Data and code for sub-diurnal asymmetric warming has amplified atmospheric dryness since the 1980s

Atmospheric vapor pressure deficit (VPD), defined as the difference between near surface saturated vapor pressure (SVP) and actual vapor pressure (AVP), serves as a common indicator for evaluating atmospheric dryness. Rising near-surface VPD since the 1980s has been linked to increases in daily-mean surface air temperatures. However, it remains unclear whether the faster increases in daily maximum temperature (Tmax) relative to daily minimum temperature (Tmin) have played a more dominant role in the rising VPD. Here, based on sub-daily observations and atmospheric reanalysis data, we show that the faster rise in Tmax compared to Tmin over land has intensified atmospheric dryness from 1980 to 2023. This sub-diurnal asymmetric warming has led to a larger SVP increase than would have occurred with uniform temperature rise due to the near-exponential relationship between SVP and temperature. Meanwhile, AVP is more strongly influenced by Tmin, as air is typically closer to saturation during the cooler nighttime hours. Using reanalysis data, we quantify that sub-diurnal asymmetric warming has contributed to an additional ~18% increase in VPD on average over global land areas. Sub-daily station-based observations show a consistent picture, with sub-diurnal asymmetric warming contributing on average 30% to VPD intensification across all stations. Our findings indicate that sub-diurnal asymmetric warming has substantially amplified global warming’s effect on atmospheric dryness over the past four decades, with profound implications for terrestrial water and carbon cycles and wildfire risk.