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Why Does it Rain?

Updated on October 1, 2014
Keeping dry
Keeping dry | Source

Learning about rain

Rainy weather, or the lack of it, impacts us all. It brings relief when it's dry and brings chaos when it rains too much. Rain is essential to make things grow and live, but if it is polluted it can kill and destroy. Rain has the power to give life and to take life away.

Different cultures over the world have different reactions to rainy weather. When it rains, how do you feel and what does it mean to you? Are you fed up, scared, happy? We complain when there's too much or too little rain, but it is always a good subject for small talk!

So how does that water get into the clouds? Why does rain happen? Let's find out!

Do you love the sound of rain? Check out RainyMood.com and listen to soothing rain fall.

Ahh so peaceful!

How is rain made? Why does water fall from the sky?

So, how is rain made? The air around us is full of water vapor and how much depends where you are in the world - but even in the Sahara desert there is some water vapor. When rising air cools it can no longer hold the water vapor and this condenses to make clouds. The most common clouds that produce rain are from the Stratus family of clouds or the Cumulonimbus cloud.

The millions of water droplets inside the clouds collide together which in makes the droplets larger - this is called coalescence. Once they are too heavy to float, gravity makes the drops fall to earth as rain. Rain is what is known as precipitation; depending on other factors (such as temperature) precipitation can also be snow, sleet and hail.

The air around the cloud is important in causing precipitation too, as well as water vapor, air contains minuscule dust, soot, mineral and salt particles. These particles can become a nucleus for cloud droplets helping them to coalesce.

The water cycle
The water cycle | Source

How rain clouds form - convection, frontal and orographic rain.

There are three main ways that rain clouds are formed:

Cumulonimbus incus in Mykonos / Greece
Cumulonimbus incus in Mykonos / Greece | Source

1. Convection

On a hot sunny day, warm air from the ground rises upwards and as it rises it absorbs tiny water droplets. As the warm air gets higher it begins to cool because the atmosphere becomes colder the higher you go. This combination creates either cumulus clouds or the magnificent cumulonimbus cloud which is pictured above.

With a cumulonimbus cloud, the rain will generally fall to earth in heavy bursts or as a storm. This type of precipitation is common during humid summer days.



2. Frontal rain.

Air that is cold is heavier, denser and holds less water droplets than warm air. Frontal rain occurs when a front of warm air meets a front of cold air. As the warm air is less dense it rises up and moves over the cold air, and then begins to cool. This process forms the clouds from the Stratus Family of clouds, the altostratus, nimbostratus and stratus. These clouds can produce drizzle, heavy rain or bursts of precipitation.

Weather front - Illinois
Weather front - Illinois | Source

3. Orographic rain

This is when there is an obstruction, such as a mountain, in the way of warm rising air. As the air is forced to rise up over the mountain, it cools and forms clouds. Rain will then fall on the windward slopes; this is the upwind direction of the slope.

As the cloud passes over the mountain to the leeward (downwind) side it sinks, gaining warmth and evaporates.

It is common to see a mountain bathed in sunshine on one side and raining on the other, an odd but wonderful sight!

Orographic clouds
Orographic clouds | Source
Rain gauge
Rain gauge | Source

How rain is measured

Rain is measured in millimeters per hour. You can easily measure rain fall yourself by buying a water gauge - see the picture on the left for an example.

Fix the water gauge to a fence post or if it comes with a post bang it directly into the ground. Make sure that no excess water fall from trees or gutters will get into the gauge because this will give inaccurate results.

Measure the rainwater in the gauge cylinder every day at the same time, holding the cylinder up to eye level rather than look down at it to ensure a more accurate reading.

Raindrop after the storm
Raindrop after the storm | Source
Source

Rain intensity

The intensity of rain is classified into six grades:

1. Very light: when the precipitation rate is < 0.25mm/hour

2. Light: when the precipitation rate is between 0.25mm/hour - 1.0mm/hour

3. Moderate: when the precipitation rate is between 1.0mm/hour - 4.0mm/hour

4. Heavy: when the precipitation rate is between 4.0mm/hour - 16.0mm/hour

5. Very heavy: when the precipitation rate is between 16.0mm/hour - 50mm/hour

6. Extreme rain: when the precipitation rate is > 50.0mm/hour

Excerpt from worldpossible.org (GNU Free Documentation License)

Raindrops vary in size depending on the intensity and type of rain, this raindrop chart above illustrates the different sizes.

