Northern China's sinking city

By the BBC's Elettra Neysmith

The northern Chinese city of Tianjin is reported to have sunk about two metres (6.5 feet) over the past few years.

Experts say an expanding funnel-shaped area is taking shape on the North China Plain, which they believe is being caused by underground tapping for water, used for agricultural irrigation or drinking water.

Massive water depletion is to blame

They are now calling for water saving measures to halt the problem.

The past few years have seen a big increase in the construction of irrigation works in parts of China.

But now, in Tianjin, experts believe those projects are having unforeseen consequences.

Land levels have dropped by about two metres in Tianjin and predictions are that the problem can only worsen.

More than 30 funnel shaped areas have been discovered in northern China as a result of underground water tapping.

It is thought these funnels will eventually join together covering an area of 40,000 square kilometres (15,400 square miles).

Growing problem

In Hebei province alone 40bn cubic metres (1400bn cubic feet) of water are extracted each year, reducing water levels by around 12m over the last decade.

It is a phenomenon that is being seen around the world.

During the 1980s, in what was the United Nations International Water Decade, millions of boreholes were sunk across the globe in a well-publicised effort to provide the world's poor with safe drinking water.

But some environmental groups believe it is a practice that is misguided and unsustainable.

As well as causing land sinkage, which damages buildings and pipelines, the lowering of water tables also means the water reached has a greater salt content, as well as a bigger risk of natural chemicals.

The result is costly treatment processes for those that can afford them, and for the world's poorest - the risk of deformity, and even death.