S. Di Gregorio

A Cellular Automata model for soil erosion by water

Abstract A Cellular Automata model for soil erosion by water, SCAVATU, was developed. It involves a larger number of states in comparison to the previous models, including altitude, water depth, total head, vegetation density, infiltration, erosion, sediment transport and deposition. The model was applied to the small catchment of the Fiumara Armaconi, Calabria, Southern Italy. First simulations gave encouraging results, even if field erosion data is needed for validation and future calibration and setting of the CA parameters. The model is susceptible to improvement and could represent a valid alternative to classic physically based methods, for the description of complexity through simple local rules.

A parallel cellular tool for interactive modeling and simulation

The paper discusses Camel, an interactive parallel programming environment based on cellular automata. With Camel users can develop high-performance applications in science and engineering. Examples in geology, traffic planning, image processing, and genetic algorithms show its usefulness.

A parallel cellular automata environment on multicomputers for computational science

This paper describes CAMEL (Cellular Automata environMent for systEms modeLing), a scalable software environment based on the cellular automata theory implemented on a Transputer-based parallel computer. Cellular automata were originally defined as a theory to model the basic mechanisms of dynamic systems, permitting a new approach which is in many cases simpler and more efficient than the traditional approach based on partial differential equations. Today, cellular automata become more attractive because they are suitable to be effectively and naturally implemented on parallel computers achieving high performance. CAMEL allows a user to program computational science applications exploiting the computing power offered by highly parallel computers in a transparent way. CAMEL implements a cellular automaton as a SPMD program. A load balancing strategy is used to minimize time costs in case of not uniform intervals for transition steps. In the paper the programming environment and the parallel architecture of CAMEL are presented and some experiments are discussed.

Computer simulation of natural phenomena for hazard assessment

Hazard assessment of dangerous natural phenomena is increasingly important as the toll in loss of human life and property in the media attests. The frequent and varied use of simulation methodologies is changing the attitudes of scientists in their approach to solving hazard problems. This process is leading towards the future possibility of managing complex natural, artificial, and mixed systems, the complexity of which excludes analytical solutions, or even worse, the use of differential equations. Powerful computers now allow approximate numerical methods based on space/time discretisation to be developed for quantitative modelling and simulation of complex phenomena. Furthermore, other challenges may arise due to the nature of the phenomena: some parameters of the model cannot be independently determined, either for fundamental reasons (e.g. they may be empirical, not physical) or for practical reasons (e.g. direct measures are not allowed); their values could possibly be found by comparing the model outcome with a set of experimental data. The papers collected in this issue are a selection of the original 35 studies presented at session NH23 of the EGS-AGU-EUG Joint Assembly (Nice, April 2003). They represent, in the opinion of the guesteditors, an interesting window on the difficult problem of analysing complex natural phenomena through modelling techniques, and on evaluating the associated hazards. For example, the research of Yuk, Yim & Liu (submarine mass-movement generated waves) and that of Patra, Nichita, Bauer, Pitman, Bursik & Sheridan (debris flows) use methodologies for finding approximate solutions to complex systems of differential equations, to describe the natural phenomena under study. Simulations validate these models on real cases or

Mount ontake landslide simulation by the Cellular Automata model SCIDDICA-3

Abstract Cellular Automata (CA), a paradigm of parallel computing, represent an alternative to differential equations and are used for modelling and simulating very complex phenomena; CA models have been developed by our research group for the simulation of landslides. We present SCIDDICA-3, our most efficient model, a two-dimensional CA model together with the simulation results of the Mount Ontake (Japan) debris avalanche which occurred in 1984. Landslides are viewed as a dynamic system based exclusively on local interactions with discrete time and space, where space is represented by square cells, whose specifications (states) describe physical and chemical characteristics (friction, viscosity, altitude, debris thickness, etc.) of the corresponding portion of space. At the time t=0, cells are in states which describe initial conditions; the CA evolves then changing the state of all cells simultaneously at discrete times. Input for each cell is given by the states in the adjacent cells; the outflow computation from the cells gives the evolution of the phenomenon. The comparison between the real and simulated event is satisfying within limits to forecast the surface covered by debris.

