Category Archives: Weather
Independent, skeptic-funded study confirms Global Warming is real
The Berkeley Earth Surface Temperature study has just released a summary of a recently completed global land warming analysis showing “reliable evidence of a rise in average world land temperature by approximately one degree Celsius since the mid-1950s.” Yeah, we’ve heard that before, but this is one study that even skeptics may have to believe.
Here’s why the Berkeley Earth Project is different from all previous studies on global warming:
- It’s independent. No government sponsored or directed the Berkeley Earth Project, so none of the researchers involved had to deal with the same kind of political pressure as previous studies.
- It’s non-profit, supported by donations. The private sector is almost entirely responsible for funding the Berkeley Earth Project, and the largest single donation ($150,000) came from the Charles G. Koch Charitable Foundation, noted multi-million dollar supporter of climate change skepticism.
- It’s open source. Got a problem with the results? The entire data set along with the programs used to analyze said data set are all online, ready for anyone to explore.
- It uses more data than any other study. The Berkeley Earth Project’s temperature database consists of records from 39,000 temperature stations around the world, amounting to 1.6 billion individual measurements. This is about five times the amount of data used in most previous climate change studies.
- It directly addresses the concerns that skeptics raised about previous studies. This includes the potential effect of urban heat islands, the quality of temperature monitoring stations, and selection bias risk.
Let’s just assume, for a moment, that the Berkeley Earth Surface Temperature study is legit. What exactly did they find? Well, in a nutshell, global warming is definitely real. Since the mid-1950s, average global land temperatures have risen by nearly two degrees Fahrenheit. For what it’s worth, this agrees very closely with previous global warming studies that were dismissed by skeptics for one reason or another. The Berkeley study also found that pretty much everything that climate change skeptics used to discredit previous studies ultimately made no statistically significant differences to the overall result.
So at this point, what’s obviously going to happen is that global warming skeptics and deniers will get together and say, “okay, you’ve convinced us, we’re sorry for all that merciless slandering and we should get together and talk about what climate change means for the future of our planet.” Right?
Yeah, probably not. What’s probably going to happen is that deniers will continue to deny the science without much of a foundation just because they can, or they’ll shift the topic from whether global warming exists to whether humans are causing it. What it really comes down to, though, is that the Earth’s climate is changing, and those changes are starting to have a direct impact on our lives. That impact is only going to increase, and whatever the cause is, if there are things we can do to help keep this planet stable, it just seems like a no-brainer to try our best to make that happen.
Berkeley Earth, via Discover
Independent, skeptic-funded study confirms Global Warming is real
Do Bacteria Play Role in Weather Events?
Hail. (Credit: © RRF / Fotolia) – Do Bacteria Play Role in Weather Events? High Concentration of Bacteria in Center of Hailstones, Researchers Report
Researchers have discovered a high concentration of bacteria in the center of hailstones, suggesting that airborne microorganisms may be responsible for that and other weather events.
They reported their findings May 24, 2011 at the 111th General Meeting of the American Society for Microbiology in New Orleans.
“Bacteria have been found within the embryo, the first part of a hailstone to develop. The embryo is a snapshot of what was involved with the event that initiated growth of the hailstone,” says Alexander Michaud of Montana State University in Bozeman, who presented the research.
Michaud and his colleagues analyzed hailstones over 5 centimeters in diameter that were collected on the University campus after a storm in June 2010. The large hailstones were seperated into 4 layers and the meltwater from each layer was analyzed. The number of culturable bacteria was found to be highest in the inner cores of the hailstone.
“In order for precipitation to occur, a nucleating particle must be present to allow for aggregation of water molecules,” says Michaud. “There is growing evidence that these nuclei can be bacteria or other biological particles.”
Michaud’s research is part of a growing field of study focusing on bioprecipitation, a concept where bacteria may initiate rainfall and other forms of precipitation including snow and hail. The formation of ice in clouds, which is necessary for snow and most rainfall events, requires ice nuclei (IN), particles that the ice crystals can grow around.
Story Continues -> Do Bacteria Play Role in Weather Events?
