New climate research reveals growing risk of water shortages and flooding in California

Feb 07, 2006
A waterfall on the North Fork of the American River
A waterfall on the North Fork of the American River, in the foothills of California’s eastern Sacramento Valley. ©2003 American River Conservancy

If the world continues to burn greenhouse gases, California may have an increased risk of winter floods and summer water shortages, even within the same year. This scenario may be more severe in future El Niño years.

New research by Lawrence Livermore National Laboratory (LLNL) scientists shows that global warming is likely to change river flows in ways that may result in both increased flood risk and water shortages. The predictions assume atmospheric carbon dioxide concentration doubles from preindustrial levels.

The amount of water flowing in California’s rivers needs to be just right. Too much brings a risk of flooding; too little causes reservoir levels to drop.

As temperatures warm as a result of carbon emission, more rain than snow falls at higher elevations. For the areas that do receive snow, melt occurs sooner.

The research shows that this well-known scenario – in which global warming causes an increase in wintertime river flows and a reduction in spring and summer flows – is more robust than previously thought.

“It seems unlikely that any changes in precipitation will be large enough to eliminate these problems,” said Philip Duffy, an LLNL physicist and director of the Institute for Research on Climate Change and its Societal Impacts, a University of California Intercampus Research Program. Furthermore, in an El Niño (a naturally occurring climate fluctuation) season, these problems may be more severe.

California’s water infrastructure is very efficient at providing an adequate water supply and minimizing flood risk. The system, however, works well only in a climate that includes large amounts of mountain snow. Melting snow keeps reservoirs full in the late spring and summer, after rain and snowfall have stopped. Snow acts as a natural reservoir, with a volume close to that of manmade reservoirs.

As global warming ensues, more precipitation will be in the form of rain rather than snow. Also, what snow remains will melt earlier in the year. These changes will result in higher river flow rates in California’s major rivers during winter and lower flows during spring and summer, when flows are largely from snowmelt.

“Even if total flows over the whole year are the same, these changes could jeopardize water supplies, because it may not be possible for reservoirs to capture the increased winter flows,” said Edwin Maurer, a professor at Santa Clara University and lead author of the research that appears in the Jan. 27 edition of the journal Geophysical Research Letters. “This problem would be compounded by an increased risk of wintertime flooding resulting from higher river flow rates,” he said.

This would force water managers to reduce reservoir water levels to provide extra space for capturing increased winter flood surges, which would further reduce the overall year’s water supply.

“In an El Niño year, which brings more rain than a typical year, there would be an increase (versus today) in the year-to-year variability in river flow rates, which would make life complicated for people who manage the water supply,” Duffy said.

The researchers simulated only monthly mean river flows, so they can’t quantitatively assess flood risk, which depends on daily-timescale river flows. However, the monthly flows are high enough to indicate that flood risk would be much higher.

“In particular, there will be increased wintertime river flows and lower spring and summer flows whether future precipitation increases or decreases modestly,” Maurer said. “It seems unlikely that the potential problems can be avoided by changes in precipitation.” This finding was published earlier this year by Maurer and Duffy.

The newest paper by Maurer, Duffy, and Seran Gibbard of LLNL’s AX Division investigates effects on California river flows of a hypothetical future-climate El NiÑo. El NiÑo is a naturally occurring climate oscillation that typically produces increased precipitation, river flows and flood risk in California.

The team’s work has some limitations: The researchers assumed that the strength of an El Niño, as measured by departures of sea-surface temperatures from long-term average values, will be the same in the future as today. They did this because climate models don’t agree on how the strength of an El Niño is likely to change.

Source: Lawrence Livermore National Laboratory

Explore further: Start of dwarf planet mission delayed after small mix-up

Related Stories

Heinz Awards honors six for solving critical human issues

Apr 23, 2015

A Massachusetts Institute of Technology researcher who has developed artificial human "microlivers" that can safely test the toxicity of drugs without endangering lives is one of six people chosen to receive Heinz Awards.

International experts analyze impacts of Ethiopian dam

Apr 22, 2015

According to present plans, the Grand Ethiopian Renaissance Dam (GERD)—now under construction across the Blue Nile River in Ethiopia—will be the largest hydroelectric dam in Africa, and one of the 12 ...

China's struggle for water security

Apr 18, 2015

Way back in 1999, before he became China's prime minister, Wen Jiabao warned that water scarcity posed one of the greatest threats to the "survival of the nation".

Recommended for you

The riddle of galactic thin–thick disk solved

Apr 24, 2015

A long-standing puzzle regarding the nature of disk galaxies has finally been solved by a team of astronomers led by Ivan Minchev from the Leibniz Institute for Astrophysics Potsdam (AIP), using state-of-the-art ...

Giant cosmic tsunami wakes up comatose galaxies

Apr 24, 2015

Galaxies are often found in clusters, with many 'red and dead' neighbours that stopped forming stars in the distant past. Now an international team of astronomers, led by Andra Stroe of Leiden Observatory ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.