Possibility of global water shortage increases

Are we running out of water Early in 2001, the Rio Grande River failed to reach the Gulf of Mexico for the first time. With that nefarious event the Rio Grande joined a growing list of once-mighty rivers that are running dry from overuse:  the Colorado River in the U.S., the Yaqui in Mexico, the Indus in Pakistan, the Ganges in Bangladesh, the Yellow and Tarim in China, and the Murray in Australia, along with many other rivers large and small.
Not surprisingly, fisheries in these once-bountiful rivers have crashed.  After all, fish do need water.
We’ve tapped underground water sources pretty heavily as well.  The water level in the Ogallala Aquifer in the Midwestern U.S. has dropped more than 150 feet in some places, leaving many farmers’ wells bone dry.
As water is sucked out of aquifers, the overlying soil and rock can compact or collapse into the dewatered void, causing tall buildings to teeter in Mexico City, automobiles to tumble into sinkholes in Florida, or swallowing tourists on the fringes of the shriveling Dead Sea in Israel and Jordan.
With so many rivers, lakes and aquifers going dry, we have to ask:  Are we running out of water?
The Big Picture
 The glass-half-full answer is no……. at least not at the planetary level.  Today there is just as much water on the planet as there was when the first signs of life appeared.
Every year, about 110,000 billion cubic meters of water falls on the land surface of our planet as rain or snow.  That annual endowment of water would cover all land to nearly a meter deep if it was spread evenly.
More than half of all of that water evaporates quickly or gets taken up by trees, shrubs, and grass.
More than a third flows out to the coasts, where it helps to maintain the delicate salt- and freshwater balance of estuaries, without which much of our seafood industry would collapse.
Of all the water falling on land, we’re consuming less than 10% to grow our crops, supply our homes, keep our industries running, and generate electricity.
Every bit of the water that falls on land or in the ocean or is used for human endeavors is eventually evaporated back up into the sky as water vapor, replenishing our planet’s never-ending freshwater cycle.  No water is actually ‘lost’ in that global cycle.
So what’s the problem?  Surely we can’t be in trouble if we’re depleting less than 10% of the Earth’s naturally renewable water, and the water cycle keeps bringing that water back year after year?
Here’s the catch:  the water that falls from the sky isn’t evenly distributed around the globe, and our needs for that water aren’t the same everywhere.
So why can’t we just move water from places of abundance to places of shortage?  Why can’t we take the fresh water flowing to the Arctic Circle and redirect it to the parched cities of the American Southwest?
Such plans have been on the drawing boards of big water dreamers for decades.  In truth, the only thing that has stopped these initiatives is the fact that far less costly alternatives usually exist for meeting our water needs in the near term.  We only have to look to the South-North Water Transfer Project in China for a bellwether of what may come.  The Chinese will invest $62 billion to build a pipe-and-canal system to move water over hundreds of kilometers from the Yangtze River to parched cities and farms in the north.  As the New York Times reported last year, “It would be like channeling water from the Mississippi River to meet the drinking needs of Boston, New York and Washington.”
But here’s another catch:  Even if we could move water over great distances in a cost-effective manner, it takes a tremendous amount of energy to do so.  Nearly 20% of all electricity used in California – whose statewide plumbing system is reminiscent of a Rube Goldberg design – is spent moving water around.  The energy required to move water – and its associated carbon emissions — is not inconsequential in the efforts to arrest climate change.  Until we have abundant clean energy sources to power such re-plumbing of the planet’s water sources, we should not be investing in them.
And yet one more important consideration:  We should be careful about ‘robbing Peter to pay Paul.’ As we dry up a river or lake to harvest or export its water, the health of fish populations and natural freshwater ecosystems plummet.  In virtually all of the large rivers that have begun to go dry, fisheries have been decimated, leading to severe hardship for local people that depend upon that food source for their subsistence and livelihoods.  Last year, I published a journal paper with colleagues at The Nature Conservancy that suggested that depletion of a freshwater source by more than 20% will likely have harmful ecological and social consequences.
The conclusion that should be drawn from all of this:  we need to take stock of our local water sources and manage them wisely.  As my water colleagues like to say, that “All politics — and water — are local.”
Taking Stock of the World’s Local Water Accounts
 Nearly half of all the water that falls on land ends up in a river, lake, or aquifer before being used or flowing out to sea.   We can think of these freshwater sources as individual water accounts.  Some examples: the Colorado River basin, the Great Lakes basin, and the Ogallala Aquifer.
But unlike money accounts, it is untenable to move large volumes of water from account to account.  Therefore, it only makes sense to pay close attention to the balance in our local water accounts.
When managing these water accounts, it is quite helpful to think of them in much the same way as you think about your personal bank account: over the course of the year, you make some deposits and you take out some withdrawals.  If you continuously take out more than you deposit, you’re headed for trouble.
The bankruptcy of our unsustainable water use can be measured in the drying of rivers and the drawing down of aquifers.  In many river basins and aquifers we are taking out more than is deposited by rain or snow.
Until recently, we have not had a decent balance sheet or map to tell us how our water accounts were doing.
The map above is a good first measure of how much water is being depleted from our global water stocks.
This recently published map is a fruit of the labors of an Ethiopian PhD student named Mesfin Mekonnen and his mentor, Arjen Hoekstra at the University of Twente in The Netherlands. (disclosure: I was a small-bit co-author on the paper that included this map). To produce this map, Mekonnen and Hoekstra calculated how much of the water in each freshwater source was being depleted by agriculture, industry, and domestic uses.  They then compared the volume of water being depleted with the amount of water flowing into rivers, lakes, and aquifers each year.  For any month of the year in which the cumulative water depletion exceeds 20% of the water falling from the sky, they flagged as being “moderately water scarce.”  The map shows how many months are determined to be water scarce in each of more than 400 river basins globally.
An important conclusion from this study:  in nearly half of the water basins evaluated, more than 40% of the renewable water supply is already being depleted.
As with any map depicting global conditions, this one surely has its inaccuracies.  Better data are available in many locales, which can reveal a more accurate reading of the status of local rivers, lakes and aquifers.  But with this study, Mekonnen and Hoekstra have finally given us an initial answer to what may be the most pressing question of our time:
How much water is left?