HR: 1340h
AN: B33D-1060    [Abstracts]
TI: Dealing With Spatiotemporal Processes In Soil Moisture As Critical Point Phenomena
AU: * Di Domenico, A
EM: antodido76@tiscali.it
AF: Department of Engineering and Physics of the Environment (DIFA), University of Basilicata, Via dell'Ateneo Lucano, 10, Potenza, PZ 85100 Italy
AU: Laguardia, G
EM: giovanni.laguardia@jrc.it
AF: Institute for Environment and Sustainability, Joint Research Center (EC), Via E. Fermi 1, Ispra, VA 21020 Italy
AU: Fiorentino, M
EM: fiorentino@unibas.it
AF: Department of Engineering and Physics of the Environment (DIFA), University of Basilicata, Via dell'Ateneo Lucano, 10, Potenza, PZ 85100 Italy
AB: Soil moisture can exhibit two distinct preferred states which control the mechanism of lateral redistribution of water content, namely local and non-local control (Grayson et al 1997). They are responsible at the macroscopic scale of the structure assumed by soil moisture patterns which can be random or organised. The switching mechanism between local and non-local control can be described in terms of the dominance of vertical over lateral water fluxes respectively or vice-versa due to the continuous rise of soil moisture which leads at certain point to sharp increase of hydraulic conductivity. An interesting feature which can be useful for the description of some properties of soil moisture patterns is surely the connectivity, which is able to represent the interconnected path through the spatial pattern. An increasing interest in hydrology for this property is related to the understanding of runoff response. Based on this consideration, it is worth to look at the soil moisture process as a system subject to phase change. A physical system is subject to a phase transition process when it shows a discontinuous change of a macroscopic feature of the system under a continuous change of a system's state variable. A critical point phenomenon is a particular process in which the phase transition evidences a scale-invariant behaviour. Phase change is the first property to be checked in order to investigate a physical phenomenon through the percolation theory (Stauffer and Aharony, 1991). This theory is widely used in many sciences, such as geology, hydrogeology, seismology. The principal advantage of percolation theory is that it provides universal laws which determine the geometrical and physical properties of a system. Referring to the concepts of percolation theory, an algorithm in order to individuate the critical behaviour of a river basin soil moisture patterns has been developed. The relations between the occupation probability in the soil moisture spatial patterns and the normalized size of the largest cluster (percolation probability) and the behaviour of the system under changing grid scales have been investigated. The power trends of the occupation probability and the normalized size of the largest cluster, describing the soil moisture patterns as a function of certain reduced units near the critical point, yielding critical exponents, have been also investigated. They should give evidence of the criticalnature of soil moisture patterns. The exponents give way to the possibility of classifying the process in a certain universalityclass, which is the central property of percolation theory. The developed algorithm has been tested on the soil moisture maps of some basins located in Southern Italy obtaining interesting results: in fact the normalized size of the largest cluster shows a sharp change in correspondence of a certain value of the occupation probability; this value is then confirmed under changing grid scale. This result should give evidence of critical behaviour, which should be corroborated by the value of critical exponent β for the percolation probability achieving from its scatter plot on a log-log scale.
DE: 1866 Soil moisture
DE: 1869 Stochastic hydrology
SC: Biogeosciences [B]
MN: Fall Meeting 2005