Question

A model of Earth’s water budget shows that the precipitation on oceans is 420,000 km3 and the precipitation on land is 130,000 km3. If the evaporation from land is 90,000 km3, how much is the evaporation from oceans?

90,000 km3
130,000 km3
460,000 km3
550,000 km3

Answer 1

To find the evaporation from oceans, we can set up the water budget equation based on the given data:

1. Total precipitation = Precipitation on oceans + Precipitation on land
\[
\text{Total Precipitation} = 420,000 \, \text{km}^3 + 130,000 \, \text{km}^3 = 550,000 \, \text{km}^3
\]

2. Total evaporation = Evaporation from oceans + Evaporation from land
\[
\text{Total Evaporation} = \text{Evaporation from Oceans} + 90,000 \, \text{km}^3
\]

Because the total precipitation must equal total evaporation (assuming no change in water storage), we can set the equations equal to each other:
\[
550,000 \, \text{km}^3 = \text{Evaporation from Oceans} + 90,000 \, \text{km}^3
\]

Now, solve for evaporation from oceans:
\[
\text{Evaporation from Oceans} = 550,000 \, \text{km}^3 - 90,000 \, \text{km}^3
\]
\[
\text{Evaporation from Oceans} = 460,000 \, \text{km}^3
\]

Therefore, the evaporation from oceans is **460,000 km³**.