XI'NING, Feb. 16(Xinhuanet)-- A remote sensing survey has shown that the desert area of the Qinghai-Tibet Plateau, also called the roof of the world, has increased over the past three decades.

The survey was launched jointly by the China Aero Geophysical Survey and Remote Sensing Center for Land and Resources(AGRS), Jilin University, Chinese Academy of Geological Sciences, Qinghai Provincial Geological Survey Academy and Hebei Provincial Geological Survey Academy beginning 2003.

The survey focuses on desert area changes, ice line changes, river and lake changes, and geological disasters, said Sun Yangui,a senior engineer with Qinghai Provincial Geological Survey Academy.

The plateau's desert area exceeds 506,075 sq km, about 19.5 percent of the region's total area, up 38,743 sq km, or 8.3 percent, from the 1970s.

The desert areas are mainly in the northern Tibet Plateau, basins in southern Tibet including the upper and middle reaches ofYarlung Zangbo River and its major branches including the lower reaches of Nyangqu River, Lhasa River and Nyang River, and the Qaidam Basin, Gonghe Basin and Qinghai Lake areas.

Salinized soil covers 79,373 sq km, about three percent of the region's total area, and approximately 20,069 sq km or 20.2 percent less than in the 1970s. The disappeared salinized land wasbelieved to have turned into desert, according to experts.

Grassland on the Qinghai-Tibet Plateau has also decreased. Grassland shrank to 43,742 sq km in 2002 from 57,814 sq km in the 1970s, down about 14,072 sq km or 24.3 percent from the 1970s.

Experts ascribed the grassland reduction to desert expansion.

Global warming has caused less rainfall in Qinghai-Tibet Plateau which has degenerated the environment in the area. Increased human activities are also blamed for the environmental changes, experts say.

The Qinghai-Tibet Plateau encompass China's Tibet Autonomous Region, Qinghai Province, and some parts of Xinjiang Uygur Autonomous Region, Gansu Province, Sichuan Province and Yunnan Province. The plateau covers an area of 2.5 million sq km, about one fourth of China's land territory.

The plateau is the source of numerous rivers running through China and other countries in south Asia and east Asia.

Due to its special geological structure, the"roof of the world" is vulnerable to environmental changes and each environmental index change in the area will inevitably be followed by world climate and environmental changes, experts say.