Rain
Rain comes from water that evaporated into the air, rose, cooled, and gathered in clouds. When the droplets grow heavy enough, they fall. Most of that water started in oceans, lakes, soil, and plants.
On this page: where rain comes from, how clouds form, how the water cycle works, and why rain falls in drops.
Read the answer below. In Giant, kids talk with characters and keep the adventure going.
Rain
The Sun warms oceans, lakes, wet ground, and leaves. Some of that water turns into invisible vapor and rides up. High air is cooler. The vapor condenses, which means it turns back into tiny liquid drops on bits of dust. Billions of those drops make a cloud. When they bump and grow, gravity wins. They fall as rain. The water is not new. It is the same supply Earth has been recycling for a very long time.
~2 mm
Typical raindrop
Evaporate
Water becomes vapor
Condense
Vapor becomes droplets
Cycle
Same water, new trip
Warm, moist air rises. As it rises it expands and cools. Water vapor sticks to tiny specks, called condensation nuclei: dust, salt, even pollen. Those coated specks become cloud droplets. A cloud is a crowd of them, light enough to stay up until they grow. Different heights and temperatures make different cloud shapes. Rain often falls from thicker clouds that have had time to fatten their drops.
The water cycle is the loop. Evaporation and plant breath put vapor in the air. Condensation builds clouds. Precipitation is the fall: rain, snow, sleet, or hail. Water runs into rivers and soaks into soil, then heads back to the ocean or up again. You drink water that has been in this loop. The cycle has no start button. It is always running.
Cloud droplets start tiny, much smaller than a raindrop. They bump, stick, and grow. In cold clouds, ice crystals can grow and then melt on the way down. Surface tension, a kind of water-skin, pulls a falling blob toward a rounded drop. Wind can squash it. A drop is the size water can hold together while it falls. That is why rain is drops, not a solid blue sheet.
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