THE DETECTION OF INCREASING VULNERAVILITY TO FLASH FLOOD IN PERI-URBAN AREA OF ULAANBAATAR, MONGOLIA THROUGH SPATIAL ANALYSIS OF VHR SATELLITE IMAGERIES

摘要

During the last 15 years, the growth of urbanization in Ulaanbaatar, the capital city in Mongolia, has been rapidly accelerated. In a peripheral area of Ulaanbaatar, residential areas called "ger areas" have developed rapidly in an unplanned manner owing to a land reform policy enacted in 2003, which allows Mongolians to have free private land for residential purposes and considerable migration caused by a natural hazard. Mongolia is a mostly arid country where it would be widely unknown that flood was one of the relevant disaster threats. The low precipitation and high evaporation of surface water are a result of the low absorptive capacity of the soil and, accordingly, higher than normal precipitation often results in runoffs, which have the potential to become flash floods. According to the land privatization law in the land reform policy, privatizing lands near water including flood prone areas is not allowed for Mongolian citizens. But in fact, ger areas have been encroaching on flash-flood prone areas. This study clarifies the both direct and indirect factors of ger areas expansion and the actual situation of their spatial distribution over flash-flood prone areas in the peripheral area of Ulaanbaatar using VHR satellite imageries. Those results showed disordered developments of house construction on the flash-flood prone areas spatially. Considering the factors of ger areas formulation based on previous studies and the detected results in this study, it was clarified that residents' first priority in making decision about their living places was not security from hazards but accessibility to urban areas. In addition, this study pointed out the fact that social infrastructure constructions were contributing to the formation of ger areas in flash-flood prone areas. The Mongolian government should not only develop legal systems for ger areas formation but also conduct initial inquiries immediately.