The urban expansion is always an inevitable issue in our human history and has become more intensive during a past several decades with explosive population growth of the world. The urban expansion is sometimes praised as a result of economic development, but at the same time, it might induce serious problems such as traffic jams, soaring price of real estate, trash problems, and shortage of natural resources. Thus, it is one of serious concerns many countries are facing. Therefore, a lot of modeling techniques have been introduced, discussed and developed for this problem (Batty, 1971; Forrester, 1969, Makse et al., 1995). Among them, cellular automaton (CA) is one of most dominant techniques, because both of the urban expansion and the CA inherently and similarly include complexity in their behavior. CA was initially introduced by John von Neumann and Stanislaw Ulam as a simple model for biological process such as self-production (Burks, 1971). CA may express any non-ABSTRACT Cellular Automaton (CA) consists of a regular grid cells of which states change according to simple repetitive rules regulated by their contiguous and adjacent cells, which often expresses an unexpected complexity. Thus, CA is one of the major techniques to imitate and/or assess complex behaviors of natural systems. CA can be applied to physical and biological phenomena, such as turbulence in fluid, patterns of biological growth, and wildfire, and also some human-induced phenomena such as urban growth that is the main target of this review. In 1970s, cellular approach was initially adopted in geography, showing the clue to the urban growth application. To overcome the limitation or constraints the conventional standard cell-space models inherently include, alternative formulations were theoretically proposed in 1980s. And the pioneering work applied to realistic cities was conducted in 1990s. Subsequently, numerous models have been presented by relaxing original rules to express reality and by introducing some additional techniques such as geographical information system and system dynamics, thus far. This paper reviews 87 published cellular automata studies on urban growth simulations, urban land use change assessments, urban planning and related information from 18 countries, and examines the characteristics of each relaxation method. In addition, the scale problems are frequently discussed in the validation of the CA model is addressed.

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Development and economic growth of cities in Northern Mongolia seriously depend on its national urban planning policy and also the accompanying social infrastructure. In addition, the city expansion might be restricted by water resources, as the area has only 300-400 mm of annual precipitation. In this research, despite of its inherent difficulty thus, development of Darkhan city in Northern Mongolia is simulated using a Cellular Automata Model for better decision-making in planning. The model is modified to accommodate to the locality of the city growth, in which ger that is a typical temporal residence of nomads is introduced as a part of the city. Population growth is assumed to be expressed by a logistic function with coefficients derived originally from an actual statistical record and fluctuated according to dynamically-changing water resources deficiency. The urban growth is regulated by these population dynamics as well as a potential of respective land for development that is given by the distances from a station, roads and a cluster of residence. Calibration is successfully executed and the fractal dimensions of the real urban area and simulated one become 1.56 and 1.60, respectively. The simulated results with several scenarios during 2008-2030 indicate that Darkhan might develop with fluctuation and attain to a certain magnitude, only if water demand increases gradually. Otherwise, Darkhan city, especially ger area might shrink due to water resources deficiency.

Groundwater resources at Dalad, Inner Mongolia were investigated by groundwater metering in 2013 as supplementary investigation during 2002-2006. Since Dalad is located in the middle reach area of the Yellow River basin and classified as arid or semi-arid area with less than 360mm precipitation and more than 2,200mm potential evaporation, the river water is not sufficiently supplied to the area and therefore, irrigation and industrial waters inevitably depend on groundwater resources. As a result of the investigation, groundwater levels at almost of all the observation wells have descended remarkably since 2005 and especially the decreases in the southern part of the objective area are severe by a range of 0.8-5.4m. The groundwater amount in the southern part in 2013 is roughly estimated to be 2.91×10 7 m 3 , which proves a distinct downward trend. According to the autoregressive-like forecasts, including the Holt-Winters method, the unconfined groundwater in the southern part would be unavailable in the middle of 2030's. The groundwater amount of the objective area is also decreasing severely and the increase in irrigation and industrial waters must be its potential reasons, except the decrease in the precipitation during 2005-2013. The change of the groundwater usage and flows might decrease the discharge of the Yellow River through the groundwater seepage and it is not only a water resources problem in this area, but also in the basin scale. Therefore, the groundwater management in this area is a pressing issue and should be done by local government or some water-utilization association against both irrigation water and industry water users. The water resources are inherently including uncertainty, so continuing observation is essential to maintain the water resources at Dalad.