Please educate me if I am wrong, but I have been of the understanding that the Earth has the same amount of water in/on it that it has had for thousands of year, perhaps millions. It is just a matter of distribution. Some zones get way more than they need, and others have droughts.
Sure thing. This will be a bit long, because it’s a complex topic. First off, the only water that counts here is fresh water. Sea water’s not very useful for drinking, irrigation, washing, or industrial purposes.
So we’re focused on fresh water. For the entire history of the United States (and longer for older countries that dig wells) we’ve been relying on subterranian water reserves for a huge portion of our fresh water. Aquifers have a history of having a lot of clean, fresh water.
The first problem is that it takes a long time for them to fill up, and in the last hundred years we’ve been pulling water out faster than they’ve been refilling. That trend has been getting worse as more people have used more water. So those water sources are actually running out – there’s not as much there as there used to be. Once we pull it out of the ground, it becomes part of the water cycle, being moved around as rainstorms, or more often flowing down to the sea. Either way, it was once a reliable source of water, and now it’s not.
The second problem is snowpack. This is part of the drought (water shortage) that California has been facing. Normally large parts of California rely on the snow that accumulates in the mountains during the winter to provide water as it melts. The recent drought has meant that in some places where snowpack – and so water reliability – has been measured, there has been no snow for the first time in recorded history. That means no water. There are a LOT of people around the world that rely on similar patterns of snowfall, and because weather patterns are changing around the world, water availability is too.
And then there’s the question of what makes for “good” water. The reality is that we’ve “removed” a lot of water from the equation by polluting it. Removing some pollutants from water is very, very difficult and expensive, and as with desalination, we don’t currently have the infrastructure to do it at any meaningful scale.
This is why people are so up in arms over hydro-fracking. The waste products of it really are toxic – there’s no question about that, if pour it in the ground, things die. And there’s a real risk that it’s getting in ground water near fracking sites. Once groundwater is poisoned, there is NO method to make it clean again.
Then there’s the issue of changes in temperature. Let’s look at rainforests, for a moment. What’s a rainforest? It’s a place that gets so much rain that water is no longer a limiting resource. Life in rainforests gets so dense and weird and beautiful because there’s just water EVERYWHERE, and so things can grow everywhere. There are temperate rainforests, and there are tropical rainforests. In both cases, the amount of available water is more than local life can use up.
But here’s the thing – tropical rainforests get much, much more rain than temperature rainforests, even though the “saturation” effect is about the same. Why is that? Because tropical rainforests are hotter. The water they get evaporates much, much faster. That means that a place in the tropics that gets the same rain as the Smokey Mountains (one temperature rainforest, at least historically), is NOT a rainforest. It can’t be, because there’s not enough water available.
And that’s the other part. If rainfall stays the same, but temperatures rise, the amount of available water decreases, because more of it evaporates. We’re already seeing the effects of this. In California, before the drought started, we were already seeing some plant species dying out at higher altitudes and repopulating themselves at lower altitudes because while rainfall had stayed steady, temperature had risen, meaning available water had decreased. On the other side of the country in the Appalachians, a decrease in AVAILABLE water and an increase in temperature have meant that some salamander species have been shrinking at a rate of around 1% per generation since the 1980s.
The total quantity of water contained on Earth is much the same as it has been, but that has no meaning if that water is not available for our use, or the use of other life forms.
That’s what is meant by water scarcity.