Urban populations, especially vulnerable communities, are facing increasing flood risks due to the rising frequency of floods caused by climate change and rapid growth. Effective mitigation requires moving beyond physical and environmental approaches to embrace social dimensions. This study examined the prevailing social drivers of floods in flood-prone communities in Metro Manila, Philippines using social data acquired through a door-to-door household survey. Responses were assessed using exploratory and combined qualitative and quantitative analyses. The findings of this study show that the decision to remain in flood-prone areas is influenced by attachment to homes and acclimatization to the environment, convenience of accessible amenities to fulfill basic needs, livelihood dependence, economic considerations, house ownership, and perceived safety from floods. When choosing a place to live, the complex tradeoffs of residents are reflected, wherein daily economic concerns outweigh the possible flood damage. By understanding the social drivers of residency, policymakers and community leaders can develop targeted interventions and formulate strategies to address the root causes of the problem, leading to effective interventions and enhancing the resilience of urban communities.

International frameworks such as the Sustainable Development Goals and the Sendai Framework for Disaster Risk Reduction 2015−2030 require the quantification of country-based flood risk. However, few approaches at the global scale include the three necessary components (hazard, exposure, and vulnerability) for determining disaster risk and are country-based assessments, owing to major challenges such as limited data availability and vulnerability proxy selection. Therefore, in this study, a method was developed with the following features: Incorporating the hazard, exposure, and vulnerability components; Applicable to the vast majority of countries in the world; Visualizing priority countries and illustrating effective measures and strategies; Clear and easy to understand by leaders and decision makers of international organizations, governments, and other stakeholders; Identifying each country’s challenges and providing guidance on specific issues for more detailed investigation and policy creation; Including more extensive factors compared with past studies. In Asia and the Pacific, the Flood Risk Index computed by the developed method is compared with the fatality ratio, and the results show that improving flood resilience secures people and society regardless of the magnitude and frequency of floods. Analysis at the global scale visualizes regional tendencies and indicates that countries closer to the equator have higher flood risk. Analysis of country-based flood risk based on five indicators demonstrates that the developed method can assist international organizations, governments, and other stakeholders to further examine country-specific conditions and establish and implement policies and strategies toward building a resilient society and achieving international targets.

Urban flooding increasingly challenges rapidly expanding cities in developing countries. Migration, weak urban planning, and unregulated land use collectively intensify flood risk. Effective flood mitigation requires understanding the dynamic interactions between physical and social processes that shape urban vulnerability. This study examines how migrant households in flood-prone areas adapt over time to enhance resilience. The study applies a dynamic flood risk framework using settlement-duration cohorts from 560 peri-urban households in Phnom Penh. Findings show that rapid in-migration into flood-prone zones has increased physical exposure to flood hazards. Migrants’ adaptation and resilience, however, develop gradually, reducing vulnerability only over time. Newer migrants remain highly vulnerable due to insecure housing, limited renovation, and restricted access to flood information. Long-term migrants face structural and economic challenges, including low income, limited access to credit, and deteriorating housing conditions. Mid-term migrants demonstrate the strongest adaptive capacity, supported by stable income, housing investment, and access to flood information. Overall, the study contributes to more dynamic urban risk frameworks that incorporate demographic and socioeconomic transitions. These insights are relevant for other rapidly growing cities, particularly those in Southeast Asia.

Rapid peri-urban expansion has intensified flood risk in Southeast Asian cities through wetland loss, rural–urban migration, and delayed infrastructure development. This study examines the spatial and temporal dimensions of flood risk in Phnom Penh, Cambodia using a multi-factor framework based on hazard, exposure, vulnerability, and coping capacity. Vulnerability and coping capacity are analysed at both community and household levels. Migrant settlement duration captures differences in exposure and adaptive capacity over time. A composite flood risk index is constructed from survey data using the Rank Order Centroid weighting method. Results show that exposure is the dominant driver of flood risk, exceeding the influence of hazard intensity and largely shaping spatial patterns. Community-level vulnerability and coping capacity exert stronger effects than household-level characteristics, highlighting the importance of infrastructure and local settings. Flood risk varies across migrant groups: new migrants face the highest risk due to elevated exposure and vulnerability, while long-term migrants experience lower risk as adaptive capacity improves over time. However, risk reduction varies across groups, with persistent challenges linked to infrastructure and disaster preparedness systems. These findings highlight the importance of community-scale resilience strategies and targeted infrastructure investment to reduce flood risk in rapidly urbanising cities.

Flooding poses a major hazard to rapidly urbanising cities in Southeast Asia, and risks are projected to intensify under climate change. Accurate risk assessment, however, is hindered by scarcity of hydrological and topographic data. Focusing on the Lower Prek Thnot River Basin, a peri-urban catchment of Phnom Penh, Cambodia, the study applied the Rainfall–Runoff–Inundation model and systematically augmented inputs: hourly satellite rainfall data, field-surveyed river cross-sections and representation of hydraulic infrastructure such as weirs and pumping. Validation used Sentinel-1 SAR-derived flood-extent maps for the October 2020 event. Scenario comparison shows that rainfall input and channel geometry act synergistically: omitting either degrades performance and spatial realism. The best configuration (Sim. 5) Accuracy = 0.891, Hit Ratio = 0.546 and True Ratio = 0.701 against Sentinel-1, and reproduced inundation upstream of weirs while reducing overestimation in urban districts through pumping emulation. At the study’s 500 m grid, updating land use from 2002 to 2020 had only a minor effect relative to rainfall, geometry and infrastructure. The results demonstrate that targeted data augmentation—combining satellite products, field surveys and operational infrastructure—can deliver robust inundation maps under data scarcity, supporting hazard mapping and resilience-oriented flood management in rapidly urbanising basins.

The present study discusses sediment transport processes in the drainage basin of the Kelani River using the RSR model which is able to evaluate bedload and suspended load and their sediment size distribution at any cross-sections of stream channels. This model was applied to the 2016 and 2018 flood events to investigate temporal and spatial characteristics of sediment transportation. Simulated results show that the accumulated bedload volumes are comparable to the accumulated suspended load in these flood events. Besides, they show that the material of the suspended and bedload tend to mix in the peak flood stage, and the field data on the upstream and downstream sediment size distribution are similar to those of bedload and suspended sediment, respectively.