Simulation of permafrost and seasonally frozen ground conditions on the Tibetan Plateau, 1981-2010

Permafrost and seasonally frozen ground conditions on the Tibetan Plateau were investigated using the Community Land Model, version 4 (CLM4), forced by a suite of new, high-resolution data. This new data set was highly accurate and had an advantage in the frozen ground simulations for its fine temporal and spatial resolution. The simulated current (1981-2000) near-surface permafrost area was 151.50x10(4)km(2), which is close to, but slightly larger than, the range from previous studies (111.80 similar to 150.0x10(4)km(2)). The simulated current active layer thicknesses ranged from 0 to 4.74m, with an average of 2.01m. The other frozen ground parameters, such as the maximum freezing depths for seasonally frozen ground, the date of freeze start, the date of freeze end, and the freeze duration at 1m depth, were also examined. Considering the issue of scale mismatch, the simulated soil temperature and other frozen ground parameters were reasonable compared to our observations. In response to the Plateau warming of approximately 0.44 degrees C/decade from 1981 to 2010, the near-surface permafrost area decreased at a rate of 9.20x10(4)km(2)/decade, and the area-mean active layer thickness increased by 0.15m/decade. The area-mean maximum freezing depth of the seasonally frozen ground decreased by 0.34m/decade. At a depth of 1m, the dates of freeze start for permafrost and seasonally frozen ground delayed linearly by 3.8 and 4.0days/decade, respectively, while the dates of freeze end for them advanced linearly by 5.9 and 4.6days/decade, respectively. These trends in the dates of freeze start and freeze end resulted in freeze durations that were shortened by 9.7 and 8.6days/decade for permafrost and seasonally frozen ground, respectively. These results give detailed permafrost and seasonally frozen ground states as well as their changes, which will be useful for studying frozen ground's response to climate change and frozen ground engineering stabilization.