Precipitation is the word for water falling from the sky. Whether it is a soft sprinkle or a blizzard of snowflakes, precipitation is simply water returning to Earth from the atmosphere. This process keeps our entire planet hydrated and healthy.
The Big Journey: Precipitation and the Water Cycle
Precipitation is part of the water cycle, where water constantly moves around the Earth. This journey begins when the sun’s warmth heats water in oceans, lakes, and rivers, turning it into an invisible gas called water vapor. This process is known as evaporation, sending the water up into the sky.
Once the water vapor rises high into the atmosphere, it meets cooler air. This cooling causes the vapor to change back into tiny liquid water droplets, a process called condensation. These droplets cling together around specks of dust or salt, forming the clouds we see every day.
As more droplets join together, the clouds become heavier. When the water droplets or ice crystals become too heavy for the air to hold up, gravity pulls them back down to the ground. This falling water is the final step in the cycle, becoming precipitation.
Meet the Types: Rain, Snow, Sleet, and Hail
The type of precipitation that falls depends on the temperature of the air between the cloud and the ground. Rain is the most common form, occurring when the air temperature is warm enough to keep water droplets liquid all the way down. These liquid drops fall directly from the cloud to the Earth’s surface.
Snow forms when the entire column of air, from the cloud down to the ground, is below the freezing point of water. Water vapor in the cloud turns directly into ice crystals, which then stick together to form snowflakes. Because the air is constantly cold, the ice crystals never melt before they land.
Sleet starts as snowflakes high up that melt completely into rain when they pass through a layer of warm air. However, before the drops reach the ground, they encounter a layer of air below freezing temperature. This cold air causes the liquid raindrops to refreeze into tiny, clear pellets of ice that bounce when they hit the surface.
Hail usually happens during powerful summer thunderstorms. It begins as small ice crystals that are caught by strong rising currents of air, called updrafts, and are tossed high into extremely cold parts of the storm cloud. Each time a hailstone is lifted, it collects a new layer of frozen water, growing bigger until it becomes too heavy for the updraft to support. These hard balls of ice then crash down to the ground.
Why Water Falling From the Sky Helps Us
Precipitation is necessary for all life on Earth. It is the primary way our planet receives and recycles fresh water, which is the kind of water people and animals can drink.
The rain and snowmelt fill up our lakes, rivers, and underground stores, giving us the water we need to survive. Plants soak up this water through their roots, allowing farmers to grow the food we eat. Without the regular return of water from the sky, our world would become dry.