Erosion of Natural Cooling Infrastructure in Southeast Asian Cities: Comparative Land Surface Temperature Effects of Wetland and Paddy Loss in Phnom Penh and Can Tho

Lik Ren Tai 

Rapid urbanisation across Southeast Asia is displacing two natural cooling resources: urban water bodies and peri-urban paddy fields. The biophysical relationship between land cover and land surface temperature (LST) is established at regional and continental scales, but conversion-attributable, satellite-derived quantification of wetland and paddy loss at city scale, compared directly within a single study design, has not previously been undertaken. This study compares urban wetland loss in Phnom Penh, Cambodia, and paddy conversion in Can Tho, Vietnam, across six anchor epochs (2000–2024), using Landsat-derived land-cover classification and a difference-in-differences design to isolate conversion-attributable LST anomalies from background warming. In Phnom Penh, water-body loss produced a DiD-corrected anomaly of 7.13°C, concentrated in a small number of large, documented infilling events. In Can Tho, paddy loss produced a smaller anomaly of 0.55°C, diffused across thousands of small, independent conversions. The comparative synthesis does not resolve to a single answer: measured as per-unit-area intensity, Phnom Penh's loss is roughly seven times more severe; measured as total city-wide impact, Can Tho's larger converted extent gives greater aggregate impact instead. This asymmetry reflects a structural contrast in how the two cities lose cooling infrastructure, Phnom Penh through concentrated, large-scale events and Can Tho through diffuse, many small conversions, with direct implications for mitigation design in each context. The findings show that the thermal cost of cooling-infrastructure loss cannot be captured by a single metric: it depends on which resource is lost, how much, and whether severity or scale is the question being asked.