Abstract
In regions affected by seasonal and permanently frozen conditions soil moisture influences the thermal regime of the ground as well as its ice content, which is one of the main factors controlling the sensitivity of mountain permafrost to climate changes. In this study, several well established soil moisture monitoring techniques were combined with data from geophysical measurements to assess the spatial distribution and temporal evolution of soil moisture at three high elevation sites with different ground properties and thermal regimes. The observed temporal evolution of measured soil moisture is characteristic for sites with seasonal freeze/thaw cycles and consistent with the respective site-specific properties, demonstrating the general applicability of continuous monitoring of soil moisture at high elevation areas. The obtained soil moisture data were then used for the calibration and validation of two different model approaches in permafrost research in order to characterize the lateral and vertical distribution of ice content in the ground. Calibration of the geophysically based four-phase model (4PM) with spatially distributed soil moisture data yielded satisfactory two dimensional distributions of water-, ice- and air content. Similarly, soil moisture time series significantly improved the calibration of the one-dimensional heat and mass transfer model COUP, yielding physically consistent soil moisture and temperature data matching observations at different depths.
Highlights
Soil moisture is a key factor controlling the energy and mass exchange processes at the soilatmosphere interface
Repeated geophysical surveys (ERT, refraction seismic tomography (RST)) as well as spatial frequency domain reflectometry (FDR) (S-FDR) measurements are performed to assess the two dimensional spatial distribution of soil moisture in the ground. Using this comprehensive dataset we develop a methodology to link the various methods and use the resulting dataset to calibrate and validate two types of model approaches, which are currently used in permafrost research: (1) the geophysically based four-phase model (4PM) (Hauck et al, 2011), that combines Electrical Resistivity Tomography (ERT) and RST measurements to quantify the spatial variability of ice, water, and air content in the near subsurface and (2) the coupled heat and mass transfer model (COUP) (Jansson and Moon, 2001; Jansson, 2012), that uses atmospheric forcing as input to reconstruct the entire energy and water balance for one soil column
The VWC evolution described here is mainly driven by the ground temperature and the in situ snow cover, which is typical for high-altitude permafrost sites (e.g., Hilbich et al, 2011)
Summary
Soil moisture is a key factor controlling the energy and mass exchange processes at the soilatmosphere interface. In regions affected by seasonal and permanent frozen conditions soil moisture is of particular relevance It influences the physical properties of the subsurface (e.g., ice content, thermal conductivity, heat capacity, hydraulic conductivity, electrical conductivity, and permittivity), the energy and water exchange processes with the atmosphere (e.g., changing albedo, evaporation, Soil Moisture Data for Permafrost Models infiltration rates, refreezing rates, latent heat release, ground heat flux, runoff, Hinkel et al, 2001; Boike et al, 2003, 2008; Westermann et al, 2009, 2011; Scherler et al, 2010) and the characteristics of different permafrost landforms (e.g., differences of the above for soil, bedrock, rock glacier with coarse-or finegrained blocky material, talus slopes, steep, or flat terrain, Rist and Phillips, 2005). The efforts made in that direction lead to the creation of the International Soil Moisture Network (Dorigo et al, 2011) and before that the global soil moisture data bank (Robock et al, 2000)
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