Science Snippets: Megaflood Headed for U.S.

Draft script:

Anthropogenic climate change has many consequences. Most people are aware that these include increasing global temperatures, increased variation in local temperatures, more precipitation, and reduced ability to predict local weather. However, there’s even more.

According to the headline of an article at BBC Science Focus, A biblical megaflood could hit the US at any moment. And that’s only the beginning. The subhead of this article published 6 April 2026: “A flood, the scale of which has not been seen in centuries, is coming, scientists say. Can we prepare before it hits?”

The first paragraph provides a terrifying overview: “California. The Golden State. Home to almost 40 million people and the world’s fourth-largest economy, it is a global capital of technological innovation and the epicentre of the entertainment industry. But beneath the glitz and glamour, prosperity and prestige, the state is a natural disaster hotspot.”

The following paragraph tells a tale with which most Californians are familiar: “From earthquakes to wildfires, Californians are accustomed to battling the forces of nature. In 2025 alone, wildfires ravaged more than 500,000 acres of land statewide, killing 31 people and causing hundreds of billions of dollars worth of damage.”

California is one of the dozen U.S. states I have called home. Because of its size and location along the Pacific Ocean, California hosts a tremendous level of biological diversity. From tiny marine organisms to towering redwood trees, California is home to organisms small and large. The state’s tremendous variety of ecosystems supports many economic activities. As a result, the state is home to casinos, state and national parks, and myriad businesses. It is also home to natural disasters that range from floods to droughts. The abundance of people in the state poses a constant target for these disasters. A megaflood poses a near-term threat to the state and its nearly 40 million inhabitants.

The article in BBC Science Focus continues with a summary of recent wildfires: “Wildfires – and how to prevent, mitigate and fight them – have dominated California’s disaster planning in recent years. And with good reason: the state has been in a constant state of drought for 25 years, only becoming drought-free for the first time this January [, 2026]. The last five years in particular have seen some of the worst fire seasons in living memory, with millions of acres scorched.”

The following four paragraphs pose a warning: “But California is built on extremes at both ends. Alongside vast wealth sits deep poverty; alongside years of drought and fire come episodes of torrential rain and devastating floods.

Only in 2023, hundreds of thousands were left without power as storms and flooding battered the state. Highways collapsed, trains derailed, and thousands were evacuated from their homes.

That sounds bad enough, but according to the latest research, episodes like this pale in comparison to what’s to come.

Scientists and officials are now preparing for not one threatening storm, but a 30-day maelstrom of megastorms unlike anything seen in the state for almost 200 years. Such a scenario was always possible, but rising global temperatures are making it more likely – and far more destructive.”

The storm system has already been named, as explained in the following paragraph: “This storm system, dubbed ‘ARkStorm 2.0’, could strike this year or in 60 years – no one knows for sure. Whenever it does, it is likely to be one of the most costly disasters in global history. The only question is whether California can prepare in time.”

The next subsection begins with an explanation of an ARkStorm: “Short for ‘Atmospheric River 1,000-year Storm’, the ARkStorms are hypothetical – yet very plausible – megastorm scenarios. Those familiar with weather on the US West Coast may already know [atmospheric rivers] … well.”

“Though often strong rainfall events, … [atmospheric rivers] are important to water supplies in the region, contributing up to 50 per cent of California’s annual precipitation.

However, when these systems stall, or multiple hit in quick succession, they can dump extraordinary amounts of rain and snow in a short time, dramatically raising the risk of landslides, river flooding and reservoir overflow.”

The following four paragraphs provide a short summary of what happens when anthropogenic climate change is added to the historical mix of rainstorms: “In 2010, a team of interdisciplinary scientists led by the US Geological Survey developed the first ARkStorm scenario: a sequence of super-strong atmospheric rivers striking California just days apart.

Far from being a speculative worst-case, the scenario was designed to mirror real historical events, including devastating storms in 1861-62 that lasted 45 days and turned hundreds of miles of the Central Valley into an inland sea.

Today, if an ARkStorm hit, it would be the most costly geophysical disaster of all time. In such an event, damages are expected to exceed $1tn, with flood depths in some areas up to 6m (20ft). Millions of people would need to be evacuated, as water invaded populated areas from San Francisco to Los Angeles.

In 2022, researchers revisited the ARkStorm scenario to factor in one – pretty important – factor that was left out of the original analysis: our old friend climate change. Suffice to say that if the first scenario was troubling, ARkStorm 2.0 was truly mind melting.” In other words, the sequel increases the level of horror beyond the original ARkStorm.

The article in BBC Science Focus includes an embedded link to a peer-reviewed, open-access article in the renowned Science Advances. Created by two scholars, the article is titled Climate change is increasing the risk of a California megaflood. It was published 12 August 2022.

The Abstract of the peer-reviewed, open-access paper in Science Advances tells the tale: “Despite the recent prevalence of severe drought, California faces a broadly underappreciated risk of severe floods. Here, we investigate the physical characteristics of ‘plausible worst case scenario’ extreme storm sequences capable of giving rise to ‘megaflood’ conditions using a combination of climate model data and high-resolution weather modeling. Using the data from the Community Earth System Model Large Ensemble, we find that climate change has already doubled the likelihood of an event capable of producing catastrophic flooding, but larger future increases are likely due to continued warming. We further find that runoff in the future extreme storm scenario is 200 to 400% greater than historical values in the Sierra Nevada because of increased precipitation rates and decreased snow fraction. These findings have direct implications for flood and emergency management, as well as broader implications for hazard mitigation and climate adaptation activities.”

That last sentence is a typical understatement in a peer-reviewed paper: “These findings have direct implications for flood and emergency management, as well as broader implications for hazard mitigation and climate adaptation activities.”

My interpretation: These findings are directly related to abrupt, irreversible climate change. They indicate what we already know: Our time is short. In addition, they provide relevant information about the many topics that keep me awake at night. May your own experiences be rooted in ignorance, and therefore in bliss.