Applying genetic algorithms for calibrating a hexagonal cellular automata model for the simulation of debris flows characterised by strong inertial effects

In modelling complex a-centric phenomena which evolve through local interactions within a discrete time-space, cellular automata (CA) represent a valid alternative to standard solution methods based on differential equations. Flow-type phenomena (such as lava flows, pyroclastic flows, earth flows, and debris flows) can be viewed as a-centric dynamical systems, and they can therefore be properly investigated in CA terms.SCIDDICA S_4a is the last release of a two-dimensional hexagonal CA model for simulating debris flows characterised by strong inertial effects. S_4a has been obtained by progressively enriching an initial simplified model, originally derived for simulating very simple cases of slow-moving flow-type landslides.Using an empirical strategy, in S_4a, the inertial character of the flowing mass is translated into CA terms by means of local rules. In particular, in the transition function of the model, the distribution of landslide debris among the cells is obtained through a double cycle of computation. In the first phase, the inertial character of the landslide debris is taken into account by considering indicators of momentum. In the second phase, any remaining debris in the central cell is distributed among the adjacent cells, according to the principle of maximum possible equilibrium.The complexities of the model and of the phenomena to be simulated suggested the need for an automated technique of evaluation for the determination of the best set of global parameters. Accordingly, the model is calibrated using a genetic algorithm and by considering the May 1998 Curti–Sarno (Southern Italy) debris flow.The boundaries of the area affected by the debris flow are simulated well with the model. Errors computed by comparing the simulations with the mapped areal extent of the actual landslide are smaller than those previously obtained without genetic algorithms. As the experiments have been realised in a sequential computing environment, they could be improved by adopting a parallel environment, which allows the performance of a great number of tests in reasonable times.     

Zoning grassland protection area using remote sensing and cellular automata modeling—A case study in Xilingol steppe grassland in northern China

Grassland degradation has become a serious environmental problem in China due to climate variability and human disturbances in the arid and semi-arid areas. Establishing grassland protection areas (GPAs) is regarded as an effective measure to protect grassland. This paper presents a new method to support the local government's effort in zoning of GPAs. It integrates a cellular automata (CA) model with geographical information system (GIS) and remote sensing. The proposed method includes two major steps: 1. to extract “seed points” of candidate GPAs using remote sensing techniques and GIS; 2. to simulate the zoning of GPAs using a CA model. The performance of the proposed method is evaluated using a case study in Xilingol steppe grassland in Inner Mongolia Autonomous Region of China. The results show that the integrated approach can rapidly find candidate GPAs that satisfy the zoning requirement. It has demonstrated that the proposed method of grassland protection zoning provides valuable decision support tools for government and planning agencies.     

Complex systems in aeolian geomorphology

Aeolian geomorphology provides a rich ground for investigating Earth surface processes and landforms as complex systems. Sand transport by wind is a classic dissipative process with non-linear dynamics, while dune field evolution is a prototypical self-organisation phenomenon. Both of these broad areas of aeolian geomorphology are discussed and analysed in the context of complexity and a systems approach. A feedback loop analysis of the aeolian boundary-layer-flow/sediment-transport/bedform interactions, based on contemporary physical models, reveals that the system is fundamentally unstable (or at most meta-stable) and likely to exhibit chaotic behaviour. Recent field-experimental research on aeolian streamers and spatio-temporal transport patterns, however, indicates that sand transport by wind may be wholly controlled by a self-similar turbulence cascade in the boundary layer flow, and that key aspects of transport event time-series can be fully reproduced from a combination of (self-organised) 1/f forcing, motion threshold, and saltation inertia. The evolution of various types of bare-sand dunes and dune field patterns have been simulated successfully with self-organising cellular automata that incorporate only simplified physically-based interactions (rules). Because of their undefined physical scale, however, it not clear whether they in fact simulate ripples (bedforms) or dunes (landforms), raising fundamental cross-cutting questions regarding the difference between aeolian dunes, impact ripples, and subaqueous (current) ripples and dunes. An extended cellular automaton (CA) model, currently under development, incorporates the effects of vegetation in the aeolian environment and is capable of simulating the development of nebkhas, blow-outs, and parabolic coastal dunes. Preliminary results indicate the potential for establishing phase diagrams and attractor trajectories for vegetated aeolian dunescapes. Progress is limited, however, by a serious lack of appropriate concepts for quantifying meaningful state variables at the landscape scale. State variables currently used in the bare-sand models are far from capturing the rich 3D topography and patterns and are not sufficiently discriminative to distinguish different attractors. The vegetation component in the extended model, and indeed ecogeomorphic systems in general, pose even graver challenges to establishing appropriate state variables. A re-examination of older concepts, such as landscape entropy, perhaps complemented by recent developments in information theory, may be a potentially fruitful avenue for research, although the outlines of such an implementation are still rather vague.     

