In the past decades, the climate in Qinghai-Xizang (Tibet) Plateau is becoming warmer and therefore relatively dry, and this has resulted in the retreating of most glaciers, the uplifting of the snow lines, permafrost degradation, lakes areas shrinking, some swamps and wetlands becoming dry, the surface salinity increasing, some fixed sand dunes becoming active, and the wind erosion on the surface becoming stronger. Meanwhile unreasonable economic activities destroyed the vegetation and soil layers. Such phenomena converted non-desert lands and grasslands into deserts. At present, the desertification phenomenon is spreading. The desert area in Qinghai province was 597×104 km2 in the 1960s. However, it expanded to 790×104 km2 in the 1980s, which corresponds to the 10.95% of the total provincial area. From 1959 to 1977, within 18 years, 193×104 km2 of desert area was added. This means that the desertification area expanded 10.722×104 km2 per year on average. The expansion rate was 1.8% .
As reported by Lanzhou Institute of Desert Research, Chinese Academy of Sciences, in 1993, the desert area was 1860.9 km2 in the middle basin area of the Yaluzangbu River, Lahsa River and Nyingchi River in Tibet, which is equivalent to 97.5% of the total cultivated area in the region. In the surrounding area of Zhaling Lake and Eling Lake, in the upper part of Huanghe (Yellow) River, the sand dunes are expending and the active sand dunes are overlapping the grasslands. This has resulted in the area of useful grasslands shrinking annually. The active sand dunes, moving sand and frigid hungriness in the banks of the Tongtianhe River, in the upper part of Changjiang River, are now expanding southeasterly along the Tongtianhe River valley. There were swamps and wetlands before the 1950s in the Ruoergai area. But now most parts have become grasslands and, even worse, some parts are deserts. At present, the desert grasslands are distributed in valley terrains and their surrounding hill slope areas of the Huanghe River, the Baihe River and the Heihe River.
In the Qinghai-Xizang (Tibet) Plateau , continuous permafrost, island discontinuous permafrost, and deep seasonal frozen soil are common. Some of the factors that contributed to desertification in the Qinghai-Xizang (Tibet) Plateau are similar to other desert regions. However, some of the factors are related to the frozen soil. Desertification requires following conditions: abundant material sources, dry climates, windy and sparse vegetation. In other words, these factors can be summarized as natural factors and human-induced factors. The natural factors include the climate, frozen soil conditions, and material sources.
Desertification in Qinghai-Xizang (Tibet) Plateau is part of Chinese desertification. In the past decades, due to the climate warming, the climate condition in Qinghai-Xizang (Tibet) Plateau has been relatively dry. This has resulted in permafrost degradation and other environmental problems. In addition, the vegetation and the soil layer were also destroyed by unreasonable economic activities. Cultivated and grassland lands have become deserted. Nowadays, the desertification is still expending. In this paper, the factors affecting the desertification in Qinghai-Xizang (Tibet) Plateau were examined, and the desertification as well as its relationship with permafrost degradation was also discussed.
Introduction
