providing much-needed water for crops as well as raising river and pond levels, which helps aquatic creatures and plants.

It has also allowed water companies and farmers to fill up on water storage more than they would normally be able to do at this time of year.

However, there have been two unusually dry years, in particular the winters, which have left soils dried out and underground aquifers depleted.

Getting enough rain in winter is important because that is when groundwater supplies - which provide much of the water supplies in the South East - can be recharged.

As we move into the summer months, rain can be good for the countryside and crops, but with most of the water taken up by plants or evaporating in warmer temperatures, it does not get down to the groundwater stores to replenish them.

And in summer, rivers are very dependent on water flowing out of the ground to maintain levels.

Pauline Smith, national drought co-ordinator for the Environment Agency, said the rain was beneficial to recharging groundwater supplies, but it was too early to tell just how much of an effect it was having.

She added: "Some of the rain will be going into the ground because we have had a whole month of spells of rain, some of them extremely heavy.

"While some of it is running off, some will be seeping into the soils and going into the ground."

But she said given that the wet April was preceded by two dry winters and that groundwater levels were at record low levels in some areas, it may not be enough to recharge supplies.

"We may need to wait until next winter to go back to normal," she said, adding that swathes of England were still in drought.

While it may seem extraordinary for there to be flooding and flood warnings in the midst of a widespread drought, it is not actually that surprising.

Before the latest downpours, the Environment Agency had been warning of the possibility of flash flooding because heavy rain can run off dry, compacted soils straight into rivers which become swollen, or causing surface water floods.

Some of the areas affected by the devastating summer floods in 2007 had experienced very dry conditions in the run-up to the heavy rain which deluged parts of the Midlands, Yorkshire and the South West in June and July of that year.

PA