Crossposted with www.thegreengrok.com.
We've all heard about peak oil, but is there such a thing as peak water?
The concept of peak production in a resource like oil was first advanced by M. King Hubbert in a paper [pdf] presented in a 1956 meeting of the American Petroleum Institute and later included in the industry publication Drilling and Production Practice (1956).
The idea was pretty straightforward: given a needed resource with a finite stock, production will tend to increase with rising demand until the resource becomes depleted, at which point production will decline even though demand continues to increase. Prices will then rise until a substitute can be found for the resource.
Hubbert's paper, which predicted that production of oil in the United States would peak sometime between 1965 and 1970, was greeted with mixed reviews in 1956 (see here, here and here). As it turned out, U.S. oil production peaked [pdf] in 1970.
Today the discussion around peak oil is focused on global production. There is little argument that worldwide production will eventually peak; the question is when.
Some argue we have already or have very nearly reached peak oil (see here, here and here); others argue we are many decades away (see here, here [pdf], and here). To a large extent, the peak oil debate hinges on how sanguine one is that newer technologies, like the now infamous deepwater offshore drilling, will make previously unrecoverable resources recoverable.
The Arguments Supporting Peak Water
Great, but what does this have to do with water? Unlike oil, there is no possibility of humans using up our water resource any time soon.
The total amount of water we humans use each year amounts to about 1,400 cubic miles while the total amount of water on the Earth is around 330 million cubic miles.
Of course, most of that is salt water, but even in terms of the amount of fresh water on the Earth -- about eight million cubic miles -- the amount we use is minute.
However, most of the fresh water on the planet is in the form ice. If we consider just the sources of fresh water from rain and such, the numbers change considerably. By some estimates, we humans use about 50 percent of these fresh-water flows for one purpose or another.
But even so, water is a renewable resource. Even if we used all of the water resource, there would still be water when we're through with it. Peak oil, okay, but surely there's no such thing as peak water, right?
In a fascinating article published in the Proceedings of the National Academy of Sciences, Peter Gleick and Meena Palaniappan of the Pacific Institute argue that peak water does exist and can serve as an important concept for water managers.
Gleick and Palaniappan offer three definitions for their peak water concept:
- peak nonrenewable water, referring to resources such as those found in groundwater systems whose natural recharge rates cannot keep up with either production rates and/or contamination problems and so production peaks and then declines,
- peak renewable water, referring to resources whose availability is limited by constraints from flow rates, and
- peak ecological water, referring to resources whose total value from human use is exceeded by "the total costs of ecological disruptions and damages."
Peak Nonrenewable Water
The most obvious application of the peak water concept applies to water use from groundwater systems that are being drawn down much faster than their recharge rates.
Of particular concern in this regard is the use of deepwater aquifers whose recharge rates are so slow that we refer to the water in these systems as "fossil water."
For all intents and purposes we can think of this resource as a nonrenewable resource, much like oil, and therefore one that can reach a peak production rate.
Examples where current withdrawals threaten to exhaust supplies include the Ogallala Aquifer in the United States and the aquifer system in the Quaternary System hole in the North China plains.
Peak Renewable Water
But even when water is derived from a renewable resource such as a river, a peak can be reached if extraction and usage rates rise to the level of total supply. For example, consider the Colorado River. Since the 1960s, its flow of water into the Gulf of California has been non-existent (except for a few years of anomalously high rainfall).
What that means is that virtually every extractable drop of water in the river system is already being used. It is appropriate to say, therefore, that the peak in water production from that system has arrived.
The challenge for water managers in the Colorado River Basin is allocating a limited resource rather than further extraction.
Peak Ecological Water
Perhaps the most interesting and controversial aspects of Gleick and Palaniappan's peak water concepts is the one they call peak ecological water.
Fundamental to this concept is that water systems provide valuable resources to society in addition to the water per se -- water provides services for all sorts of plants and animals and their habitat. As water is withdrawn from an ecosystem, these services are degraded. The more withdrawn, the greater the degradation. At some point, the authors argue, the monetary loss in the value of the ecosystem services from water withdrawal can exceed the monetary value of the water withdrawal. At that point, Gleick and Palaniappan argue, the peak in ecological water is reached, a case of diminishing returns where further water withdrawal is economically ill-advised.
Need an example of a peak ecological resource? Look no further than the region blanketing the news these days. The Mississippi River Delta and the Gulf of Mexico, where the changes we've made to river flow and the pollution we've added to their environs have helped shrink important wetlands and barrier islands and helped spawn huge summertime dead zones.
And while we're on the topic, there's another example of an ecological peak in a resource. It also applies to the gulf, but it doesn't involve water. It involves oil. I doubt if there's any argument that the ecological damage done by the oil spill far outweighs the economic value of whatever oil was or could have been extracted from that well. Does it exceed the value of all the oil in the gulf? We'll have to see, but it seems to me that as far as the gulf is concerned, we've reached the threshold for peak ecological oil.