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Severe flooding has swept across California following torrential rainfall.
Flood warnings have been put in place for much of the coastal region of the state, beginning from San Luis Obispo down to Santa Maria and Santa Barbara. Flash flood warnings are also in place for Burbank and Los Angeles.
Montecito, on the coast, has also been evacuated due to severe flooding.
The severity of the flooding is due to the ongoing drought gripping the state. The phenomenon may seem surprising—but it is actually very common.
California has been in the grips of a drought for the past two decades. This summer saw incredibly dry conditions, not just in California, but throughout much of the Western U.S.
In July the U.S. Drought Monitor reported that one-third of all land in California, Texas, Oregon, Nevada, Utah and New Mexico was classified as experiencing extreme or exceptional drought.
Hannah Cloke, a professor of hydrology at the University of Reading told Newsweek: "Floods appear after a period when we've all been talking about conserving water and making sure we're looking after our groundwater resources and our reservoirs because we're in a drought situation. But it really does happen all the time, because they're just extremes of the water cycle."
Floods happen during drought as the ground is so parched that the water fails to saturate. This then results in a flash flood.
"Serious drought is often followed by some very serious floods. And it can be a very surprising phenomena. Sometimes you can actually be in drought and have floods at the same time. Because of course, droughts are much slower phenomena," Cloke said.
Back to the River
"They rely on this water that trickles down through the soil into the rock to be stored. So it's a really slow pathway back to the river. And so you can actually not have enough water in your water stores under the ground in the rocks and in the reservoirs and then have your rivers flooding at the same time. It's a very, very strange phenomena indeed."
If there is very heavy rainfall in a place experiencing severe drought, the water will often just run straight off the land into rivers. This means the rainfall will not do much to hydrate the dry soil.
"If you're in an urban area in the city, it's going straight into that drainage system, which flushes straight to the river," Cloke said.
"And in very big river catchments in big river basins, and that can cause very serious floods quite quickly downstream. But at the same time, the water hasn't been able to trickle down through the soil."
Although this often happens after very dry spells, it does not always. Some studies show more gradual recoveries to drought where flooding was not an issue, Simon Parry, a hydrologist at the UK Centre for Ecology & Hydrology told Newsweek.
"The misconception that all droughts end in flooding might arise from the more memorable and newsworthy nature of abrupt changes from dry to wet conditions, as well as a cluster of notable recent examples," Parry said.
Floods Don't Solve Droughts
While the wet weather has been welcome to much of the state, as rainfall has risen water levels at drought stricken reservoirs. Parts of the state have also exited their "extreme drought" status, the U.S. Drought Monitor reported.
But the state has a long way to go before its drought troubles are over.
Even though the heavy storms have brought so much torrential rain at once, it does not make up for the past three years, which have been particularly dry.
"In relation to current events in California, it is unlikely the substantial flooding being reported can really be considered as flooding that marks the end of drought. California's drought conditions have persisted over the last decade or longer," Parry said.
"As such, a series of storms, however severe, or even one wet year, however extreme, is very unlikely to be sufficient to end drought conditions that have been so severe for so long.
"Instead, this is likely to be a mid-drought wet spell—a common occurrence during multi-year droughts—that might provide some limited drought relief, along with very significant disruption and destruction from flooding and its impacts. However, once the wet season has ended drought conditions are very likely to remain," he added.
Do you have a tip on a science story that Newsweek should be covering? Do you have a question about drought? Let us know via science@newsweek.com.
Update 1/12/23 ET 4:03 a.m: This article was updated to include additional quotes
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About the writer
Robyn White is a Newsweek Nature Reporter based in London, UK. Her focus is reporting on wildlife, science and the ... Read more
