Simulated Effect Of Soil Freeze-Thaw Process On Surface Hydrologic And Thermal Fluxes In Frozen Ground Region Of The Northern Hemisphere

Soil freeze-thaw process is closely related to surface energy budget, hydrological activity, and terrestrial ecosystems. In this study, two numerical experiments (including and excluding soil freeze-thaw process) were designed to examine the effect of soil freeze-thaw process on surface hydrologic and thermal fluxes in frozen ground region in the Northern Hemisphere based on the state-of-the-art Community Earth System Model version 1.0.5. Results show that in response to soil freeze-thaw process, the area averaged soil temperature in the shallow layer (0.0175 -0.0451 m) decreases by 0.35 degrees C in the TP (Tibetan Plateau), 0.69 degrees C in CES (Central and Eastern Siberia), and 0.6 degrees C in NA (North America) during summer, and increases by 1.93 degrees C in the TP, 2.28 degrees C in CES and 1.61 degrees C in NA during winter, respectively. Meanwhile, in response to soil freeze-thaw process, the area averaged soil liquid water content increases in summer and decrease in winter. For surface heat flux components, the ground heat flux is most significantly affected by the freeze-thaw process in both summer and winter, followed by sensible heat flux and latent heat flux in summer. In the TP area, the ground heat flux increases by 2.82 W/m(2) (28.5%) in summer and decreases by 3.63 W/m(2) (40%) in winter. Meanwhile, in CES, the ground heat flux increases by 1.89 W/m(2) (11.3%) in summer and decreases by 1.41 W/m(2) (18.6%) in winter. The heat fluxes in the Tibetan Plateau are more susceptible to the freeze-thaw process compared with the high-latitude frozen soil regions. Soil freeze-thaw process can induce significant warming in the Tibetan Plateau in winter. Also, this process induces significant cooling in high-latitude regions in summer. The frozen ground can prevent soil liquid water from infiltrating to deep soil layers at the beginning of thawing; however, as the frozen ground thaws continuously, the infiltration of the liquid water increases and the deep soil can store water like a sponge, accompanied by decreasing surface runoff. The influence of the soil freeze-thaw process on surface hydrologic and thermal fluxes varies seasonally and spatially.