New research shows that dry weather is coming on more quickly than before, with little advance warning.
From: Grist
May 16, 2022 – By Diana
Kruzman -- September in Oklahoma is typically a rainy season, when farmers take
advantage of the state’s third-wettest month to plant winter wheat. But last
year, many were caught off guard by abnormally dry weather that descended
without warning. In the span of just three weeks, nearly three-quarters of the
state began experiencing drought conditions, ranging from moderate to extreme.
Fast-moving droughts
like this one are developing more and more quickly as climate change pushes
temperatures to new extremes, recent research indicates — adding a new threat
to the dangers of pests, flooding, and more long-term drought that farmers in
the U.S. already face. Known as “flash droughts,” these dry periods can
materialize in as quickly as five days, often devastating agricultural areas
that aren’t prepared for them.
During last year’s
drought in Oklahoma, Jonathan Conder, a meteorologist for a local news station
in Oklahoma City, marveled at the speed and severity of the event. Tulsa, the
state’s second-largest city, went 80 days without more than a
quarter-inch of rain, while temperatures in southwestern Oklahoma climbed
into the triple digits.
“This is huge for
Oklahoma,” Conder said during his broadcast on October 1. “Our
agricultural community, the farmers who plant wheat, they may not even be able
to plant if they don’t get two inches of rain.”
The threshold for
drought conditions differs by location, with the U.S. Drought Monitor using
data on soil moisture, streamflow, and precipitation to categorize droughts by
their severity. While typical droughts develop over months as precipitation
gradually declines, flash droughts are characterized by a steep drop in
rainfall, particularly during a season that normally receives plenty, along
with high temperatures and fast winds that quickly dry out the soil. They can
wither crops or prevent seeds from sprouting, delaying or diminishing the
harvest.
Now, flash droughts are
coming on faster and faster — making them more difficult to predict and more
damaging, according to a recent study published in Nature Communications. The
research, from scientists at the University of Texas and Hong Kong Polytechnic
University, found that in the last 20 years, the percentage of flash
droughts developing in under a week increased by more than 20 percent in the
Central United States.
“There should be more
attention paid to this phenomenon,” said Zong-Liang Yang, a geosciences
professor at the University of Texas and one of the study’s co-authors, as well
as “how to actually implement [these findings] into agricultural
management.”
Scientists have long
warned that warming temperatures and shifting rainfall patterns due to climate
change pose a threat to the cash crops of the Midwest and Great
Plains, primarily corn, wheat, and soybeans. But flash droughts are a
relatively new area of research, Yang said, with the term gaining usage only in
the last couple of decades.
The increase in their
severity and frequency, though, is already being felt across the U.S. In 2012,
a flash drought struck the Central U.S. in the middle of the growing
season, causing an estimated $31.2 billion in crop losses. Another
flash drought hit Montana, North Dakota, and South Dakota in the spring of
2017, leading to more than $2.6 billion in agricultural losses, along with
“widespread wildfires, poor air quality, damaged ecosystems, and degraded
mental health,” according to a study published in the Bulletin of the
American Meteorological Society.
Flash droughts are also
a global problem, with Brazil, India, and multiple countries in Africa facing
the worst impacts. In 2010, a flash drought followed by a heatwave in
Russia temporarily halted wheat exports, a major disruption for
communities across the Middle East that depend on the country’s grain.
The damage flash
droughts can cause depends on the crop and the time of year, said Dennis Todey,
director of the Midwest Climate Hub for the U.S. Department of Agriculture.
Corn is the most vulnerable during its pollination season in mid-summer, while
soybeans are affected in August and wheat during planting season in the
spring.
Drought is a natural
part of the climate in this region, Todey said, particularly in the western
part of the Corn Belt — a region that encompasses the Midwest and the Great
Plains. Many farmers have learned to adapt and integrate dry conditions into
their planting cycles. But what makes flash droughts so dangerous is their
rapid onset, Todey said, leaving little time for agricultural producers to
prepare.
“Drought most times is
thought of as a slow-starting and then a slow-stopping event,” Todey said. “In
a flash drought setting … instead of just starting to dry out gradually, you
have surfaces that dry out very quickly, you have some newly planted crops that
are starting to be stressed more quickly.”
Many farmers don’t know
if they’re starting to experience a drought, though, until expected rains fail
to appear. Rainfall in mid-October helped ease the flash drought that began in
Oklahoma in September, but after that a much longer drought set in, said Keeff
Felty, a fourth-generation wheat and cotton farmer in the southwestern part of
the state. As a result, some of his crop never germinated, while his overall
yield dropped when it came time for the harvest.
“There’s a lot of
information out there, and you have to avail yourself of what works best for
you, but you also have to be prepared for it to go totally south,” Felty said.
“Nobody saw [the drought] coming, and it’s just a fact of the weather that we
don’t have any control over it. It’s just life.”
Typical droughts can
last months or even years — the western U.S. is currently experiencing its
third decade of “megadrought” — while flash droughts can end more quickly,
within weeks or months, Yang said. And they can hit in relatively wet areas,
including the eastern part of the country, where drought conditions are much
more rare than in the West.
The main reason they’re
occurring faster, Yang said, is climate change. As the air warms, it can lead
to more evaporation and dry out the soil. This can occur even in areas that can
expect to receive more rainfall overall because of climate change, because
scientists project that rainfall will be unevenly distributed — falling in more
extreme events and making other parts of the year drier.
“Every [recent] decade
we have seen is the warmest decade in history,” Yang said. And with the world
on track to blow past a global temperature that’s 1.5 degrees Celsius (2.7
degrees Fahrenheit) higher than the pre-industrial average, he expects to see
both flash droughts and longer droughts occurring more frequently.
Researchers are working
on improving their models to better predict flash droughts, Yang said, with the
help of new technologies such as more granular satellite monitoring and machine
learning. The main marker they look for is high rates of evapotranspiration,
when plants suck up water from the soil and then release it into the air
through their leaves — a process that accelerates with high temperatures and
winds and can be monitored with special cameras that detect fluorescence, or
the heat emitted by plants.
If farmers can know
when to anticipate a flash drought, Todey said, they can skip or delay
planting, or reduce their fertilizer usage when they know a crop won’t grow.
They can also adjust their planting schedule and take better care of their soil
by minimizing tillage, which dries it out even more. But with less and less
time to prepare for flash droughts, Todey said, some may have to make difficult
choices about whether to plant at all.
“Agricultural producers
naturally adapt to changing conditions,” Todey said. “But eventually there
comes a point where [losses] become more frequent. People start going, ‘Okay,
this isn’t working.’”
https://grist.org/agriculture/flash-droughts-are-midwests-next-big-climate-threat/
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