The Qinghai-Xizang Plateau is warming at roughly twice the global average rate, which makes the expectation straightforward: its permafrost should be losing ice. A study led from the College of Environmental Sciences and Engineering at Peking University, with colleagues at the Alfred Wegener Institute, Nanjing Normal University and the Chinese Academy of Sciences, finds the opposite across much of the region. More than a third of the plateau's permafrost, concentrated in the central plateau, has gained ice since 2000.
The field evidence came from boreholes, compared in pairs where one hole had been drilled before 2000 and a nearby hole afterwards. The newer hole generally held more ice, and the additional ice sat mostly near the bottom of the layer that thaws each summer. Weather records supply the mechanism: annual rain and snow in the westerly-influenced interior plateau rose by 60 per cent after 2000, and summer meltwater seeping to the base of the active layer refreezes there.
Model simulations separated the two competing drivers. A computer model of soil heat and water flow showed that holding precipitation constant while warming continued converted ice gains into losses, whereas holding temperature steady while increasing rainfall caused ice to grow. The researchers conclude that rapid precipitation increase may outweigh temperature in driving ground ice change. The work was published in Science Advances.
The practical stakes are substantial. Roads, buildings and bridges across the plateau rest on frozen ground whose volume is apparently shifting in ways that temperature-based projections would miss, and the plateau feeds rivers supplying around two billion people downstream. The authors argue that rainfall trends, not temperature alone, should guide where engineers expect frozen ground to gain ice and move.