Nav: Home

More rain and less snow means increased flood risk

January 27, 2020

As the world warms and precipitation that would have generated snowpack instead creates rain, the western U.S. could see larger floods, according to new Stanford research.

An analysis of over 400 watersheds from 1980 to 2016 shows that winter floods driven by rainfall can be more than 2.5 times as large as those driven by snowmelt. The researchers also found that flood sizes increase exponentially as a higher fraction of precipitation falls as rain, meaning the size of floods increased at a faster rate than the increase in rain.

The study, which appears in the January issue of Water Resources Research, is particularly salient for people planning infrastructure while taking global warming into account. As Northern Californians saw during the Oroville Dam crisis in 2017 when a spillway failure forced more than 180,000 residents to evacuate, warm storms can pose big problems.

"The Oroville Dam crisis is a good example of how existing infrastructure is already vulnerable to flooding," said lead author Frances Davenport, a PhD student in Earth system science at Stanford's School of Earth, Energy & Environmental Sciences (Stanford Earth). "These results show that warming alone - even without changes in precipitation amounts - could lead to changes in the size of floods."

While it might seem obvious that a greater fraction of precipitation falling as rain would cause bigger floods, the new research reveals that rainfall and flood size have a non-linear relationship. For example, a storm with 100 percent rain has 25 percent more liquid precipitation than a storm with 80 percent rain, but the researchers found that the average flood is 33 percent larger, meaning that the floods grow at a faster rate than the increase in liquid precipitation.

Future infrastructure needs

The results could inform management of reservoirs that not only secure the region's water supply but also provide a buffer for flooding, according to senior author Noah Diffenbaugh, the Kara J. Foundation Professor at Stanford Earth.

"Planners are being asked to project forward what kind of conditions today's infrastructure will have to withstand in the coming years and decades," Diffenbaugh said. "Both the shape and magnitude of our non-linear results have the potential to benefit planners in Western states that are trying to integrate the changing nature of snow hydrology into their decisions."

The researchers evaluated 410 watersheds using daily streamflow measurements from the U.S. Geological Survey to identify the largest precipitation events and the time periods with the highest streamflow. They then analyzed these events by comparing the amount of rain, snow and snowmelt leading up to and following each event.

In collaboration with economist and co-author Marshall Burke, an assistant professor of Earth system science, the researchers adapted methods from econometrics - a branch of applied statistics - to account for other influences like soil characteristics, slope and land-use change, in order to tease out the impact of precipitation alone. According to the authors, the analysis is one of the early attempts to apply these econometric techniques to hydrology.

"By using this econometric method, we can look at how flooding has varied across the full range of historical variability in each watershed," Davenport said. "This allows us to identify patterns that may not yet be evident in long-term flooding trends."

The results are useful to water managers thinking about long-term flood risks, especially in areas expected to experience warming and continued variability in the total amount of precipitation, according to the researchers. They were motivated to focus their analyses on the western U.S. because the same dams and reservoirs used to store water for the dry season also provide flood control during the wet season, with snow playing an important role in each.

"We've seen in recent years the real-time tension between keeping water in the reservoir so it can be used later in the year, and letting it out so that there's space available to prevent flooding from the next storm," said Diffenbaugh, who is also the Kimmelman Family Senior Fellow at the Woods Institute for the Environment. "States like California are well aware that as the snow hydrology of the western U.S. continues to change, the infrastructure that was designed and built around the old climate of the last century will continue to be pushed to its limits. Our results shed new light on how rapidly planners can expect extreme runoff to intensify as precipitation becomes more dominated by rain throughout the region."
-end-
Co-author Julio Herrera-Estrada conducted research for the study while a postdoctoral researcher at Stanford Earth. Diffenbaugh is also an affiliate of the Precourt Institute for Energy. Burke is a center fellow at the Freeman Spogli Institute for International Studies and, by courtesy, at the Woods Institute for the Environment.

Funding for the research was provided by Stanford University.


Stanford's School of Earth, Energy & Environmental Sciences

Related Flooding Articles:

Climate change: Extreme coastal flooding events in the US expected to rise
Extreme flooding events in some US coastal areas could double every five years if sea levels continue to rise as expected, a study published in Scientific Reports suggests.
Study find delta helps to decrease the impact of river flooding
Most coastal cities and ports face a double threat from storm surge and river flooding.
Texas A&M researchers develop flooding prediction tool
By incorporating the architecture of city drainage systems and readings from flood gauges into a comprehensive statistical framework, researchers at Texas A&M University can now accurately predict the evolution of floods in extreme situations like hurricanes.
Study finds flooding damage to levees is cumulative -- and often invisible
Recent research finds that repeated flooding events have a cumulative effect on the structural integrity of earthen levees, suggesting that the increase in extreme weather events associated with climate change could pose significant challenges for the nation's aging levee system.
NASA's Aqua satellite reveals flooding in Japan from Typhoon Hagibis
Typhoon Hagibis made landfall in Japan over the weekend of October 12 and 13, bringing damaging winds, rough surf and flooding rains.
Extreme flooding from storm surge and heavy precipitation projected to increase higher probability of compound flooding from precipitation and storm surge in Europe under anthropogenic climate change
Risk of compound flooding, which can result when rapid sea level rises associated with storms occur along with heavy rains, is currently concentrated along Mediterranean countries but will greatly increase for Northern European in the future as the climate warms, according to a new modeling study.
Changing climate linked to major changes in flooding across Europe
The impact of a changing climate on the severity of flooding has been demonstrated in the largest-scale study of its kind.
Researchers develop better way to determine coastal flooding risk
Researchers have developed a new methodology for building computer models that paves the way to better understanding the flood risks faced by coastal communities.
Houston's urban sprawl increased rainfall, flooding during Hurricane Harvey
Princeton and University of Iowa researchers found that Houston's urban landscape directly contributed to the torrential rainfall and deadly flooding of Hurricane Harvey in 2017.
Evidence of outburst flooding indicates plentiful water on early Mars
The presence of water on Mars has been theorized for centuries.
More Flooding News and Flooding Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Climate Mindset
In the past few months, human beings have come together to fight a global threat. This hour, TED speakers explore how our response can be the catalyst to fight another global crisis: climate change. Guests include political strategist Tom Rivett-Carnac, diplomat Christiana Figueres, climate justice activist Xiye Bastida, and writer, illustrator, and artist Oliver Jeffers.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Speedy Beet
There are few musical moments more well-worn than the first four notes of Beethoven's Fifth Symphony. But in this short, we find out that Beethoven might have made a last-ditch effort to keep his music from ever feeling familiar, to keep pushing his listeners to a kind of psychological limit. Big thanks to our Brooklyn Philharmonic musicians: Deborah Buck and Suzy Perelman on violin, Arash Amini on cello, and Ah Ling Neu on viola. And check out The First Four Notes, Matthew Guerrieri's book on Beethoven's Fifth. Support Radiolab today at Radiolab.org/donate.