‘All the birds returned’: How a Chinese project led the way in water and soil conservation

China’s Gansu province, located in the convergence zone of the Loess plateau, the Mongolian plateau and the Qinghai-Tibet plateau, where persistent water conservation efforts have taken effect. Photograph: Xinhua/Alamy

It was one of China’s most ambitious environmental endeavours ever.

The Loess plateau, an area spanning more than 245,000 sq miles (640,000 sq km) across three provinces and parts of four others, supports about 100 million people. By the end of the 20th century, however, this land, once fertile and productive, was considered the most eroded place on Earth, according to a documentary by the ecologist John D Liu.