A Spatial Relationship between Housing Estate Locations and Flooded Areas under the Comprehensive Land-Use Plan of Chiang Mai City

Abstract

Urban expansion in Chiang Mai has proceeded alongside a 135% increase in housing estate developments between 2011 and 2024, across the low-lying Chiang Mai-Lamphun Basin. This terrain is characterized by water accumulation, slow drainage, and elevated flood risk during heavy upstream rainfall - conditions reflected in the severe flood events of 2011 and 2024. This study examines spatial relationships between housing estate locations, flood extents, and terrain-based susceptibility to flooding within the Chiang Mai Comprehensive Land-Use Plan (2012), using GIS and the Relative Elevation Model (REM) to classify terrain-based physical susceptibility into three levels.

Findings show that 1) housing estates expanded into suburban areas along major transportation corridors, with single-detached house projects remaining the dominant type, large-scale projects recording the highest growth at 210.8% compared with 2011, and most projects falling within the medium-to-high value range; 2) flood extent within the Chiang Mai City Comprehensive Plan Area increased from 46.26 square kilometers across 13 subdistricts in 2011 to 103.18 square kilometers across 25 subdistricts in 2024; and 3) over 75% of project locations fall within areas of medium to high terrain-based susceptibility to flooding. The projects developed after 2011 continued to appear in previously flooded areas, while those unaffected in 2011 were inundated in 2024. These patterns suggest that the terrain is a foundational determinant of susceptibility, and flood history alone inadequately provides a complete basis for site-level risk assessment. Physical site characteristics should therefore be considered prior to development, and terrain-based susceptibility data should contribute to project design and land-use planning to reduce exposure to flooding in highly susceptible areas.