Revisiting the 1669 Etnean eruptive crisis using a cellular automata model and implications for volcanic hazard in the Catania area

Abstract Cellular Automata provide an alternative approach to standard numerical methods for modelling some complex natural systems, the behaviour of which can be described in terms of local interactions of their constituent parts. SCIARA is a 2-D Cellular Automata model which simulates lava flows. It was tested on, validated by, and improved on several Etnean lava events such as the 1986–1987 eruption and the first and last phase of the 1991–1993 event. With respect to forecasting the surface covered by the lava flows, the best results were acceptable. The model has been used to determine hazard zones in the inhabited areas of Nicolosi, Pedara, S. Alfio and Zafferana (Sicily, Italy). The main goal of the current work in the Etnean area from Nicolosi to Catania has been the verification of the volcanic hazard effects of an eruptive crisis similar to the event that occurred in 1669. The simulation uses the volcanic data of the 1669 eruption with present-day morphology. Catania has been affected by some historical Etnean events, the most famous one being the 1669 eruption, involving 1 km 3 of lava erupted over the course of 120 days. The simulation of ephemeral vents and the use of different histories within the experiments have been crucial in the determination of a new hazard area for Catania. In fact, during the simulation the city was never affected without the introduction of ephemeral vents, proving the fact that lava tubes played a fundamental role in the 1669 Catania lava crisis.

Analysing Lava Risk for the Etnean Area: Simulation by Cellular Automata Methods

The model SCIARA, based on the “Cellular Automata” paradigm, is a versatile instrument whose scope is to analyse volcanic risk from lava flows.The possible fields of intervention are:[(a)] Long term forecasting of the flow direction at various eruption rates and points of emission by locating potential risk areas and permitting the creation of detailed maps of risk;[(b)] The possibility to follow the progress of an event and predict its evolution;[(c)] The verification of the possible effects of human intervention on real or simulated flows in stream deviation.A risk scenario has been developed for the Etnean territories of the towns of Nicolosi, Pedara and S. Alfio, simulating possible episodes with different vent locations along the fracture opened in the 1989 eruption and successively activated in the 1991–1993 eruption.The main characteristics of lava flows, that might be dangerous to the inhabited areas, have been analysed on the basis of the carried out Cellular Automata.

High performance scientific computing by a parallel cellular environment

Abstract This paper describes CAMEL, a parallel environment for designing scientific applications based on the cellular automata mathematical model. CAMEL is an interactive environment designed to support the development of high performance applications in science and engineering. It offers the computing power of a highly parallel computer, hiding the architecture issues from a user. The system can be used both as a tool to model dynamic complex phenomena and as a computational model for parallel processing. By CAMEL a user might write programs to describe the actions of thousands of simple active agents, then observe the global complex evolution that arises from all the local interactions. The paper presents the programming environment and a significant application in the area of soil decontamination.

Simulating the Curti–Sarno debris flow through cellular automata: the model SCIDDICA (release S2)

Cellular automata (CA) are based on a regular division of the space in cells. Each cell embeds an identical finite automaton, whose input is given by the states of neighbouring cells. The transition function r of the CA is made of a set of rules, simultaneously applied, step by step, to each cell of the cellular space. Rules are derived by subdividing, in computational terms, the physical phenomenon into a set of independent, elementary processes. By properly combining each elementary result, the behaviour of the phenomenon can be simulated. Debris flows are dense mixtures of sediment and water, which surge down the slopes and along the drainage system, characterised by severe destructive potential. They can be described in terms of local interactions among their elementary portions, and can thus be efficiently modelled through CA. Debris-flows rheologic equations cannot be easily solved without making substantial simplifications. By applying CA, a phenomenological description––able to overcome resource computational limits––can be obtained. On May 1998, hundreds of soil slip-debris flows were triggered by exceptional rains in Campania (Italy), mostly on the slopes of Pizzo dAlvano. Aiming at modelling purposes, the Curti debris flow was selected as a case study, among the whole population of landslides triggered by the event. The general frame of SCIDDICAS2 is inherited from previous releases, recently applied for the simulation of the 1992 Tessina (Italy) earth flow and of the 1984 Mt. Ontake (Japan) debris avalanche. Since its S1 release, the model satisfactorily simulated the Curti–Sarno debris flow. Latest improvements to the transition function led to the S2 release, and to better simulations (presented here). SCIDDICA exhibits a notable flexibility in modelling and simulating flow-like landslides. It could be usefully applied in hazard mapping (also through a statistical approach), and in evaluating the effects of either human works or ‘‘accidents’’ along the path of the flow. � 2002 Elsevier Science Ltd. All rights reserved.

On reversibility in cellular automata

The notion of reversibility, or backward determinism, for cellular automata is investigated. Various intuitively different definitions are offered which coalesce in three inequivalent properties. Two of these are the well-known injectivity and surjectivity properties of the global transition function of a cellular automaton. We complete the investigation for one-dimensional cellular automata giving effective conditions for the third property. We end with some examples and comments on the relations between local and global phaenomena in cellular automata.