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Human activities have driven the northern desert southward by approximately 300 kilometers over the past 3,000 years.

This was the conclusion of a team of scientists from the Earth Environment Research Institute under the Chinese Academy of Sciences, the University of Western Australia and the University of Arizona in the United States.

However, from a mass of data on environmental changes from ancient times to the present affecting the desert-loess transition zone near the big bend of the Yellow River in north China, the scientists also held that greater rainfall from changes in the East Asia monsoon pattern currently affecting the semi-arid to arid areas in this region was likely to help prevent and reverse desertification.

On the basis of their research findings between 1999 and 2001, the scientists found that human activities have accelerated the desertification process in this area. Their findings were published this year in the science magazine Holocene 12.

Over more than 3,000 years, a growing population, incessant agricultural activities, excessive tree-felling and frequent warfare damaged the natural vegetation, causing soil erosion and intensifying desertification in this area, said Dr. Zhou Weijian, chief scientist of the State Key Laboratory of Loess and Quaternary Period Geology under the CAS.

However, an ongoing active monsoon climate brought 200-400 mm of rainfall to the area annually, good conditions for preventing and reversing desertification, he said.

The scientists focused on two periods - the last glacial maximum period, dating back 13,000 to 21,000 years, and the Holocene precipitation optimum period, dating back 5,000 to 10,000 years.

With the use of geological evidence, analysis of the environmental index and a detailed chronological framework, the scientists were able to "restore" the original environment during the chosen periods and evaluate desert margin position changes.

In China, Zhou said, precipitation was related to the position of the summer monsoon. During the last glacial maximum period, the continental monsoon was very weak, and dry weather caused the desert margin on the Ordos Highlands and monsoon front to shift southward.

(Xinhua News Agency October 26, 2002)