The number of the wells that are part of a 2,000-year-old irrigation system still in use in northwest China's Xinjiang Uygur Autonomous Region has decreased from 1,784 to 614 during the past half century, according to local water resources department.

Experts say the decline is affecting farmers' ability to irrigate their crops, and modern technology is to blame.

"Declining groundwater levels caused mainly by the sharp rise of motor-pumped wells are the cause of the ongoing disappearance of the ancient irrigation wells," said Wfuer, general secretary of the Xinjiang Karez Research Association.

Since the 1950s, 1,170 wells - called karezs - have dried up, and their annual water production level has decreased by 381 million cubic meters. As a result, some 12,700 hectares cannot be irrigated by the ancient water system, said Wfuer.

With an average 23 karezs disappearing every year, an irrigation system invented by local people will die out in 20 to 25 years without effective protection, said Wfuer.

Wfuer called for policies to be issued by the local government for the effective protection of an irrigation system that boasts such a long history.

The karez, mainly used in the Hami and Turpan areas of Xinjiang, where it is hot and dry, dates back to the Han Dynasty (206 BC-AD 220). It is considered one of the three great projects of ancient China, along with the Great Wall and the Beijing-Hangzhou Grand Canal.

As an irrigation system using underground water, the karez consists of four parts: a hole as deep as 50 to 60 meters, an underground canal, an above-ground canal and a small reservoir. The system has many advantages, such as little evaporation from season to season and little percolation. A karez can provide a stable water supply that does not consume energy or cause pollution.

Wandering underground over 5,000 kilometers, the karez has also been called "the underground Great Wall."