Introduction
A mountain is always having two sides, one is known as the windward side and another is known as the leeside. The former side is always windy and gets more rain as the rain-loaded clouds strike on this side. Whereas the latter side does not get enough rain a d is also relatively low windy. The rain shadow effect is a zone of the leeside of a mountain range. The amount of rainfall here is much less than on the windward side of a mountain.
Different types of natural phenomena occur in nature. Rainfall is one such natural phenomenon. The main cause of rain is the presence of water vapor in the air and the presence of dust floating in the air to hold this water vapor. Along with these two factors, the most important factor is the tendency of the air to rise.
When a water vapor floating in the sky falls to the earth’s surface in the form of water droplets due to the gravitational force of the earth, it is called rain. Rainfall is divided into different categories according to the type and characteristics. Relief rainfall is a type of rain. Rain shadow effect is related to the orographic rainfall. Now here we discuss the rain shadow effect description and definition (1) & (4).
What is rain shadow?
Humid water vapor from the oceans causes heavy rainfall on the windward side of the mountain. The amount of water vapor in the air is very low when it reaches the opposite slope or leeward side across the mountain, so there is very little rainfall. This slope of the mountain is called the rain shadow effect (1).
Example of rain shadow effect
- The Tibetan plateau is the best example. The climate is arid due to the leeward slope of the mountains as there is no rainfall beyond the Himalayas.
- The Arabian Sea part of the southwest monsoon flows from the southwest, interfering with the Western Ghats Mountain on the west coast, and causing heavy rainfall on the western slopes of the hills. Crossing the Western Ghats, these winds blow over the Deccan plateau and Madhya Pradesh, but due to the shortage of water vapor, the rainfall is less. Therefore, the eastern part of the western mountain is in the rain shadow effect.
- The humid water vapor from the Bay of Bengal came over Bangladesh and obstructed the Garo-khasi-jaintia hills, causing heavy rainfall in the cherrapunji-mawsynram region of Meghalaya state situated on the windward slopes of those mountains. Shillong, the capital of Meghalaya, is situated on a leeward slope of these mountains. So it is known as the rain shadow effect. The amount of rainfall here is very low (1) & (3).
Some interesting facts
1. A rain shadow area is a dry area,
2. It is located on the leeward slope of the mountain.
3. This zone is mainly seen in relief or orographic rainfall.
4. Rain shadow zone is always away from the wind.
5. If the wind comes from the west, then the rain shadow zone is located in the east.
6. This zone is mainly formed when moist air moves towards a set of hills and are forced upwards by them.
7. In this case the humid air often comes from the sea or other large water bodies.
8. The amount of water vapor in the air of this region is less so the amount of rainfall is less here (2) & (5).
Rain shadow effect Causes and description
Cause
The main cause for the rain shadow effect is that the warm humid air rises to the top of the mountain as a result of orographic lifting. As the atmospheric pressure decreases with increasing altitude, the air expands and as it reaches the cooling point, the air reaches its dew point.
This dew point is not the same as the constant pressure dew point that is usually mentioned in the weather forecast. At the dew point, the moisture condenses on the hill and causes rain on the top of the mountain.
The wind loses a lot of moisture and becomes dry due to the rain on the windward slope before the air enters the leeward slope. Typically, the slope of a mountain becomes warmer due to thermal contraction as the air descends. This increases its moisture absorption and creates a dry zone. This zone is the rain shadow zone (1).
Description
When water vapor is obstructed in the mountains as it flows over the earth’s surface, it rises up the mountain and expands and cools. As a result, water vapor condenses and causes heavy rainfall on the mountain slopes.
After crossing the mountain, the wind descends from the top down the slope in the opposite direction. Therefore, as the temperature rises, so does the ability to retain water vapor. This is why rainfall is very low on the leeward side of the mountain and its adjoining areas. It is known as the rain shadow effect (1).
Q&A
1. What is the rain shadow effect?
Humid water vapor from the oceans causes a lot of rainfall on the windward slope of the mountain. There is very little rainfall when these winds cross the mountain and reach the opposite slope or leeward slope. This slope of the mountain is called the rain shadow zone or effect.
2. What is the rain-shadow effect?
When water vapor is blown over the surface of the earth, it is obstructed by mountains, and rises expand,s and cool. As a result, water vapor condenses and causes heavy rainfall on the windward slope of the mountain.
Crossing the mountain, when the wind reaches the leeward slope of the mountain, the water vapor in the air decreases. Then the amount of rainfall in that area is less. This area of the mountain is known as the rain shadow effect.
3. What is the rain shadow effect?
When water vapor is interrupted by mountains, it rises, expands, and cools. As a result, the water vapor condenses and a lot of rain falls on the windward side of the mountain. When the wind crosses the mountain and reaches the other side (leeward side) of the mountain, it has less water vapor. As it descends, it warms up and absorbs more water vapor. Due to this, there is very little rainfall on the leeward side of the mountain. This region is called the rain shadow effect.
4. What is the rain-shadow effect?
The water vapor is interrupted by the mountain, which causes heavy rainfall on the windward slopes. As the wind crosses the mountain and reaches the other side of the mountain, the amount of water vapor in them decreases. Then the air descends, warms up, and absorbs more water vapor without leaving it. Due to this, the rainfall in this region is very low. This region of the mountains is known as the rain shadow effect.
5. What is the rain-shadow effect?
Rain shadow effect is a dry zone of a mountain. Here the amount of rainfall is very low. This zone is located on the leeside part of the mountain where the amount of water vapor is much less.
As an example, the eastern edge of the Western Ghats Mountains is a rain shadow effect.
Written By: Manisha Bharati
Reference
1. Savindra Singh. Climatology. Pravalika Publications, Allahabad. Chapter 9: Fogs, Clouds, and Precipitation. Page No: 174 to 201.
