Dry autumns and winters may lead to fewer tornadoes in the spring, according to new analysis of long-term data

Global warming will likely mean more unpredictable weather, scientists say, and a new study by researchers at the University of Georgia pins down, possibly for the first time, how drought conditions in an area’s fall and winter may effect tornado activity the following spring.
The study, published today in the journal Environmental Research Letters, is specific to Georgia and the Southeast, but further study could reveal patterns that might make this more general—including the already tornado-prone Great Plains.

“Our results suggest that there is a statistically significant reduction in tornado activity during a tornado season following drought the preceding fall and winter,” said Marshall Shepherd, a meteorologist and lead author of the study. On the other hand, wet autumns and winters examined in the study had nearly twice as many spring tornado days as drought years did.

The research gives hope that one day meteorologists and climatologists may be able to predict the severity of a spring tornado season the way they now do for hurricanes. Other authors of the paper were Thomas Mote, also of the University of Georgia, and Dev Niyogi of Purdue University. Shepherd and Mote are in department of geography in the UGA Franklin College of Arts and Sciences.

The genesis for the research was the severe Atlanta tornado in March 2008, and Shepherd’s interest in how tornadoes form during severe drought years.

While such tools as Doppler radar have increased our ability to “see” tornadoes as they form, predicting a tornado season’s potential severity has remained elusive. The Intergovernmental Panel on Climate Change projected in 2007 that the frequency and severity of droughts may increase over time, but very little is known about drought conditions affect the frequency or intensity of severe weather hazards such as tornadoes.

To help understand how fall and winter weather might affect spring tornado seasons, the research team acquired the historical database of severe thunderstorms and tornado occurrences from 1951-2006 from the Storm Prediction Center of the National Oceanic and Atmospheric Administration. They also analyzed storm data reports from the National Climactic Data Center and meteorological drought conditions using historical rain gauge and Tropical Rainfall Measuring Mission (TRMM) satellite data from the National Aeronautics and Space Administration (NASA).

Using a number of tools of scientific analysis, the team primarily focused on tornado activity from March-June in Georgia and the Southeast. What they found was shocking, Shepherd said, yet plausible.

On average, wet autumns and winters presaged nearly twice as many spring tornado days in the study area as prior drought seasons. Springs following wet winters and falls were also five to six times more likely to have multiple tornado days than antecedent drought years.

“We do not suggest that soil moisture or precipitation the previous fall and winter exert a direct control on which individual storms will spawn tornadoes,” said Shepherd. “But these long-term seasonal relationships in the study area are striking.”

Correlating historical records and tornado activity has been difficult at best for scientists over the years. For one thing, the National Weather Service did not implement its watch and warning system until the mid-1950s, and only with advent of advanced radar techniques and ground examination of storm sites have researchers been able to say categorically that a certain storm even was a tornado. Also, studies linking tornadic activity with the El Niño cycle have been contradictory.

While it clearly seems that wet falls and winters lead to more severe spring tornado seasons, antecedent seasonal drought scenarios in north Georgia were almost never associated with above-normal tornadic activity the following spring over the 50-years period of the study.

The results for north Georgia were essentially replicated for the larger region encompassing Tennessee, Georgia, Alabama and Mississippi. For this entire region, a stunning 75 percent of years characterized by meteorological drought in falls and winters had below-normal tornado seasons in the spring.

While the new study, which was supported by grants from NASA, offers strong clues about how spring tornado seasons form, the authors urge caution in interpreting the findings until the analysis is repeated for other locations.

Just how the connection works between fall-winter rainfall and spring tornado seasons remains unclear. One possibility is that the atmosphere uses soil moisture “memory” from the fall and winter to modify conditions suitable for severe weather. A related hypothesis is related to “soil moisture” pockets and storm initiation.

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U.N. Climate Change Conference Considers Ancient Soil Replenishment Technique in Battle against Global Warming

Former inhabitants of the Amazon Basin enriched their fields with charred organic materials-biochar-and transformed one of the earth's most infertile soils into one of the most productive. These early conservationists disappeared 500 years ago, but centuries later, their soil is still rich in organic matter and nutrients. Now, scientists, environmental groups and policymakers forging the next world climate agreement see biochar not only as an important tool for replenishing soils, but as a powerful tool for combating global warming.

