ings for Mumbai’s water levels from 1994 to 2005
or after 2010. The Maharashtra government says
local sea levels are rising 1. 2 millimeters a year,
based on those incomplete data.
In 2017, a team from NASA’s Jet Propulsion
Laboratory, or JPL, launched an app to demonstrate how melting ice sheets would affect
293 major port cities across the globe. The
scientists measured the melt using NASA’s GRACE
satellites, which detect gravity changes from the
ice loss. To boost accuracy, the team recently
added a component to the app that accounts for
the fact that water expands as it warms.
Still, true sea level rise projections involve com-
plex computer modeling of overlapping systems.
The JPL app doesn’t do that. “So it’s risky” to put
too much stock in the numbers it spits out, says
JPL sea level and ice supervisor Eric Larour. “But
the real risk is that people underestimate that this
is going to get worse.”
For Mumbai, the JPL app foresees at least
another 2.9-centimeter rise in coastal water
in 10 years — and 14. 4 centimeters in the next
Those estimates could soon be revised upward.
Larour’s team plans one more update to include
research published in the June 13 Nature show-
ing that Antarctic ice sheets are melting three
times as fast as they were 25 years ago (SN: 6/7/18,
p. 6). That much melting, Larour says, is “a big,
The JPL team hopes to have a single, detailed
modeling app for the world within two years,
using NASA’s high-resolution satellite images of
water levels and of land gradients, “so that peo-
ple can use it in active mitigation policy,” Larour
says. “A lot of areas at risk in South Asia — India,
Bangladesh, Sri Lanka — and across Asia don’t
have the information to do this.”
Economic gains lost
It’s not easy to find a coastal megacity taking
decisive and effective action against future flood
risks. Bangladesh has long built coastal sea walls
of stacked mud, which may help prevent ocean
storm surges from cascading inland to Dhaka.
Fast-sinking Jakarta is working on its own giant
sea wall as well. But walls won’t help Mumbai;
they would prevent rain-driven freshwater floods
from draining out after the monsoon.
Massive structural engineering is not the answer.
Many scientists suggest that cities lighten their
burden on the land by maintaining natural coastlines, protecting sand dunes and preserving forests or even growing more of them. At the least,
cities should refrain from making development
decisions that will make things worse, such as
paving over water-absorbent soils or building on
natural floodplains. Governments can also improve
storm drains, offer voluntary relocation packages
or even consider introducing ferries rather than
trying to raise or maintain existing roads.
“We need to evolve to a situation where we’re
more congruent with nature, rather than fighting
it,” says urban planning expert Amrita Daniere of
the University of Toronto, codirector of the Urban
Climate Resilience in South East Asia Partnership.
The group is aiding flood-preparation efforts in so-called second-tier cities, each still home to millions
of people. “It’s too difficult to influence policy and
practice in a megacity,” she says.
There are cities like Bangkok, the capital of
Thailand, that may be just too vulnerable. Built
atop an estuary feeding into the Gulf of Thailand,
the city — also sinking — is on track to go mega by
2030. “It wouldn’t shock me if they had to move
the capital in 20 years,” Daniere says.
Cities that don’t own up to their vulnerability
risk squandering economic gains made in the last
few decades, economists say. Some cities could
face a financial reckoning even before flooding
worsens. The mere notion of increasing risk is
enough to spook investors.
“That could have a domino effect on other cities,
with bigger consequences for the global financial
system,” says Gregory Unruh, an expert in sustainable business strategy at George Mason
Sea rise scenarios
Global sea level rise
could be kept to a
lower projection range
(blue) if humankind
curbs greenhouse gas
emissions. Today, the
world is on track for a
much higher level of rise
(tan). SOURCE: IPCC 2014
2040 2060 2080 2100
Global mean sea level rise projections (relative to 1986–2005)