Variations in soil temperature from 1980 to 2015 in permafrost regions on the Qinghai-Tibetan Plateau based on observed and reanalysis products

摘要

Soil temperature is an important physical variable of soil and plays a key role in controlling the underground hydro-thermal processes in permafrost regions on the Qinghai-Tibetan Plateau (QTP). Daily soil temperatures were observed at five different vegetation cover sites (alpine wet meadow, alpine meadow, alpine steppe, alpine desert steppe and alpine desert) from 2012 to 2015 in permafrost regions on the QTP. The performance of three reanalysis soil temperature products (National Centers for Environmental Prediction Climate Forecast System and Climate Forecast System Reanalysis (CFSR), European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim), and Global Land Data Assimilation System (GLDAS-NOAH)) at four depths (0-10, 10-40, 40-100 and 100-200 cm) was evaluated using the observation data. The results revealed that the CFSR soil temperature products had the best performance at most sites and that GLDAS-NOAH and Era-Interim had the poorest performance. However, the original CFSR soil temperature products underestimated the lowest temperatures. The calibration models for CFSR soil temperature products were established using the observed daily soil temperature from 2013 to 2015 and were validated with observed data from 2012. The results showed that the calibrated CFSv2 products were closer to the observations at different depths in the study sites. Moreover, we investigated the variations of seasonal and annual mean soil temperature from 1980 to 2015 at depths of 0-10, 10-40, 40-100 and 100-200 cm using the soil temperature calibration results. It was found that the soil temperatures at different depths all warmed fastest in spring, more slowly in winter and slowest in autumn at most sites. In addition, the average annual soil temperature exhibited significant warming trends in the permafrost regions on the QTP. The effect was largest with alpine desert steppe and smallest with alpine wet meadow, with statistically significant rates of 0.0599, 0.0468, 0.0438, 0.0282 and 0.0145 degrees C/year in alpine desert steppe, alpine desert, alpine steppe, alpine meadow and alpine wet meadow, respectively. This research provides a foundation for understanding the thermal properties of permafrost on the Qinghai-Tibetan Plateau under climate change.