Adaptation to Sea Level Rise: A Multidisciplinary Analysis for Ho Chi Minh City, Vietnam. Issue 12 (29th December 2017) - Scussolini, Paolo
Abstract: One of the most critical impacts of sea level rise is that flooding suffered by ever larger settlements in tropical deltas will increase. Here we look at Ho Chi Minh City, Vietnam, and quantify the threats that coastal floods pose to safety and to the economy. For this, we produce flood maps through hydrodynamic modeling and, by combining these with data sets of exposure and vulnerability, we estimate two indicators of risk: the damage to assets and the number of potential casualties. We simulate current and future (2050 and 2100) flood risk using IPCC scenarios of sea level rise and socioeconomic change. We find that annual damage may grow by more than 1 order of magnitude, and potential casualties may grow 5–20‐fold until the end of the century, in the absence of adaptation. Impacts depend strongly on the climate and socioeconomic scenarios considered. Next, we simulate the implementation of adaptation measures and calculate their effectiveness in reducing impacts. We find that a ring dike would protect the inner city but increase risk in more rural districts, whereas elevating areas at risk and dryproofing buildings will reduce impacts to the city as a whole. Most measures perform well from an economic standpoint. Combinations of measures seem to be the optimal solution and may address potential equity conflicts. Based on our results, we design possible adaptation pathways for Ho Chi Minh City for the coming decades; these can inform policy‐making and strategic thinking. Plain Language Summary: While sea levels gradually rise, concerns about coastal floods become higher, especially in low‐lying cities in the tropics. In Ho Chi Minh City, Vietnam, floods are already large and frequent. Here we look at how coastal floods, and their impacts, will evolve on this city during the coming decades. Using different scenarios of sea level rise and socioeconomic growth, we calculate that risk, in terms of urban damage and potential casualties, may increase even more than 10‐fold, if adaptation measures are not taken. We then simulate the realization of different adaptation measures: a ring dike, elevating part of the city, retrofitting buildings, and changing land use, and their combination. Most measures have the potential of reducing a considerable part of flood risk. The ring dike has the disadvantage that it would protect the inner city while increasing risk in outer districts; if implemented, it should therefore be combined with other measures. Also, the economic performance of most measures seems highly positive, suggesting that adaptation will generate high returns on investment. We conclude our analysis by generating possible adaptation pathways, to inform decisions on the type and timing of adaptation in Ho Chi Minh City. Key Points: Ho Chi Minh City's flood damage may increase beyond 1 order of magnitude in the next decades due to sea level rise and growth Several adaptation measures could effectively be applied and yield high economic returns on investment Analysis of adaptation pathways shows that combining measures over time can effectively reduce damage and risk to human lives