How mountains can hog the rain
The interplay of land and sky can create distinct microclimates.
It’s easy to see weather as being purely atmospheric. Sun, clouds, rain, wind, highs, lows — all of these come from above or swirl all around us.
But as much as weather affects us on the ground, the ground can also help shape the weather. While bodies of water are obvious contributors to weather events, Earth — and a lot of it — can greatly reciprocate in this transaction between land and sky.
Mountains reign supreme on the landscape, standing proudly in their gentle grandeur. Formed by the violent physics beneath our feet, chains of mountains grow to be so large and imposing that they can create their own weather.
In a phenomenon called the "orographic effect," the walls of Earth created by mountain ranges can impact the amount of rainfall each side of a "wall" receives.
It begins when wind blows warm, moist air toward mountains. Given their size and scale, the mountains block the wind from moving around them, forcing the air to blow upward. As the warm air rises higher and higher, in an attempt to flow over the mountaintops, it cools.
The once-warm, moist air begins to morph under the cooler temperatures, with its moisture condensing and creating clouds. If enough moisture is present, the clouds can burst into rain or snow.
This precipitation drenches the windward side of the mountain, often resulting in lush, green environments. However, the opposite occurs on the leeward side.
The air, having dropped its payload of precipitation, finally flows over the mountaintop and down the other side. As it descends, the air warms once again, but it has much less moisture.
Because of this, the environment on this leeward side is essentially robbed of rain. Deserts called "rain shadows" form, remaining dry for as long as the nearby mountains stand tall.
One example of the orographic effect occurs on the Big Island of Hawaii. There, the Kohala and Mauna Kea volcanoes block the northeasterly Pacific trade winds, causing greater amounts of rain to fall on their northern slopes while creating dry, desert conditions on their southern slopes.
In Washington, the Cascade Mountains cut down the middle of the state to create two large climatic regions. The western, ocean-facing side of the mountains is rich and green, whereas the eastern side is drier with near-desert conditions.
And one of the driest and hottest places on the planet is the result of the orographic effect. Death Valley, straddled between California and Nevada, lives up to its name of death and desolation because of the rain shadow caused by two mountain ranges: the Sierra Nevada and Pacific Coast Range.
This interaction between land and sky shows that weather doesn’t occur in isolation. The atmosphere is merely a playground where sun, water and Earth come together and create amazing weather events.