Geog問題!!有關water cycle!!

vegetation is useful in preserving water in the soil.
trees need water to grow and at the same time,
they grow branches and leaves, which can shade the soil from direct sunlight and thus reduce the evaporation rate in the soil.

in farms, the density of vegetation is lower,
also, soil will become completely bare after havesting.
there will be serious soil erosion, and water will easily leach away..
so, you find that farmland is usually drier.