Reality and fiction of models and data in soil hydrology

Abstract

The objective of this paper is to contribute to the ongoing discussion on strengths, weaknesses, opportunities and trends of existing modeling approaches in soil hydrology. In modern hydrology, complexity of models and detail of data grow at increasing pace. The prevailing attitude has been that if a model is comprehensive enough, it should be possible to represent the site uniqueness with a specific set of model parameters. Recent advances in instrumentation have revealed complexity of flow pathways that may be easily perceived but difficult to represent in mathematical terms without making strong simplifying assumptions. This implies that many different model structures could be consistent with available observations. The same appears to be true for parameter sets obtained by calibration for a specific model. The multiplicity of models and the parameter deficit are the emerging issues that present both obstacles and opportunities for hydrologic modeling. We present a comprehensive case study of using integrated data to build a model of groundwater pollution for a watershed, and use this case study to illustrate current opportunities and problems related to quantifying soil variability with remote sensing, geophysical methods and topographic information. The value of pedotransfer functions and publicly available databases is discussed. Mismatch between measurement and modeling scales creates the need to incorporate scale effects in the hydrologic models. Techniques for comprehensive comparative evaluation of models need to be developed and tested. In the absence of unique model selection criteria, it can therefore be best to consider a variety of alternative models based on reasonable alternative hypotheses