A simplified approach for determining hydrologic behavior and depth of soils at basin scale.

Land-surface models at basin scale usually employ various combinations of land-use and soil class data to parameterize the major hydrologic processes. Even though soil exerts a major influence on hydrologic processes, soil hydraulic behavior is still difficult to quantify at relatively large scales. Recently soil hydraulic parameterization for hydrologic modeling can be conveniently carried out using pedotransfer rules, which are based on the knowledge of basic soil physical and chemical variables, such as bulk density, textural composition, and organic matter content. However, the availability of this basic information can be rather limited over large land areas. Therefore, in this work we explore the feasibility of employing morphological features to retrieve basic soil data being then used in pedotransfer functions (PTFs), as well as soil depth being viewed here as an indicator of the lower boundary condition. The proposed approach is applied in the Agri River basin (approximately 1770 km2), in Southern Italy (Basilicata Region), where we assessed relationships among soil depth and texture with morphological attributes, such as elevation, slope gradient, slope orientation (aspect), and surface curvature. Climatic conditions were defined using mean annual rainfall and climatic indices. The results show an enhanced correlation between soil depth and slope when accounting for the local vegetation types. As expected, texture can be conveniently linked to parent material obtained from lithology. We show an application of the method to derive soil parameters from morphological and vegetation coverage data (DEM, Corine Land Cover, etc.), which are actually available for almost all national basins.