Projections of Heat Stress in Vietnam Using Physically-Based Wet-Bulb Globe Temperature

The wet-bulb globe temperature (WBGT) is a widely used index for assessing heat stress. However, many studies on heat stress under climate change rely on simplified WBGT calculations, which may introduce biases. In this study, high-resolution climate data and the physically-based WBGT model are employed to provide a more reliable assessment of future heat stress impacts across Vietnam and its seven sub-climatic regions. Projected changes are analyzed for three future periods — the near future (2021–2040), mid-future (2041–2060), and far future (2081–2100) — relative to the baseline period (1995–2014) under three Shared Socioeconomic Pathways (SSPs): SSP1-2.6, SSP2-4.5, and SSP5-8.5. Additionally, changes are assessed across different global warming levels (GWL), ranging from 1.5°C to 4°C above the pre-industrial level. Long-term trends throughout the studied period are also examined. The findings reveal significant increases in heat stress across Vietnam in the future. A major concern is the substantial increases in the number of days exceeding impact-relevant heat stress thresholds, most notably in the Red River Delta and Mekong River Delta, two most densely populated and agriculturally critical subregions of Vietnam. Heat stress emergence and intensity are closely linked to the radiative forcing of SSP scenarios and the GWLs, with higher forcing scenarios and warmer GWL producing more severe conditions and a greater frequency of exceedance days. The most severe impacts are projected under SSP5-8.5 as well as GWLs of 3°C and 4°C, indicating the urgent need to limit future warming to mitigate the risk of heat stress. Biases in simplified WBGT calculations are also discussed, suggesting significant overestimations of exceedance days in most of Vietnam. Such biases could lead to misleading assessments, unnecessary alarms, and potentially flawed adaptation strategies, highlighting the critical need for accurate WBGT modeling in climate impact research.