Water balance/budget= the balance between inputs (precriptation)+ outputs (runoff, evapo-traspiration, soil and groundwater storage)- within a drainage basin.
Rivers= present on the surface = stores = capable of releasing water + there is direct surface runoff.
= Dynamic relationship=River levels rise + fall - short term following heavy rainfall + often show an annual pattern (called the river's regime) = discharge.
The water balance formula =
Precipitation (P) = streamflow (Q) + evapo-transpiration (E) + or - changes in storage (S)
P = Q + E + or - S
Precipitation > evapo-transpiration = pores of the soil = filled with water.
Soil = saturated= excess water =difficulty infiltrating into the ground= surface run off.
The water balance of a particular location= studied using a water budget graph.
Shows - relationship between temperature, precipitation and evaporation- rates over the year.
During the months - precipitation > evapo-transpiration= soil recharged = water surplus= available to supply rivers and streams.
Months- precipitation< evapo-transpiration= water deficit= unable to supply rivers and streams.
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