The 1000-Year Storm That Blasted California

California faced some extreme weather at the beginning of 2024. The heavy rainfalls and the massive number of mudslides lead to news teams throwing around a term. The storm was called the 1000-year storm. But what exactly does that mean, and does the storm actually occur every 1,000 years?

There’s a lot of misunderstanding surrounding the 1000-year storm, a lot of which has to do with its name. However, despite the confusion, the storm is just as deadly as it sounds. While the 2024 storm was dangerous destroying many buildings and taking several lives, compared to the last 1000-year storm, the casualties, and flooding weren’t nearly as bad as they could have been. The last 1000-year storm in California managed to flood an entire city for over six months.

To learn more about the 1000-year storm, when it happened, and some examples of when the storm last occurred, continue reading below.

Not Actually Every 1,000 Years

Despite the name, the storm doesn’t occur every 1,000 years. What the name instead means is that the storm has about a 1 in 1,000, or 0.1 percent chance, of a storm occurring in California in any given year.

Additionally, the name didn’t come because the storms have a habit of happening every 1,000 years. According to studies of sediment and historical records, a storm of this proportion happens about every two centuries, with records of such a storm dating back over two millennia.

What Makes a Storm a 1000-Year Storm?

Generally, a 1000-year storm is determined by the amount of rainfall in 24 hours. Currently, the National Oceanic and Atmospheric Administration (NOAA) defines a 1000-year storm as having at least 11.5 inches in 24 hours.

The storms are caused by atmospheric rivers, usually during a strong El Nño, or La Niña event. Atmospheric rivers are long stretches throughout the atmosphere that help to transport water vapor, similar to how normal rivers operate. When these rivers converge, it can lead to disastrous storms.

California isn’t the only state to get these storms. In fact, they can happen anywhere, and basically at any time. For example, in 2016, West Virginia also faced a 1000-year storm.

2024 Marked One Such Storm

Though about one storm every 200 years in California is the average, it’s not an exact number. 2024 marked the next 1000-year storm, about 40 years early.

During this storm, there were 12.64 inches of rain in less than 24 hours. Additionally, 307 landslides in Los Angeles alone were reported.

Severe Rain, But Over a Shorter Period

While Los Angeles did get quite a bit of rainfall in a short period of time, with places like Oxnard getting 3 inches of rain in one hour, the rain didn’t last as long as it could have.

The last 1000-year storm to date lasted over a month. However, this rainfall only went on for about a day before ceasing. It was still a major event, with floods and mudslides causing death, injuries, and loss of belongings, but not as bad as many feared. Chief National Weather Service meteorologist in Los Angeles, Ariel Cohen, said the storm was likely in the top three worst storms in recent history.

The Last Storm Happened in 1861-1862

Before the storm in early 2024, the last storm dubbed a “1000-year storm” was in 1861 and went on through a little of 1862.

The rain started on Christmas Eve in 1861 and proceeded to go on for 43 days. During this storm, the rivers flooded, turning Central Valley into a sea that stretched over 300 miles long and 20 miles wide.

Sacramento Was Underwater

As Central Valley flooded, Sacramento was flooded, with water reaching 10 feet high in many places. Thousands of people died during the rainstorm and hundreds of thousands of cows. It took six months for Sacramento to dry out again.

In addition to heavy rains and floods, mudslides were common. The areas surrounding Central Valley are steep, and it didn’t take much rain at all to cause dozens of mudslides .

Every 200 Years

For major storms before 1861, a study of the land and core soil samples provided answers. Based on marsh core samples and sediment core samples of San Francisco Bay, the storm titled the “1000-year storm” really occurs about once every two hundred years .

1100, 1400, and 1650 marked the dates for the three previous storms. These dates were provided based on when soils were massively disturbed, such as by landslides, and when the bay was filled more with freshwater than seawater.

However, with climate change influencing weather patterns across the globe, it remains to be seen if the 1000-year storms in California and other parts of the world increase, decrease, or have even more disastrous consequences.

Up Next:

• Fire Season in California: Peak Timing and Highest Risk Areas
• The Biggest April Snowstorm in California History Dumped an Absurd Amount of Snow
• Will California Really “Fall Into the Ocean” When the Big One Hits?

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