Impacts of future sea level rise on fluvial and coastal flood risk in Bangkok, Thailand

Abstract

Many communities in low-lying coastal cities around the globe already live with threats from sea level rise, coastal flooding and the impact of climate change. Likewise, Bangkok, the capital of Thailand, one of the low-lying coastal mega-cities in Southeast Asia and also the most populous city with its population of more than 10 million, already faces flooding driven by heavy rain and other events. Without doubt, climate change impacts on Bangkok may now be unavoidable. Over decades, the rapid changes of urbanization and human activities have made Bangkok more vulnerable to the risks of flooding both directly and indirectly; this has been significantly proved in the past decade of extreme weather influencing the big floods. The Great Flood of 2011, which was Thailand’s worst flood in decades, caused the highest- ever economic loss from a freshwater flood disaster worldwide, especially Bangkok and its vicinity which was inundated for two months. This research aims to evaluate the socio- economic impacts and future flood risks due the impact of climate change’s induced sea level rise in Bangkok Metropolitan region (BMR), Thailand.

This research purposefully highlights the importance of flood risk management in BMR. In order to minimize the impact of floods to the population, an effective flood management is needed. Flood risk management helps to reduce the risk to people from flood events; it helps to ensure that they understand the nature of the risks, are prepared and learning to live with this risk. For more frequent extreme weather, an effective plan will be crucial to enable more practical and effective adaptation in the changing of climate. Therefore, to achieve proactive planning and flood management, hydrodynamic models have a high potential to contribute a statistical analysis for better decision making for policy makers. In this study, LISFLOOD- FP model was constructed to simulate the 2011 Great Floods in Bangkok, Thailand under the scenarios of sea level rise; 2030, 2050, 2100 and 2150 with different river flow rates. The impacts caused by the rise in sea level along with the changes in river flow velocity were examined in the scenario results. Flood impact was analysed to determine the areas of flood extent and hazard with the projected sea level rise, and how likely the population in the diverse aspects of the society will be affected if this 2011 flood event reoccurred, particularly, those vulnerable populations and communities who may have a significant impact of flooding. The scenario results signify that the extent of flooded areas is strongly influenced by sea level rise, not the change in flow velocity. The result with no changes in flow velocity in the upcoming sea level rise projection of 0.39m by 2050 shows an increase in the extent of flooded areas by 14.56% or 628.7 km2. Especially, under the highest scenario of global sea level rise by 2100, about 87% of the study area will be inundated.

All in all, this study reveals that flood risks in Bangkok will be increased given that the projection of sea level rise will make the city more vulnerable to flood risks by :(i) highlight the socio-economic impact to diverse population across 50 districts of Bangkok and its vicinity, particularly, the residents with lower income will more likely be affected by the impact of sea level rise; (ii) identify the population who will be most at risk in flood. Additionally, along with the ongoing subsidence problems in Bangkok, this will increase the magnitude of the problems. Although the flood protection in Bangkok has been significantly upgraded since the great flood in 2011, it is not proven that these changes would be able to protect or reduce the impact of flooding in BMR. Especially, BMR and its vicinity, taking into account multiple key risk drivers if coinciding with severe flooding, it will exacerbate of SLR, as there is no significant policy available to mitigate the impact of SLR for both short and long terms.