Why cities sink

AFP English

Numerous cities around the world are sinking, putting more and more residents in flood zones. This phenomenon, called subsidence, affects every continent to different degrees, but the majority of the exposed population live in Asia. Explanations in videographic. VIDEOGRAPHIC

Transcript

00:00The sinking of land due to natural and man-made causes, a phenomenon known as subsidence,

00:12is pushing an increasing number of people into flood zones.

00:16Subsidence is a natural phenomenon linked to movements of tectonic plates or to the

00:21accumulation of sedimentary layers in shallow basins, but the phenomenon has accelerated

00:26due to human factors.

00:29The weight of buildings, for instance, and also the weakening of soils caused by the

00:34development of underground infrastructure, vibrations from road traffic, extraction of

00:39minerals and especially unregulated pumping of underground water from aquifers.

00:45An aquifer is an underground layer of porous and permeable rock containing water which

00:50provides a natural support to urban zones, where some big cities are sinking by over

00:5525 centimetres per year.

00:58The artificial covering of soils with, for example, bitumen and concrete, make the surface

01:03impermeable, preventing the refilling of underground water sources by rainwater, which further

01:09weakens this natural support.

01:11But the phenomenon of subsidence can be contained if timely action is taken.

01:16Cities can limit the artificial covering of surface soil, limit urban concentration or

01:20ban pumping from aquifers and by providing alternative water sources.

01:28For more UN videos visit www.un.org

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