Consecutive atmospheric rivers cause far more damage

As relentless storms cause widespread flooding across California, a study led by researchers from Stanford University and co-authored by University of Florida geographer Katy Serafin sheds light on the driving force behind the torrential downpours: atmospheric rivers.

Analyzing 30 years of weather and economic loss data, the team discovered that when atmospheric rivers occur sequentially, the economic damage more than triples the expected losses compared to standalone events.

These findings surpass initial expectations, showing the negative impacts of consecutive atmospheric rivers when they strike around the globe.

Rivers in the atmosphere

These elongated regions, often described as “rivers in the sky,” are responsible for transporting a large portion of water vapor outside the tropics.

Their strength varies, with the average river carrying water vapor roughly equivalent to the flow at the mouth of the Mississippi River.

In extreme cases, they can transport up to 15 times that quantity. Upon landfall, they release moisture as rain or snow.

While atmospheric rivers contribute approximately half of California’s annual precipitation and replenish the state’s snowpack, they can also be associated with extreme events that lead to catastrophic damage.

Water management 

The study, published January 19 in Science Advances, highlights atmospheric rivers’ crucial role in providing up to half the region’s annual water while emphasizing the challenge of managing substantial water delivery in short time spans.

“When it rains, it can take a while for that rain to move through a watershed naturally, and in many places, we also trap water in reservoirs for use during dry conditions for irrigation and other purposes,” Serafin said.

“Emergency and water managers are constantly balancing flood risks with water shortage needs, especially in states like California where you move between exceptionally dry and exceptionally wet years.”

Economic losses from atmospheric rivers

Serafin, now an assistant professor in the Department of Geography, mentored lead author Corinne Bowers while a postdoctoral researcher at Stanford.

She continued as an advisor throughout Bowers’ completion of her PhD last year. Together with co-author Jack Baker, they aimed to better understand a correlation in previous studies.

In their initial research effort, they found that stronger atmospheric rivers (rated on a scale of 1 to 5) led to higher economic losses in California.

The researchers noted a significant trend in median flood losses but emphasized a wide range around each median.

“For example, prior research found that a category 3 or 4 event could produce losses between $10,000 to over $1 billion across the state,” Serafin said.

“A category 5 event could produce losses between about $5 million to over $1 billion.”

Consecutive events

Based on anecdotal evidence and recent events, the team hypothesized that consecutive atmospheric river events might be more damaging than isolated, single events — contrary to the traditional categorization of losses.

“We’re generally really worried about individual large events that cause hazards and how these events might change in the future — this applies not only to atmospheric rivers but also to hurricanes, which maybe we’re a little more familiar with here in Florida,” Serafin said.

She recalls the exacerbating impacts felt across the state in the 2022 hurricane season, when Hurricanes Ian and Nicole packed a double punch to coastlines within six weeks of each other, causing major dune erosion and widespread structural damage.

Global impact of atmospheric rivers

Serafin cautions that while compounding weather events is a hot topic right now, and a lot of research has examined clusters of events and their formation, there is less focus on demonstrating the overall impacts of these events.

“Our results further add to the necessity of viewing flood risks from atmospheric rivers in a broad lens, taking into account what has happened over the past few weeks to months with current forecasts and predictions,” she explained.

The researchers hope their findings can provide a new perspective to help the broader public better prepare for flood risks by clearly communicating the compound nature of these risks.

“Our work really shows that we need to consider the likelihood for multiple, back-to-back events for predicting damages, because damage from multiple events could be far worse than from one event alone,” Serafin concluded.

More about atmospheric rivers

As discussed above, atmospheric rivers are long, narrow regions in the atmosphere that transport most of the moisture from the tropics towards the poles.

These ribbons of vapor can carry an amount of water vapor roughly equivalent to the average flow of water at the mouth of the Mississippi River.

When these moisture-laden air masses hit a landmass, they often release this water in the form of rain or snow, significantly affecting the weather patterns of the regions they pass over.

Role of atmospheric rivers in climate and weather

Scientists study atmospheric rivers to understand their impact on climate and weather. These systems play a crucial role in distributing heat and moisture around the planet, which are essential components for weather systems.

As mentioned previously, these extreme weather events can lead to beneficial rain or snow that replenishes water supplies and supports agriculture.

However, when atmospheric rivers make landfall, they can also cause extreme weather events, including heavy rainfall that leads to flooding, landslides, and other hazardous conditions.

Preparation and impact mitigation

The research into atmospheric rivers helps meteorologists predict these events more accurately, allowing for better preparation and mitigation of their potential impacts.

For instance, forecasting the path and intensity of an atmospheric river can help communities prepare for possible flooding, safeguarding lives and property.

Understanding atmospheric rivers is also vital for water management. Regions that depend on the precipitation from these systems for their water supply need accurate forecasts to manage their resources effectively.

This is especially true in places like California, where atmospheric rivers are a major source of the annual precipitation.

New technology improves forecasting efforts

Efforts to monitor and study atmospheric rivers, like the study discussed above led by Katy Serafin, have increased in recent years, thanks to advancements in satellite technology and atmospheric science.

These tools allow scientists to track these phenomena more accurately, leading to improved weather forecasts and climate models.

In summary, atmospheric rivers are a critical component of the Earth’s weather and climate system. They play a significant role in shaping weather patterns, influencing water resources, and affecting the lives of people around the world.

As our understanding of these dynamic systems improves, so does our ability to prepare for and respond to the challenges they present.

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