# Water balance

The water balance , also regional water balance , refers to the balance of precipitation , evaporation , runoff and storage changes in relation to an area and a period. The water balance plays a major role in determining how much water is available for use in a region. The available amount is usually less in arid than in humid climates.

This is based on the water balance or water balance equation :

${\ displaystyle N = A + V \ pm \ Delta S}$

changed:

${\ displaystyle 0 = NAV \ pm \ Delta S}$

Where N is the precipitation, A is the runoff, V is the evaporation and ΔS is the storage change in the subsoil. V can be the potential or the real evaporation. For sufficiently long periods of time, ΔS = 0.

One speaks of a negative climatic water balance when the potential annual evaporation is greater than the precipitation for one year. A positive water balance is when the real evaporation is smaller than the precipitation, so surface runoff and infiltration of the water into the soil is possible.