What Climate Change Means for Tennessee Page: 2 of 2
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Droughts, Navigation, and Hydroelectric Power
Droughts also pose challenges for water management. If the
spring is unexpectedly dry, reservoirs may have too little water
during summer. During droughts, TVA and the Corps of Engineers
release water from dams to keep the Tennessee and Cumberland
rivers navigable. These rivers support $35 billion in annual
shipping. The agencies try to keep channels at least eleven
feet deep, because lower river levels can force barges to carry
smaller loads, which increases transportation costs. During the
drought of 2007, however, TVA could only release enough water
to keep some channels nine feet deep. This release meant that
lake levels were lowered tens of feet, which caused problems for
recreational swimming and boating. If droughts become more
severe, TVA and the Corps of Engineers will face this type of
problem more often.
Dry years diminish the amount of electricity that TVA can produce
from its 19 hydroelectric dams in Tennessee, which provide
12 to 15 percent of the electricity produced in the state.
During the 2007 drought, TVA's hydroelectric plants produced
30 percent less than normal, which forced TVA to meet demand
by using more expensive fuel-burning power plants.
Two views of a boat ramp in Douglas Lake during the 2007 drought. The lake
is nearly dry and the 330-foot ramp is completely out of the water.
Changing the climate can harm aquatic ecosystems. Warmer
water lowers the level of dissolved oxygen in surface water,
which can severely limit fish populations. Because fish cannot
regulate their body temperatures, warmer water can make a
stream uninhabitable for fish that require cooler water. Warmer
temperatures can also increase the frequency of algal blooms,
which can be toxic and further reduce dissolved oxygen. Summer
droughts may amplify these effects, while periods of extreme
rainfall can increase the impacts of pollution on streams.
Changing the climate will have both beneficial and harmful
effects on agriculture. Longer frost-free growing seasons and
increased concentrations of atmospheric carbon dioxide tend to
increase yields for many crops during an average year. But more
severe droughts and more hot days are likely to reduce yields,
especially in the western half of Tennessee: 70 years from now,
that part of the state is likely to have 15 to 30 more days with
temperatures above 95 F than it has today. Even on irrigated
fields, higher temperatures are likely to reduce yields of corn,
and possibly soybeans. Warmer temperatures are also likely to
reduce the productivity of dairy and other cattle farms.
Higher temperatures and changes in rainfall are unlikely
to substantially reduce forest cover in Tennessee, but the
composition of those forests may change. Forests cover about
half the state, dominated by oak and hickory trees, and the
forest products industry employs 180,000 people. Although more
droughts would reduce productivity, longer growing seasons
and increased carbon dioxide concentrations could more than
offset those losses. Nevertheless, climate change is likely to
increase the damage that certain insects and diseases cause in
Hot days can be unhealthy-even dangerous. High air tem-
peratures can cause heat stroke and dehydration, and affect
people's cardiovascular and nervous systems. Certain people are
especially vulnerable, including children, the elderly, the sick,
and the poor. Warmer air can also increase the formation of
ground-level ozone, a key component of smog. Ozone has
a variety of health effects, aggravates lung diseases such as
asthma, and increases the risk of premature death from heart or
lung disease. EPA and the Tennessee Department of
Environment and Conservation have been working to reduce
ozone concentrations. As the climate changes, continued
progress toward clean air will become more difficult.
The Smoky Mountains have always had a natural blue haze. But air pollution
has increased that haze, and higher ozone levels could increase it further.
This photo shows how haze obscures the view from the Look Rock Tower in
Great Smoky Mountains National Park. Credit: National Park Service.
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United States. Environmental Protection Agency. What Climate Change Means for Tennessee, pamphlet, August 2016; United States. (digital.library.unt.edu/ark:/67531/metadc949213/m1/2/: accessed May 27, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.