Ceres, Francesca (2009) Parametrizzazione di modelli idrologici per la gestione dei sistemi agro-forestali. [Tesi di dottorato] (Unpublished)

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This thesis aims at developing appropriate tools for a quantitative description of space-time dynamics of the main hydrological processes evolving in the soil-vegetation-atmosphere (SVA) system at a local scale (pèdon or field scales). In this study we discuss two basic aspects of the problem: (i) to set-up techniques for a suitable parameterization of hydrologic models with a particular reference to the environmental conditions of the Mediterranean ecosystems, (ii) to implement and compare simulation models that describe the various processes with different levels of complexity. The techniques traditionally proposed for evaluating the field water capacity, FWC, have been critically analyzed in order to highlight their limitations, especially with respect to the texture classes of soils and the vertical layering of the soil profiles. Regarding uniform soil profiles, the water content at field capacity as determined by using the Richards equation has been compared to the simplified practice of calculating FWC as the soil water content at a given value of the matric pressure head, h (usually h=-1/3 bar). The results obtained show that appropriate field capacity values are obtained only by selecting the matric pressure head h appropriately in relation to the soil texture. Instead, in case of layered soil profiles, the vertical heterogeneities can affect the FWC value, even in a remarkable manner. Specifically, this study has shown that FWC can significantly depend on the hydraulic conductivity characteristic of the soil near the lower boundary of the layered soil profile. A section of the study then focused on comparisons between simulations of water balance obtained using different hydrological models. Simulations from models that use the Richards equation or simplified bucket-type models have been compared. It is shown that the climatic seasonality, typical of the Mediterranean environments, exerts on the dynamics of surficial water contents in the soil. Rainfall variability during the vegetative season and that one evolving during the quiescent phase is responsible for different transpiration conditions and for evolutions of the water content in the soil characterized by specific trends. During the vegetative season, major controlling factors are the transpiration trend with respect to rainfall which assumes low values. During the quiescent season, on the other hand, the main controlling factor is rainfall trend.

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