Changes in frozen ground in the Source Area of the Yellow River on the Qinghai–TibetPlateau, China, and their eco-environmental impacts

Abstract

The Source Area of the Yellow River is located in the mosaic transition zones of seasonallyfrozen ground, and discontinuous and continuous permafrost on the northeasternQinghai–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),deep (>8 m) and two-layer permafrost. Since the 1980s, air temperatures have been rising at an average rateof 0.02 °C yr−1. Human activities have also increased remarkably, resulting in a regionaldegradation 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 °C. General trends of permafrost degradation include reduction in areal extent fromcontinuous and discontinuous to sporadic and patchy permafrost, thinning of permafrost,and expansion of taliks. Isolated patches of permafrost have either been significantlyreduced in areal extent, or changed into seasonally frozen ground. Degradation ofpermafrost has led to a lowering of ground water levels, shrinking lakes and wetlands, andnoticeable change of grassland ecosystems alpine meadows to steppes. The degradation ofalpine grasslands will cause further degradation of permafrost and result in thedeterioration of ecological environments as manifested by expanding desertification andenhancing soil erosion.