A) Raindrops are not tear-shaped, as most people think.

B) Very small raindrops are almost spherical in shape.

C) Larger drops become flattened at the bottom, like that of a hamburger bun, due to air resistance.

D) Large raindrops have a large amount of air resistance, which makes them begin to become unstable.

E) Very large drops split into smaller raindrops due to air resistance.


Acid rain damaged trees
Acid rain damaged trees | Source

What is acid rain? The result of air pollution

There are terrible reports of lakes in Sweden that look beautifully crystal clear, but this is because everything in that lake is dead - plants and fish. Rivers, wetlands and lakes are affected by acid rain either falling directly into them or from water running off the land. Although some plants and animals are more resistant to the effect of acid rain than others,but species that these animals may depend on to live are not. Nature operates in cycles and chains, if these are disturbed in some way it will have a domino effect as each factor links to another to work properly.

Acid rain affects trees by washing away the minerals and nutrients in the soil that help trees to grow.

Acid rain can also introduce or exacerbate harmful substances in the soil, such as aluminium which can make it hard for plants and trees to take up water.

Trees and plants have a protective waxy layer on their leaves, which can wear away when acid rain falls making them open to disease and unable to photosynthesize properly.

Acid Damaged Gargoyle
Acid Damaged Gargoyle | Source

Acid rain is not just harmful to nature; it can erode buildings, statues, vehicles, pipes and cables. Old buildings are particularly vulnerable to acid rain; the Great Pyramids, Statue of Liberty and the Capitol building in Washington all show signs of acid erosion. All buildings are subject by erosion from precipitation naturally, but acid rain speeds up that process. Acid rain doesn't affect humans in the same way as buildings, forests and lakes - we can walk through an acid rain puddle without it dissolving our skin. But it can cause health problems for people, such as asthma and other respiratory problems as the acid is present in the water vapor around us.

So what's being done about it? To reduce acid rain pollution we need to reduce emissions, find alternative sources of energy, conserve energy and restore the damage. Learn how you can do your bit here: How To Prevent Acid Rain

Monsoon season

The monsoon season is a period of time during the year when an area receives large amounts of rain.

Monsoon occurs when there is a shift in global wind patterns, when the winds that usually blow from the land to the sea change direction. When the winds reverse (blowing from the sea to the land), convection occurs, and large clouds roll in.

Monsoon rain is intense and as well as giving great relief to dry areas it can also create landslides and extreme flooding too.

Rain dancers, Mumbai, India
Rain dancers, Mumbai, India | Source

When you think of the monsoon season, you most probably think of India, but monsoons can be found all over the world. Asia, Australia, Europe, USA and Africa all experience monsoon weather, to varying degrees of intensity. For example, the Arizona monsoon in the US, from June to September, shares many of the same features as the Indian monsoon, but is not as strong.

The "European monsoon" is also known as the "return of the westerlies", occurring in late June where a gathering of westerly wind from the Atlantic Ocean become saturated with moisture.

Coconino National Forest, AZ - Monsoon Rains
Coconino National Forest, AZ - Monsoon Rains | Source

India's climate is dominated by a wind system that flows either from the south west or the north east. Wind from the northeast brings a dry heat and an area of ow pressure from December to May. By May temperatures can reach over 100 degrees Fahrenheit, and there is always lots of speculation as to when the winds will change and bring the much needed monsoon. By June the winds change to a south-westerly direction bringing clouds full of moisture from the sea. There are often pre monsoon showers for a few days before the main event and when the monsoon arrives it is spectacular; with intense rainfall, thunderstorms and lightening that continues for about a week. After the first "burst of the monsoon" it doesn't rain continually, but there will be torrential rain at least once a day for a few hours. Some years the monsoon is light, which is disastrous for farmers who depend on these rains to grow their crops. Other years it can be so heavy it brings flash floods and landslides, where whole villages can be washed away - which is equally damaging.

