There are about 325 million cubic miles of water on Earth at any given time. Out of this water 99% of it is either in salty oceans or is trapped in glaciers and ice caps. Only about 1% is available as fresh water.
If this small amount of fresh water were not re cleansed and recycled every day our rivers and lakes would soon dry up and the water we do have would need to go through a costly cleansing process. Thankfully the Sun purifies our saltwater and returns it to the land in the form of rain for us.
Each year the Sun evaporates about 95,000 cubic miles of water. Out of this about 71,000 cubic miles of that water fall back into the ocean and become part of the unusable salt water. Only about 24,000 cubic miles fall on the land and about 9,000 cubic miles of that run off in streams and rivers and flow into the ocean.
This leaves us with 15,000 cubic miles of water per year in the form of "ground water." This purified water gives us enough water for each person on Earth to receive 22,000 gallons of fresh water a year.
Unfortunately our rain doesn't fall evenly. Mountains, winds, and ocean currents make the rain fall more in some areas than others. If the amount of rain were even every square inch of the Earth would receive about 32 inches of rain a year. Some parts of the Earth get 150 inches of rain per year while some get less than 10. This variation is why we have deserts and rain forest climates. While location on the earth is a significant factor a major difference between the two is just that one has more water than the other.
As the Sun warms the water in the ocean, water evaporates into the air. In the air the vapor rises quickly into the atmosphere because water vapor is less dense than air. As it rises, it cools and condenses to form small drops of water again. These droplets are called clouds.
As these droplets float around they collect bits of dust out of our atmosphere. As the droplets gather dust they become heavier and when the droplets collide with each other they form larger and larger drops until they weigh more than the air and fall to the ground. Sometimes it is hot enough that the drops evaporate again and disappear before reaching earth which doesn't make farmers happy during droughts. Raindrops fall at different speeds; some raindrops are small and they appear in the form of mist, others are quite large and can fall to the ground at speeds of up to 20 miles per hour.
These droplets don't always fall as rain, they can also freeze in the air and fall as hail, sleet, and snow. In fact, a droplet may melt and refreeze several times before it finally hits the ground.
Plants absorb only a small percent of the rain that falls to Earth. What is left is either absorbed into the ground and forms underground aqua fores or reevaporates and continues as part of the water cycle. Some water however makes its way into a plant's cells, becoming a part of the actual plant.
Heavy rains also change the way rivers flow. Most rivers are caused by a constant flow of water flowing in the same spot over a period of time. Water moves more rapidly along the outer bend of a curve in a river and because of this there is more erosion on the outer side than the inner side. This causes the river to become even more twisted as the bend gets bigger and bigger.
©Copyright 1998 Elizabeth
Beckett, Holly Bernitt, and Vishwa Chandra.