Human Activities Accelerates Desert Expansion in China

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Last updated at: (Beijing Time) Thursday, October 24, 2002

Human Activities Accelerates Desert Expansion in China

Research bore out that due to human activities, deserts in north China have moved three latitudes southward, equal to 300 kilometers.

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Research bore out that due to human activities, deserts in north China have moved three latitudes southward, equal to 300 kilometers.

The research also discovered that the treatment of desertification is most likely to yield positive results in semi-to-whole arid zones within the three latitudes, which are sensitive to the cycle of eastern Asia monsoon. Semi-arid areas are generally covered with grasslands and shrubberies, while arid areas by moving, semi-moving and fixed dunes.

By studying quantitative information about the ancient environment change, which was collected in the transitional belt from deserts to the Loess Plateau in north China, scientists with Institute of Earth Environment under Chinese Academy of Sciences, the University of Western Australia and the University of Arizona confirmed that human activities have given a huge boost to the desertification process.

Chief scientist Dr. Zhou Weijian with State Key Laboratory of Loess and the 4th Century Geology CAS said that they selected two geological periods, the last glacial maximum that was 21,000 to 13,000 years ago and the Holocene precipitation optimum which was 10000 to 5000 years ago. Through geological investigation, environmental indexes analysis and reliable 14-C dating, they "restored" features of ancient environment.

The monsoon strength determines the rainfall amount. During the last glacial maximum, the weakest period of Chinese continental monsoon, the dry climate led to the rapid expansion of desert. As the monsoon withdrew from its forward position, deserts in the Ordos Plateau expanded to 30°N southward, and the Kubuqi desert was finally linked with the Maowusu desert.

By contrast, during the Holocene precipitation optimum, the strongest period of monsoon activity, the desert fringe advanced to 41°N northward together with the monsoon forward position. Meanwhile, the humid climate turned Maowusu desert into a vast grassland.

Today, the late period of the Holocene precipitation optimum (from 5000 years ago to present), the forward position of monsoon still lingers on 41°N, while the desert fringe grows south to 38°N.

Mr. Zhou Weijian explained, " The test of environmental indexes as well as comprehensive analysis combined historical documents with environmental archaeology verified that human activities in the past 3000 years are the main cause leading to the three latitudes' distance between the desert fringe and the monsoon forward position."

According to archaeological data, cultural types such as the Microlithic Culture and the Yangshao Culture were once densely distributed in these three latitudes, indicating there were meadows at that time and the settlement of mankind in later age was near the Yellow River. Today, the majority of excavated settlements are scattered in deserts.

In the past 3000 years, increased population, agricultural activities and deforestation as well as frequent wars have severely damaged natural vegetation, resulted in soil erosion and sped up desertification. Hence, meadows in some areas have turned into semi-moving dunes or desert belts, while moving dunes are expanding.

Capital of Western Xia Kingdom Tongwan, built at the beginning of 5th century, now is buried in the Maowusu Desert. However, historical documents show the then city was built on a fertile land with adequate freshwater. The frequent wars in the middle and late Tang Dynasty did great damages with forests destroyed by fire, natural pasturelands trampled by battle horses, and farmlands laid aside in waste. Till A.D.822, dunes grew as high as city walls of Tongwan in gale-blowing days.

The research gives a clear picture of how human activities have participated in the cause of natural environment, and provided reference of great value for ecological treatment in a more purposeful way. Zhou Weijian added that the active monsoon climate brings about a precipitation of 200 to 400 mm annually to these three latitudes, a favorable climate condition for desertification treatment.

By PD Online Staff Zhu Lizhen

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