For a basin, in a given period Δt there is no change in the groundwater and soil water status. If P-precipitation, R = total runoff, E = Evapotranspiration and Δs increase in the surface water storage in the basin, the hydrological water budget equation states
1
P = R - E + ΔS
2
R = P + E - ΔS
3
P = R + E + ΔS
4
E = P - R + ΔS