Why Floods Can Happen After a Drought

Why Floods Can Happen After a Drought

Why Floods Can Happen After a Drought

Severe flooding swept across California following torrential rains.

Flood warnings have been put in place for much of the state’s coastal region, from San Luis Obispo to Santa Maria and Santa Barbara. Flash flood warnings are also in place for Burbank and Los Angeles.

Montecito, on the coast, was also evacuated due to severe flooding.

The severity of the flooding is due to the ongoing drought plaguing the state. The phenomenon may seem surprising, but it is actually very common.

Floods and drought
A picture shows flash flooding and parched soil due to drought. California is experiencing flash flooding after a decades-long drought.
djperry/mesut zengin/Getty

California has been in the grip of a drought for two decades. This summer has seen incredibly dry conditions, not just in California, but across much of the western United States.

In July, the US Drought Monitor reported that a third of all land in California, Texas, Oregon, Nevada, Utah and New Mexico was classified as experiencing extreme or exceptional drought. .

Hannah Cloke, professor of hydrology at the University of Reading, said Newsweek“The floods come after a period where we’ve all talked about conserving water and making sure we take care of our groundwater resources and our reservoirs because we’re in a drought situation. But it really happens every time, because these are just extremes of the water cycle.”

Floods occur during drought because the soil is so parched that water fails to saturate. This then results in a flash flood.

“A severe drought is often followed by very severe floods. And that can be a very surprising phenomenon. Sometimes you can actually be in drought and have floods at the same time. slower,” Cloke said.

Back to the river

“They rely on this water trickling through the ground into the rock to be stored. So it’s a very slow path to the river. And so you can’t get enough water in your water supplies under the ground in the rocks and in the reservoirs and your rivers are overflowing at the same time. It’s really a very, very strange phenomenon.”

If there are very heavy rains in a place that is experiencing severe drought, water will often flow directly from the ground into rivers. This means that rainfall will do little to hydrate dry soil.

“If you’re in an urban area of ​​the city, it goes straight into this drainage system, which empties directly into the river,” Cloke said.

“And in very large river basins in large river basins, and it can cause very severe flooding quite quickly downstream. But at the same time, the water couldn’t flow through the ground.”

Floods do not solve droughts

While wet weather has been welcome across much of the state, the rainfall has pushed water levels up in drought-stricken reservoirs. Parts of the state have also emerged from their “extreme drought” status, the US Drought Monitor reported.

But the state still has a long way to go before its drought problems end.

Even though the heavy storms have brought so many torrential rains at once, it doesn’t make up for the past three years, which have been particularly dry.

“The assumption that a rain load will solve a drought problem is absolutely not true, especially if it lasts more than a year, if it is a multi-year drought. It will take many years to fill those stores again, and because they’re sort of very long-term storage,” Cloke said.

Do you have any advice on a science story Newsweek should cover? Do you have a question about drought? Let us know via science@newsweek.com.

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