Bangladesh, India's neighbor, in particular suffers from devastating floods during this time as it lies on a flood plain between the Ganges and Brahmaputra rivers.


Floods, Morpeth, UK
Floods, Morpeth, UK | Source

The effects of flooding and why floods happen

Floods occur on ground that is flat, broad and situated near rivers or a main waterway. When it rains too much the water in the river bursts or overflows the banks, which can happen at any time of year. A flood generally happens over several days as the water level rises. However flash floods can occur very rapidly with no warning turning a calm river into an instant fast moving flood literally in minutes. Flood water can be deceptive too as to how deep in can be and how strong the current is, it can catch people off guard. Only 6 inches of rushing flood water is enough to knock a person off their feet.

Floods can cause terrible damage to people's homes and buildings, floods can ruin people's lives and livelihoods. The damage left behind a flood can take years to correct. Wildlife is also affected by flooding when flood damage to businesses and factories cause toxic leaks of chemicals.

Ganges Delta
Ganges Delta | Source

Bangladesh is known for its huge and devastating floods, both river flooding from the four major rivers leading off from the Ganges and coastal floods from the Bay of Bengal happen here every year. Particularly bad floods occur about every 10 years; the last two were in 1998 and 2004. As the country is very poor it finds it even more difficult to provide facilities to cope with flooding. For example medical care is scarce to treat people injured by the water or people who have caught a waterborne disease. The 2004 flood affected more than 19 million people.

Roe Deer in Hoh Rainforest
Roe Deer in Hoh Rainforest | Source

What is a rain forest?

Rain forests are characterized by their high rainfall and the density and height of foliage and plants.

They are the world's oldest ecosystems and are home to a variety of wonderful animals and plants, over 30 million species.

As rain forests are so dense, not much precipitation reaches the ground as the trees act as umbrellas. Half the rain forest's precipitation is actually from evaporating moisture from the trees.

There are two types of rain forest, temperate and tropical. Temperate rain forests are found in areas that have a mild climate, and consist of coniferous trees, ferns and mosses. The average rainfall in a temperate rain forest is about 100 inches - a lot of rain! Trees in these forests can be very old, ranging from 500 to 1000 years. The largest temperate rain forests are found along North America's Pacific Coastline. One such temperate rain forest is found along the Olympic Peninsula, Washington and has been made famous by the popular Twilight Series by Stephanie Meyer.

Streams of light in the Amazonian mist
Streams of light in the Amazonian mist | Source

Tropical rain forests are found near the equator and lie between the tropics of Cancer and Capricorn. These are tall, hot and dense jungles that receive on average 80-400 inches of rain per year. Broadleaf plants and trees inhabit these forests, the trees do not live as long as the temperate forest trees, with an age of 50 to 100 years.

The largest rain forest in the world is the Amazon in South America, which consists of 5.5 million kilometers and spreads into 8 nations: Brazil (with 60 percent of the rain forest), Colombia, Peru, Venezuela, Ecuador, Bolivia, Guyana, Suriname and French Guiana. Tropical rain forests help regulate global weather by absorbing carbon dioxide in the air; too much carbon dioxide contributes to global warming.

Both types of rain forest are endangered. This is due to trees being cleared for people to build on, to use for agricultural land, plantations and logging.

You would think that due to the rich plant and animal life of rain forests that the soil would be rich too - this is not the case. The soil can only be used a short time before it runs out of nutrients. This doesn't stop the land being cleared. Scientists have discovered that the destruction of rain forests is one of the main reasons for climate change, second only to Energy Sector. This fact becomes more terrifying when you consider this against the fact that 200,000 acres of rain forest are being destroyed everyday and more than 20% of the Amazon has already disappeared.

So why can't we stop this from happening?

Well the main reason is that the people that live near tropical rain forests are often very impoverished and they are paid money by logging companies to cut down the trees. They need this money to survive.

It has been said by scientists that if we lose the rain forests, we lose the battle against climate change.

