科研之友
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摘要
The soil moisture content of active layer is a key parameter characterizing the climate, hydrology and ecological processes in permafrost regions. For a long time, due to the limited observations in permafrost regions, soil moisture datasets, e. g. , generated through remote sensing retrievement, model simulation, data fusion and assimilation have large biases. We collected 1 072 active layer soil moisture samples in the permafrost area in the Tuotuo River source area in the hinterland of the Qinghai-Tibet Plateau during the comprehensive field campaign from October to November 2020. Based on these samples, we analyzed the active layer soil moisture characteristics in spatial, and evaluated two soil moisture products, i. e. , Global Land Data Assimilation System(GLDAS-Noah)and the reanalysis data released by the fifth-generation European Center for Medium-Range Weather Forecast(ERA5-Land). The results showed that in the investigated region, the average active layer thickness is about 2. 72 m, and the soil mass moisture content(total moisture content)of the active layer is about 14. 0%. The active layer soil moisture was positively correlated with vegetation development, except for alpine swamp meadow type. In the alpine meadow and alpine grassland environment, along with the soil depth increases, the soil moisture decreased first and then increased again. The active layer soil moisture content of the of different topography presents upper slope>lower slope>middle slope>flat slope. The moisture content in the sunny slope is higher than in the shady slope, but the patterns of soil moisture profile change with depths were similar. We also compared the soil moisture in a depth of 0~350 cm in the permafrost active layer and in the same depth in talik. The soil moisture profiles along the depth both increase first, then decrease, and then increase again. But the soil moisture content in the permafrost active layer is larger than that in the same depth of talik. Compared with measured data, GLDAS-Noah assimilated moisture product is biased less than 10%, which is more accurate in this area during the investigation period than ERA5-Land reanalysis soil moisture product, and both two soil moisture products cannot correctly describe the soil moisture profiles. The results provide a scientific basis for the optimization of model freeze-thaw parameterization in a data assimilation system and the development of remote sensing moisture products.
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