How soon will the drought be over?

It is the question many people are asking: when will the drought be over, and how much rain will it take for things to return to normal?

Contrary to public perception, a drought does not end with a few days of rain.

Water must flow back into rivers, reservoirs, and the stores beneath our feet in the tiny spaces between soil, sand, and rock. This can take months.

According to scientists, the key question is not "Has it rained?" but "have water resources recovered?"

Dr Katie Facer-Childs from the UK Centre for Ecology & Hydrology says there is not a straightforward answer to when this drought might end, because it has not been caused simply by a lack of rainfall, but also higher than average temperatures.

"This year we've gone through meteorological, soil moisture, and river flow drought," says Facer-Childs.

Meteorological drought is when rainfall is below normal.

Next comes soil moisture drought, which begins to affect agriculture. Soil is like a type of reservoir - those stores are depleted by thirsty trees and plants, and evaporation during hot temperatures.

Then comes river flow drought, where river levels fall, and, finally, if dry conditions persist for long enough, groundwater and reservoir levels decline, leading to the most serious impacts.

"However, we have not yet reached severe groundwater and reservoir drought, so that means there's hope," says Dr Katie Facer-Childs.

The British Geological Survey says no groundwater sites around the UK are currently reporting record lows - with nearly half at normal levels.

The first clear indication usually comes in late autumn and winter, when we typically see more rainfall and experts can assess whether that water is moving through rock layers into underground stores, known as aquifers.

Dr Kevin Collins, senior lecturer in environment and systems at The Open University, says even when autumn rains arrive, people often assume the drought is over.

But sustained rainfall is needed over months rather than a few heavy rainfalls.

Hydrologists should know by February or March whether aquifers and human-made reservoirs have been replenished. But recovery from the environmental impacts can take years.

A dry winter will make the current drought worse and heighten government concerns.

Prof Tim Palmer of Oxford University says it will be "catastrophic" for the UK next year if the rains do not come.

There is some hope. Over Europe, there are signals for a wetter-than-average autumn, potentially influenced by global ocean changes, including the developing El Niño weather phenomenon. However, there remains considerable uncertainty.

• What is El Niño and why could it mean record temperatures?

"The government needs to start planning for a worst-case scenario where the rains don't return in sufficient amounts this winter, and next summer is similar to the last two," Prof Palmer says.

Parts of the UK have experienced a flash drought - a type of drought that develops very rapidly, driven by extreme heat, very low rainfall and exceptionally high water demand.

The problem is that once conditions become extremely dry, subsequent heavy rainfall can trigger flash flooding because the land is unable to absorb the water effectively.

This creates a cycle of rapid swings between drought and flooding, which is what people mean by weather whiplash.

As the climate warms, scientists say rapid swings between wet and dry conditions are increasing and are expected to get worse.

A recent study found the UK is likely to experience faster transitions between droughts and floods, especially in south-east England and parts of the north-west of the country.

Researchers warn this growing "volatility" could make water supplies, agriculture and infrastructure harder to manage as conditions switch rapidly between extremes.

Neil Entwistle, from Rebalance Earth – and a former professor at the University of Salford says: "We're in the new normal. And that new normal is we'll get a lot of heavy rain and short amounts of rain."

He argues that floods and droughts are "two sides of the same coin".

For centuries, the UK has modified landscapes to move water off the land as quickly as possible by draining uplands and peatlands, straightening rivers and disconnecting rivers from floodplains.

As a result, when rain falls it moves rapidly and can cause flooding.

"This is a wake-up call that we do need to see a fundamental shift in how we think about water," he says.