Historic and projected changes in vapor pressure deficit suggest a continental‐scale drying of the United States atmosphere

Summary

Abstract Via air temperature increases and relative humidity changes, climate change will modify vapor pressure deficit (VPD), which is an important determinant of water vapor and CO 2 exchange between the land surface and atmosphere. VPD is the difference between the water vapor the air can hold at saturation ( e s ) and the actual amount of water vapor ( e a ). Here we assess changes in VPD, e s , and e a in the United States (U.S.) for the recent past (1979–2013) and the future (2065–2099) using gridded, observed climate data and output from general circulation models. Historically, VPD has increased for all seasons, driven by increases in e s and declines in e a . The spring, summer, and fall seasons exhibited the largest areal extent of significant increases in VPD, which was largely