Our Water Planet – How Much Do You Know?

This post is part of our participation in Blog Action Day 2010, which is on the topic of Water.

As R. Buckminster Fuller reminded us, we are all traveling aboard “spaceship Earth”…all 6+ billion of us. What makes our spaceship so unique (as far as we know), and vital, is the presence of a great deal of water. One would think, then, that everyone of us would be quite familiar with the stuff — and the watery facts that enable our very survival. But how much do we really know the about the water on our water planet? What follows are the basic facts, courtesy of our space-faring  friends at NASA*.

Total estimated amount of water on planet Earth:

  • 1.39 billion cubic kilometers (331 million cubic miles)
  • 96.5% of this total is found in our oceans.  The remaining 3.5% breaks down as follows:
  • 1.7% in the polar icecaps, glaciers and permanent snow cover.
  • Another 1.7% is stored in groundwater, lakes, rivers, streams, and soil.
  • A tiny fraction of the remaining .1% exists as water vapor in our planet’s atmosphere (but this small amount drives much of the planet’s precipitation cycles through the transport of its latent heat content).
  • Another fraction of this small remainder is found in the living cells of all the plants and animals in our biosphere.

World’s Groundwater Running Low

Returning to that 1.7% that is stored in groundwater (aquifers), lakes, rivers, streams and soil…these sources are also from whence we derive our drinking water and water for agriculture. And, according to a recent study and news report, groundwater levels are depleting faster than they can be replenished. Approximately 70 – 80% of this usage is for agriculture which is pumping water out of the ground at double the rate that occurred in the 1960’s.

Using a sophisticated model of water flow across the planet’s land masses, researchers (Bierkens et al) in the Netherlands calculated how much of this water sinks into, runs off of or evaporates from land areas across the globe. As it turns out, the bulk of this pumped water (over 95%) ultimately ends up in our oceans, where it contributes to global sea level increases. This contribution is estimated to be 25% of the global sea level rise since 2000. Only a small fraction of this pumped water is able to return to the aquifers that were its sources.

Basin flood irrigation of wheat.

The study identified several global “hot spots” where agricultural usage of groundwater (and hence depletion) is most intense; these hot spots are:  Iran, northeastern Pakistan, northeastern China, northwestern India, southeastern Spain, the central United States, California’s Central Valley and Yemen.

This is not good news for global agriculture (both small scale and large scale farming) which is the foundation of economic growth, especially in the developing world. But nearly everyone on the planet, particularly urban dwellers (where the majority of humans live), is impacted by this depletion, as a large percentage of the global population depends on foods grown in one or more of these agricultural hot spots.

Slowing groundwater depletion/usage will require better (less water intensive)  irrigation methods that redirect water over the landscape such that more of it can be reabsorbed into the ground to replenish the aquifers. This will also mean planting crops that require less water consumption and are more resistant to drought. This may likely mean using so-called “landraces” (such as certain durum wheat varieties from African seed banks; see my 2009 article) and/or genetically modified crops that require less water.

* Source:  NASA Earth Observatory article (cited source in article: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather)

Top Photo: Earth — Pacific Ocean; MODIS image; NASA

Bottom Photo: Basin flood irrigation of wheat; USDA

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