Analysis of urban expansion and flood risk change in Da Nang city in Central Vietnam

Type Journal Article - Journal of the Japanese Agricultural systems society
Title Analysis of urban expansion and flood risk change in Da Nang city in Central Vietnam
Volume 29
Issue 3
Publication (Day/Month/Year) 2013
Page numbers 123-134
Flood is widely considered to be the most hazardous, frequent, and widespread source of disaster risk throughout the
world. Urban expansion into flood zone areas and the possible effects of climate change are further elevating the risk of
flooding. In Vietnam, Da Nang is one of the cities with the highest rate of urbanization. However, during the last 10
years, Da Nang has been faced with flood disasters that have caused loss of life and damaged livelihoods and
infrastructure, as well as disrupted economic activities. This study analyses the urbanization process and flood risk, and
their relationship, using remote sensing and geographic information system techniques. Time series Landsat TM/ETM
images and multi-seasonal ALOS images were analyzed to generate temporal land use/cover maps (for 1990, 2001,
2007, and 2010), which were then utilized to analyze the urban expansion process. Flow direction characteristics
derived from the Aster GDEM (30 m resolution) and the past flood experiences obtained from ALOS PALSAR image
was integrated to analyze and rank the potential flood hazard zones. Flood risk was then obtained by evaluating the
flood hazard and demographic vulnerability with a ranking matrix in two-dimensional multiplication model. The results
show that Da Nang has experienced a high rate of urbanization over the past 20 years, the approximate rate of increased
built-up in the area was 220 %. The main directions of urbanization are seen in the West, Northwest, South, and
Southeast and along the coastal line. The flood risk analysis represents that the most of the major high and moderate
risk areas are located in the depression lowlands as well as along the banks of river channels. By overlaying expanded
urban/settlements during 20 years (from 1990 to 2010) with those flood risk areas, we identified that some of
urbanization have clearly invaded into the higher risk areas of flood. The potential risk revealed by such
urban/settlement expansion into the relatively high flood risk areas increased from 1.9 to 3.5 % (nearly twofold) in the
urbanization periods of 1990-2001 and 2007-2010, respectively.

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