20-Infiltration Processes and Soil Moisture Dynamics.

Abstract

The description of soil moisture dynamics is a challenging problem for the hydrological community, as it is governed by complex interactions between climate, soil and vegetation. Recent research has achieved significant advances in the description of temporal dynamics of soil water balance through the use of a stochastic differential equation proposed by Laio et al. (2001). The assumptions of this model simplify the mathematical form of the soil water loss functions and the infiltration process. In this model, runoff occurs only for saturation excess that represents an excellent mathematical approximation producing a simple expression for the probability density function of the infiltration, but does not account for limited infiltration capacity of soil. In the present work, such a characteristic has been incorporated in the soil moisture model with the aim to understand the consequences of such hypothesis on the soil water balance dynamics. The comparison between the two models (the original version and the modified one) have been carried out via numerical simulations. Results show that limited infiltration capacity may influence the soil moisture Probability Density Function (PDF) reducing its mean and variance and increasing the skewness. Major changes in the PDFs have been found for climate characterized by storms of short duration and high rainfall intensity, in humid climates, and in the cases where soil have a low permeability.