Thunderstorms: Why drought can lead to dangerous flooding

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It might seem that a good rain is what we need after weeks of hot and dry weather.

The Met Office has predicted heavy rain and storms this week.

They are not likely to replenish dry soils and could cause flash flooding.

There is a reason why rain may not be what we need.

Many parts of the UK have seen less than average rain this summer.

The UK Centre for Hydrology and Ecology says that this has left the soils dry and hard.

The soil can't absorb the rain if it falls at high speeds. The water is on the surface. The water runs off quickly on the sloped surfaces.

The effect is similar to pouring water at high speed onto concrete.

The grounds of our gardens, parks and farmlands are now potentially as dry as tarmac and concrete gets. He says that areas that aren't tarmac will behave like tarmac when it rains.

Prof John Quinton is a soil scientist at the University of Lancaster and he talks about the effects of dry weather.

When water hits a waterproof jacket, it forms droplets on top and then runs away.

There is a layer of material that keeps out water when organic matter in the soil dries out.

The water stays on the surface instead of entering the soil.

It is difficult to not notice how the dry spell has killed off vegetation in parks and fields.

They form a cover over the soil to protect it from the rain.

Vegetation breaks up large storms of rain into small droplets. The soil structure is damaged by the big drops, meaning less water can enter.

If it rains hard enough, the UK is vulnerable to flash flooding.

Water can move very quickly in hilly terrain and that's where it's at high risk.

The potential is always there despite the fact that it is unlikely to be as bad as last summer.

Large amounts of rain can be delivered byThunderstorms, but usually in a small area. The soil needs more time to recover.

Light rain over a number of hours will bring soils back to normal levels.

It's likely that weeks of above-average rain is needed to end the dry spell.

The record-breaking temperatures seen in July would not have been possible without human-caused climate change, according to scientists.