Under what environmental conditions would you expect to find the thickest vadose zone?

Under what environmental conditions would you expect to find the thickest vadose zone?

• A. Desert
• B. Subtropical grassland
• C. Tropical rainforest
• D. Temperate forest

Answer: (A)

The amount or thickness of the vadose zone is governed by how deep the water table sits—the unsaturated layer from the surface down to groundwater. In a desert, rainfall is scarce and evaporation is high, so little water actually makes it down to recharge the aquifer. When infiltration does occur, much of it is lost near the surface, and the groundwater table tends to lie very deep. That means the unsaturated, or vadose, zone is very thick. In more humid environments like tropical rainforests or temperate forests, there is much more rainfall and recharge, so water tends to accumulate closer to the surface and the water table sits shallower, producing a thinner vadose zone. Subtropical grassland would also have more recharge than a desert, so its vadose zone is typically not as thick as in the desert. So, the desert represents conditions that drive a deep water table and a thick vadose zone.

The amount or thickness of the vadose zone is governed by how deep the water table sits—the unsaturated layer from the surface down to groundwater. In a desert, rainfall is scarce and evaporation is high, so little water actually makes it down to recharge the aquifer. When infiltration does occur, much of it is lost near the surface, and the groundwater table tends to lie very deep. That means the unsaturated, or vadose, zone is very thick.

In more humid environments like tropical rainforests or temperate forests, there is much more rainfall and recharge, so water tends to accumulate closer to the surface and the water table sits shallower, producing a thinner vadose zone. Subtropical grassland would also have more recharge than a desert, so its vadose zone is typically not as thick as in the desert.

So, the desert represents conditions that drive a deep water table and a thick vadose zone.