A = water vapor advected into the control volume
E = evaporation from the land surface
Q = runoff to ocean, including surface and ground water
C = water vapor returned to the ocean
C' = water vapor in transit, at leeward side of control volume
C" = water vapor discharge, at leeward side of control volume
Pa = fraction of precipitation
derived externally (advected moisture)
Pe = fraction of precipitation derived internally
(evaporated moisture)
Eg = evaporation from bare ground
Ev = evaporation from vegetated surfaces
Ew = evaporation from water bodies
Qs = surface runoff
Qg = groundwater runoff
