Space
6increased tidal floods, the moon’s oscillating
orbit—a tide-altering phenomenon scientists have
studied since 1728—also contributes to the rise
in floods. With everyday tides, the moon pulls
on Earth, causing the water to bulge. This pro-
tuberance—which can stretch to as much as 55
feet—marches around the planet as it rotates,
causing a rise-fall pattern in water levels. But the
moon’s orbit also wobbles by a total range of about
10 degrees while circling Earth. Picture a spinning
coin on a tabletop: right before the coin falls to the
table, it takes on a wobbly movement, spinning but
also undulating up and down. This movement fol-
lows an 18.6-year pattern. For half of the cycle, the
wobble shrinks the difference between high and
low tide. The other half of the cycle amplifies tides,
meaning high tides are higher and low tides are
lower. In the early 2030s, the moon’s tidal suppres-
sion cycle will head into amplification.
While it was obvious tidal f looding has become
more common around the country, says Thomp-
son, it was unclear how bad flooding might be in
the next few decades. To answer that, the team col-
lected data from 89 coastal tide gauges across the
U.S. and studied all the possible changes that could
occur over time: tides, nodal moon cycles, sea level
rise, and natural f luctuations like El Niño events.
The researchers predict a rapid increase in tidal
f looding around the mid-2030s. But it’s the rate of
change in some locations that was eye-opening for
the team, says Thompson.
For instance, La Jolla, California, near San Diego,
will remain steady at about 20 f looding events per
year for the next decade, but from 2033 to 2043
“you get this really rapid change,” says Thompson.
The f looding days almost triple as sea levels and
tide amplification from the moon cross a tipping
point where f looding transitions from occasional
to commonplace. The team also generated models
for Honolulu, Boston, and St. Petersburg, Florida,
which saw similar dramatic increases.
These floods also tend to occur in clusters.
Thompson compared tidal f lood forecasts to hur-
ricane season predictions. However, tidal f loods
are dependent on a number of conditions, such as
weather, elevation, and local sea levels, and research
revealed that different locations around the U.S.
will experience these clusters at different times.
Thompson calls tidal f looding a threshold-based
problem: You don’t see it until it creeps into view
and affects your daily life. “The real impact of this
wobble is not catastrophic f looding—we’re talking
about inches,” he says.
Runoff from overwhelmed roads and storm
drains can create troublesome puddles, says
Miyuki Hino, Ph.D., an environmental social sci-
entist at Universit y of North Carolina, Chapel Hill,
who was not involved in this study. Flood waters can
pick up waste from failed septic tanks, along with
oil and carcinogenic heav y metals that linger on the
streets. “There are definitely health reasons why
you would want to avoid any amount of water,” she
says. Wading through polluted waters can lead to
skin rashes, infections, and gastrointestinal issues.
Rising tide waters can also seep into privately
owned wells, contaminating fresh sources of drink-
ing water and leading to future health problems.
Coastal communities have about a decade to
update their roads, sewage systems, and sea walls
before tidal f looding increases exponentially,
according to this research. “We can’t wait until it
starts happening to do it,” says Thompson. “We
have to start now.”FLOODING DAYS ALMOST
T R I P L E A S S E A L E V E L S A N D
TIDE AMPLIFICATION FROM THE
MOON CROSS A TIPPING POINT.
PROTECT YOUR
HOME FROM AN
EXTRA-HIGH TIDE
▶ KNOW YOUR RISK
The first step in fortifying your home
from flooding is to understand your risk.
Do you live in a flood plain? Has your
neighborhood flooded in the past? Sites
like First Street Foundation’s FloodFactor
can help you figure that out.▶ PUT IN A SUMP PUMP
Installing a sump pump in
low-lying areas—like your
basement—diverts excess
water into a well or specialized
drainage system to prevent an
unwanted indoor pool.▶ GET YOUR HVAC
OFF THE GROUND
Lifting your entire house is a tall
order, but raising your electrical,
plumbing, and HVAC systems
can save thousands of dollars in
costly repairs down the line.30 November/December 2021