Towards a hydrologically motivated soil texture classification

While currently used texture classifications are based on pedological background and practical reasons with respect to soil mapping and analyses, a possible soil texture classification motivated by soil hydrology should be based on similar hydrological fluxes or a similar soil water regime. Therefore, this paper proposes a procedure how to evaluate the appropriateness of currently used texture classifications and how to derive a new soil texture classification based on a similar behaviour of soils with respect to hydrological processes. Long-term hydrological modelling of water balance terms, using a physically based soil-atmosphere-transfer scheme, serves as the basis of a similarity analysis of 5050 possible realisations of the soil texture triangle. Cluster analysis is then used for analysing similar hydrological behaviour of virtual soil columns. Spatial patterns of similar realisations (= clusters) in the soil texture triangle based on annual water balance terms such as actual evapotranspiration and runoff are compared to those based on soil hydraulic parameters and currently used soil texture classes. The results show that clusters based on soil hydraulic parameterisation of the retention and conductivity characteristics are relatively similar to current soil texture classes while hydrological model simulations suggest different spatial patterns of similar behaviour in the soil texture triangle. Additionally, the mean as well as maximum within-cluster variability of simulated water flows is remarkably smaller compared to the within-texture class variability of simulated water flows. A hydrologically motivated soil texture classification therefore could improve the general applicability of classified soil data for hydrological modelling purposes. Modelling uncertainty would become independent of the soil texture class. Therefore, hydrologic similarity would be represented in a better way. However, realising such a hydrologically motivated soil texture classification scheme would require a restructuring of existing soil texture classifications. (C) 2010 Elsevier B.V. All rights reserved.