Potential of Blue-Green Infrastructure for stormwater management in informal settlements upgrading programmes: Case study of Baan Mankong in Bangkok, Thailand

Cities increasingly rely on Blue-Green Infrastructure (BGI), such as green roofs or pervious pavements, to manage stormwater. The upgrading of informal settlements, areas characterised by low access to basic services, provides an opportunity to incorporate BGI in many Global South cities. However, few studies examine the hydrologic performance of BGI for the urban forms and climate conditions of such upgrading projects. Here, we explore the potential of BGI in reducing runoff volume in the Baan Mankong program in Thailand, a world-acclaimed, government-supported informal settlements upgrading initiative. Using the PCSWMM hydrological software, we compare the effectiveness of BGI scenarios in reducing runoff for different housing typologies. BGI scenarios include green roofs, pervious pavements, and raingardens in three existing sites and one reimagined design. Retrofitting the sites with green roofs and pervious pavements was generally the most effective option, although the results depend on the site design (2% to 48% runoff reduction in high rainfall events). An alternative design with less built-up area significantly reduced flooding (36% to 60% runoff reduction in high rainfall events). Overall, our study provides insights into the hydrological trade-offs and opportunities of implementing BGI in upgraded informal settlements, both for retrofitting upgrading projects and future flood-resilient designs.