WPWT - Our Water World (Lesson)
Our Water World
Water, water everywhere. But how much of it is useful?
Earth is the water planet. From space, Earth is a blue ball, unlike any of the other planets in our solar system. Life, also unique to Earth of the planets in our solar system, depends on this water. While there's a lot of saltwater, a surprisingly small amount of it is freshwater.
Distribution of Water
Earth's oceans contain 97% of the planet's water. That leaves just 3% as freshwater, water with low concentrations of salts. Most freshwater is trapped as ice in the vast glaciers and ice sheets of Greenland.
How is the 3% of freshwater divided into different reservoirs? How much of that water is useful for living creatures? How much for people?
A storage location for water such as an ocean, glacier, pond, or even the atmosphere is known as a reservoir. A water molecule may pass through a reservoir very quickly or may remain for much longer. The amount of time a molecule stays in a reservoir is known as its residence time.
To explore our watery world, please watch these videos. Links to an external site.
Water World Links to an external site.
Our Thirsty World Links to an external site.
Water, Water Everywhere! Links to an external site.
Click through this presentation to see several examples of water reservoirs. (All images from wikimediacommons.org)
The image below shows the mean precipitation, globally, over a year. Compare the different parts of the planet and the precipitation. What does it mean for life there?
Will water cause the next war?
Wars have been fought over oil, but many people predict that the next war will be fought over water. Certainly, water is becoming scarcer.
Water Distribution
Blue means there is a lot of river water for each person who lives in the river basin. Salmon pink means there is very little river water for each person who lives in the river basin.
Over time, there will be less water per person within many river basins as the population grows and global temperatures increase so that some water sources are lost. In 2025, many nations, even developed nations, are projected to have less water per person than now (Figure below).
The same map but projected into 2025.
Water Shortages
Water scarcity is a problem now and will become an even larger problem in the future as water sources are reduced or polluted and the population grows. In 1995, about 40% of the world's population faced water scarcity ( Figure below). Scientists estimate that by the year 2025, nearly half of the world's people won't have enough water to meet their daily needs. Nearly one-quarter of the world's people will have less than 500 m3 of water to use in an entire year. That amount is less water in a year than some people in the United States use in one day.
Water supply compared to the population.
Droughts
Droughts occur when a region experiences unusually low precipitation for months or years (Figure below). Periods of drought may create or worsen water shortages.
Human activities can contribute to the frequency and duration of droughts. For example, deforestation keeps trees from returning water to the atmosphere by transpiration; part of the water cycle becomes broken. Because it is difficult to predict when droughts will happen, it is difficult for countries to predict how serious water shortages will be each year.
Extended periods with lower than normal rainfall cause droughts.
Effect of Changing Climate
Global warming will change patterns of rainfall and water distribution. As the Earth warms, regions that currently receive an adequate supply of rain may shift. Regions that rely on snowmelt may find that there is less snow and the melt comes earlier and faster in the spring, causing the water to run off and not be available through the dry summers. A change in temperature and precipitation would completely change the types of plants and animals that can live successfully in that region.
Water Scarcity
Water scarcity can have dire consequences for the people, the economy, and the environment. Without adequate water, crops and livestock dwindle and people go hungry. Industry, construction, and economic development are halted, causing a nation to sink further into poverty. The risk of regional conflicts over scarce water resources rises. People die from diseases, thirst, or even in the war over scarce resources.
California's population is growing by hundreds of thousands of people a year, but much of the state receives as much annual rainfall as Morocco. With fish populations crashing, global warming, and the demands of the country's largest agricultural industry, the pressures on our water supply are increasing.
Conflicts Over Water
As water supplies become scarce, conflicts will arise between the individuals or nations that have enough clean water and those that do not (Figure below). Some of today's greatest tensions are happening in places where water is scarce. Water disputes may add to tensions between countries where differing national interests and withdrawal rights have been in conflict. Just as with energy resources today, wars may erupt over water.
The projection suggests there may not be enough freshwater; the nations in brown may not be able to afford to supply their citizens with fresh water.
Water disputes are happening along 260 different river systems that cross national boundaries. Some of these disputes are potentially very serious. International water laws, such as the Helsinki Rules, help interpret water rights among countries.
RESOURCES IN THIS MODULE ARE OPEN EDUCATIONAL RESOURCES (OER) OR CREATED BY GAVS UNLESS OTHERWISE NOTED. SOME IMAGES USED UNDER SUBSCRIPTION.