Functional Sensitivity Study of Pedotransfer Functions for use in Land Surface Models

Pedotransfer functions (PTF) are used in land surface models (LSMs) and hydrological models to translate easily available soil properties, such as soil texture, into soil hydraulic parameters required in the functional descriptions of hydraulic properties. Various PTFs are in use and even more are available in the literature. In many LSMs so called class transfer functions are embedded, which predict the hydraulic parameters for the 12 USDA soil classes and most of them are based on the Brooks-Corey parameterization. In the work presented, we performed a sensitivity study of 13 PTFs, five for the Brooks Corey (BC) and eight for the Mualem van Genuchten (MvG) hydraulic model; four are class transfer functions (2x MvG and 2x BC). Water flow simulations were performed using HYDRUS-1D with run-off in a 200cm deep soil profile with various complexity ranging from homogeneous bare soil to variably layered soil covered with vegetation. Driving variables comprised 30 years of climate data from North-Rhine Westphalia (1982- 2011). The results were analysed in terms of instantaneous and cumulative net infiltration, actual evapotranspiration, deep drainage (sub-surface run-off), and root zone water content. The results indicate systematic differences in simulated fluxes between the runs with different PTFs, especially under extreme (wet or dry) conditions. The results might help to identify preferred PTFs for the use in LSMs