Read more and support Rain forest Alliance at www.rainforest-alliance.org


The rainiest places on Earth - If you hate wet weather, you won't want to live here!

show route and directions
A markerRecord for the greatest annual average at 467.4 inches -
Mawsynram, India
get directions

B markerRecord of most in 1 month (July 1861 - 364.0 in), 1 year (Aug 1860 to July 1861 - 1,042 in) & 2 -
Cherrapunji, India
get directions

C markerBarst in Guadeloupe had the most rainfall in 1 minute in 11/26/1970 at 1.5 inches -
Guadeloupe
get directions

D markerThe most rainfall in 42 minutes on 6/22/1947 at 12.0 inches -
Holt, USA
get directions

E markerThe most rainfall in 12 hours on 26/01/1980 at 46 inches -
Grand Ilet, La Reunion
get directions

F markerThe most rainfall in 24 hours at Foc Foc on La Reunion Island on 08/01/1966 at 71.9 inches -
La Reunion
get directions

The driest place on Earth

The Atacama Desert is the driest place on Earth, a place scientists call absolute desert. It is 600 miles long stretching from Peru to Northern Chile on the Pacific Coast. The desert consists of salt basins, sand and lava flows and is virtually barren, even bacteria are scarce! With the Andes on one side and the Chilean Coastal range on the other, this desert is in a rain shadow and sees on average just 0.04 inches of rain per year. Some areas have never had recorded rainfall and there are dried up lakes that appear to have not had any rain for thousands of years.

Due to it's lunar landscape NASA use the Atacama to test instruments for finding life on Mars, both Viking 1 and Viking 2 were tested here - neither found life in Atacama's soils.

Atacama desert, Chile
Atacama desert, Chile | Source
Cloud seeding plane
Cloud seeding plane | Source

Rainmaking - artificial precipitation.

Cloud Seeding is a way to change the amount of precipitation in a cloud, making the droplets large enough to fall as rain. This is achieved by inserting silver iodide and dry ice into a cloud; these chemicals act as nuclei onto which the droplets can collect - making them larger, heavier and more likely to fall.

There are three different ways to cloud seed: static, dynamic and hygroscopic. Static cloud seeding involves spreading silver iodine in the cloud via airplane, silver iodine acts as a nucleus for the droplets to collect on. Dynamic seeding is a complex procedure that tries to boost the vertical air flow into the clouds; this encourages more water to pass through the clouds. Hygroscopic seeding involves shooting flares or rockets at the cloud which contain salts; these salts grow in size as the water joins with them.

China has been experimenting with cloud seeding for years to help during times of drought and clear air pollution. During the Olympic Games in 2008, China actually managed to keep the rain away! August (when the Olympics are) is typically a wet season for Beijing, and China did not want rain potentially ruining the games. They used 1,104 rain dispersal rockets from 21 sites in the city, making sure any clouds that may rain did before the opening ceremony.

The Art of Rain By Mitchell D. Wilson

Falling Down, pooling up,

Out of the sky, into my cup.

What is this wet that comes from above,

That some call disaster, and others find love.

The harder it falls, the less it is nice,

The colder it falls the harder the ice.

The rain has an art that I may not get,

So I stand still here and get soaking wet.


Source

Rain: do you love it or hate it?

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    • profile image

      ratetea 4 years ago

      I love rain! I've found it both beautiful and calming since I was very young. I love how informative and deep this page is, how you get into meteorology and ecology too!

    • ArtByLinda profile image

      Linda Hoxie 4 years ago from Idaho

      Very informative lens, I love rain, the smell of fresh rain is so unique and cleansing, however if it rained daily I would miss the blue sky very much. Blessed!

    • profile image

      anonymous 4 years ago

      Your weather facts and graphics are really great. New knowledge and interesting pictures. What a fun lens.

    • uneasywriter lm profile image

      uneasywriter lm 4 years ago

      Living in the Pacific Northwest I see a lot of this rain stuff. Although, I may complain often about all the rain, when I was on the road and away from the region for periods of time, I missed. Nice well put together lens about rain. Thank you

    • justramblin profile image

      justramblin 4 years ago

      Great job,. so much information. You really did lots of research. Now I'm off to learn more about the red-blood rain you mentioned. Wow. Thanks

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