Research Forecasts Increased Chances For Stormy Weather
Pastor Dale Morgan
Research Forecasts Increased Chances For Stormy Weather*
by Staff Writers
West Lafayette IN (SPX) Dec 05, 2007
Researchers who study severe weather and climate change joined forces to
study the effects of global warming on the number of severe storms in
the future and discovered a dramatic increase in potential storm
conditions for some parts of the United States. The Purdue
University-led team used climate models to examine future weather
conditions favorable to formation of severe thunderstorms - those that
produce flooding, damaging winds, hail and sometimes spawn tornadoes.
"It seems that areas in the U.S. prone to severe thunderstorms now will
likely have more of them in the future," said Robert Trapp, the Purdue
associate professor of earth and atmospheric sciences who led the
research team. "We can't predict individual storms, but we can project
the number of days with conditions conducive to storm formation."
The study found that by the end of this century the number of days that
favor severe storms could more than double in locations such as Atlanta
and New York. The study also found that the increase in storm conditions
occurs during the typical storm seasons for these locations and not
during dry seasons when such storms could be beneficial. The findings
will be published online this week in the Proceedings of the National
Academy of Sciences.
"Hopefully, the results of this work will help raise awareness of the
changing weather and increase long-term preparations for severe weather,
such as emergency response plans," Trapp said. "Areas close to the main
sources of humidity, primarily the Gulf of Mexico and the Atlantic, show
the most significant increases in potential for storms."
Noah Diffenbaugh, who collaborated with Trapp on this study, said the
research findings illustrate how a relatively small increase in
temperature can have a dramatic effect on day-to-day weather.
"It is easy to look at global warming just in terms of the average
increase in temperature, but the effects are much more far-reaching,"
said Diffenbaugh, who is a member of Purdue's Climate Change Research
Center. "We know from the past that extremes in weather and individual
severe storms can be devastating. This study makes a strong statement
that a few degrees of global warming could make these severe events much
more common than they are today."
The study results were compared to current environmental conditions and
past environmental conditions shown to produce severe thunderstorms.
Harold Brooks, a member of the research team and researcher at the
National Severe Storms Laboratory in Norman, Okla., said bringing
together experts in climate modeling with experts in severe storms to
examine how climate change may affect weather was a new approach to a
problem important to both groups of researchers.
"Identifying the environmental conditions that favor certain weather has
been at the heart of forecasting research," Brooks said. "We applied
that forecasting model to the data from climate change research. It is
the same way your local forecaster predicts tomorrow's weather, but we
took it out over a long time period. Although we can't say if a storm
will occur, we can tell from the data how severe a storm will be if it
occurs."
Brooks said individual storms were not examined in this study because
they are too small for the current climate models to analyze and, in
addition to certain environmental conditions, a trigger is needed to
initiate a storm.
"We know the basic ingredients for making a severe thunderstorm are
warm, moist air near the ground, cold, dry air higher above the ground,
winds that increase in intensity from the ground up and a storm
trigger," he said. "We have most of the recipe, and this is a good first
look, but whether or not storms will initiate is an unknown."
Some triggers, such as topography, will remain constant. Others, such as
storm fronts, could be changed by future global weather conditions, he said.
Research suggested global warming would lead to an increase in humid air
that fuels severe thunderstorms, however, it also suggested global
warming would reduce strong winds that contribute to the storms.
"This study was the first to include both of these key factors in order
to see which would have a greater influence on overall environmental
conditions," said Diffenbaugh, who also is an assistant professor of
earth and atmospheric sciences at Purdue. "The result was a general
increase in days more favorable to storm creation. It appears that the
increase in warm, humid air near the surface outweighs the reduction in
strong winds higher in the atmosphere."
In addition, the study showed a strong seasonal and regional variation
in the effects of climate change.
"Some areas were only affected slightly, while others more than doubled
the chance for severe thunderstorms," Diffenbaugh said. "Also, the
storm-favorable conditions appear to occur during the same seasons as
they do today, with an extension of the season in some areas. This
increases the seasonal extremes, as opposed to more storms spread
throughout the year. It is essentially a longer, more intense storm
season - sort of a feast or famine."
The team, which also included Michael Baldwin, a Purdue assistant
professor of earth and atmospheric sciences, and Purdue research
assistant Eric Robinson, looked at weather conditions over the U.S.
landmass from the middle to latter part of 21st century, using the
regional climate model and three global climate models.
Diffenbaugh said the team used multiple climate models to achieve
thorough research results and to reduce the impact of an idiosyncrasy of
an individual model.
"The fact that there is so much agreement between the different models
increases our confidence in the findings," he said.
Pairing the high resolution of the regional model with multiple global
climate models achieves a greater depth of research results, Diffenbaugh
said.
Climate models are sophisticated computer programs that incorporate as
many details about the complex workings of the environment as possible.
Hundreds of dynamic processes, such as ocean currents, cloud formations,
vegetation cover and the increase in atmospheric greenhouse gases, are
included. The models produce data of the net effects for square-shaped
plots over the Earth's surface. The smaller these squares are, the
better the resolution the model can provide.
A model must factor in so many changing variables that a full analysis
can require months of nonstop computational effort. The Rosen Center for
Advanced Computing on Purdue's campus provided the powerful computing
required for this study.
Jeremy Pal, one of the lead developers of the regional climate model
used in this study and a co-author of the paper, said the regional
climate model offers the most detailed picture available today of what
is happening across the United States.
The regional model divides the landmass of the United States into a grid
of cells spaced 25 kilometers, or 15.6 miles, apart and provides
information about the conditions occurring for each cell. This adds
detailed information to the data from the global models.
"For example, for Indiana the regional model gives information for
specific counties, while a global model would have one set of average
data for the entire state," said Pal, who also is a professor of civil
engineering at Loyola Marymount University and a member of the
Intergovernmental Panel on Climate Change and the Abdus Salam
International Centre for Theoretical Physics in Trieste, Italy. "The
regional model has a higher resolution and provides information on the
tens-of-miles scale. Global models give data on the hundreds-of-miles
scale. The use of four different models in this study makes the results
more robust."
Trapp said the next step is to use even higher-resolution models to
explicitly study thunderstorms, which can address some of the
limitations of the current research.
"One question is whether severe storms in the future will be stronger
than those of today," he said. "Another is how often the future storms
will spawn tornadoes."
This work stems from the Climate and Extreme Weather Initiative within
the Department of Atmospheric Sciences at Purdue and the Purdue Climate
Change Research Center. The National Science Foundation supported this
research.