Review and Classification of Modeling Approaches of Soil Hydrology Processes

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