Question

If the precipitation (P) in a region is 450 mm/year, evapotranspiration (ET) is 200 mm/year, and the change in storage ($\Delta$S) is 80 mm/year, what is the value of quick flow (Q)?

• A. 170 mm/year
• B. 450 mm/year
• C. 250 mm/year
• D. 280 mm/year

Hint:

• The basic water balance equation is: Inputs = Outputs + Change in Storage.
• For a catchment: Precipitation (P) = Evapotranspiration (ET) + Runoff (Q) + Change in Storage ($\Delta$S).
• Runoff (Q) is often referred to as quick flow or total streamflow in this context.
• Rearrange to find Q: Q = P - ET - $\Delta$S.
• Ensure all units are consistent (here, all are mm/year).

Answer 1

The Correct Option is A

To determine the value of quick flow (Q), we need to use the water balance equation.

1. Understanding the Concepts:

- Precipitation (P): The total amount of water falling as rain, snow, etc., in a given area and time.
- Evapotranspiration (ET): The sum of evaporation and plant transpiration from the Earth's land surface to the atmosphere.
- Change in Storage (ΔS): The change in the amount of water stored in the region (e.g., in soil, groundwater, surface water).
- Quick Flow (Q): The component of streamflow that responds rapidly to precipitation events; also known as surface runoff or direct runoff.

2. Water Balance Equation:

The water balance equation states that the total inflow of water into a region must equal the total outflow plus the change in storage. In this case, the equation is: \[ P = ET + Q + \Delta S \]

3. Given Values:

\( P = 450 \text{ mm/year} \)
\( ET = 200 \text{ mm/year} \)
\( \Delta S = 80 \text{ mm/year} \)

4. Calculating Quick Flow (Q):

We need to rearrange the water balance equation to solve for Q: \[ Q = P - ET - \Delta S \] Substituting the given values: \[ Q = 450 - 200 - 80 = 170 \text{ mm/year} \]

Final Answer:

The value of quick flow (Q) is 170 mm/year.