Mainstreaming Rain Gardens into Chiang Rai's Sustainable Development Agenda: A Desk-Based Policy Framework

Urban flooding and wetland degradation remain persistent challenges for secondary cities in Northern Thailand, including Chiang Rai. Conventional drainage and flood-control measures are limited in their ability to manage high-intensity rainfall while also supporting biodiversity and community well-being. This paper develops a desk-based policy framework to mainstream rain gardens as a nature-based solution (NbS) within Chiang Rai's sustainable development goals. Drawing on international literature on Japanese rain garden design and global low-impact development (LID) practices, the study adapts technical principles such as infiltration media layers, micro-topographic water retention, and plant zoning for potential use in tropical northern Thailand. Secondary data, including urban planning documents, national climate adaptation strategies, and open-source geospatial datasets, are synthesized to identify opportunities for integrating local governance. The framework proposes three pathways: (i) regulatory measures, like adding rain garden credits into urban building codes and stormwater management guidelines