What Climate Change Means for Tennessee Page: 1 of 2
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Tennessee's climate is changing. Although the average
temperature did not change much during the 20th century,
the state has warmed in the last 20 years. Average
annual rainfall is increasing, and a rising percentage of
that rain is falling on the four wettest days of the year. In
the coming decades, the changing climate is likely to
reduce crop yields, threaten some aquatic ecosystems,
and increase some risks to human health. Floods may be
more frequent, and droughts may be longer, which would
increase the difficulty of meeting the competing demands
for water in the Tennessee and Cumberland rivers.
Our climate is changing because the earth is warming.
People have increased the amount of carbon dioxide in
the air by 40 percent since the late 1700s. Other heat-
trapping greenhouse gases are also increasing. These
gases have warmed the surface and lower atmosphere of
our planet about one degree (F) during the last 50 years.
Evaporation increases as the atmosphere warms, which
increases humidity, average rainfall, and the frequency of
heavy rainstorms in many places-but contributes to
drought in others.
Natural cycles and sulfates in the air prevented much of
Tennessee from warming during the last century. Sulfates
are air pollutants that reflect sunlight back into space.
Now sulfate emissions are declining, and the factors that
once prevented Tennessee from warming are unlikely to
Temperature change (*F):
-1 -0.5 0 0. 1 1.5 2 2.5 3 3.5
Rising temperatures in the last century. Tennessee has warmed
less than most of the United States. Source: EPA, Climate Change
Indicators in the United States.
Changing Water Availability
Annual precipitation in Tennessee has increased approximately
5 percent since the first half of the 20th century. But rising tem-
peratures increase evaporation, which dries the soil and decreases
the amount of rain that runs off into rivers. Although rainfall during
spring is likely to increase during the next 40 to 50 years, the
total amount of water running off into rivers or recharging ground
water each year is likely to decline 2.5 to 5 percent, as increased
evaporation offsets the greater rainfall. Droughts are likely to be
more severe, because periods without rain will be longer and very
hot days will be more frequent.
Flooding is becoming m
more severe in the A A
Southeast. Since -
1958, the amount of I
precipitation falling . I .
during heavy rain-
storms has increased
by 27 percent in
the Southeast, and
the trend toward
rainstorms is likely to
continue. To prevent
serious floods, the
Authority (TVA) and
the U.S. Army Corps
of Engineers release
water from the
reservoirs behind The Cumberland River flooded parts of Nashville in
dams they operate 2010, damaging many businesses, including the
Grand Ole Opry. Credit: USGS.
before the winter
flood season. Doing so lowers water levels and provides a greater
capacity for the reservoirs behind those dams to prevent flooding.
Nevertheless, the dams cannot prevent all floods. In May 2003,
for example, heavy rains exceeded TVA's dam capacity, flooding
low-lying areas in Chattanooga and other parts of Hamilton County;
in 2010, high flows in the Cumberland River flooded Nashville.
Here’s what’s next.
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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/m1/1/?rotate=90: accessed December 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.