The water cycle is a continuous process driven by solar energy. It begins when the sun heats water in oceans, lakes, and rivers, causing evaporation. Water vapor rises into the atmosphere, cools, and condenses into clouds. Finally, precipitation returns water to Earth as rain, completing the cycle.
Evaporation occurs when solar energy heats water molecules at the surface. This heating increases their kinetic energy, causing them to move faster. The fastest-moving molecules gain enough energy to overcome the attractive forces holding them in the liquid and escape into the atmosphere as water vapor.
Water vapor rises through different atmospheric layers, experiencing decreasing air pressure and temperature with altitude. This process is called adiabatic cooling. As vapor parcels ascend from the warm troposphere through the stratosphere and beyond, they cool significantly due to the expansion caused by lower atmospheric pressure.
Condensation requires tiny particles called condensation nuclei to begin. These microscopic particles include dust, pollen, and salt crystals that provide surfaces for water vapor to condense upon. When humidity reaches saturation and temperature drops, water molecules cluster around these nuclei, forming the first water droplets that will eventually become clouds.
Cloud development occurs when millions of water droplets cluster together in the atmosphere. Different atmospheric conditions create distinct cloud types. Cumulus clouds form from vertical air currents in unstable conditions. Stratus clouds develop in stable, layered air masses. Cumulonimbus clouds result from strong updrafts and can tower high into the atmosphere, often producing thunderstorms.