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Why Does it Rain?

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 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.

Cumulonimbus incus in Mykonos / Greece

Cumulonimbus incus in Mykonos / Greece

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

There are three main ways that rain clouds are formed:

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.

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!

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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.

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

Information from Cumulus Wiki

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.

Raindrop sizes

Acid rain damaged trees

Acid rain damaged trees

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 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

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

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.

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.

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

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

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

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

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.

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.

© 2010 LadyFlashman

Rain: do you love it or hate it?

ratetea on January 16, 2013:

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!

Linda Hoxie from Idaho on November 12, 2012:

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!

anonymous on November 01, 2012:

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

uneasywriter lm on October 31, 2012:

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 on October 31, 2012:

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

Pat Goltz on October 30, 2012:

I welcome rain in the desert. Too depressing when it rains every day all year, or when it is cloudy in the afternoons all year. Catalytic converters release sulfur into the air, which forms sulfuric acid, and causes acid rain, which then destroys buildings. Environmentalists need to be very careful what changes they advocate, because more often than not, they make things worse. Thank you for a very informative and interesting lens!

Susan R. Davis from Vancouver on October 30, 2012:

I live in the Pacific Northwest. I love AND hate it, depending on my mood.

Tea Pixie on October 29, 2012:

Rain. It's a part of so many of my days! I laughed at the rain-mood link you provided at the beginning of this article. I clicked on it and had to turn it off because IT IS RAINING RIGHT NOW where I live. hee hee hee I have also shared your link to the story about raining spiders. eouwwwww ;)

irenemaria from Sweden on October 29, 2012:

Rain is a must to keep the wells full. It washes the leaves on the trees and water the flowers too.

Jogalog on October 29, 2012:

I don't mind rain too much, but of course I prefer sunshine.

sybil watson on October 21, 2012:

Wow, what a fabulous lens! Living in Hawaii, I love the rain and our rainforests (we have cloud forests too!). However, I'm sure i wouldn't love it as much if it were cold.

IncomeFromHomeT on October 12, 2012:

Half the time I love the rain and half the time I hate it! We seem to either have way too little of it or way too much of it!

anonymous on September 16, 2012:

A beautifully presented and excellently written article on glorious rain, something to be celebrated this year in the US with all the drought...may the rain fall gently on your roof and may you look out your window to enjoy a beautiful rainbow when our friend the sun peeps its way through!

Mamabyrd from West Texas on August 28, 2012:

I love the rain!! I lived in the Netherlands for three years and it didn't really rain but it drizzled all of the time now I live in west Texas and it rarely rains.

Rosyel Sawali from Manila Philippines on August 07, 2012:

Very nice lens.. timely I found it! It's raining really bad where I am right now.. floods everywhere.. nowhere to go but stay home..^_^

BeyondRoses on July 22, 2012:

As a child, I experienced a flood. I don't like to be in the rain, but I love the idea of rain, and it makes for lovely photos and poems.

Tia Novak on July 18, 2012:

I am not a big fa of rain but I don't mine if it falls.

Kerri Bee from Upstate, NY on July 08, 2012:

I love it. As a kid, I used to go out with my Dad and drive around during thunderstorms and he played some thrashing loud classical music.

CottageHomestead on July 05, 2012:

WOW! What a wonderful and refreshing lens....makes me thirsty. :)

JoshK47 on June 23, 2012:

Popping back in here to bless this wonderful lens about rain - one of my favorite things in the world!

Anastacia Gutierrez on June 21, 2012:

What an impressive lens chocked full of knowledge and education! I LOVE (in case you didn't catch that - L.O.V.E.!!!!) the rain. Living in the desert means I often go into deprivation...but the monsoons are a wonderful season full of water and lightning.

anonymous on June 21, 2012:

Love all the photos and great info thx

mel-kav on May 05, 2012:

Great information here. Thanks for sharing.

neuromancer lm on April 18, 2012:

Nice. I just love summer rains, for the rest of the year I kinda hate it tho.

mistyblue75605 lm on April 12, 2012:

:)P Nicely done! Thanks for sharing!

mistyblue75605 lm on April 12, 2012:

Great lens and coverage of info on here!

aruraza on March 08, 2012:

Great lens well done. I remember a storm in Bangkok, it left my hair streaked in grime.

Miha Gasper from Ljubljana, Slovenia, EU on February 23, 2012:

I think I outgrown romantic walks under rain, but rainy day, warm bed and good book is still very close to my perception of perfection. Thanks for all interesting facts. It is very informative lens.

flicker lm on February 11, 2012:

Loved this lens! I learned so much. We had severe flooding in my area not too long ago, which affected many people. Even small brooks were raging. Fortunately, my house is on high enough ground that it was not affected.

gregoryolney lm on September 04, 2011:

I'm at home and it's bloody pouring :-(

CruiseReady from East Central Florida on September 03, 2011:

Beautifully done! Sure do wish Texas and Oklahoma, and other states that are som drought-ridden right now would get some good, soaking rains.

Tolovaj Publishing House from Ljubljana on July 04, 2011:

Nothing better than a good book on a rainy day:)

JoshK47 on June 30, 2011:

I love a nice, steady driving rain, as long as it's not causing any destruction. I also rather enjoy driving in the rain, but it may just be because it helps keep me concentrating on the road and leads to less getting distracted.

Dinostore on March 10, 2011:

This topic deserves alot of time and effort, and you really did a great job here! Thumbs up and fav'd. :)

puerdycat lm on December 16, 2010:

Rain, glorious rain! My sympathies exactly! Raised where it really rains, I live in a semi dessert and never get the chance to get tired of rain!

anonymous on December 09, 2010:

I love rain. In my area of the country, we have way too many floods but I still love watching it ran. There is something magical about it. Your pictures are beautiful!

julieannbrady on December 06, 2010:

I didn't think that I would be singing the praises of rain until I moved here -- now, when it rains ... it IS glorious rain!

jlshernandez on October 15, 2010:

Great lens on rain. We've been stranded on the freeway in Florida years ago when a sudden rainstorm pounded on the car and the visibility was zero. We waited it out and witnessed lightning strike a meadow and caused a fire. Thumbs up.

ShamanicShift on September 29, 2010:

Beautiful design tweaks and lots of information, presented well.

anonymous on July 15, 2010:

i'm very happy when it rains)))

poutine on April 27, 2010:

Fascinating to read all the facts about rain.

I live in a relatively normal rain area.

KarenTBTEN on April 26, 2010:

Very nicely done. I live in a city known for rain (Seattle) and used to live in a city known for its lack of rain (Tucson).

Wednesday-Elf from Savannah, Georgia on April 25, 2010:

I am a big fan of 'weather', so naturally was drawn to your story about rain, especially as it is currently raining at my location :-). Excellent review of rain and the rain facts you included were fascinating. 5*

RinchenChodron on April 24, 2010:

You did a thorough and fabulous job of covering all aspects of rain! Great job Five STARS***** It has been raining hard in Denver the last two days and I find it depressing - much prefer sun myself, but it does turn the world GREEN!!

Werkpaardje on April 23, 2010:

I was very pleased when you mentioned Suriname as being part of the the largest tropical rain forest in the world. The rain forest is in the south of Suriname and if you are looking for adventure, then I think this is the right place to start. You might experience strange smells, weird sounds, dangerous looking animals... Best way is to come over and find out for yourself. 5*

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