\begin{equation}
A_{moi} = max(\, 0.1, \frac{\sum_{i=1}^{n} H_{i}e^{-z_{i}/\zeta}\Delta_{i}}{ \sum_{i=1}^{n} e^{-z_{i}/\zeta}\Delta_{i}} \,)
\end{equation}
where $A_{moi}$ is the plant available moisture, $H_{i}$ is the soil humidity (relative soil moisture) of the $i$-th layer, $z_{i}$ is the depth of the layer, and $\Delta$ is its thickness. $\zeta$ is the root density profile, which is 1.5m for trees and 0.3m for grasses (Krinner et al., 2005).

