Water for Food
Water Number: Around 80% of water consumed by humans goes to agriculture, globally and in California.
Dr. Peter Gleick
San Francisco Chronicle
05/01/2009
Agriculture -- the production of food and fiber -- is of vital importance for humanity. To paraphrase a popular ad from a few years ago, without food, life itself would be impossible. So for this post, here is an agricultural water number:
Water Number: Around 80% of water consumed by humans goes to agriculture, globally and in California.
Before I explain what I mean by this number (and the way I've phrased/presented it), readers should know that the number itself is neither good nor bad -- it's just a number. At the global level, it also isn't very meaningful -- much more important is the regional use and availability of water. But, still, agriculture is certainly the dominant human use of water in much of the world. It just takes a lot of water to grow things, whether it is water from rain, or water from sophisticated and complex irrigation systems. And we do need to grow things.
Humans use water for many things, from agriculture to our personal home use to water used in commercial and industrial activities. Some of this water is "consumed" -- by which I mean made unavailable for immediate reuse in the same watershed or location -- typically by being embodied in a product (i.e, turned into a beverage, or evapotranspired into the atmosphere, or so badly contaminated that it cannot be reused). Some water used by humans is not consumed, such as water used for power-plant cooling, which is sometimes just used once and returned back to a river (albeit slightly warmer). Thus total "withdrawals" of water are larger than water actually "consumed" in an area (water basin). But the vast majority of water that humans consume goes to agriculture, and with climate change contributing to a water crisis in many key agricultural areas from Australia to California, we will need to manage our use to grow more food with less water. But you can't manage what you don't measure.
You see, the quality of these global data stinks (to use a highly technical term): only a few estimates have been made and these are a combination of measurements, modeled use, and frankly, guesses, since no one, or no organization, accurately monitors global water use. And these numbers typically don't even include what Malin Falkenmark calls "green" water -- the rainfall component used directly by crops. The numbers almost everyone uses on global water use come from work done a decade ago for UNESCO by Dr. Igor Shiklomanov and his colleagues at the State Hydrologic Institute of St. Petersburg, Russia. Shiklomanov estimates that in 2000, total global consumptive use of water was around 2180 cubic kilometers, of which agricultural consumption was around 1830, or about 84%. If someone were to come up with numbers as low as 70% or as high as 90%, I wouldn't be surprised, so most people use 80% as a good estimate for agricultural consumption.
In California, we're slightly better at measuring water use, though remarkably enough, not much better. Even here, no one really knows how much water agriculture uses because no one actually measures it all. Farmers and irrigation districts don't measure or report actual use. We don't really know how much of the water applied on a field is used productively. Groundwater pumping frequently isn't monitored or reported. The best water use estimates for California come from the Department of Water Resources, and in their last Water Plan, they reported that somewhere around 43 million acre-feet (AF) of water were "used" by humans for urban and agriculture in 2000 (considered a "normal" year), of which 34.2 million AF went to agriculture, or 79%.
So what? Is it bad that agriculture uses so much water? Not if you believe that people need to eat. But it is an important number nonetheless...