Christoph Steiner, a University of Georgia research scientist in the Faculty of Engineering, was a major contributor to the biochar proposal that was submitted by the United Nations Convention to Combat Desertification last week at the United Nations Climate Change Conference meeting in Poland. The new climate change agreement will replace the Kyoto Protocol, which expires in 2012.

"The potential of biochar lies in its ability to sequester-capture and store-huge amounts of carbon while also displacing fossil fuel energy, effectively doubling its carbon impact," said Steiner, a soil scientist whose research in the Amazon Basin originally focused on the use of biochar as a soil amendment. At UGA's Biorefinery and Carbon Cycling Program, he now investigates the global potential of biochar to sequester carbon. He also serves as a consultant to the UNCCD, a sister program to the climate change convention.

Steiner explained that almost any kind of organic material-peanut shells, pine chips and even poultry litter-can be burned in air-tight conditions, a process called pyrolysis. The byproducts are biochar, a highly porous charcoal that helps soil retain nutrients and water, and gases and heat that can be used as energy.

But because the carbon in biochar so effectively resists degradation, it also can sequester carbon in soils for hundreds to thousands of years, effectively making it a permanent "sink"-a natural system that soaks up carbon dioxide from the atmosphere. Soils containing biochar made by ancient Amazon people still contain up to 70 times more carbon than surrounding soils and have a higher nutrient content. Steiner said scientists estimate biochar from agriculture and forestry residues can potentially sequester billions of tons of carbon in the world's soils.

Biochar also avoids the disadvantages of other bioenergy technologies that deplete soil organic matter, said Steiner.

"Removing crop residues for bioenergy production reduces the organic matter accumulating on agricultural fields and thus the soil organic carbon pool, which depends on constant input of decomposing plant material. In contrast, pyrolysis with biochar carbon sequestration produces renewable energy, sequesters CO2 and cycles nutrients back into agricultural fields."

"This unique system ideally utilizes waste biomass, and thus does not compete with food production," said Steiner. Currently most waste biomass decomposes or is burned in the field. Both processes release carbon dioxide stored in the plant biomass-for no other use than getting rid of it. Biochar can capture up to 50 percent of the carbon stored in biomass and establishes a significant carbon sink, as long as renewable resources are used and biochar is used as a soil amendment.

To address our world's climate change dilemma, said Steiner, "We need a carbon sink in addition to greater energy efficiency and renewable energy. Acceptance of the UNCCD proposal in Poland is a first step to make carbon trading based on biochar a reality.

"This has not only consequences for mitigating climate change, but also for agricultural sustainability, and could provide a strong incentive to reduce deforestation, especially in the tropics."

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More Variable and Uncertain Water Supply: Global Warming’s Wake-Up Call for the Southeastern U.S.

The second major drought of the last decade is a wake-up call for the Southeast United States, showing the region’s vulnerability due to its reliance on scarce supplies of fresh water.

The region has been operating under the best-case water availability for the last 50 years, during which drought conditions were relatively rare. But, the region has historically experienced regular droughts. Global warming is the future wildcard, potentially causing both more extremely dry periods and more heavy rainfall events. At the same time, warming-induced sea-level rise will increase the risk of saltwater intrusion into important groundwater aquifers.

A new report from National Wildlife Federation offers the latest scientific research on global warming and water supplies, competition for resources, demographic factors, and how to better prepare for managing the region’s water availability challenges.

“Since 1960, the region’s population doubled and water use for municipalities, irrigation, and thermoelectric power more than tripled. The Southeast is one of the fastest growing parts of the country,” said Amanda Staudt, Climate Scientist for National Wildlife Federation.

In fact, 58 of the 100 fastest growing counties in the nation are in the nine states of the Southeast. The report includes information about Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, Tennessee, and Virginia.

More Variable and Uncertain Water Supply: Global Warming’s Wake-Up Call for the Southeastern U.S. details how:

Water supplies in the Southeastern United States will be more variable and uncertain in the coming decades;
Rapidly expanding population, irrigation, and thermoelectric power use has increased water demand;
Recent droughts underscore the Southeast’s vulnerability;
The astonishing biodiversity of the Southeast is at risk; and
The Southeast should plan for increasing variability in water supplies.
Strategies for meeting the increasing demand for water in the Southeast have not typically accounted for the regular occurrence of drought, as illustrated by recent droughts. During 2007 alone, crop losses are estimated at more than $1.3 billion and wildfires ravaged 600,000 acres in Georgia and Florida.

