Why rain on dry ground isn't always great news

The weather has been changing a lot across the country recently.

After parts of the UK experienced the fifth heatwave of the year just a couple of weeks ago, cooler and wetter conditions have now arrived.

That's brought rain whereas this summer has seen less rainfall than usual.

Heavy rain and thunderstorms have been forecast for parts of England and Wales this week.

For many people, the rain will be welcome after such a dry spell when parts of the country have been in drought.

However, while you might think that rain is good news for very dry ground, that's not always the case, and could make flooding more likely.

But why does this happen? Keep reading to find out...

More than half of England and all of Wales have been declared to be in a drought this summer.

A drought is when there has not been enough rain for a long time, so rivers, reservoirs and underground water supplies get very low.

As a result, more than 25 million people living in those areas have water restrictions, such as hosepipe bans.

So, many are welcoming the rainfall this week, hoping it will help end the drought and rise water levels across the whole of the UK.

But some experts are warning of rain causing flash flooding on very dry soil.

This is because dry land does not absorb water as well.

"When we have a drought, the land gets very hard, and that makes it harder for the water to soak in," Andrew McKenzie, a floods expert from the British Geological Survey, explained to Newsround.

And because the rain can't soak in, it makes it harder for the water to drain away properly.

Downpours from intense summer thunderstorms can fall faster than the water can soak into the ground.

Instead it can collect and pool on the surface, and on sloped surfaces water rapidly runs off, which can cause flash flooding.

BBC Weather's Jennifer Bartram adds that even heavy summer thunderstorms don't mean an end to a drought, as rivers, groundwater levels and reservoirs can still be depleted for months.

The Met Office - the UK's weather service - has issued two separate yellow warnings - one for Wednesday, and the second for Thursday.

The Wednesday warning covers much of the Midlands, East Anglia and parts of northern and southern England - as well as the far east of Wales.

Some areas could see 20-30mm of rain possible in just one hour, while other places could see 40-50mm of rain fall over a few hours.

You can read more about that here.