Changes in frozen ground in the Source Area of the Yellow River on the Qinghai--Tibet Plateau, China, and their eco-environmental impacts Focus on Climate Change on the Tibetan Plateau

The Source Area of the Yellow River is located in the mosaic transition zones of seasonally frozen ground, and discontinuous and continuous permafrost on the northeastern Qinghai--Tibet Plateau. Vertically, permafrost is attached or detached from frost action. The latter can be further divided into shallow (depth to the permafrost table 8 m) and two-layer permafrost. Since the 1980s, air temperatures have been rising at an average rate of 0.02 degree C yr-1. Human activities have also increased remarkably, resulting in a regional degradation of permafrost. The lower limit of permafrost has risen by 50--80 m. The average maximum depth of frost penetration has decreased by 0.1--0.2 m. The temperatures of the suprapermafrost water have increased by 0.5--0.7 degree C. General trends of permafrost degradation include reduction in areal extent from continuous and discontinuous to sporadic and patchy permafrost, thinning of permafrost, and expansion of taliks. Isolated patches of permafrost have either been significantly reduced in areal extent, or changed into seasonally frozen ground. Degradation of permafrost has led to a lowering of ground water levels, shrinking lakes and wetlands, and noticeable change of grassland ecosystems alpine meadows to steppes. The degradation of alpine grasslands will cause further degradation of permafrost and result in the deterioration of ecological environments as manifested by expanding desertification and enhancing soil erosion.