Dampened Diurnal Cycles of Hot‐Wet Extremes in Urban Areas Contrast With Thermally Driven Daytime Stress in Rural Landscapes of Beijing‐Tianjin‐Hebei Region

Abstract Hot‐wet extremes (HWEs) are intensifying in the Beijing–Tianjin–Hebei region, but their fine‐scale diurnal urban–rural contrasts remain unclear. Using summer observations from 1,962 automatic weather stations during 2016–2024, we identify threshold‐exceeding HWE days and show that urban areas experience more compound day–night and independent nighttime HWEs, whereas rural areas are more often affected by independent daytime days. This contrast is especially evident for nighttime extremes in recent years. A thermodynamic decomposition of wet‐bulb temperature ( Tw ) shows that temperature dominates diurnal Tw variability (>60%) in both environments, but cities exhibit dampened diurnal thermal amplitudes and a larger nocturnal relative humidity contribution (∼36%). These results suggest that urban nighttime humid‐heat risk is more closely associated with relative‐humidity regulation than with absolute moisture alone, highlighting the need to consider nighttime moisture conditions, alongside temperature reduction, in heat‐risk mitigation.