text size: small medium large
Do
you know what the Water Cycle is? It's also called the Hydrologic
Cycle. We would not be able to live on Earth without it. Do you know
your clouds? They are both related.
About 70% of the Earth is covered with water, and 97% of that is part of the salty oceans. Only a small portion of the Earth's water is freshwater. This includes such things as rivers, lakes, and groundwater. Freshwater is needed for drinking, farming, and washing. There is even water in the form of ice at the poles. Without water, life as we know it would not exist.
Few rivers flow into the Pacific Ocean since it is bordered by mountains. However, many large rivers flow into the Atlantic Ocean, carrying sediment from the land. This process is one step of the water cycle.
One process which tranfers water from the ground back to the atmosphere is evaporation. Evaporation is when water passes from a liquid phase to a gas phase. Rates of evaporation of water depend on things like the temperature, humidity, and wind.
Water that is held in lakes and rivers evaporates directly into the atmosphere. Some of the water in the ground may also be returned to the atmosphere by way of evaporation through the soil surface. Of course, the ocean is the greatest source for water evaporated into the atmosphere.
Another way that water goes back into the air is transpiration. Transpiration is the process by which plants return water to the atmosphere. After absorbing water from the ground, plants release water through their leaves. Transpiration helps plants stay cool, in the same way perspiration keeps humans and animals cool.
Water
that goes back into air often forms clouds. Clouds come in all sizes and
shapes, and they can form near the ground or high in the atmosphere. Clouds
are groups of tiny water droplets or ice crystals in the sky. They are
associated with different kinds of precipitation depending on the atmosphere's
temperature.
Cloud types are classified by height and appearance. The shape depends on the way the air moves around it. If air moves horizontally, clouds form in layers. However, clouds grow upward if air movement is vertical.
At any given time, clouds cover about 50% of the Earth. We would not have rain, thunderstorms, rainbows or snow without clouds. The atmosphere would be quite boring if the sky was always clear.
When the clouds can no longer hold moisture, the moisture falls back
to Earth as rain, snow, sleet, or hail. All of these are known as precipitation.
