Have you ever looked out of a window on a stormy day and wondered where all the water falling from the sky has come from? The water cycle is a collection of processes that recycles water from the ocean. 97% of the world’s water is stored in oceans and seas, 2% is stored in ice, and 1% is fresh water in the air or in rivers and lakes. The following activities will help students understand the steps of the water cycle by creating visual aids.
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The water cycle has no starting point, but because the ocean contains the most water, many cycles often use the ocean as a starting point. The ocean covers 76.5% of the Earth’s surface and so absorbs a huge amount of the Sun's energy. As the ocean absorbs the energy, it heats up. Some of this energy causes the water to evaporate. This warm, moist water is less dense than the cooler air around it. This less dense air rises, and as it rises, it cools. This water then condenses to form clouds. Water forms larger droplets and will fall back down to earth due to gravity. What state it falls to earth as depends on the temperature.
If it is really cold, the precipitation will fall as snow, frozen rain, or hail, but if it is warmer, it will fall as rain. Some precipitation falls back into bodies of water and the rest falls onto land. Some that falls as snow can build up as icecaps and glaciers; this water can stay frozen for thousands of years. Some of the water that hits the ground runs into rivers. This is called surface runoff. Some water may flow into lakes while some will flow into rivers and then ultimately back into the ocean. Other water infiltrates the ground and travels underwater. Some of it is stored underground and some of this water flows back into the ocean.
The water cycle also plays a vital role in the survival of plants, as they need water to survive. Most plants need water in their leaves, the location where photosynthesis mainly takes place. In order to move this water, the plant uses small tubes in the plant's stem called xylem. The plant uses a process called transpiration to move water. Transpiration is the process where water on the plants evaporates. Temperature, humidity, light, and wind speed can all affect the rate of transpiration. Some of the water is stored in the plant and is released when the plant tissues decompose.
Not every country has a clean plentiful supply of water. Some countries don’t have a lot of rainfall due to their location. Talk with your students about the environmental and social issues surrounding water around the world.
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