How does rain occur?

Rain occurs when water vapor rises, cools, condenses into tiny droplets to form clouds, and the droplets grow heavy enough to fall back to Earth as precipitation.

The water cycle in simple steps

1. Evaporation: Heat from the Sun turns liquid water from oceans, lakes, rivers, and wet soil into water vapor that rises into the air.
2. Transpiration: Plants release water vapor through their leaves; this adds moisture to the air.
3. Cooling and condensation: As moist air rises, it expands and cools. Cooler air cannot hold as much vapor, so vapor condenses on dust or salt particles, forming tiny cloud droplets.
4. Cloud growth: Many droplets gather to make clouds. In cold parts of clouds, ice crystals can form and grow.
5. Droplets become heavy: Small droplets collide and merge (coalescence), or ice crystals grow and fall, melting into raindrops on the way down.
6. Precipitation (rain): When drops are heavy enough to overcome rising air and drag, they fall as rain. If air is cold, precipitation may fall as snow or hail.

Why air rises (three main causes)

Factors that influence rain

• Humidity: More moisture means more potential rain.
• Temperature: Warm air holds more vapor; cooling triggers condensation.
• Topography: Mountains enhance rainfall on windward sides; leeward sides can be dry (rain shadow).
• Aerosols: Tiny particles act as nuclei for droplets and crystals.
• Wind patterns: Monsoons and trade winds carry moist air over land.

Everyday signs rain is coming

• Dark, tall clouds (cumulonimbus) building up.
• Falling air pressure and gusty winds.
• Sudden drop in temperature and smell of wet earth after first drops.

Why rainfall matters

• Freshwater supply: Fills rivers, lakes, aquifers.
• Agriculture: Waters crops and supports food security.
• Climate balance: Moves heat and moisture around the planet.