No protection of permafrost due to desertification on the Qinghai–Tibet Plateau

Abstract

Desertification of tundra regions may form an escalating cycle with permafrost degradation where more permafrost thaw leads to continued desertification. This traditional viewpoint has been challenged in recent reports that state desertification protects the underlying permafrost. However, our measurements of soil temperature from nine sites in the Honglianghe River Basin, interior QinghaiTibet Plateau, show that desertification can degrade permafrost. If one compares the permafrost temperatures at sites with thin sand covers (e.g. site Yu-7, permafrost temperature of −0.64 °C; site Yu-6, permafrost temperature of −1.15 °C) with that of site Xie-1 (−0.65 °C, with a 120-cm-thick sand cover), the permafrost temperature is not significantly different. It is clear that a thick sand cover does not influence the underlying permafrost temperature. Our observations support traditional geocryological knowledge which states that, under most circumstances, desertification does not protect, but rather degrades, permafrost.Permafrost is defined as ground that remains continuously at or below 0 °C for at least two consecutive years 1 . Permafrost is a product of long-term energy exchange between the ground surface and atmosphere and is therefore a condition of ground climate 2 . The difference in the macro-scale distribution of permafrost is controlled by the climate 3 ; however, the difference in the local conditions, such as the topography, vegetation, snow cover, soil and geological conditions, can significantly modify the thermal impacts of the climate 4-6 and result in local-scale anomalies in permafrost distribution 3 . One of the local-scale factors influencing permafrost distribution is dominantly surface cover, e.g. vegetation, snow cover, and water 7 . Many studies have presented the thermal effects of local-scale surface cover on the active layer processes, e.g., the hydrothermal regimes and ground freezing-thawing in the active layer, active layer thickness, and thermal states of permafrost 3,[8][9][10][11] . However, little focus has been placed on the hydrothermal impacts of desertification (sand layer or dune formation over the frozen ground) on the thermal regimes of soils in the active layer and the underlying permafrost.Permafrost underlies approximately 70% of the land area of the Qinghai-Tibet Plateau (QTP), the highest and most extensive plateau permafrost on Earth 12-14 . Observational evidence demonstrates that warming, thawing and degrading of the plateau permafrost has occurred during the past few decades 11,13,[15][16][17][18][19] . The effect of permafrost degradation in the Qinghai-Tibet Plateau dries the ground surfaces because the active layer usually thickens, the permafrost table lowers and vegetation becomes more fragmented and sparse. The result is an increase in wind action, enhanced deflation and Aeolian deposition, and increased potential risk of desertification 16,[20][21][22] . Since the 1960s, grassland deterioration and desertification have occurred in some parts of the QTP 23-25 and N...

Vegetation Changes along the Qinghai-Tibet Plateau Engineering Corridor Since 2000 Induced by Climate Change and Human Activities

“…When the active layer depth dropped below 3 m, increasing areas covered with alpine meadows showed accelerated degradation. Thus, the active layer depth of 3 m to 3.2 m (i.e., the depth of the orange range in Figure 8 used nine sites of soil temperatures in Honglianghe River Basin along the QT Highway to prove the traditional geocryological knowledge, which states that desertification will accelerate the degradation of permafrost under most circumstances [32]. However, the global temperature is expected to continue to increase [33].…”

Permafrost Thaw with Thermokarst Wetland-Lake and Societal-Health Risks: Dependence on Local Soil Conditions under Large-Scale Warming

“…This implies greater groundwater recharge and flow with the potential to carry more thaw-released organic material to downgradient surface waters [3]. Furthermore, with regard to the debated permafrost protection that may be provided by sand covering (desertification) [24,25], the relatively small differences in ice-content results between the simulated MS and NS cases suggest only small such protection effects.…”

“…thawing by sand layer or dune formation over the frozen ground (desertification) [24,25]. Local elevation conditions also influence the permafrost dynamics and, in resolving the permafrost thaw complexity, low elevation and southern sites may be particularly useful as relatively early representatives of forthcoming warming effects.…”

“…Regarding influences on landscape conditions, including the evolution of thermokarst lakes and wetlands, local soil and hydrogeological differences may be essential for the spatial variability of permafrost thaw under the same large-scale surface temperature [1]. Great spatiotemporal complexity is also suggested for the evolution of permafrost peatlands under warming [23], and there is ongoing debate about the potential protection of permafrost against thawing by sand layer or dune formation over the frozen ground (desertification) [24,25].…”

Climate Changes and Associated Multiscale Impacts on Watershed Discharge over the Upper Reach of Yarlung Zangbo River Basin, China

“…e extensively developed seasonal frozen soil and permafrost contribute a large portion of WD in the upper reach of the YZRB. In the context of global warming, both seasonal frozen soils and permafrost have undergone a noticeable degradation, leading to a significant increase in thickness of the active layer [38,39]. Conversely, the increasing active layer thickness of frozen soil posed a great impact on WD variations and meanwhile involved the associated unknown responses to climate change, such as higher evaporation, greater water storage in the soil profile, and less surface runoff yield.…”