from pg.38 of Lu, N. and J.W. Godt, 2013. Hillslope Hydrology and Stability. Cambridge University Press. 437pp.)
\[ e_s=610.49 \cdot \exp\frac{17.625\cdot T_C}{T_C+243.04}, \]
Saturation Vapour Pressure (\(e_s\)) [Pa=N/m²], where \(T_C\) is air temperature in degrees Celsius. Plotting this relationship between temperatures -30°C and 50°C (R²=1):