Carbon Dioxide Controls Earth''s Temperature, New Modeling Study Shows
Various atmospheric components differ in their contributions to the greenhouse effect, some through feedbacks and some through forcings. Without carbon dioxide and other non-condensing greenhouse gases, water vapor and clouds would be unable to provide the feedback mechanisms that amplify the greenhouse effect. (Credit: NASA GISS)
Water vapor and clouds are the major contributors to Earth”s greenhouse effect, but a new atmosphere-ocean climate modeling study shows that the planet”s temperature ultimately depends on the atmospheric level of carbon dioxide.
The study, conducted by Andrew Lacis and colleagues at NASA”s Goddard Institute for Space Studies (GISS) in New York, examined the nature of Earth”s greenhouse effect and clarified the role that greenhouse gases and clouds play in absorbing outgoing infrared radiation. Notably, the team identified non-condensing greenhouse gases — such as carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbons — as providing the core support for the terrestrial greenhouse effect.
Without non-condensing greenhouse gases, water vapor and clouds would be unable to provide the feedback mechanisms that amplify the greenhouse effect. The study”s results are published Oct. 15 in Science.
A companion study led by GISS co-author Gavin Schmidt that has been accepted for publication in the Journal of Geophysical Research shows that carbon dioxide accounts for about 20 percent of the greenhouse effect, water vapor and clouds together account for 75 percent, and minor gases and aerosols make up the remaining five percent. However, it is the 25 percent non-condensing greenhouse gas component, which includes carbon dioxide, that is the key factor in sustaining Earth”s greenhouse effect. By this accounting, carbon dioxide is responsible for 80 percent of the radiative forcing that sustains the Earth”s greenhouse effect.
The climate forcing experiment described in Science was simple in design and concept — all of the non-condensing greenhouse gases and aerosols were zeroed out, and the global climate model was run forward in time to see what would happen to the greenhouse effect.
Without the sustaining support by the non-condensing greenhouse gases, Earth”s greenhouse effect collapsed as water vapor quickly precipitated from the atmosphere, plunging the model Earth into an icebound state — a clear demonstration that water vapor, although contributing 50 percent of the total greenhouse warming, acts as a feedback process, and as such, cannot by itself uphold the Earth”s greenhouse effect.
“Our climate modeling simulation should be viewed as an experiment in atmospheric physics, illustrating a cause and effect problem which allowed us to gain a better understanding of the working mechanics of Earth”s greenhouse effect, and enabled us to demonstrate the direct relationship that exists between rising atmospheric carbon dioxide and rising global temperature,” Lacis said.
Article Continues -> http://www.sciencedaily.com/releases/2010/10/101014171146.htm
Population Change: Another Big Influence on Climate Change
Changes in population, including aging and urbanization, could significantly affect global emissions of carbon dioxide over the next 40 years, according to a new study. (Credit: iStockphoto)
Changes in population, including aging and urbanization, could significantly affect global emissions of carbon dioxide over the next 40 years, according to a new study.
The study, published in the Proceedings of the National Academy of Sciences (PNAS), was conducted by researchers from the National Center for Atmospheric Research (NCAR), the International Institute for Applied Systems Analysis (IIASA), and the National Oceanographic and Atmospheric Administration. It was funded by a European Young Investigator””s Award*, the Hewlett Foundation, and the US National Science Foundation.
By mid-century it is estimated that global population could rise by more than three billion people, with most of that increase occurring in urban areas. The study showed that a slowing of that population growth could contribute to significantly reducing greenhouse gas emissions. By 2050, the researchers found that if population followed one of the slower growth paths foreseen as plausible by demographers at the United Nations, it could provide 16 to 29 percent of the emission reductions thought necessary to keep global temperatures from causing serious impacts. The effect of slower population growth on greenhouse gas emissions would be even larger by the end of the century.
“If global population growth slows down, it is not going to solve the climate problem, but it can make a contribution, especially in the long term,” says the study””s lead author and NCAR scientist Brian O””Neill.
Study co-author and IIASA scientist Shonali Pachauri says that slower population growth will have different influences, depending on where it occurs. “A slowing of population growth in developing countries today will have a large impact on future global population size. However, slower population growth in developed countries will matter to emissions too because of higher per capita energy use,” says Dr Pachauri.