From networks to uses patterns: the digital divide as seen from Africa

This paper gives an account of the work carried out in the AFRICA’NTI research network, which gathered together a hundred, mostly African, researchers. The results were presented at the conference on “the North–South Digital Divide” in 2003 and 2004 (see www.africanti.org). From network to uses patterns, it first questions the way in which the subject is defined. This is a controversial question; should we speak of a “ditch” rather than of “fracture”? This depends on the point of view, but also on the geopolitical situation, and is difficult to measure. The digital divide may be less important than it is usually believed. This paper presents several types of approaches dealing with the opportunities of new technologies for Africa, geographical aspects stressing the diversity of the situations considered, and the importance of a multilevel systemic analysis based on case studies. It is shown that a slow down in the dynamics of equipment has been observed in Africa for both mobile telephony and the Internet. This then raises the question of a risk of regression for the continent, based on the idea that inequalities in access and uses of ICTs matter less than whether these uses improve the living conditions of the poor people concerned.     

Preliminary Cellular-Automata Forecast of Permit Activity from 1998 to 2010, Idaho and Western Montana

For public land management in Idaho and western Montana, the U.S. Forest Service (USFS) has requested that the U.S. Geological Survey (USGS) predict where mineral-related activity will occur in the next decade. Cellular automata provide an approach to simulation of this human activity. Cellular automata (CA) are defined by an array of cells, which evolve by a simple transition rule, the automaton. Based on exploration trends, we assume that future exploration will focus in areas of past exploration. Spatial-temporal information about mineral-related activity, that is permits issued by USFS and Bureau of Land Management (BLM) in the last decade, and spatial information about undiscovered resources, provide a basis to calibrate a CA. The CA implemented is a modified annealed voting rule that simulates mineral-related activity with spatial and temporal resolution of 1 mi² and 1 year based on activity from 1989 to 1998. For this CA, the state of the economy and exploration technology is assumed constant for the next decade. The calibrated CA reproduces the 1989–1998-permit activity with an agreement of 94%, which increases to 98% within one year. Analysis of the confusion matrix and kappa correlation statistics indicates that the CA underestimates high activity and overestimates low activity. Spatially, the major differences between the actual and calculated activity are that the calculated activity occurs in a slightly larger number of small patches and is slightly more uneven than the actual activity. Using the calibrated CA in a Monte Carlo simulation projecting from 1998 to 2010, an estimate of the probability of mineral activity shows high levels of activity in Boise, Caribou, Elmore, Lincoln, and western Valley counties in Idaho and Beaverhead, Madison, and Stillwater counties in Montana, and generally low activity elsewhere.     

空间复杂性与地理元胞自动机模拟研究

面对具有非线性、非平衡、自相似、自组织等复杂性特征的空间复杂现象,基于传统的牛顿力学和微分方程数学的地理模型显得力不从心,非线性科学作为解决地理复杂现象的有效工具成为地理学研究的前沿.基于对地理复杂性的分析、作者提出了一种基于元胞自动机(Cellular Automata)的地理模型框架,并在地理信息系统集成的基础上,对美国安阿伯波市的城市增长与扩散进行了生动地模拟和预测.     

