Future VPD and precipitation projections

Changes in mean May-October VPD and total annual precipitation for each SSP-RCP scenario at 2030, 2050, 2075, and 2100 are presented in Projected change (%) in the mean May-to-October VPD by ecoregion under four SSP-RCP scenarios at 2030, 2050, 2075, and 2100 relative to 2018 based on the mean of six GCMs and Projected change (%) in the total annual precipitation by ecoregion under four SSP-RCP scenarios at 2030, 2050, 2075, and 2100 relative to 2018 based on the mean of six GCMs respectively. The changes are the mean of the changes from the six GCMs. Changes for each individual GCM can be found in the VPD and Precipitation worksheets of the supplementary spreadsheet included in the Climate Change Projections release.

VPD increases throughout the U.S. under all scenarios out to 2100 and the magnitude increases with global warming levels. The largest increases tend to be in the northeast and as the climate changes this spreads southwest and west. This gradient from northeast to southwest coincides with areas of lowest to highest present-day seasonal aridity.

Under SSP2-4.5, by 2030 the model domain is at least 1-5% more arid. By 2050, the north is projected to be 10-20% higher and everywhere else at least 5-10%. Under SSP5-8.5, most of the domain is 10-20% more arid by 2050. Note that under SSP1-2.6, the reduction in global warming between 2075 and 2100 results in reduced seasonal aridity.

Precipitation changes are both positive (wetter) or negative (drier) and the magnitudes of those changes are lower than for VPD. There is also some disagreement among the GCMs about the directional change in precipitation for specific scenarios and time-horizons, whereas all the GCMs agree that VPD will increase. By 2030, most of the model domain is 1-5% wetter and there is little difference among the four scenarios. By 2050, generally the northern half of the domain is wetter (5-10%) and the southern half is drier (-5% to -1%).