Scientists have long known that changes in population will have some effect on greenhouse gas emissions, but there has been debate on how large that effect might be.
Article Continues -> http://www.sciencedaily.com/releases/2010/10/101011150354.htm
Experimental Explanation of Supercooling: Why Water Does Not Freeze in the Clouds
Droplet of a gold-silicon liquid alloy on a silicon (111) surface. Pentagonal clusters formed at the interface exhibit a denser structure compared to solid gold and prevent the liquid from crystallization at temperatures as low as 300 Kelvin below the solidification temperature. (Credit: Graphics by M. Collignon)
Supercooling, a state where liquids do not solidify even below their normal freezing point, still puzzles scientists today. A good example of this phenomenon is found everyday in meteorology: clouds in high altitude are an accumulation of supercooled droplets of water below their freezing point.
Scientists from the Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA), the Centre National de Recherche Scientifique (CNRS) and the ESRF have found an experimental explanation of the phenomenon of supercooling. Their research is published today in Nature.
Supercooled liquids are trapped in a metastable state even well below their freezing point, which can only be achieved in liquids that do not contain seeds that may trigger crystallization. Clouds at high altitude are a good example for this: they contain tiny droplets of water that, in the absence of seed crystals do not form ice despite the low temperatures. In everyday life, though, there is usually some crystalline impurity in contact with the liquid that will trigger the crystallization process, and therefore the freezing. Controlling solidification behaviour is important for applications ranging from hail prevention up to technological processes such as welding and casting or even the growth of semiconductor nanostructures.
Supercooling was discovered already in 1724 by Fahrenheit, but even today the phenomenon remains a subject for intense discussions. Over the last 60 years the very existence of deep supercooling has led to speculations that the internal structure of liquids could be incompatible with crystallization. Models propose that a significant fraction of the atoms in liquids arrange in five-fold coordinated clusters. To form a crystal however, one needs a structure that can be repeated periodically, filling the entire space. This is not possible with five-fold coordinated clusters. In the two-dimensional analogue, a plane cannot be filled by pentagons only, whereas triangles, rectangles or hexagons can fill a plane perfectly. In this example, pentagons are an obstacle to crystallization.
Until today there was no experimental proof that this five-fold coordinated structures are at the origin of supercooling. The researchers from the CEA, CNRS and ESRF studied the structure of a particular liquid, a gold-silicon alloy, in contact with a specially decorated silicon (111) surface, where the outermost layer of the solid featured pentagonal atomic arrangements. Their findings confirmed that a strong supercooling effect took place. “We studied what happened to the liquid in contact with a five-fold coordinated surface,” explains Tobias Schülli, first author of the paper. The team performed the control experiment with the same liquid exposed to three-fold and four-fold coordinated surfaces, which reduced the supercooling effect dramatically. “This constitutes the first experimental proof that pentagonal order is at the origin of supercooling,” explains Tobias Schülli.
It was during their studies, originally focusing on the growth of semiconducting nanowires, that the scientists discovered the unusual properties of these liquids. As they were observing the first stage of growth of nanowires, they could see that the metal-semiconductor alloy they used remained liquid at a much lower temperature than its crystallization point and so they decided to investigate this phenomenon. These liquid alloys are popular in applied research as they enable the growth of sophisticated semiconductor nanostructures at low growth temperatures. Most of these nanowire structures are grown on silicon (111), the same surface used by the team. Semiconducting nanowires are promising candidates for future electronic devices. Prominent examples are solar cells, where scientists are working on the integration of silicon nanowires in order to increase their performance.
Story Source:
Adapted from materials provided by European Synchrotron Radiation Facility.
Journal References:
- T. U. Schülli, R. Daudin, G. Renaud, A. Vaysset, O. Geaymond & A. Pasturel. Substrate-enhanced supercooling in AuSi eutectic droplets. Nature, 2010; 464: 1174-1177 DOI: 10.1038/nature08986
- A. Lindsay Greer. Materials science: A cloak of liquidity. Nature, 2010; 464: 1137-1138 DOI: 10.1038/4641137a
http://www.sciencedaily.com/releases/2010/04/100421133114.htm
Traditional Inuit Knowledge Combines With Science to Shape Weather Insights
Inuit forecasters possessing generations of environmental knowledge are helping scientists better understand changes in Arctic weather. (Credit: Photo courtesy Shari Gearheard, CU-Boulder National Snow and Ice Data Center.)
