Water covers more than 80 percent of the earth’s surface. It is found in oceans, lakes, rivers, and even ice caps and glaciers. Water is also found underground in aquifers. The water that exists today is the same water that existed billions of years ago. This is because water is what we call a limited renewable resource.
Water is a renewable resource because it travels through the oceans, rivers, ground, and atmosphere; it is always moving! It falls from the sky as rain or snow into our oceans, lakes, and rivers and onto land. Precipitation that falls on the land enters the groundwater through percolation or travels to streams, rivers, and lakes as runoff. Water in streams and rivers is carried to the oceans, where it evaporates and forms clouds—where the cycle starts all over again!
Water is also a limited resource. We will always have the same amount of water on the earth, but we can't always use as much as we need. One reason is that 97 percent of the earth's water is saltwater, and saltwater is not good for people and wildlife and many plants. Of the remaining 3 percent, which is freshwater, nearly 75 percent is frozen in glaciers, making it unavailable to us. Another reason that water is a limited resource is that pollution, increased human demand for water, and changes in precipitation patterns can decrease both the quality and amount of water available to people, plants, and wildlife.
Water and Weather on the Move
Water evaporating from the oceans, lakes, rivers, and streams moves to the atmosphere. Air carries the moisture up, and if conditions are right, it forms clouds. Wind moves these clouds around the globe. The wind that carries the clouds that bring rain is called the jet stream. The jet stream changes its pattern with each season. In other words, the jet stream will carry weather patterns, such as precipitation and temperature, in different directions or over different routes during each season. Think about four different routes you could take to a friend’s house, and during each season you would take a different route—that's what the jet stream does.
If the jet stream changes its pattern or is blocked by “ridges” or “troughs” of air in the atmosphere, the normal weather for a place can be much different for a period of time. It’s almost as if the jet stream has hit a road block or taken a detour!
When the jet stream hits a road block or takes a certain detour and is not bringing the clouds that produce rain, a drought can occur. These patterns in the jet stream could change for many reasons. Scientists are still uncovering the answers, but many think that influences such as differences in the amount of snow and ice cover, the amount of vegetation (trees or grasses) covering the land, the moisture in the soil, and ocean surface temperature and currents can cause these patterns to change. Let's learn more about the causes of drought.