Impact of soil hydraulic parameter uncertainty on soil moisture modeling

For simulations in basins where soil information is limited to soil type maps, a methodology is presented to quantify the uncertainty of soil hydraulic parameters arising from within‐soil‐class variability and to assess the impact of this uncertainty on soil moisture modeling. Continuous pedotransfer functions were applied to samples with different texture within each soil class to construct discrete probability distributions of the soil hydraulic parameters. When propagating the parameter distributions through a hydrologic model, a wide range of simulated soil moisture was generated within a single soil class. The pedotransfer function was found to play a crucial role in assessing the uncertainty in the modeled soil moisture, and the geographic origin of the pedotransfer function (region specific versus nonregion specific) highly affected the range and shape of the probability distribution of the soil hydraulic parameters. Furthermore, the modeled soil moisture distribution was found to be non‐Gaussian. An accurate uncertainty assessment therefore requires the characterization of its higher‐order moments. As an extension of this research, we have shown that applying continuous region‐specific pedotransfer functions to the central point of a soil class is a better alternative to standard (often nonregion‐specific) class pedotransfer functions for determining an average set of soil hydraulic parameters.