Distribution of the Earth's Water

Distribution of the Earth's Water

The distribution of water on the Earth’s surface is extremely uneven. Only 3% of water on the surface is fresh; the remaining 97% resides in the ocean. Of freshwater, 69% resides in glaciers, 30% underground, and less than 1% is located in lakes, rivers, and swamps. Looked at another way, only one percent of the water on the Earth’s surface is usable by humans, and 99% of the usable quantity is situated underground.

All one needs to do is study rainfall maps to appreciate how uneven the distribution of water really is. The white areas on the map below had annual rainfall under 400 mm for the last year, which makes them semi-arid or arid. And, remember, projections are for significant aridification to occur in many dry regions and for more severe rainfall events to characterize wet regions.

Water is one of the most widely distributed substances across the world’s surface and is crucial for a variety of aspects of human health, development and well-being as well as for the functioning of natural ecosystems. It has been recognised as a fundamental human right internationally and consequently needs to be managed both effectively and efficiently to ensure that global water needs are met. The distribution of water across the globe is uneven and the availability thereof becoming an increasingly major concern. The main water use sectors, grouped in terms of agriculture, industrial (includes industrial activities, mining and energy) as well as municipal/domestic, recreational and environmental water use, have an influence on water availability through physical water abstraction as well as through water degradation. Global challenges in terms of water availability and water use are highlighted. Focus is placed on the availability, distribution and use of freshwater resources on a global scale.

How Water Is Distributed

When you look at an image of Earth, it's easy to understand that 70% of its surface is covered with water. This is because all that blue you see is water in the oceans - about 97% of all the water on Earth! Ocean water is very salty, much too salty for us to drink, so in the oceans it stays.

That leaves only about 3% for all other water on Earth, which is all freshwater. But even most of that is not available to us! Of that 3%, 2/3 of it (so about 68% of all the freshwater, which is about 2% of all the total water on Earth) is frozen in ice caps and glaciers. While this may sound like an untapped resource, it's actually beneficial to us that this water is frozen where it is because it helps regulate sea levels and global temperatures on Earth.

So we still have 1% of all the water on Earth left to distribute. About 30% of Earth's freshwater (approximately 0.6% of all water on Earth) is found as groundwater. This is one resource we do take advantage of - it's where we get much of our water for drinking and irrigating agricultural crops.

Surface water, which is all the lakes, rivers and streams on Earth, makes up about 0.3% of all the freshwater (about 0.009% of all water on Earth). Think about all the large rivers we have on our planet, like the Nile, the Amazon, the Colorado and the Mississippi. All of these rivers and all of their streams don't even add up to 1% of Earth's total water! And what's even more amazing is that of all the surface water, rivers make up a measly 2%. Most surface water is found in lakes, which constitute more than 85% of all surface water.

Activity 1

1. What is the distribution ofwater on Earth?

2. Why is water important for Earth?

3. How is the Earth divided into land and water?

Activity 2

Term	Definition
freshwater	Water thet contains little or no dissolved salt
Reservoir	Storage location for a substance such as water. The atmosphere is a reservoir for carbon dioxide
Residence time	Amount of time, on average,a substance remains in a resevoir