Intensification of Heat Extremes in Southeast Asia: Spatial–Temporal Analysis of Temperature Trends and Heat Events (1940–2023)

This study investigates the intensification of heat extremes in Southeast Asia from 1940 to 2023 using the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis version 5 (ERA5) data, validated against Global Historical Climatology Network (GHCN) station observational (r = 0.83). Regional warming rates range from 0.138°C to 0.240°C per decade, with the 25-year trend indicating a stable increase of 0.198°C/decade (SD = 0.029). Key extreme temperature indices show significant increases: warm nights (TN90p) rose by 2.9 days/decade, warm days (TX90p) by 7.4 days/decade, maximum daily minimum temperatures (TNx) by 0.19°C/decade, and maximum daily maximum temperatures (TXx) by 0.33°C/decade. Spatial analysis reveals stronger warming in mainland areas—especially Thailand and Vietnam—than in maritime regions. Seasonal analysis highlights summer as the most affected season, though all seasons exhibit significant warming. Since 2000, there has been a marked rise in the frequency of extreme heat events. The top 1% hottest months have become more common, with moderate, severe and extreme heat events increasing by 0.39, 0.27 and 0.17 months/decade, respectively. Multi-month heat events, while still largely seasonal, have expanded in duration and spatial coverage, with some lasting up to 6months. Prolonged multi-month heat and expanding extreme temperatures signal intensifying regional warming, demanding urgent adaptation despite remaining seasonal.