Using skills passed down through generations, Inuit forecasters living in the Canadian Arctic look to the sky to tell by the way the wind scatters a cloud whether a storm is on the horizon or if it’s safe to go on a hunt.
Thousands of miles away in a lab tucked in Colorado’s Rocky Mountains, scientists take data measurements and use the latest computer models to predict weather. They are two practices serving the same purpose that come from disparate worlds.
But in the past 20 years, something has run amok with Inuit forecasting. Old weather signals don’t seem to mean what they used to. The cloud that scatters could signal a storm that comes in an hour instead of a day.
Now researchers are combining indigenous environmental knowledge with modern science to learn new things about what’s happening to the Arctic climate.
“It’s interesting how the western approach is often trying to understand things without necessarily experiencing them,” said Elizabeth Weatherhead, a research scientist with the University of Colorado at Boulder’s Cooperative Institute for Research in Environmental Sciences. “With the Inuit, it’s much more of an experiential issue, and I think that fundamental difference brings a completely different emphasis both in defining what the important scientific questions are, and discerning how to address them.”
For years, researchers had heard reports of unpredictable weather coming in from Arctic communities. But the stories didn’t seem to match up with the numbers. By scientific measurement, weather around the world appeared to be growing more persistent with less variation. The disparity left scientists scratching their heads, said Weatherhead.
“I had been hearing about this problem from other environmental statisticians for a number of years,” said Weatherhead, who also works closely with the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory in Boulder, Colo., and who is chief author on a new study on the subject. “But the Inuit used a different language than what we statisticians used, and none of us could really figure out what matched up with their observations.”
That’s where Shari Gearheard, a scientist with CU-Boulder’s National Snow and Ice Data Center, also part of CIRES, comes in. Gearheard lives in Clyde River, Nunavut, Canada, an Inuit community on eastern Baffin Island, and for the past 10 years has been working with Inuit hunters and elders to document their knowledge of the environment and environmental change.
Weather has a special importance in Arctic environments, where a reliable forecast can mean the difference between life and death. There are members of the Inuit community who possess the skills to predict the weather, but that knowledge is dying off as both the culture and climate change, according to the scientists.
“The impacts of that are a loss of confidence in those forecasters and concerns about incorrect forecasts,” said Gearheard. Forecasters don’t want to send somebody out to go hunting if they’re going to be unsafe and be in poor weather conditions.”
Gearheard meticulously collects the stories told to her by the Inuit and makes systematic records of indigenous environmental knowledge. Through this, patterns begin to emerge, she said.
Of special importance were changes experienced by the Inuit during the spring, a time of transition for many environmental processes. During spring, the Inuit would notice that the top layer of the snow melted during the day and then would refreeze at night, forming a crust.
“In fact, in a lot of places, the season is named after a particular process by the Inuit,” said Gearheard. “In cases like this where the Inuit are not seeing that process anymore, it is an indicator to them that something had changed.”
Gearheard’s records created a resolution of detail for Arctic weather observation that, by bringing the two studies together, gave Weatherhead the information she needed to bridge indigenous knowledge with scientific knowledge. “What was incredibly helpful was Shari’s detailed description of what they were experiencing on what sort of timescales,” said Weatherhead. “That really allowed us to start focusing on our statistical tests and try to find exactly what matched their observations.”
Statistical analysis of day-to-day temperatures at Baker Lake, Nunavut, showed that in May and June the persistence of temperature had recently declined, matching Inuit reports of greater unpredictability at that season. “People hadn’t previously looked at persistence in this way,” said CIRES fellow Roger Barry, also director of the World Data Center for Glaciology at the National Snow and Ice Data Center at CU-Boulder and a study co-author along with Gearheard.
What they found was a scientific story more in line with what people were witnessing on the ground. Weather along the Arctic latitudes was behaving more unpredictably than in other parts of the world.
