Transformation of Larch-Dominated Forests and Woodlands into Mixed Taiga - Permafrost simulations with HTSVS&rsquo soil model
Nicole
Mölders, University of Alaska Fairbanks, Geophysical Institute and College of Natural Sciences and Mathematics, Department of Atmospheric Sciences, 903 Koyukuk Drive, Fairbanks, AK 997, molders@gi.alaska.edu
(Presenting)
Elissa
Levine, NASA’s GSFC, Biospheric Sciences Branch, Greenbelt, MD 20771, elissa.r.levine@nasa.gov
A stand-alone version of the soil model of the Hydro-Thermal Soil Vegetation Scheme (HTSVS) was built in order to allow it to be loosely coupled with the FAREAST gap model. Soil specific parameters (porosity, permanent wilting point, specific heat capacity, pore-size distribution index, water potential at saturation, volumetric water content at field capacity and permanent wilting point) were calculated from the data on measured percentage fraction of clay and sand at the Yakutsk site in central Siberia. The stand-alone version was run for the period between April 1, 2000 to October 30, 2000 for the Yakutsk site. The soil model was driven by observed soil temperature and moisture at the soil surface. Results showed that the soil model captures the observed seasonal course of soil temperature well and soil moisture acceptably. Various sensitivity studies were carried out to examine the impact of soil ice on soil temperature, the impact of the number of soil layers used on the accuracy of the results, the sensitivity to the lower boundary condition, the sensitivity to the depth of the bottom of the simulated soil profile, the sensitivity to the choice of the soil type beneath 0.97m depth (which was estimated since no information was available for that depth), and the forcing at the upper boundary conditions. Results showed that 20 layers and a depth of -30m produced better results than 30 layers and a depth of -30m or 20 layers and a depth of -20m. Assuming an annual course of soil temperature at the lower boundary in -2 or -3m depth provides typically larger discrepancies between simulated and observed soil temperatures than with a simulation at a -30m depth and a constant soil temperature of -9.5oC at the bottom of the soil profile. Simulated soil temperature and moisture conditions are sensitive to assumptions about the soil profile below 0.97m. Soil temperatures can be predicted more accurately, if frozen soil physics are considered. There is a slight sensitivity to the assumption of the initial partitioning of total soil water between the solid and liquid phase as well as the assumption of the total soil water content.
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