Step-by-step explanation:
A valid water balance equation for a watershed can be expressed as:
P = R + ET
In this equation:
P represents precipitation, which is the input of water into the watershed in the form of rain or snowfall.
R represents runoff, which is the portion of precipitation that does not infiltrate into the soil or get absorbed by vegetation but instead flows over the surface and leaves the watershed through streams or rivers.
ET represents evapotranspiration, which is the combined process of evaporation from water bodies and the soil surface, as well as transpiration from plants. It represents the loss of water from the watershed back into the atmosphere.
The equation states that the total amount of water entering the watershed through precipitation (P) must be equal to the sum of the water that leaves the watershed as runoff (R) and the water that is lost through evapotranspiration (ET). This is based on the principle of conservation of mass, which means that water cannot be created or destroyed; it can only change its form and move between different reservoirs within the hydrologic cycle.
By using this water balance equation, hydrologists and water resource managers can estimate the amount of water available in a watershed, track water movement within the system, and understand the relationship between precipitation, runoff, and evapotranspiration in a particular region. This information is crucial for water resources management, flood forecasting, and understanding the overall hydrological behavior of a watershed.