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.

东南亚国家已经从以农村为主的城市迅速发展为以城市为主的社会，导致城市土地的迅速增加。城市土地的增加主要发生在三角洲和洪泛区，使人类和人力资产遭受洪灾危害。在这里，我们使用一种新的建模方法来评估东南亚大陆五个国家当前和未来的洪灾风险，该方法考虑了城市土地系统的差异。为此，我们在两种截然不同的情况下，按照城乡梯度绘制了城市土地图，并预测了到2040年的城市发展。城市扩展方案主要预测新城市地区的发展，而集约化则强调已经存在的城市地区的居民数量增加。随后，我们基于典型的建筑材料，使用沿农村-城市梯度的不同土地系统类别的国家特定暴露值，评估了因洪水风险而产生的预期年度损失。结果表明，在两种情况下，所有国家和地区的预期年度洪灾损失都将增加，从泰国的+ 8％到老挝的+ 211％。我们表明，较好的发展途径是与环境有关的。在集约化情景中，柬埔寨和老挝的洪灾风险增幅最大，而在城市扩张情景中，缅甸，泰国和越南的洪灾风险增幅最大。结果表明，在两种情况下，所有国家和地区的预期年度洪灾损失都将增加，从泰国的+ 8％到老挝的+ 211％。我们表明，较好的发展途径是与环境有关的。在柬埔寨和老挝，对于集约化情景，洪水风险的增加最大，而对于缅甸，泰国和越南，在城市扩张情景中，洪水风险的增加最大。结果表明，在两种情况下，所有国家和地区的预期年度洪灾损失都将增加，从泰国的+ 8％到老挝的+ 211％。我们表明，较好的发展途径是与环境有关的。在柬埔寨和老挝，对于集约化情景，洪水风险的增加最大，而对于缅甸，泰国和越南，在城市扩张情景中，洪水风险的增加最大。