Review and Classification of Modeling Approaches of Soil Hydrology Processes

To use soil hydrology processe (SHP) models, which have increasinglyextended during the last years, comprehensive knowledge about these models and theirmodeling approaches seems to be necessary. The modeling approaches can be categorized aseither classical or non-classical. Classical approaches mainly model the SHP through solvingthe general unsaturated flow (Richards) equation, numerically or analytically. Due to a numberof shortcomings of classical approaches, a trend toward the application of non-classical modelshas been initiated in recent years. Artificial neural networks and fuzzy logic systems are twomain kinds of non-classical approaches. In this study, existing modeling approaches of SHPwith an emphasis on recent trends were reviewed and compared. Also, modeling approaches ofsoil hydraulic functions are reviewed briefly as a main part of SHP models. Finally,classifications for SHP models from different viewpoints are presented.