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How is frozen ground responding to climate change?

The Tibetan Plateau has experienced significant warming and wetting since the mid-1990s, which has substantially altered the thermal properties of its frozen ground. A new study led by the Chengdu University of Information Technology in China has found that the dual effect of this wetting and the projected increase in precipitation of the Plateau in the future is rapidly becoming a critical factor in determining the thermodynamics of the frozen ground.

“In the face of the greatest increase in the occurrence frequency of heavy precipitation over the entire Tibetan Plateau, we need to address how warming and wetting might be jointly influencing the thermal responses of the permafrost and seasonally frozen ground to climate change,” said study lead author Xuewei Fang, an expert in Atmospheric Sciences at Chengdu.

The scientists used the average annual precipitation as a criterion to divide the Tibetan Plateau into four different regions: an arid zone (with annual precipitation below 200 mm), a semi-arid zone (200–400 mm), a semi-humid zone (400–800 mm), and a humid zone (above 800 mm). The analysis revealed that, compared to the 1961–1990 period, the average annual air temperature and precipitation over the Tibetan Plateau between 1991 and 2010 increased by 0.72C and 75.64 mm, respectively, with the arid and semi-arid regions becoming warmer and wetter, and the humid and semi-humid zones becoming warmer but drier.

Moreover, by comparing the freezing and thawing durations of the ground surface in these two time frames, the researchers discovered that the wetting in drier areas before the 1990s prolonged the freezing duration of the frozen ground, while the continuous wetting after the 1990s reduced the thawing period. These findings suggest that the significant wetting in arid regions has exerted the opposite warming effect on the permafrost since the 1990s, shrinking the frozen area by 28 percent.

By contrast, the decline in precipitation in the humid zones has prolonged the thawing duration in seasonally frozen ground since the 1990s, due to the fact that the drying and warming environment enhances heat loss at the ground level, thereby decreasing the heat supply for the melting of ice and extending the thawing process.

“Next, we plan to investigate how energy and water fluxes in the frozen ground interact with wetting and warming conditions,” Dr. Feng concluded.

The study is published in the journal Advances in Atmospheric Sciences

By Andrei Ionescu, Staff Writer

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