Calcite formation in microbial mats: modeling and quantification of inhomogeneous distribution patterns by a cellular automaton model and multifractal measures

The evolution of early diagenetic calcite cements in microbial mats of recent supratidal sediments of the southern North Sea is modeled in a two-dimensional microscale approach by a cellular automaton model (CAM). Calcite is traced out in the model by virtual calcium distribution patterns obtained from runs under different assumptions concerning sediment-intrinsic conditions. For justification of the CAM, real calcium distribution patterns, documented by scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM/EDX), are quantitatively compared with the virtual patterns on the basis of multifractal analyses. The formation of high magnesian calcite as a consequence of biogenic anaerobic decomposition of organic matter starts at certain initial calcite domains. In this stage an inhomogeneous and multifractal calcium distribution is characteristic. Nearly complete remineralization of organic matter leads to monofractal behavior of generalized fractal dimensions (D_B(q) ±1.84). The CAM results confirm that calcite formation is a self-determining morphogenetical process and diffusive transport processes of reactants within the mat affect the biogenic calcite formation.     

模拟固体中波动过程的细胞自动机建模研究

从统计物理的原理出发，首先分析了采用细胞自动机研究波动问题的建模方法，给出了一种研究弹性介质中纵波传播过程的细胞自动机模型，讨论了该模型中粒子数密度函数所满足的运动方程和对应的宏观方程。为了检验方法的正确性，对同一数值模型将细胞自动机方法的计算结果与波动方程的有限差分解进行了对比。结果表明，本文所采用的方法是可行的。     

Population growth and its spatial distribution as factors in the deforestation of Nang Rong, Thailand

Frontiers constitute a major source of global land cover change hot spots, with forests and grasslands being converted into agricultural uses. As such, frontiers provide an opportunity to see how people manipulate the land and their lives in the context of social, cultural and environmental constraints. This paper examines frontier settlement and land cover change in Nang Rong district, Northeast Thailand for the last half century. It uses a Cellular Automata (CA) model to explore the land cover consequences of alternative patterns of settlement in a setting where people establish dwelling units in nucleated villages and work agricultural plots that surround villages. Forested land around the center of a village is converted into agricultural uses in an inverse relationship to the distance from the village center, but frequently modified by biophysical conditions. Land at the center of the village may be reforested after the village is established as a source of shade as well as fruit and other products. Model variation in land cover change is more sensitive to the spatial reach of village households than their temporal reach, suggesting the important role that technology plays in how villagers travel to their fields (walking versus motorized transit).     

基于约束性CA的大都市郊区城镇增长的情景模拟与管控——以武汉市江夏区为例

大都市郊区是快速城镇化进程中空间演变最为频繁、人地矛盾最为突出的区域,尤其在中国加快推进“就地就近”城镇化战略的背景下,把握大都市郊区小城镇土地利用时空变化过程及其演变机制,对制定科学合理的管控政策和优化都市空间结构具有重要的现实意义。约束性元胞自动机(constrained Cellular Automata, constrained CA)能够通过简单的规则模拟复杂的城市动态演化过程。本文将土地利用总体规划指标、城镇空间发展战略布局、土地利用开发适宜性等,嵌入约束性CA的转换规则中,采用Logistic逐步回归法分析土地利用空间影响因素,对严格约束下的武汉市江夏区2020年土地利用进行情景模拟分析,并提出城市增长管控手段。结果表明：①研究时段内,江夏区城镇用地呈低效外延式扩张,土地利用集约节约程度较低,其人口规模并未有较大增长,对主城区人口的分散作用尚未真正形成;②约束性CA在模拟大都市郊区演化方面具有较高的可靠性,能够真实反映近郊小城镇的未来空间布局与结构,模拟结果与土地利用规划和城市规划较为契合;③将规划目标导向与现实发展趋势下的模拟结果进行叠加分析,可确定城镇增长需求与规划指标调控间冲突的空间分布,从而划定土地督察的重点监测区域,为加强大都市近郊区的违法用地监查和土地利用管控提供先验的预警知识。