The Heat of Urban Growth: How Land Use Drives Bangkok’s Rising Temperature Extremes

A World Bank study reveals that Bangkok’s dense urbanization significantly intensifies heat stress, especially at night, with some areas up to 6.4°C hotter than nearby rural zones. Seasonal and land-use variations highlight the urgent need for climate-responsive urban planning.

In a landmark study by the Urban, Disaster Risk Management, Resilience and Land Global Department of the World Bank, supported by the Global Facility for Disaster Reduction and Recovery (GFDRR), researchers Juan A. Acero, Vivek K. Sinh, and Steven L. Rubinyi offer a comprehensive look at how Bangkok’s expanding urban sprawl is intensifying heat stress across the city. Using the advanced Weather Research and Forecasting (WRF) model alongside the Building Effect Parameterization (BEP) and Building Energy Model (BEM), the study captures how land use, building morphology, and seasonal weather conditions interact to form intense Urban Heat Island (UHI) effects across the Bangkok Metropolitan Administration (BMA). The research simulated three distinct periods, December 2019, March 2020, and July 2020, representing Bangkok’s cool and dry, hot and dry, and wet monsoon seasons. The findings are both compelling and concerning: Bangkok’s tropical heat is not only worsening, but it is increasingly dictated by how the city is built.

Extreme Heat Builds Overnight in the Cool and Dry Season

Of all the seasonal simulations, December revealed the most intense urban-rural temperature differences. During early morning hours, compact city zones were found to be up to 6.4°C hotter than nearby rural areas. This stark temperature contrast was concentrated in central districts like Pom Prap Sattru Phai, Samphanthawong, and Ratchathewi, where up to 100% of the area experienced nighttime UHII values above 4°C. The most affected populations reside in high-density areas with limited greenery and high-rise infrastructure. In contrast, outer districts like Nong Chok and Lat Krabang remained relatively cooler, often with mean UHII close to zero. This thermal disparity is particularly alarming as it affects people's ability to recover from daytime heat stress during sleep, while also pushing up nighttime energy demand due to increased air conditioning usage.

Scorching Days, Subtle Nights in the Hot and Dry Season

March, which typifies the hot and dry season, is paradoxically less intense in UHII terms despite being the hottest month in absolute temperatures. This is primarily because low soil moisture levels reduce the cooling potential of rural zones, narrowing the urban-rural thermal gap. While average urban temperatures soar past 34°C, the UHII effect remains relatively modest, with nighttime differentials hovering around 1°C. However, areas such as Don Mueang and Sai Mai still recorded evening UHII values above 4°C, highlighting that localized urban form continues to drive heat concentration. Notably, this period sees the emergence of a unique phenomenon: the urban cool island. During daytime hours, urban temperatures occasionally fall below those of rural surroundings, attributed to dense building structures blocking solar radiation and the delayed heating of shaded surfaces. But these cool spells are brief, and by evening, the heat returns with force.

Monsoon Rains Moderate the Heat, but Not Everywhere

July's wet monsoon season brings much-needed moisture and cloud cover, creating generally lower UHII levels compared to December. Yet the cooling effect is uneven. While soil moisture helps rural areas retain lower temperatures, central districts still experience significant nighttime heat retention, with Pathum Wan reaching UHII levels of 3.9°C. Unlike the hot and dry season, the monsoon period does not foster daytime cool islands, as moist rural surfaces maintain cooler conditions throughout. Even though evening and night-time UHII values are lower than in the dry season, approximately 85% of Bangkok’s population still experiences a temperature differential of 2–4°C. This continued exposure, even under favorable weather conditions, shows the persistent nature of urban heat in dense metropolitan areas.

Built Environment Shapes the Intensity of Heat

One of the clearest messages from the study is that land use directly influences the severity of urban heat. Compact high-rise areas consistently recorded the highest UHII values, reaching daily averages of 3.6°C in December. These were followed by compact mid-rise and industrial zones. Low-rise residential areas with greenery had lower UHII levels, and naturally vegetated zones such as croplands and forests recorded the lowest, but still notable, heat differences. Interestingly, these natural zones within BMA were not entirely free from urban heat influence, often registering UHII of around 1°C due to the advection of warm air from nearby city centers. Even more revealing is the timing of UHII peaks, which typically occur just before sunrise. These pre-dawn surges in temperature are especially problematic because they coincide with the hours when people most need their bodies to cool down from the previous day’s heat.

A Call for Climate-Responsive Urban Planning

The implications of Bangkok’s urban heat problem go far beyond discomfort. Medical studies cited in the report show that every 1°C rise in temperature beyond 29°C can increase mortality risk by 2–6%. When combined with high air pollution levels, which Bangkok often suffers from, the health risks multiply, sometimes increasing by more than 20% in total. Furthermore, rising nighttime temperatures increase reliance on air conditioning, putting a strain on the city’s energy infrastructure and deepening environmental degradation. The study also reveals that UHI primarily affects daily minimum temperatures rather than daytime highs. For instance, during the wet monsoon season, minimum temperatures in urban zones were up to 6°C higher than in rural sites. This asymmetric warming alters the city’s entire thermal profile. For Bangkok, the path forward must involve greening urban centers, promoting reflective materials, revising zoning laws, and integrating climate models into infrastructure planning. As the city grows and climate change accelerates, adapting the urban form will be critical to ensuring resilience, equity, and livability for its millions of residents.