The rain shadow effect is a weather phenomenon that occurs near mountain ranges. Wet weather systems prevail on one side of a mountain, and it enjoys much rainfall and even snow, but the other side gets little or no precipitation and becomes a desert. That's quite interesting, and in this article, we look at the causes, effects, and examples of rain shadows.
Understanding the rain shadow effect
A rain shadow desert is a warm, dry patch of land on the leeward or protected side of some mountains. Rain shadows form when mountain ranges are situated parallel to coastal areas.
The side of the mountain facing the sea gets more rainfall as the mountain peak intercepts moisture-laden air and forces it to precipitate. On the windward sides of mountain ranges, you'll find land rich with vegetation and freshwater sources because more precipitation falls there.
The other side, however, experiences an entirely different climate. The lee sides receive less precipitation and cloud cover because all the water vapor has been spent on the windward sides. All the leeward side gets is a warm, dry air mass that further sucks up moisture in the air.
Related read: How Is Rain Formed? — Definition, Types, And More.
What causes rain shadows?
Prevailing winds and the presence of mountain ranges have a profound effect on local weather patterns. Both factors work together to create rain shadows. Before we explore how that works, let's understand what prevailing winds are.
Prevailing or trade winds are predictable wind movements that occur regularly in particular locations. These winds are a result of atmospheric pressure. The winds blow from east to west due to the Coriolis effect of the earth’s rotation. The effect makes winds move anti-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
Prevailing winds accumulate moisture as they travel over water and land. The warm, moist air rises as it hits the windward side of a mountain range. As warm air rises, it cools, and the water vapor in the air reaches its dew point. Clouds form and soon become saturated because cold air cannot hold moisture. Then rain or snow falls. This is what we call orographic precipitation.
Remember, it is a moist air mass that causes rainfall on the windward side. However, when the same mass of air passes over the top of the mountain, it is depleted and dry. The cold, dry air moves down the leeward side, offering very little or no rain. The clouds warm up and dissipate.
As the descending air mass starts to warm, it pulls water vapor from the environment. Unfortunately, there's not enough moisture in the air for significant precipitation to form. That's how a rain shadow occurs.
Effects of rain shadows on the environment
Rain shadows cover more than one-third of the earth’s land mass. These biomes are important economically and environmentally.
Rain shadows contribute to the biodiversity of the earth. Many deserts and semi-arid regions around the world exist because of the rain shadow effect.
It may sound incredulous to you, but the lack of moisture in arid ecosystems is essential for some plants and animals to survive. Some deserts are among the last remaining areas of untouched wilderness where endangered species survive.
About 20% of the world's inhabitants make their homes in the arid1 and semi-arid regions. Usually, these folks are nomadic pastoralists or farmers. They grow important desert crops and rear goats, camels, sheep, alpacas, cattle, horses, etc.
Examples of communities that live in arid and semi-arid areas are the Bedouins of Arabia, the Massai of Kenya, and the Rajasthani nomads of India. We also have the Atacameño people living in the Atacama desert.
In dry, hot climates, many vital minerals, precious metals, and salts are formed in deserts. Over 75% of oil reserves and 50% of the world's copper and uranium are in arid lands.
Other resources concentrated in deserts include borax, silver, iron, gold, tungsten, salt, potash, and uranium.
Does climate change affect rain shadows?
A rain shadow depends largely on melting snow for water supply as well as what little rainfall it receives. Global warming will cause unsustainable moisture loss during evaporation. That could increase the burden of water scarcity in the region to a catastrophic extent.
12 Examples of rain shadow areas
Rain shadows are found close to many of the world’s mountain ranges. Some rain shadows experience drier climates than others. Let's look at some examples of rain shadow deserts around the world and the mountains responsible.
For more related weather, our selection of rain quotes and sayings is ready to inspire a smile on a gloomy day.
1. The Tibetan Plateau
The Himalayan mountain range stretches for about 1,550 miles. It is part of a mountain belt stretching from North Africa to the Pacific Ocean coast in Southeast Asia. The Tibetan Plateau is the rain shadow cast by the Himalayas.
2. The Gobi Desert
The Himalayan mountains cause the same phenomenon that occurs in the Tibetan Plateau to occur in the Gobi Desert. The area is a semi-arid region with just 5% of sand; the rest comprise grasslands, rivers, and lakes.
3. The Great Basin
The Sierra Nevada mountain range casts a rain shadow that forms the Great Basin. It is the largest desert biome in the U.S. They describe the area as a cold desert because precipitation falls there mostly in the form of snow.
4. The Death Valley
We have the Death Valley desert on the east side of the Sierra Nevada mountains. It is one of the driest places on earth, receiving a maximum rainfall of 4.5 inches per year.
5. The Atacama Desert
The Andes mountains of South America cast a rain shadow that formed the Atacama desert in Chile. The area is one of the driest places on earth. Some areas of the Atacama desert have never recorded rainfall.
6. East of the Southern Alps
The New Zealand Southern Alps intercept rain, causing clouds coming from the Tasman Sea. The west side gets so much rainfall that there's a flooding problem. But on the east side, semi-arid conditions exist.
7. The Kanto Plain
The Japanese Alps create a rain shadow across the plains of Tokyo. In the winter months, the Kanto Plain receives lower precipitation compared to the rest of Japan.
8. The Dry Basins of Washington and Oregon
To the east of the Cascade Mountains, we have the dry basins of Oregon and Washington. These areas make up the rain shadows cast by mountains. The larger part of the region is semi-arid.
9. The Mojave Desert
The Mojave desert of southern California exists in the rain shadow created by the Sierra Nevada and Transverse mountain ranges. The area gets a maximum of 9 inches of rain annually.
10. Patagonia Desert
We also know the Patagonian desert as the Patagonian Steppe. It is Argentina's largest desert. Located in South Argentina, the area is a rain shadowed by the Andes mountains.
11. San Luis Valley
The Rocky Mountain range, also known as the Rockies, stretches from New Mexico to Canada. The Rocky Mountains cast a rain shadow in the San Luis Valley in Colorado.
12. The Sahara Desert
The Atlas Mountains in Northwest Africa extend from Morocco to Tunisia and Algeria. The mountains create the rain shadow that we know as the Sahara desert.
The rain shadow effect occurs because mountains intercept warm, humid air masses. The air cools as it is pushed up, bringing precipitation to the windward side. However, the leeward side of a mountain is usually a dry region because it doesn't get enough precipitation.
Heiner, M., Davaa, G., & Kiesecker, J. M. (2020). Shifting Winds in the Mongolian Gobi Desert: Nature and Traditions Face the Modern Era. Elsevier eBooks.