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NEWS | FEATURES | RESILIENCE

drils from the nearby Bay of Bengal. At 66, largest drainage, which flows into the Bay
Sardar remembers conditions before the of Bengal. Monsoon rains routinely put a
wall, when flooding during very high tides quarter of the country underwater. The
was the norm here. Until that fateful day in flooding brings hardship, but it also nur-
2009, the flooding appeared to be banished. tures the rice that feeds one of the most
Bangladesh, a vast river delta that barely densely populated nations on Earth.
rises above the sea at the best of times, is The country itself is born from those riv-
buffeted by natural forces including flood- ers. An estimated 1 billion tons of sand and
ing rivers and cyclones blowing in from silt flow downstream every year and settles
the bay. Over decades, the country has de- in the delta, counteracting relentless ero-
veloped defenses: warning systems, storm sion. Geologically, Bangladesh is a giant
shelters, salt-resistant crops, and 139 pol- sandbox, 90 meters deep in places.
ders near the coast—a 5700-kilometer net- Ainun Nishat knows those rivers with
work of walls to protect farmland from an intimacy earned by spending 4 decades
inundation. But humanmade infrastructure studying them. Sitting in his third-floor
is not infallible and can cause problems of office at BRAC University’s Centre for
its own. That’s starkly apparent across the Climate Change and Environmental Re-
country’s polders, which have disrupted a search in Dhaka, the engineer describes
fragile standoff between water and land and how good intentions have brought
are now straining to hold back the water. unexpected consequences.
As climate change compounds that threat Polders—the name is borrowed from
with rising seas and stronger storms, Ban- the Dutch, who used a similar strategy to
gladeshis who have spent years building Polder 32 resident Jaharul Sardar, who narrowly carve farmland from marshes—were first
barricades are considering what was once escaped a 2009 flood, remembers when the walls built in Bangladesh in the 1960s. But al- Downloaded from
unthinkable: letting the water in. It’s re- ringing his home kept him safe. though polders allow more intensive farm-
silience by bending, not resisting. And it’s ing, Nishat says, “They are also a problem.”
tougher to do than it sounds. home to 165 million people, experiments The walls impede the natural movement of
Other countries are trying similar ap- in resilience underscore the challenges of water and sediment. Rivers now funneled
proaches. Vietnam recently adopted plans rearranging a crowded landscape. “You between artificial embankments are filling
to allow more flooding in the upper reaches can’t remove the polders now,” says with silt. Land inside the polders, starved
of the Mekong delta. The Netherlands, re- Anisul Haque, a hydraulic modeler at the of new soil that would otherwise flow in,
nowned for building some of the world’s Bangladesh University of Engineering and is sinking. Polders are turning into bath- http://science.sciencemag.org/
most sophisticated sea walls, is adapt- Technology (BUET) in Dhaka who studies tubs that, if something goes wrong, can fill
ing suburbs for controlled river flood- coastal flooding. “So what can you do?” with water.
ing. On the other end of the spectrum sits Meanwhile, sea level is projected to rise
Indonesia, which is planning a $40 billion, RIVERS ARE THE MIDWIVES of Bangladesh. 0.4 to 1.5 meters on the Bangladesh coast
40-kilometer-long sea wall to shield its cap- The Ganges and Brahmaputra pour from by 2100. Episodes of extremely high water
ital city, Jakarta, from the Java Sea. the Himalayas and converge with the driven by storms and tides, which today
Here in a country the size of Iowa that’s Meghna River to form the world’s fourth occur once a decade, will probably happen

NATURE’S STRATEGIES on March 1, 2018
Squirrels with a rainy day fund

currying around the South Dakota prairie, 13-lined ground
squirrels (pictured, right) mark the approach of winter
by bingeing. By the time a squirrel holes up to hibernate, its
weight will have soared by about 40%, thanks to extra fat
S that will tide the creature over until spring.
During droughts, migrations, bleak winters, and other chal-
lenges, organisms often face times when resources are scarce.
To get by, the ground squirrel, like many other creatures, stock-
piles resources to use later. It can gain more than 2% of its body
weight in a single day as it gorges on seeds, grasshoppers, and
other delicacies.
But the tactic has downsides. A roly-poly rodent is easier prey
for a hawk or coyote. The rainy day fund also can run out prema- PHOTOS: (TOP TO BOTTOM) TANMOY BHADURI; GRACHEVA LAB
turely. So once a squirrel is nice and tubby, it enters hibernation, ments. But somehow, the squirrel dodges the health problems
slashing its energy expenditure by 90%. Its body temperature that plague obese people. Although it develops some of the
drops to just above freezing and its heart rate falls to as low as metabolic defects of type 2 diabetes, the animal isn’t sick. And
5 beats per minute, down from the usual 350 to 400. by spring, it is lean and spry and ready to begin the cycle again.
Packing on the fat requires metabolic and behavioral adjust- —Mitch Leslie

982 2 MARCH 2018 • VOL 359 ISSUE 6379 sciencemag.org SCIENCE
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