Nature-Based Solutions for Sustainable Planning: Is the 5% Green Space Guideline for Peri-Urban Residential Development in Thailand Sufficient?

Rapid peri-urban sprawl is intensifying flood risk by replacing natural landscapes with dense, impervious residential developments. Thailand’s land use regulations require a 5% minimum green space allocation for new housing developments as a measure to promote livability and well-being. Green space also has the potential to sustainably manage stormwater runoff, but for Thailand’s peri-urban development, the question remains whether 5% green space is sufficient to reduce flood risk. As such, this study critically evaluates whether this 5% green space guideline is sufficient for peri-urban runoff and flood management in peri-urban Pathum Thani, particularly given the acceleration of Bangkok’s urban sprawl over the past 30 years. Using a multi-scalar framework, we integrated GIS spatial analysis of 164 gated communities (1995–2025) with site-specific PCSWMM hydrologic modeling to test baseline conditions and Nature-based Solution (NbS) interventions against 5-, 10-, 50-, and 100-year design storms. Findings reveal developers generally adhere to the 5% guideline, thereby addressing policy while maximizing salable land space. PCSWMM simulations show the 5% baseline alone does not adequately manage runoff, with localized residential flooding expected for a 5-year design storm under current baseline conditions. Scenario testing indicates a hybrid grey–green infrastructure approach would optimally manage flooding. Given economic barriers to expanding open space, converting roads to permeable pavements offers a possible optimization strategy. Ultimately, static area-based regulations remain insufficient; policies must transition to performance-based volumetric retention targets to mitigate downstream flooding and foster resilient communities.