Modeling urban development and its exposure to river flood risk in Southeast Asia

Lars Tierolf,Hans De Moel,Jasper Van Vliet

doi:10.1016/j.compenvurbsys.2021.101620

Lars Tierolf, Hans De Moel + Show 1 more

Open Access

https://doi.org/10.1016/j.compenvurbsys.2021.101620

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Abstract

Countries in Southeast Asia have been developing quickly from a predominantly rural to predominantly urban society, leading to a rapid increase in urban land. This increase in urban land has mainly occurred in river deltas and floodplains, exposing humans and human assets to flood hazard. Here we present an assessment of current and future flood risk in five countries of mainland Southeast Asia, using a new modeling approach that accounts for differences in urban land systems. To that effect we mapped urban land on a rural-urban gradient and projected urban development until the year 2040 in two contrasting scenarios. The urban expansion scenario mainly projects the development of new urban areas, while the intensification emphasizes an increase in the number of inhabitants in already existing urban areas. Subsequently, we assessed the expected annual damage due to flood risk, using country specific exposure values for different land-system classes along the rural-urban gradient, based on typical construction materials. Results indicate that expected annual flood damage will increase in all countries and in both scenarios, ranging from +8% in Thailand to +211% in Laos. We showed that preferable development pathways are context dependent. In Cambodia and Laos, the increase in flood risk was largest for the intensification scenario, while for Myanmar, Thailand and Vietnam, the increase in flood risk was largest in the urban expansion scenario.

Highlights

Flooding is one of the most disruptive and frequent of natural haz ards, resulting in damage to the built environment, temporal displace ment and loss of life and livelihood
The worldwide impact of river flooding is expected to in crease, mainly due to climate change, increasing population density, and economic development in flood prone areas (Jongman, Ward, & Aerts, 2012; Vinke et al, 2017). This trend is especially relevant in mainland Southeast Asia, where the impact of economic development on future flood risk far surpasses that of climate change (Winsemius et al, 2016)
As using a single set tlement class only increases flood damage when the urban area in creases, our analysis reveals that in these calculations the expansion scenario will always yield the largest increase in flood risk, whilst our analysis shows the opposite for Cambodia and Laos

Summary

Introduction

Flooding is one of the most disruptive and frequent of natural haz ards, resulting in damage to the built environment, temporal displace ment and loss of life and livelihood. The worldwide impact of river flooding is expected to in crease, mainly due to climate change, increasing population density, and economic development in flood prone areas (Jongman, Ward, & Aerts, 2012; Vinke et al, 2017). This trend is especially relevant in mainland Southeast Asia, where the impact of economic development on future flood risk far surpasses that of climate change (Winsemius et al, 2016). The 2011 flooding of the Chao Phraya river resulted in an estimated damage to housing of approximately 2.7 billion US dollar (The World Bank, 2011). The combination of economic development and urban development likely leads to a large increase in building assets exposed to flood risk (Winsemius et al, 2016)

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