48 SCIENCE NEWS | May 7, 2022 & May 21, 2022SCIENCE VISUALIZEDCoastal cities around the world are sinking by up to several
centimeters per year, on average, satellite observations
reveal. The one-two punch of subsiding land and rising seas
due to climate change means that these coastal regions are
at greater risk for future flooding than previously thought,
researchers report in the April 16 Geophysical Research Letters.
Satellite measurements of ground height in and around
99 coastal cities on six continents, obtained mostly from 2015
to 2020, reveal how fast the underlying terrain is subsiding. The
maps shown here illustrate where and how fast the ground is
dropping in three cities with pronounced subsidence. (Negative
values correspond to the ground sinking; positive values corre-
spond to the ground rising.)
Previous measurements of urban subsidence tended to focus
on one city or region. But this investigation is “one of the first
to really use data with global coverage,” says Matt Wei, an earth
scientist at the University of Rhode Island in Narragansett.
About one-third, or 34, of the analyzed cities are sinking in
some places by more than 1 centimeter per year, Wei and his
team found. The largest subsidence rates — up to 5 cm/yr — are
mostly in Asian cities.
The team thinks that people are largely responsible for urban
subsidence. Looking at Google Earth imagery of regions that
were rapidly sinking, the researchers saw mostly residential or
commercial areas. That’s a tip-off that groundwater extraction
is the culprit, the team concluded. Landscapes tend to settle as
water is pumped out of aquifers (SN: 12/1/12, p. 13).
There is reason to be hopeful. In the past, Indonesia’s
Jakarta, for example, was sinking by nearly 30 cm/yr, on
average. But now subsidence there and in some other places
has slowed, possibly due to recent governmental regulations
limiting groundwater extraction. — Katherine KorneiThat sinking feeling
Average speed of ground movement (mm/yr)Average speed of ground movement (mm/yr)Average speed of ground movement (mm/yr)–50 –40 –30 –20 –10 0 10 20 305 km5 km5 km–25 –20 –15 –10 –5 0 5 10 15
–15 –10 –5 0 5 10
Chittagong, BangladeshManila, PhilippinesTianjin, ChinaALL: P.-C. WU, M. WEI AND S. D’HONDT/GEOPHYSICAL RESEARCH LETTERS2022