China's deserts expand with population growth.

Carried forward by winds and sandstorms, the dunes of northern China are expanding at an unprecedented rate, Chinese researchers say. Human activities are primarily responsible for desertification of the arid and semiarid grasslands of the area, they conclude.

The average rate of desert expansion in the region was 3,600 square kilometers per year during the 1990s, compared with 1,560 [km.sup.2] annually during the late 1950s, says Tao Wang of the Chinese Academy of Sciences in Lanzhou.

"Most [desertification] has resulted from human acts," Wang says. He notes that the desert's area and the region's population have expanded proportionally during the past 50 years. Nearly 300 million people live in and around the 385,700 [km.sup.2] that have become desert since human civilization arose in the region.

In a wind tunnel simulation of land changes, Wang and his colleagues found that economic activities typical of the region increase the rate of topsoil erosion by a factor of 4 to 10. Intensified cultivation, overgrazing, and clearing of vegetation for fuel are among the contributing activities, Wang says.

Northern China has been grappling with desertification for decades. Control measures, such as irrigating strips of vegetation along desert highways to block sand dunes from blowing onto the roads, have been employed in less than a quarter of the desertified area.