The Economist - UK (2021-11-20)

The Economist November 20th 2021 61

China

Flood­proofingcities

Soaking it up

L

ocals havea saying: “When the Budd­

ha’s  feet  are  washed,  Leshan  cannot

sleep.” The city in the south­western prov­

ince  of  Sichuan  has  reason  to  be  fearful.

Leshan lies at the confluence of three trib­

utaries of the Yangzi river. Centuries ago its

residents  carved  a  stone  statue  of  the

Buddha into a cliff face. It towers 70 metres

high,  overlooking  the  swift  currents.  In

August  2020  its  giant  toes  were  bathed  in

river water for the first time since the Com­

munist  Party  seized  power  in  1949.  Thou­

sands of residents suffered in the flood. 

But  it  is  not  only  the  ancient  threat  of

rivers  in  spate  that  unnerves  Leshan.  It  is

also  the  way  the  city  itself  has  grown.  By

the time of last year’s disaster, its built­up

area,  including  satellite  towns,  was  more

than half as big again as it was in 2000. City

planners had failed to make due provision

for floodwater runoff.

After four decades of frantic expansion,

many other cities are in similar difficulty.

They  are  poorly  prepared  for  extreme

downpours,  which  are  likely  to  become

more common as a result of global warm­

ing.  One  such  storm  in  July  over  Zheng­

zhou, the capital of the central province of

Henan, drenched the city in a year’s worth

of  rain  in  three  days  (see  picture).  Cars

were swept away or trapped in flooded tun­

nels, where six motorists died. Another 14

people drowned in the subway system. In

all,  nearly  300  were  killed.  According  to

Chinese researchers, average annual losses

from floods in China doubled from around

100bn  yuan  ($15.6bn)  in  the  decade  after

2000 to over 200bn yuan in the early 2010s. 

About  one  in  ten  Chinese  people  lived

in cities in 1950. Now six in ten do. About

70% of those cities are in floodplains. “We

overbuilt,  and  we  built  it  wrong,”  says  Yu

Kongjian,  a  landscape  architect  at  Peking

University.  Mr  Yu  was  among  the  first  to

urge that urban areas become “sponge cit­

ies”,  meaning  they  must  be  capable  of  ab­

sorbing  rain  without  creating  floods.  He

drew  inspiration  from  old  Chinese  irriga­

tion  systems,  such  as  “mulberry  fish

ponds” that act as natural reservoirs. He es­

timates that urbanisation has resulted in a

third of farmers’ ponds and half of all wet­

lands disappearing. 

The government has embraced the idea,

and  has  adopted  the  term  sponge  city.  In

2015  it  released  a  series  of  guidelines  for

building them. The aim is for 80% of cities

to collect and recycle 70% of rainwater by

2030. Local authorities have set their own
targets.  In  2018  Zhengzhou  announced  a
plan  to  ensure  that  nearly  nine­tenths  of
its  core  urban  area  would  be  “spongified”
by  2030.  This  year  Leshan  said  40%  of  its
urban  area  would  meet  the  government’s
sponge­city standards by 2025. 
Cities have long tried to prevent flood­
ing  with  hard  engineering  involving  the
“grey  infrastructure”  of  dams,  dykes  and
barriers. But urban surfaces of tarmac and
concrete cause floodwater to rush into of­
ten inadequate drains. Producing a sponge
effect  requires  measures  such  as  creating
artificial  wetlands,  planting  roadside
shrubs  and  using  permeable  materials  to
build pavements and plazas. 
The flooding in Zhengzhou shocked the
country.  It  left  many  Chinese  wondering
whether  sponge  cities  were  all  they  were
cracked  up  to  be.  After  all,  a  lot  of  money
has  been  flowing  into  spongification.  Ex­
perts  reckon  that  implementing  the  gov­
ernment’s sponge­city guidelines will cost

L ESHAN

Extreme rainfall is taking lives and causing billions of dollars in damage.

China hopes that creating “sponge cities” will help

→Alsointhissection

62 Thespreadofgraffiti

63 Chaguan: The Biden­Xi summit