2020-04-02_Science_Illustrated

their replacement, known as GRACE-FO.
These new satellites can measure the
microwaves that reveal water motion in the
ground far more accurately than their
predecessors, providing us with an even
more accurate picture of how ground water
changes are taking place
in different parts of
the world.

Offenders named and shamed

Day Zero does not only threaten small coun-

try towns. Cape Town in South Africa, a city

of 4.5 million people, only just escaped Day

Zero in 2018. According to scientists from

Imperial College London and the University

of Cape Town, the city was saved by reducing

the water pressure in the pipes, introducing

fees for excessive consumption, and install-

ing meters that automatically shut off the

water supply of ‘offenders’. The local author-

ities even introduced a controversial website

known as the Cape Town Water Map,

complete with colour codes indicating the

households that complied with restrictions

and those that did not.

In Sydney, as elsewhere, desalination has

been adopted as part of a long-term solution.

Some 97% of the planet’s water resides in the

the vast ocean that

covers 71% of its surface. Nations such as

Malta and the Maldives already harvest all

their water from the ocean through desali-

nation. But current methods are energy

intensive, with the side-effect of pumping

CO 2 into the atmosphere. Desalination also

leaves highly concentrated brine behind as

a waste product which is harmful to the

marine environment if released back into

the ocean. Scientists are working on solu-

tions where desalination can be powered by

cleaner energy sources such as solar cells or

wave power, and on expanding uses for the

brine in industrial processes, instead of

being released back into the ocean.

Other new technologies might offer hope,

with new techniques to extract drink-

ing water from the ocean, the air,

and from human waste.

Colours reveal

water level

4

A GPS determines

the satellites’

positions with

an accuracy of a few

centimetres, so a map of

the ground water can be
made. Red indicates falling

ground water levels –

with Australia among the

many nations affected.

PROBLEM

GROUND^ WATE

R^

LEVEL^ CHANG

ES^

INFLUENCE^

SATELLITES

.

When you

see a blue,

cloudless sky, dry soil,

and dead vegetation,

it is hard to be positive.

TRACY DOBIE

MAYOR, SOUTHERN

DOWNS, AUSTRALIA

100mm

FALL

100mRISEm

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