“That’s an incredibly important parameter to care about,” said Weatherhead. “The way I try to describe it to some people is if we get an inch of rain out at my house in the month of July, I don’t need to turn on the sprinklers. But if we get an inch of rain on July 1, and no rain after that, my lawn is dead.
“Ecosystems have evolved under a certain type of pattern. So if that is changing, that could be just as important as a small increase in temperature or some of the other changes we’re talking about,” Weatherhead said.
The new study helps scientists refine and test climate models, while also providing such models with a new category of information to consider, said Weatherhead. And Gearheard’s work with the Inuit is demonstrating the value of indigenous environmental knowledge to modern climate science.
“When we first started talking about this, indigenous knowledge didn’t have the place it does now in research,” Gearheard said. “It’s growing. People are becoming more familiar with it, more respectful of it.”
Weatherhead and Gearheard said they are intrigued by the insights that incorporate indigenous knowledge and climate studies, but they don’t want to stop there. The new study has sparked an interest in the type of environmental knowledge other communities could provide to climate scientists, from ranchers and farmers to indigenous groups. “When you treat these perspectives as different forms of evidence or knowledge and see where that takes you, that is when exciting stuff happens,” said Gearheard.
The study appears this month in the journal Global Environmental Change. The National Science Foundation and the Social Sciences and Humanities Research Council of Canada provided funding for the study.
Story Source:
Adapted from materials provided by University of Colorado at Boulder.
Journal Reference:
- Weatherhead et al. Changes in weather persistence: Insight from Inuit knowledge. Global Environmental Change, 2010; DOI: 10.1016/j.gloenvcha.2010.02.002
http://www.sciencedaily.com/releases/2010/04/100407190000.htm
Resolution Denying Climate Change Resoundingly Passes in Utah
Measure passes broadly passes with 56-17 vote, but lacks legal power
Many politicians across the U.S. have already made their mind up about climate change
and refuse to consider recent allegations of academic misconduct among prominent climate researchers, or other plausible explanations for climate change, such as sun cycles. Across the country, there are many folks that haven’t blindly accepted the theory, though.
Utah’s heavily Republican state legislature has passed a new resolution which condemns climate change alarmism. The resolution lacks any legal authority, but vocally criticizes the anthropogenic global warming community for ignoring recent developments.
The legislation, which resoundingly passed by a vote of 56-17, originally referred to global warming theory as a “conspiracy”, but that term was stricken from the measure in favor of “climate data“.
A small excerpt from the measure is:
WHEREAS, there has been a concerted effort by climate change alarmists to marginalize those in the scientific community who are skeptical of global warming by manipulating or pressuring peer-reviewed publications to keep contrary or competing scientific viewpoints and findings on global warming from being reviewed and published;
WHEREAS, the Intergovernmental Panel on Climate Change (IPCC), a blend of government officials and scientists, does no independent climate research but relies on global climate researchers;
WHEREAS, Earth’s climate is constantly changing with recent warming potentially an indication of a return to more normal temperatures following a prolonged cooling period from 1250 to 1860 called the “Little Ice Age”;
The bill points out that pending warming legislation will earn its proponents “more than $7 billion annually in federal government grants”. Originally those grants were referred to as the “the climate change ‘gravy train’”, but that language was removed from the measure.
The bill is critical of the U.S. Environmental Agency and President Barack Obama’s calls to regulate greenhouse gases nationally. Representative Mike Noel says the warming scare is an example of profiteers posing as environmentalists and exploiting the public for their own gain. He states, “Sometimes … we need to have the courage to do nothing.”
Arizona is considering similar legislation.
The only potential downside of the measures, is that they could give local environmentalists means to challenge future nuclear plant construction in the states. President Obama has championed nuclear plant construction, but says that he’s doing it to “combat climate change.”
More Mega-Snowstorms Coming — Global Warming to Blame?
Skiing Washington, D.C.’s National Mall on February 7, 2010. – Photograph by Jewel Samad, AFP, Getty Images
Get used to heavy U.S. snowstorms, scientists say. The cause, though, is a subject of hot debate.
