Examination of Urban Expansion and its Environmental Impacts using Remotely Sensed Time-Series Imagery in Ulaanbaatar, Mongolia

Urban areas are expanding rapidly because of the inability of existing urban infrastructure to sustain the population and its activities. Ulaanbaatar is one of cities in developing countries in terms of its swift development, and this has occurred particularly since its transition from a planned economy to a free-market economy in 1992. However, the insufficient authority of the current master plan and the lack of implementation of the land privatization policy since 2003 have resulted in a failure to effectively manage land use. Consequently, large numbers of residential plots have been developed in peripheral regions of the city. This research aims to clarify the urban expansion processes and understand their environmental impacts in Ulaanbaatar. Remotely sensed imagery has recently become a standard tool for the analysis of urban expansion processes, but analysis conducted using only a specific type of remotely sensed imagery can lead to a misunderstanding of such processes. Therefore, the use of multi-scale analyses using remotely sensed imagery with different spatial and temporal resolutions should be explored. In this research, very high spatial resolution satellite imagery from IKONOS and Quickbird, and medium-resolution satellite imagery from the MODerate resolution Imaging Spectroradiometer (MODIS) were mainly used. Analysis using object-based spatial data of urban components extracted from very high spatial resolution satellite imagery in a time series was used to delineate the residential-scale process of urban expansion in a fringe area. This, in combination with a spatial modeling approach, indicates that urban infrastructure significantly contributed to the urban expansion. To understand the urban expansion processes in a wider range of the city, the pixel-based analysis was applied using MODIS time series with a more spatially rough, but high frequency resolution. The breaks for additive seasonal and trend (BFAST) method, which is able to robustly and automatically derive the timing and locations of land cover changes from spatio-temporal data, was applied for the first time in urban expansion analysis. This analysis showed that land cover changes occurred at the edge of the city center region in Ulaanbaatar in earlier time, and that the changes tended to occur at a later time with increasing distance from the city center during the period 2000–2010. Owing to the population concentration, which is the primary cause of urban expansion in Ulaanbaatar, vegetation biomass and vegetation land cover around the city have been highly affected by anthropogenic pressures. Thus, environmental changes to vegetated surfaces were estimated as a proxy of the environmental impacts of urban expansion. This analysis found that vegetation biomass decreased around the urban area in grassland and forests where anthropogenic activities such as overgrazing and illegal logging were reported. This research highlights the effects of the clash between two different land management legislation frameworks, the master plan and the land privatization policy. This research not only reinforces the need for an effective urban plan for Ulaanbaatar, but also provides operational information such as maps and GIS layers for planning purposes, which document the actual extent of the urban surfaces, the patterns of development, and the location of expanded and degraded areas of urban expansion using remote sensing technologies.