Actual Water Uptake

Once the potential water uptake has been modified for soil water conditions, the actual amount of water uptake from the soil layer is calculated:

$w_{actualup,ly}=min\lfloor w''_{up,ly},(SW_{ly}-WP_{ly})\rfloor$ 5:2.2.7

where $w_{actualup,ly}$ is the actual water uptake for layer $ly$ (mm H$_2$O), $SW_{ly}$ is the amount of water in the soil layer on a given day (mm H$_2$O), and $WP_{ly}$ is the water content of layer $ly$ at wilting point (mm H$_2$O). The total water uptake for the day is calculated:

$w_{actualup}=\sum^n_{ly=1} w_{actualup,ly}$ 5:2.2.8

where $w_{actualup}$ is the total plant water uptake for the day (mm H$_2$O), $w_{actualup,ly}$ is the actual water uptake for layer $ly$ (mm H$_2$O), and n is the number of layers in the soil profile. The total plant water uptake for the day calculated with equation 5:2.2.8 is also the actual amount of transpiration that occurs on the day.

$E_{t,act}=w_{actualup}$ 5:2.2.9

where $E_{t,act}$ is the actual amount of transpiration on a given day (mm H$_2$O) and $w_{actualup}$ is the total plant water uptake for the day (mm H$_2$O).

Table 5:2-2: SWAT+ input variables that pertain to plant water uptake.