Asymmetric intensification of nighttime versus daytime precipitation extremes under warming

The intensification of the global hydrological cycle is a well-established consequence of anthropogenic climate change. However, how this intensification manifests across the diurnal cycle remains poorly understood, representing a critical blind spot in climate risk assessments. While daily-aggregated metrics consistently suggest a "wetter and more extreme" climate, they mask fundamentally different responses of daytime and nighttime precipitation to warming.Here we analyse high-resolution observational records from 2,399 stations across China spanning 1972–2024 and identify a distinct nighttime intensification regime that is increasingly dominant under warming. In regions experiencing active wetting, extreme precipitation (R95p) intensifies more rapidly at night than during the day, both in magnitude and spatial extent.This diurnal asymmetry reflects contrasting physical controls. Nighttime wetting is driven almost exclusively by increases in precipitation intensity (p < 0.001, Wilcoxon signed-rank test) and exhibits a tight thermodynamic scaling with background warming. By contrast, daytime precipitation changes arise from a heterogeneous combination of intensity and frequency adjustments, indicating a greater role for dynamical modulation.

These findings reveal a previously underappreciated amplification of nocturnal hydrometeorological hazards, including flash floods and landslides, that is systematically underestimated by daily-mean indicators. As global warming continues, the emerging dominance of nighttime precipitation extremes underscores the urgent need to incorporate diurnally resolved processes into climate risk assessment, infrastructure design and early-warning systems.