California Atmospheric Rivers: The Growing Flood Threat

What Are Atmospheric Rivers?

Atmospheric rivers are narrow corridors of concentrated moisture in the atmosphere, sometimes called "rivers in the sky." They originate over the tropical Pacific Ocean and can carry more water vapor than the Amazon River. When they make landfall on the West Coast, they can deliver extraordinary amounts of precipitation in a short time.

California depends on atmospheric rivers for a significant portion of its annual precipitation and water supply. However, the most intense atmospheric rivers can cause catastrophic flooding, landslides, and debris flows, especially in areas scarred by recent wildfires.

Recent Devastating Events

The winter of 2022-2023 brought a series of powerful atmospheric rivers to California that caused widespread flooding, killed at least 22 people, and caused billions in damage. Communities from the Central Valley to coastal regions were inundated, and the events highlighted how vulnerable California's infrastructure is to concentrated heavy rainfall.

The Sacramento Valley and San Joaquin Valley are particularly at risk. Much of Sacramento sits on a floodplain protected by a levee system that experts have compared to pre-Katrina New Orleans. A major levee failure during a strong atmospheric river could flood large portions of the state capital.

Climate Change Connection

Research indicates that climate change is making atmospheric rivers more intense. A warmer atmosphere holds more moisture, and studies project that the strongest atmospheric rivers will carry 25% more moisture by the end of the century. This means heavier rainfall, more flooding, and greater risk for communities throughout California.

Preparing for Atmospheric River Flooding

California residents should understand their local flood risk, especially in low-lying areas, near rivers and creeks, and below hillsides scarred by wildfire. Flood insurance is not commonly purchased in California, but the risk is real and growing. Check your California ZIP code for detailed flood zone information and risk assessment.