Willie Drye
Published February 12, 2010
As snowstorm-ravaged states on the U.S. East Coast dig out, scientists say the past week’s “Snowpocalypse” could be a taste of harsh winters to come—and that, strangely enough, global warming may be to blame. Others aren’t so sure.
(See “Freak Snowstorms: Fluke or Fuel in Global Warming Debate?”)
Meteorologist Joe Bastardi says the recent snowstorms may be the start of a trend of cold, snowy winters similar to those of the 1960s and 1970s.
Bastardi, of the AccuWeather forecasting service in State College, Pennsylvania, believes the February record snowfalls, though, are due more to an El Niño that formed last year than to climate change.
An El Niño occurs when Pacific waters off the northwest coast of South America become unusually warm. The event is erratic and unpredictable, but it occurs roughly every three to seven years.
In a prepared statement, Bastardi noted that the current El Niño has been “very strong, prompting many major blizzards for the mid-Atlantic region.”
The El Niño also is altering the normal flow of upper-level winds known as the jet stream, he said. That disruption is pushing cold air from northern Canada into the United States, Bastardi added.
Global Warming Fueling Snowstorms?
Cyclical patterns of heating and cooling—as opposed to long-term global warming—could herald a coming period of harsher U.S. winters, Bastardi told National Geographic News.
“We know that Earth’s cycles are changing,” he said. “The Pacific is cooling. The Atlantic will join it in several years. When you get an El Niño with a cold Pacific, you get crazy winters in the East.”
Still, other scientists say global warming is the main culprit behind this month’s eastern-U.S. snowstorms—and it could cause more heavy snowfalls in future winters.
Attributing snowstorms to warmer weather seems contradictory, but climate scientist Amanda Staudt says relatively warmer weather causes more water to be evaporated from the oceans and thus creates more moisture for winter storms, as long as temperatures remain below freezing.
As for Snowpolaclypse, said Staudt of the National Wildlife Federation in Reston, Virginia, “It’s hard to determine global warming’s effect on any particular storm, but it’s highly unusual to have these really large winter storms in one winter.”
Washington, D.C., for example, has had two two- to three-foot snowfalls this winter—which should be a once-every-300-to-400-years rarity, according to Staudt.
(Related: “‘Thundersnow’ Facts: Mysterious Snowstorms Explained.”)
Waiting … and Waiting … for More Global Warming Evidence
Like AccuWeather’s Bastardi, Staudt believes the current El Niño is contributing to this winter’s harsh U.S. snowstorms, but to a lesser extent than climate change, which she sees as a clear and present danger.
“I think there’s overwhelming evidence that global warming is happening and that human activity is responsible for it,” Staudt said.
(Related: “Five Last-Ditch Schemes to Avert Global Warming Disaster.”)
For his part, Bastardi thinks it’ll take many more winters—not to mention springs, summer, and falls—before we know for sure whether global warming is occurring in the first place.
“I feel strongly,” he said, “that we’ll get an answer in the next 20 or 30 years.”
Mapping Water Vapor for More Accurate Weather Predictions
Image credit: Mike-wise/Flickr
The same thing that limits the accuracy of your GPS unit to within a few meters also prevents meteorologists from making precise weather predictions. Atmospheric water vapor interferes with radio signals as they are sent from GPS satellites and this same vapor scrambles weather radar, making certain things like storm predictions very difficult.
One researcher believes that by creating a map of atmospheric water vapor, some of this interference could be accounted for, leading to much more accurate weather forecasts.
Roderik Lindenbergh, a researcher at Delft University of Technology, is using the Medium Resolution Imaging Spectrometer (MERIS) to develop a more complete understanding of the placement of water vapor in the atmosphere. MERIS is one of the key instruments aboard the European Space Agency’s Environmental Satellite.
By combining this data with less accurate but more up-to-date information acquired by GPS ground stations, Lindenbergh hopes to create a map that might be useful for other analysis. He commented that “this is the first time we have mapped the distribution of water vapor from two perspectives: from the ground and from space.” He went on to explain:
We are unable to see exactly how much water vapor there is at any particular height, but it is better to know just a little than nothing at all.
The data will help more than just meteorologists and disoriented drivers; Lindenbergh believes that climate scientists will be able to use the system to track greenhouse gasses and other atmospheric processes.
