"Hydrological fluxes are fluxes in the hydrologic cycle of water between the oceans, surface water bodies (lakes, rivers, and streams), groundwater in subsurface aquifers, the atmosphere, and the biosphere." (Nijssen and Lettenmaier 2004)
Nijssen, Bart, and Dennis P Lettenmaier. 2004. “Effect of Precipitation Sampling Error on Simulated Hydrological Fluxes and States : Anticipating the Global Precipitation Measurement Satellites.” Journal of Geophysical Research 109: 1–15. https://doi.org/10.1029/2003JD003497.