How rain is formed
RAIN is good for our environment and human life depends on it. It keeps everything lush and green, provides us with clean water to drink, and aids farmers in growing food. Rain makes modern life possible by providing water for agriculture, industry, hygiene, and electrical energy.
Governments, groups, and individuals collect rain for personal and public use.
There are three forms of water. It could be a gas such as water vapour or steam, solid as ice, or liquid.
Water falls from the sky as rain, which is water in a liquid state.
Raindrops fall to Earth when clouds become saturated, or filled, with water droplets.
The continuous water cycle on the earth involves rain. At the beginning of the cycle, sunlight warms the water on earth’s surface. The heat causes the water to evaporate or change into water vapour. Water vapour is pervasive in the air. When it cools, the water vapour returns to droplets of water.
Millions of water droplets bump into each other as they gather in a cloud. When a small water droplet bumps into a bigger one, it condenses, or combines, with the larger one.
As this continues to happen, the droplet gets heavier and heavier. When the water droplet becomes too heavy to continue floating around in the cloud, it falls to the ground as rain and the water cycle starts over.
Raindrops condense around microscopic pieces of material called cloud condensation nuclei (CCN).
CCN can be particles of dust, salt, smoke, or pollution. Brightly coloured CCN, such as red dust or green algae, can cause coloured rain. Because CCN are so tiny, however, colour is rarely visible.
When rain forms around certain types of pollutants, such as sulfur dioxide and nitrogen oxide, the CCN react with water to make the rain acidic. This is called acid rain.
Acid can harm plants, aquatic animals like fish and frogs, and the soil.
Sulfur dioxide and nitrogen oxide can be released into the atmosphere naturally, such as through a volcanic eruption. These pollutants can also be released by human activity such as the burning of fossil fuels.
Scientists have developed a process called cloud seeding to “plant” CCNs in clouds to cause rain. Cloud seeding may reduce drought, although there is very little evidence that it works.
Although most people think raindrops look like teardrops, they actually look more like chocolate chip cookies. Like raw balls of dough dropped on a cookie sheet, the smallest raindrops, up to 1 millimetre in diameter, are actually spherical.
At 2 millimetres raindrops start to flatten because of the air pressure pushing up on them as they fall to Earth.
This effect is increased at 3 millimetres, and depressions form on the bottom of the drops as the air pushes up on the drops harder.
At 4 millimetres raindrops actually distort into a shape that looks like a parachute.
When they get to be about 4.5 millimetres in diameter, raindrops are so big that they break apart into two or more separate drops.
Drizzle, which is smaller than rain, consists of drops smaller than 0.5 millimetre. Most of Earth’s precipitation falls as rain.
Raindrops often begin as snowflakes, but melt as they fall through the atmosphere. Snow forms in the same way rain does, but in colder conditions.
Rain falls at different rates in different parts of the world.
Dry desert regions can get less than a centimetre of rain every year, while tropical rain forests receive more than a meter.
The world record for the most rain in a single year was recorded in Cherrapunji, India, in 1861, when 2,296 centimetres of rain fell. —