The Dry Side of the Mountain
Some mountains split the land into two very different worlds. On one side, forests are thick and green. On the other side, the ground is dry and the plants are few. The mountains cause this difference, and the effect is called a rain shadow.
It starts with wind. Wind blowing off the ocean carries a lot of water vapor. When this moist air reaches a mountain, it cannot go through, so it is pushed up the slope. As air rises, it cools. Cool air cannot hold as much water vapor as warm air, so the vapor turns into tiny drops. The drops form clouds, and rain or snow falls on the side that faces the wind.
By the time the air crosses the top, most of its water is gone. The air then slides down the other side. As it sinks, it warms up and can hold water again, so clouds melt away instead of making rain. The land on that side stays dry.
Deserts and grasslands often sit in the rain shadow of tall mountain ranges. Farmers there must plan carefully for water, while the wet side can grow forests.