Hydrological losses statement, factors affecting evaporation

Hydrological losses are not actual losses

Hydrological losses (interception, depression storage, evaporation, transpiration, infiltration) are "losses" only from the point of view of direct surface runoff. The water is not destroyed; it only moves to another part of the hydrologic cycle (conservation of mass).

• Infiltrated water recharges soil moisture and groundwater and later appears again as baseflow in streams and springs.
• Evaporated and transpired water goes to the atmosphere, forms clouds and returns as precipitation.
• Interception and depression storage are eventually evaporated or infiltrated.
• Water used by plants (transpiration) is useful for agriculture and forests.

So these are only losses from the surface runoff volume; the water remains in the system and is available again.

Factors influencing evaporation

1. Vapour pressure deficit $(e_s - e_a)$: evaporation follows Dalton's law, $E \propto (e_s - e_a)$.
2. Temperature of water and air: higher temperature raises $e_s$.
3. Wind speed: removes saturated air above the surface and increases turbulence.
4. Solar radiation: provides the latent heat (about 2.45 MJ/kg).
5. Atmospheric pressure: low pressure at high altitude increases evaporation.
6. Quality of water: dissolved salts reduce vapour pressure (sea water evaporates about 2 to 3 % less than fresh water).
7. Size and depth of the water body, and heat storage in deep lakes.
8. Soil surface condition (moisture, colour, cover) for evaporation from land.