Precipitable Water \(\Pwat\)

If \(\Pwat\) is not available in the source climate dataset, it can be estimated from surface air temperature \(T\) in Kelvin and surface relative humidity \(\RH\) in percent [17].

$$\begin{align} e_\text{s} &= \exp \left( 22.33 - 49.14 \frac{100}{T} - 10.922 \left( \frac{100}{T} \right)^2 - 0.39015 \frac{T}{100} \right) \\ \rho_\text{v} &= 216.7 \frac{e_\text{s} \RH}{T 100\% } \\ H_\text{v} &= 0.4976 + 1.5265\ \theta + \exp \left( 13.6897\ \theta - 14.9188\ \theta^3 \right) \\ \Pwat &= \max(0.1, 0.1 H_\text{v} \rho_\text{v}) \end{align}$$

Where \(e_\text{s}\) is the saturation water vapor pressure (millibar), \(\rho_\text{v}\) is the surface water vapor density (g/m³), \(H_\text{v}\) is the apparent water vapor scale height (km), and \(\theta = \frac{T}{273.15\text{[K]}}\).