Here comes the rain

December 19, 2001

EVEN just a degree or two of greenhouse warming will have a dramatic impact on water resources across western North America. Teams who have modelled the climate in the area are warning of greatly reduced snowpacks and more intense flooding as temperatures inch up during the 21st century.

It's the first time that global climate modellers have worked so closely with teams running detailed regional models of snowfall, rain and stream flows to predict exactly what warming will do to the area. The researchers, from the National Center for Atmospheric Research in Boulder, Colorado, and elsewhere, were surprised by the size of the effect generated by only a small rise in temperature.

Assuming "business as usual" emissions, greenhouse gases will warm the west coast of North America by just one or two degrees Celsius over the next century, and average precipitation won't change much. But in the model, warmer winters raised the snowline, drastically reducing the crucial mountain snowpack, the researchers told the American Geophysical Union in San Francisco last week. "We realised that huge areas of the snowpack in the Sierra went down to 15 per cent of today's values," says Michael Dettinger, a research hydrologist at the Scripps Institution of Oceanography in La Jolla, California. "That caught everyone's attention."

The researchers also predict that by the middle of the century, melting snow will cause streams to reach their annual peak flow up to a month earlier. And with warm rains melting snow or drenching already saturated ground, the risk of extreme floods will rise dramatically. "We have to believe in these very warm, very wet storms," says Andrew Wood, a water resources modeller at the University of Washington, Seattle.

Since dams can't be filled until the risk of flooding is past, the models predict they will trap just 70 to 85 per cent as much run-off as they do now. This is a particular problem for California, where agriculture, industry, a burgeoning population and environmental needs already clash over limited water supplies. "We are taking this extremely seriously," says Jonas Minton, deputy director of the California Department of Water Resources.

And observations certainly back up the models. Minton points out that an increasing percentage of California's precipitation over recent decades is falling as rain rather than snow. And Iris Stewart, a climate researcher at the University of California, San Diego, has found that in the last 50 years, run-off peaks in the western US and Canada have been happening earlier and earlier. The cause seems to be a region-wide trend towards warmer winters and springs.

Dettinger has little doubt that the models point to a real and immediate problem. "It's upon us," he says, "and it's not clear what the fix is."
-end-
Author: Robert Adler

New Scientist issue: 22/29 December 2001

PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS STORY AND, IF PUBLISHING ONLINE, PLEASE CARRY A HYPERLINK TO: http://www.newscientist.com

New Scientist

Related Flooding Articles from Brightsurf:

Coastal flooding will disproportionately impact 31 million people globally
Indiana University researchers analyzed these geographic regions, which include cities like New Orleans, Bangkok, and Shanghai, using a new global dataset to determine how many people live on river deltas, how many are vulnerable to a 100-year storm surge event, and the ability of the deltas to naturally mitigate impacts of climate change.

New woodlands can help reduce flooding risk within 15 years
New research by the University of Plymouth suggests the planting of more trees could have a significant and positive effect in preventing flash flooding.

Land use change leads to increased flooding in Indonesia
While high greenhouse gas emissions and biodiversity loss are often associated with rapid land-use change in Indonesia, impacts on local water cycles have been largely overlooked.

Climate change: Coastal flooding could threaten up to 20% of global GDP
Coastal flooding events could threaten assets worth up to 20% of the global GDP by 2100, a study in Scientific Reports suggests.

River plants counter both flooding and drought to protect biodiversity
'Water plants are a nuisance in streams, blocking the flow.

Scientists predict dramatic increase in flooding, drought in California
California may see a 54 percent increase in rainfall variability by the end of this century, according to research from a UC Davis atmospheric scientist.

Multiple flooding sources threaten Honolulu's infrastructure
In a study published in Scientific Reports, researchers at the University of Hawai'i at Mānoa, found in the next few decades, sea level rise will likely cause large and increasing percentages of land area to be impacted simultaneously by the three flood mechanisms.

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.

Read More: Flooding News and Flooding Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.