Read more about water vapor:
Fighting Water Scarcity with GPS
Decreased Water Vapor in Atmosphere Slowed Last Decade’s Warming
NASA Animates Breakthroughs in Greenhouse Gas Research with New Tool (Video)
Dams Trigger Stronger Storms, Study Suggests
Aerial view of Glen Canyon Dam on the Colorado River in Page, Arizona – Photograph courtesy United States Bureau of Reclamation
Anne Minard
Published February 4, 2010
This story is part of a special series that explores the global water crisis. For more clean water news, photos, and information, visit National Geographic’s Freshwater Web site.
Scientists have long suspected that the world’s dams can create their own weather, often bringing more rain. Water in reservoirs behind dams, plus the water used to irrigate nearby land puts more moisture in the air, which falls as precipitation.
Now some researchers are sounding the alarm that dams—along with their reservoirs—might also trigger more frequent fierce storms that could be the dams’ undoing. That’s worrisome, especially in the United States, where dams are rapidly aging, according to some researchers.
Faisal Hossain, an engineer at Tennessee Technological University in Cookeville, has led several recent studies on 633 dams and about 100 rainfall nearby stations.
“The focus is not so much on average rainfall per se, but rather on the question of whether 25-year storm data that an engineer used to size a reservoir has now become a 15-year storm … as the dams aged,” he said. “It is the heavy rainfall that has tremendous implications on dam safety.”
Roger Pielke, Sr., a senior researcher at the University of Colorado at Boulder, pointed out that reservoirs behind large dams combine with land use changes accompanying dams—like more irrigated farmland—to induce rainfall changes.
Pielke and Hossain have contributed to a review article on the subject in the Dec. 1, 2009 issue of EOS, a publication of the American Geophysical Union.
Changes from China to Spain
The idea that dams can change weather patterns is not new. Studies observing such changes go back decades. A 2006 NASA-led study in the journal Geophysical Research Letters noted that China’s mammoth Three Gorges Dam has increased rainfall by a millimeter a month hundreds of kilometers from the reservoir, and reduced temperatures in the region by 1.26 degrees Fahrenheit (0.7 degrees Celsius).
The long-term studies by Hossain and his colleagues suggest that dams have particularly altered extreme precipitation patterns in arid or semiarid areas.
“The Southwest U.S., Botswana, South Africa, southern Spain and central India showed up on our radar as having experienced a trend in the extreme precipitation in [the period after the dam was built],” he said.
Hossain and his colleagues have detected up to 4 percent higher precipitation per year where dams have been built.
The research has been accepted for publication in two peer-reviewed journals: Natural Hazards Review and Water Resources Research.
Catastrophic Risk?
Hossain and his team said their findings bear on an aging waterworks infrastructure particularly in the United States, where 85 percent of dams will be at least 50 years of age by the year 2020.
“We are hearing stories here and there that certain dams nowadays are having more flooding problems, and having to keep the spillways and sluice gates open more than usual,” Hossain said, pointing to Folsom Dam, on California’s American River. “It remains to be seen if the dam itself either triggered or accelerated the flooding hazards.”
But the U.S. Bureau of Reclamation disagrees that 50 years is an advanced age for a dam.
“We don’t normally consider that a dam would have a life span,” said Brian Becker, chief of the Bureau of Reclamation’s Dam Safety Office in Denver. “A properly designed, constructed, and maintained dam can last centuries.”
The idea that the reservoir could significantly impact the hydrology raises “an interesting notion,” Becker said, “but there are a lot of factors that go into changing hydrology.”
For instance, global and regional climate change and natural variability can influence weather, he said. The Bureau of Reclamation studies hydrology at the sites of all its dams, he said—and modifies its dams accordingly—but has never specifically searched for links between the dams and those hydrological changes.
Becker points out that dam failures in the late 1960s and 1970s–including the famous Teton Dam failure of 1976–prompted federal guidelines for dam safety.
“I think the state of dam safety throughout the country is vastly improved over the years,” he said.
http://news.nationalgeographic.com/news/2010/02/100204-bad-weather-dam-repair-environment-water/
