Question

A 600-ha farmland receives annual rainfall of 2500 mm. There is a river flowing through the farmland with an inflow rate of 5 m3/s and outflow rate of 4 m3/s. The annual water storage is the farmland increases by 2.5 x 106 m3. Based on the hydrologic budget equation, determine the annual evapotranspiration amount in mm. (1 ha

Answer 1

Answer:

E = 7333.33 mm

Explanation:

The annual evapotranspiration (E) amount can be calculated using the water budget equation:

$P*A + Q_{in}*\Delta t = E*A + \Delta S + Q_{out}*\Delta t$   (1)

Where:

P: is the precipitation = 2500 mm,

Q(in): is the water flow into the river of the farmland = 5 m³/s,

ΔS: is the change in water storage = 2.5x10⁶ m³,  

Q(out): is the water flow out of the river of the farmland = 4 m³/s.

Δt: is the time interval = 1 year = 3.15x10⁷ s

A: is the surface area of the farmland = 6.0x10⁶ m²  

Solving equation (1) for ET we have:

$E = \frac{P*A + Q_{in}*\Delta t - \Delta S - Q_{out}*\Delta t}{A}$

$E = \frac{2.5 m \cdot 6.0 \cdot 10^{6} m^{2} + 5 m^{3}/s \cdot 3.15 \cdot 10^{7} s - 2.5 \cdot 10^{6} m^{3} - 4 m^{3}/s \cdot 3.15 \cdot 10^{7} s}{6.0\cdot 10^{6} m^{2}}$                                  

$E = 7333.33 mm$

Therefore, the annual evapotranspiration amount is 7333.33 mm.

I hope it helps you!