Assessment of the effectiveness of flood adaptation strategies for HCMC

Abstract

Abstract. Coastal cities are vulnerable to flooding, and flood risk to coastal cities will increase due to sea-level rise. Moreover, Asian cities in particular are subject to considerable population growth and associated urban developments, increasing this risk even more. Empirical data on vulnerability and the cost and benefits of flood risk reduction measures are therefore paramount for sustainable development of these cities. This paper presents an approach to explore the impacts of sea-level rise and socio-economic developments on flood risk for the flood-prone District 4 in Ho Chi Minh City, Vietnam, and to develop and evaluate the effects of different adaptation strategies (new levees, dry-and wet proofing of buildings and elevating roads and buildings).A flood damage model was developed to simulate current and future flood risk using the results from a household survey to establish stage-damage curves for residential buildings. The model has been used to assess the effects of several participatory developed adaptation strategies to reduce flood risk, expressed in expected annual damage (EAD). Adaptation strategies were evaluated assuming combinations of both sea-level scenarios and land-use scenarios. Together with information on costs of these strategies, we calculated the benefit-cost ratio and net present value for the adaptation strategies until 2100, taking into account depreciation rates of 2.5 % and 5 %.The results of this modelling study indicate that the current flood risk in District 4 is USD 0.31 million per year, increasing up to USD 0.78 million per year in 2100. The net present value and benefit-cost ratios using a discount rate of 5 % range from USD −107 to −1.5 million, and from 0.086 to 0.796 for the different strategies. Using a discount rate of 2.5 % leads to an increase in both net present value and benefit-cost ratio. The adaptation strategies wet-proofing and dry-proofing generate the best results using these economic indicators. The information on different strategies will be used by the government of Ho Chi Minh City to determine a new flood protection strategy. Future research should focus on gathering empirical data right after a flood on the occurring damage, as this appears to be the most uncertain factor in the risk assessment.

Preface: Flood-risk analysis and integrated management

“…When compared to risks of other large-scale engineering systems (e.g., other flood prone areas, dams and the nuclear sector) and acceptable risk criteria found in literature, the risks are relatively high -despite the recent major improvements to the flood protection system. An approach to explore the influence of sea-level rise and socioeconomic developments on flood risk for the floodprone District 4 in Ho Chi Minh City is provided by Lasage et al (2014). They show that expected annual damage (EAD) in this district could rise from USD 0.31 million to up to USD 0.78 million in 2100.…”

“…In addition to providing an approach to explore the impacts of sea-level rise and socioeconomic developments on flood risk in Ho Chi Minh City, Lasage et al (2014) develop and evaluate the effects of different adaptation strategies like new levees, dry and wet proofing of buildings and elevating roads and buildings. The benefit-cost ratios and net present values for the adaptation strategies were estimated until 2100.…”

Exposure to Floods, Climate Change, and Poverty in Vietnam

“…The inundation maps were used in an earlier flood risk study of HCMC (Lasage et al 2014), and were composed with At the national-level analysis, we overlay the flood hazard maps developed for this study with spatial socioeconomic data. For Vietnam, the World Bank has produced estimates of the number of people within each district who live below the poverty line: this "poverty map" is displayed in Map 4a, and the full methodology can be found in (Lanjouw, 5 Marra, and Nguyen 2013).…”

“…Sci. We examine these dynamics in Ho Chi Minh City, using high-resolution local-scale flood maps designed specifically for HCMC (Lasage et al 2014) and proxy for poverty using the spatial location of potential slums from the Platform for Urban Management and Analysis (PUMA) data set (World Bank 2015). The PUMA data set also has information on locations of urban expansion from 2000 to 2012.…”

Assessment of flood loss model transferability considering changes in precaution of flood-affected residents in Germany

“…The positive loss reducing effect of private precautionary measures, especially of propertylevel mitigation measures, has been confirmed by an ( 2016) increasing number of studies, either by risk assessment modelling (e.g. [21][22][23][24]), expert judgement (e.g. [25][26][27][28]) or empirical studies (e.g.…”