The document discusses the water balance of a drainage basin. It is made up of precipitation inputs, evapotranspiration outputs, and storage changes. Precipitation is the primary water input. Evapotranspiration is water released into the air by evaporation from wet surfaces and transpiration from plants. The water balance equation expresses that precipitation equals total streamflow discharge plus evapotranspiration, plus or minus changes in water storage.

1. WATER BALANCE

2. PRECIPITATION
 Precipitation in the form of rain, snow, sleet, hail, etc. makes up
the primarily supply of water to the surface. In some very dry
locations, water can be supplied by dew and fog.

3. EVAPOTRANSPIRATION (EVT)
 Evaporation is the phase change from a liquid to a gas releasing
water from a wet surface into the air above.
 Transpiration is represents a phase change when water is
released into the air by plants.
 Evapotranspiration is the combined transfer of water into the air
by evaporation and transpiration.
 Actual evapotranspiration is the amount of water delivered to the
air from these two processes. Actual evapotranspiration is an
output of water that is dependent on moisture
availability, temperature and humidity

4. POTENTIAL EVAPOTRANSPIRATION
(P.EVT)
 Potential evapotranspiration is the amount of water that would be
evaporated under an optimal set of conditions, among which is an
unlimited supply of water.
 The water loss that would occur if there was an unlimited supply
of water.

5. WATER BALANCE

6. WATER BALANCE
 The balance between inputs and outputs of a drainage basin
 It is expressed as:
P = Q + E +/- S (changes on storage)
P – Precipitation
Q – Total Streamflow (Discharge)
E – Evapotranspiration
S – Storage (in soil and bedrock)

7. WATER BALANCE