Clouds & Rivers – Supplying the World with Water

Huge bits of half-frozen steam floating in the sky. That’s probably the best non-technical description of clouds. At a more minute level, they are made up of tiny particles of frozen water, called aerosols which, together in countless billions, make a cloud. The water gets in the sky through evaporation, the process in which liquid becomes gas, usually because of heat. This could be water rising from the seas and oceans or lakes; or it could be evaporation from places with a lot of plant life, typically a tropical forest. The source of heat is almost always the sun but some evaporation of water is from thermal and volcanic sources.