What is a Rain Shadow

Wherever a mountain or mountain range is situated, there is an area of dry or barren land to the downwind side; this is the rain shadow, a meteorological effect which is effected by geographical features and is known to occur the world over, the rain shadow effect is the primary cause of leeward deserts of mountain ranges, such as California’s Death Valley.

As powerful and dynamic streams of air like the northeast and southeast trade winds circulate the planet, weather systems are created and warm, damp air is moved around, eventually this air will encounter mountain ranges. When a pocket of warm air reaches a mountain range, it is, in effect lifted up the mountain side – heat rises but the air is constantly cooling as it rises in a process known as ‘orographic lifting’, the cooling of the air often presents itself visually as large clouds, thunderstorms and heavy rain.

By the time the air current has moved high enough to reach the top of the mountain range it has shed its moisture in the form of rain giving the mountains a lush, green, fertile landscape on the windward side. When the air begins to descend on the other side of the mountain, it is dry, getting warmer again and as it falls, gradually picks up any available moisture from the landscape below thus starting the cycle all over again ready for when it meets the next range of mountains and the rain shadow effect is created once more.

There are several famous examples across the globe of the rain shadow effect, as mentioned earlier; Death Valley in California is an extreme example, as is the Gobi desert which is in the rain shadow of the Himalayas, these are incredibly dry, arid regions situated geographically near to relatively lush, green spaces. On a large scale, the Patagonia region of South America is a huge area of rain shadow land from the mountains of the Andes. On the opposite side of the equation, Seattle, Washington is situated on the windward side of the Cascades which accounts for its high and year round levels of rainfall.

There is a benefit of knowing the layout of the land in regards to rain shadows. As these regions are dictated by huge environmental forces, people over the ages have been able to learn and take advantage of the fertile, windward sides of mountains. The reliable supply of rain ensures good grazing and soil quality for farming if nothing else.