Less Pollution Means New Dams Not Needed

Less Pollution Means New Dams Not Needed



Feb 2007 - Governor 
Arnold Schwarzenegger recently called for new dams in Northern 
California and near Fresno to store more water from Sierra 
snowmelt - an initiative criticized by environmentalists. 
Now a Stanford University scientist says the elimination of 
aerosol pollution would offset some of the need for additional 
dams by increasing rainwater supply. 
"The aerosol pollution in California could be causing an 
annual loss of water supply equivalent to the storage in the 
planned upper San Joaquin River dam, with a capacity of 1.3 
million acre feet," said Stanford civil and environmental 
engineering Associate Professor Mark Jacobson. 
Jacobson co-authored the study with the late Yoram Kaufman 
from NASA's Goddard Space Flight Center, who died in May 2006. 

Aerosol particles created by vehicle exhaust, forest fires, 
dust and other contaminants can accumulate in the atmosphere 
and reduce the speed of winds closer to the Earth's surface, 
Jacobson explains. 
This reduction in wind speed results in less wind power 
available for wind-turbine electricity and also in reduced 
precipitation, according to the study by Jacobson and Kaufman. 

Their study, based on NASA satellite data of aerosol 
accumulation, measurements of wind speeds over the South Coast 
Basin in California and in China, and computer model 
simulations over California as a whole and the South Coast 
Basin, was published online December 27, 2006 in the journal 
"Geophysical Research Letters." 
In California, the wind reduction means a two to fice percent 
reduction in water supply, which "translates into 0.5 to 1.25 
million acre feet less a year," Jacobson says. An acre foot is 
the volume of water needed to cover one acre of surface area 
to a depth of one foot. 
This contributes to water scarcity in the state, which with 
its growing population will require an additional four to six 
million acre feet of water supply by 2010, according to the 
Association of California Water Agencies. 
Jacobson advocates replacing existing motor vehicles with 
cleaner ones, such as battery-electric and hydrogen-fueled 
vehicles, and substituting fossil-fueled power plants with 
networked wind farms. 
These actions would reduce particle emissions practically to 
zero, he says. The second-best option would be adding particle 
traps to existing vehicles and other sources of pollution. 
Aerosol particles may be responsible for the slowing down of 
winds worldwide. Slower winds evaporate less water from 
oceans, rivers and lakes. 
"If we want to solve the global warming problem, we have to 
replace most of the existing energetic infrastructure with 
wind and other renewable-based energy," says Jacobson, whose 
next step will be to study the effect of greenhouse gases on 
winds.

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