Climate changes will affect water supplies to communities and put the amazing biodiversity of the Southeast at risk. The river basins of the Southeast are globally renowned for fish, mussels, salamanders and other freshwater species, many of which are already imperiled. Climate change—and the increasingly extreme weather patterns it brings—now poses new threats to these species.

“Global warming presents new challenges for managing America’s water resources, especially in our southeastern states,” added Dr. Staudt. “To prevent the worst impacts of climate change and limit the impacts on communities and wildlife, we must reduce global warming pollution.”

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UGA Study Helps Clarify Role of Soil Microbes in Global Warming

Current models of global climate change predict warmer temperatures will increase the rate that bacteria and other microbes decompose soil organic matter, a scenario that pumps even more heat-trapping carbon into the atmosphere. But a new study led by a University of Georgia researcher shows that while the rate of decomposition increases for a brief period in response to warmer temperatures, elevated levels of decomposition don’t persist.

“There is about two and a half times more carbon in the soil than there is in the atmosphere, and the concern right now is that a lot of that carbon is going to end up in the atmosphere,” said lead author Mark Bradford, assistant professor in the UGA Odum School of Ecology. “What our finding suggests is that a positive feedback between warming and a loss of soil carbon to the atmosphere is likely to occur but will be less than currently predicted.”

Bradford, whose results appear in the early online edition of the journal Ecology Letters, said the finding helps resolve a long-standing debate about how unseen soil microbes respond to and influence global climate change. Other scientists have noted that the respiration of soil microbes returns to normal after a number of years under heated conditions, but offered competing explanations. Some argued that the microbes consumed so much of the available food under heated conditions that future levels of decomposition were reduced because of food scarcity. Others argued that soil microbes adapted to the changed environment and reduced their respiration accordingly.

Bradford and his team, which included researchers from the University of New Hampshire, the Marine Biological Laboratory at Woods Hole, Duke University and Colorado State University, found evidence to support both hypotheses and revealed a third, previously unaccounted for explanation: The abundance of soil microbes decreased under warm conditions.

“It is often said that in a handful of dirt, there are somewhere around 10,000 species and millions of individual bacteria and fungi,” said study co-author Matthew Wallenstein, a research scientist at Colorado State University. “Our findings add to the understanding of how complex these systems are and the role they play in feedbacks associated with climate change.”

The researchers studied soil microbes at Harvard Forest in Massachusetts, the site of a soil warming experiment that began in 1991. Scientists took soil samples from two plots, one in which buried cables heat the soil to five degrees Celsius above the ambient soil temperature (a condition that is expected to occur around 2100) and a control condition in which cables are buried but not producing heat.

In the first set of experiments, the scientists compared microbial respiration in the two groups and found lower rates of decomposition in the heated plots. This finding supported the idea that respiration decreases after a few years of warming, but didn’t explain whether the cause was substrate depletion in the warmer soils or adaptation by the microbes.

In the next set of experiments, they added the simple sugar sucrose to both sets of soils to alleviate any food limitation for the microbes. They found that microbes from both conditions increased their respiration, but that the increase was greater in the unheated control soils than in the heated soils. “That finding told us that substrate depletion played a role,” Bradford said, “but it also told us that there were other factors involved.”

The researchers then measured microbial biomass and found that there were fewer microbes in the heated soils. To test whether thermal adaptation occurred, they measured respiration while keeping temperature constant. They found that respiration rates were indeed lower in the heated versus the control soils, even when adjusting for microbial biomass.

Wallenstein pointed out that the study is among the first to demonstrate that microbes, like many plants and animals, can adapt relatively quickly to changes in climate. “This research presents a new challenge to scientists trying to predict effects of climate change on forest ecosystems because it shows that these soil microbial communities are very dynamic,” Wallenstein said. “We cannot simply extrapolate from the short-term responses of soil microbes to climate change, since they may adapt over the longer-term.”

Bradford notes that there is still much to be learned about how soil microbes respond to global warming. His team is currently working to understand whether the reduced microbial respiration in heated soils is caused by the adaptation of individual microbes, by shifts in species composition or a combination of the two factors. He warns against minimizing the role of soil microbes in global warming, even though his findings suggest that current models overstate their contribution.

“Although our results suggest that the impact of soil microbes on global warming will be less than is currently predicted,” Bradford said, “even a small change in atmospheric carbon is going to alter the way our world works and how our ecosystems function.”

The research was funded by the U.S. Department of Energy.

By Sam Fahmy
University of Georgia

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