Definition · Plain-language
Evaporation
Evaporation is the process by which liquid water gains enough energy to become water vapour, a gas, at the surface of the liquid.
The step most authors miss
Doing CRediT right? Don’t stop at the statement.
A CRediT statement credits you inside one paper. The recognition CRediT was built for happens when those roles are tied to you, persistently. Sign in with your ORCID — free — and claim your CRediT contributions on casrai.org, the home of the standard. They become a verified, portable part of your identity, not a line that disappears into one PDF.
Free: claim your contributions, then export a journal-ready CRediT statement, schema.org structured data, JATS XML, CSV or BibTeX — and preview your public profile. A membership publishes that profile publicly and verifies the journals you serve.
Liquid escaping into the air
Evaporation is the change of state from liquid to gas that takes place at the surface of a liquid. The molecules in a liquid move at a range of speeds; the fastest ones at the surface can carry enough energy to break free and escape into the air as vapour. Because the most energetic molecules leave, the liquid left behind cools slightly — this is why sweat evaporating cools your skin. Crucially, evaporation can happen at any temperature, not only when water is hot, as long as some molecules have the energy to escape.
Evaporation versus boiling
Evaporation and boiling both turn liquid into gas, but they are not the same. Evaporation is a gentle, surface-only process that occurs over a wide range of temperatures, below the boiling point, which is why a puddle can dry up on a cool day. Boiling happens only at a specific temperature — the boiling point — where bubbles of vapour form throughout the whole liquid, not just at the surface. So evaporation is slow and surface-bound; boiling is rapid and happens throughout. Both are governed by how much energy the molecules have.
Its role in the water cycle
Evaporation is the engine that starts the water cycle. Heat from the Sun warms the surface of oceans, lakes, rivers and damp soil, giving water molecules the energy to evaporate into vapour and rise into the atmosphere. Plants add to this through transpiration — releasing water vapour from their leaves — and the two together are often called evapotranspiration. The amount of evaporation depends on temperature, wind, humidity and surface area: heat, breeze and dry air all speed it up. The vapour later condenses into cloud and returns as precipitation.
Key facts
At a glance
- Definition: the change of a liquid into a gas at its surface
- Opposite of: condensation
- Driven by: heat energy, mostly from the Sun
- Differs from boiling: occurs below boiling point and only at the surface
- Speeded up by: higher temperature, wind, low humidity and large surface area
- Role: lifts water into the atmosphere to start the water cycle
Common misconceptions
What people often get wrong
Often heard: Water has to boil before it can evaporate.
Actually: Evaporation happens at any temperature, not just at boiling point. A puddle drying in cool air shows water evaporating without ever being heated to boiling.
Often heard: Evaporation and boiling are just two words for the same thing.
Actually: Evaporation is slow and happens only at the surface across a range of temperatures. Boiling is rapid, occurs at a fixed temperature, and forms vapour bubbles throughout the whole liquid.
Often heard: When water evaporates it is destroyed or used up.
Actually: The water is not lost — it changes into water vapour, an invisible gas in the air. It will later condense and fall again as precipitation in the water cycle.
Going deeper
