Thermodynamic transport mechanism of water freezing-thawing in the vadose zone in the alpine meadow of the Tibet Plateau

High altitude,cold and dry climate,strong solar radiation,and high evapotranspiration intensity have created an extremely fragile ecological and geological environment on the Tibet Plateau.Since the heat in the vadose zone is primarily generated by the external solar radiation energy,and evapotranspiration is contingent on the consumption of vadose heat,the intensity of evapotranspiration is associated with the intensity of solar radiation and the heat budget in the vadose zone.However,the spatial and temporal variation of heat budget and thermodynamic transfer process of the vadose zone in the frigid region are not clear,which hinders the revelation of the dynamic mechanism of evapotranspiration in the vadose zone in the frigid region.With the moisture content of the vadose zone in the alpine regions being the research object,the paper conducts in-situ geothermal observation tests,takes meteorological characteristics into consideration,and adopts the method of geothermal gradient and numerical computation to analyse the temporal and spatial variation rule of heat budget and thermodynamic transmission process of the vadose zone in the high and cold regions.The results show there is a positive correlation between air temperature,ground temperature,and water content of the vadose zone in both thawing and freezing periods.According to the change law of geothermal gradient,the thermodynamic transfer process of the vadose zone has four stages:slow exothermic heating,fast endothermic melting,slow endothermic cooling,and fast exothermic freezing.From the surface down,the moisture freezing rate of the vadose zone is slightly higher than the melting rate.This is of great significance for understanding the evapotranspiration dynamic process of the vadose zone and protecting and rebuilding the ecological and geological environment in the high and cold regions.

Investigation of groundwater characteristics and its influence on Landslides in Heifangtai Plateau using comprehensive geophysical methods

The occurrence of landslides in Heifangtai plateau is primarily caused by the rise in water levels due to irrigation. To accurately understand the distribution of groundwater and its impact on the landslide hazard, a combination of Electrical Resistivity Tomography(ERT), Induced Polarization(IP) and Surface Nuclear Magnetic Resonance(SNMR) methods were used in this study. By conducting a comprehensive analysis, the characteristics of water-bearing structure in vertical and groundwater distribution in horizontal were detected;and the influence of the groundwater on plateau and landslides was also identified. The results indicate that the groundwater occurs in the loess aquifer with a three-layer structure in vertical.Horizontally, the aquifer has a unified water table over the plateau, with a low water level in the north and high one in the south. The high resistivity bedrock uplift belt in the middle of the plateau forms a watershed,with the north side of the uplift belt being a relatively stable slope area with stable water content and fewer geological disasters. In contrast, the south side of the uplift belt is a disaster-prone region with vertical fissures well developed in the loess aquifers. The southern landslides are characterized by the interphase distribution of high and low electrical resistivity. The infiltration and discharge of groundwater result in the formation of a collapse belt in the low resistivity water-bearing structure of landslide, which causes the entire block with high resistivity and stable bedrock to slide. There was a newly formed landslide in a larger range at the landslide' s trailing edge. This study provides a scientific basis for the study of landslides mechanisms and disaster prevention by identifying the distribution characteristics of groundwater and analyzing its influence from a geophysical perspective in Heifangtai.