Permafrost region in the Qinghai-Tibet Plateau (QTP) is highly sensitive to global warming. The active layer lying over the permafrost is encountering the severe degradation and its thickness has been reported to increase by 20-30 cm. Warming and overgrazing - induced alpine grassland degradation has also been found in the QTP. Accurate simulation of soil hydro-thermal response to warming and degradation is essential for understanding the process and mechanism of alpine ecosystem change. However, most of the research conducted in the QTP have been focusing on the numerical simulation more than ecological dynamical process simulation. The results without consideration of ecosystem parameters cannot help us understand the ecological and environmental change very well. On the other hand, existed ecological dynamical model studies conducted in the tundra ecosystems seldom consider the unfrozen water. The unfrozen water has been proved to be a key parameter controlling the soil temperature in the active layer. To resolve the two gaps, we developed a soil temperature module that incorporates thaw and freeze process of soil liquid water and unfrozen water into Terrestrial ECOsystem (TECO) model. Using the model, we try to simulate the soil temperature and moisture in different warming and degradation scenario.
Results/Conclusions
TECO was revised with observed soil temperature and moisture in the ambient treatments through data assimilation. Air temperature is elevated by 0.3, 0.6, 1. 5, 2.5, and 4.5°C, respectively, in the warming treatment. The field water capacity is descended by 3%, 8%, and 10%, respectively in the degradation treatments. The simulation result certificates that unfrozen water content is the most critical parameter that determines the accuracy of the model. Simulated soil temperatures have better consistency with observed data (R2>0.92, P<0.01) than simulated soil moistures (R2>0.80, P<0.05). The elevation of air temperature can increase soil temperature at a depth of 0-250 cm and decrease soil moisture during the growing at a depth of 60-100 cm. The impacts of degradation on soil temperature and moisture are different with the change of season and degradation intensity. Degradation decreases soil temperature in the cold season but increases soil temperature in the warm season. Degradation decreases soil moisture at shallow layers, but increase soil moisture at the deep layer in the warming seasons. The result shows that degradation might hinder the increase of soil temperature in the cold season but cause topsoil become dry and warm in the warm season.