VPD rises by 0.64 hPa per decade in HIST and 0.27 hPa per decade in NAT; thermodynamic forcing contributes about 58% of the total continental VPD trend. Spatial VPD and temperature trends correlate at 0.83, as expected from the approximately exponential Clausius–Clapeyron increase of saturation vapour pressure with temperature.

contributing around 58% to the overall trend

The increase in VPD is consistent with rising temperature and declining soil moisture: VPD increases in both HIST and NAT since 1980 at rates of 0.64 and 0.27 hPa per decade, respectively. The thermodynamic forcing thus emerges as the primary driver of the VPD trend at the continental scale, contributing around 58% to the overall trend. Because saturation water vapour pressure increases approximately exponentially with temperature according to the Clausius–Clapeyron relation, we find an expected high correlation between the spatial patterns of VPD and temperature trends (Pearson correlation = 0.83), with the strongest increase in southeastern Europe and Spain.