A cataclysmic flood is coming for California. Climate change makes it more likely.

Millions of people, the world's fifth-largest economy and an area that produces 25% of the nation's food are at risk when the big flood comes. The capital of California will be submerged. The Central Valley will be a sea.

Researchers from the U.S. Geological Survey's Multi Hazards Demonstration Project came up with a scenario called the "ArkStorm scenario". New research shows that it will happen.

The study, published in Science Advances, is part of a larger scientific effort to prepare policymakers and California for the state's " other Big One", a flood event that experts say could cause more than a million people to flee their homes. Climate change is increasing the odds.

"Climate change has probably doubled the risk of an extremely severe storm sequence in California, like the one in the study," said Daniel Swain, a climate scientist at the University of California Los Angeles and a co-author of the study. Each degree of warming will increase that risk further.

There have been major floods in California every two hundred years. The last one took place in the 19th century. Thousands of people were killed and entire towns were destroyed.

It's sort of like a big earthquake. It is going to happen.

The Great Flood of 1862 was caused by a large amount of water in the sky. As the climate warms, scientists say atmospheric rivers will become stronger. The air is warmer.

The authors looked at two scenarios, one at the end of the century and one at the beginning of the century.

Climate change, which has already happened since 1862, makes it more likely that a flood will happen today. The storm systems will become more frequent and intense in the future. They found that end-of-the-century storms could cause up to 400 percent more rain in the Sierra Nevada Mountains.

The research will focus on what that increased intensity means on the ground and how long it will last.

There was a report published in 2011. The scale of the flooding and the economic impact would affect every part of the state and cause three times as much damage as a 7.8 earthquake. Road closings and infrastructure damage make relief efforts difficult. The economic impact would be felt around the world.

California can't afford to lag on floods because it has been behind the curve in dealing with climate-driven wildfires.

We still have time to prepare for floods.