Section 2: Hydrology

The land phase of the hydrologic cycle is based on the water balance equation:

$$SW_t = SW_0 +\sum_{i=1}^t (R_{day} - Q_{surf} - E_a - w_{seep} - Q_{gw})$$

where $SW_t$ is the final soil water content (mm H2O), $SW_0$ is the initial soil water content (mm H2O), t is the time (days), $R_{day}$ is the amount of precipitation on day i (mm H2O), $Q_{surf}$ is the amount of surface runoff on day i (mm H2O), $E_a$ is the amount of evapotranspiration on day i (mm H2O), $w_{seep}$ is the amount of percolation and bypass flow exiting the soil profile bottom on day i (mm H2O), and $Q_{gw}$ is the amount of return flow on day i (mm H2O).