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The World's Water 2008-2009
The Biennial Report on Freshwater Resources
By Peter H. Gleick ISLAND PRESS
Copyright © 2009 Pacific Institute for Studies in Development, Environment, and Security
All rights reserved.
ISBN: 978-1-59726-966-7
CHAPTER 1
Peak Water
Meena Palaniappan and Peter H. Gleick
In the past few years, discussions about the possibility of resource crises around water, energy, and food have introduced new terms and concepts into the public debate. Energy experts predict that the world is approaching, or has even passed, the point of maximum production of oil, or "peak oil." The implications of reaching this point for energy policy are profound, for a range of economic, political, and environmental reasons. More recently, there has been a growing discussion of whether we are also approaching a comparable point of "peak water," at which we run up against natural limits to availability or human use of freshwater.
To judge from recent media attention, the finite supply of freshwater on Earth has been nearly tapped dry, leading to a natural resource calamity on par with, or even worse than, running out of accessible, affordable oil. In this chapter, we evaluate the similarities and differences between water and oil to understand whether and how the concept of "peak water" is analogous to the idea of peak oil; how relevant this idea is to actual hydrologic and water management conditions; and the implications of limits on freshwater availability for human and ecosystem well-being.
Regional water scarcity is a significant and growing problem although there are many different (and often inconsistent) measures and indicators of water scarcity (Gleick et al. 2002). In some regions, water use exceeds the amount of water that is naturally replenished every year. About one-third of the world's population lives in countries with moderate-to-high water stress, defined by the United Nations to be water consumption that exceeds 10 percent of renewable freshwater resources. By this measure, some 80 countries, constituting 40 percent of the world's population, were suffering from water shortages by the mid-1990s (CSD 1997, UN/WWAP 2003). By 2020, water use is expected to increase by 40 percent, and 17 percent more water will be required for food production to meet the needs of the growing population. According to another estimate from the United Nations, by 2025, 1.8 billion people will be living in regions with absolute water scarcity, and two out of three people in the world could be living under conditions of water stress (UNEP 2007). Are we reaching natural limits to growth, long predicted by some observers? Are there peaks in availability or use of certain resources? These questions have long been debated in the energy field, and they are now being raised for other vital resources, particularly water.
Concept of Peak Oil
The theory of peak oil originated in the 1950s with the work of geologist M. King Hubbert and colleagues who suggested that the rate of oil production would likely be characterized by several phases that follow a bell-shaped curve. First, discovery and the rate of exploitation rapidly increase as demand rises, production becomes more efficient, and costs fall. Second, as oil is consumed, the resource becomes increasingly scarce, costs increase, and production levels off and peaks. Finally, increasing scarcity leads to a decline in the rate of production more quickly than new supplies can be found. This last phase would also be typically accompanied by the substitution of alternatives (Ehrlich et al. 1977). The phrase "peak oil" refers to the point at which approximately half of the existing stock of petroleum has been depleted and the rate of production peaks (Fig. 1.1).
In 1956, Hubbert predicted that oil production in the United States would peak between 1965 and 1970. And, in fact in 1970, oil production in the U.S. reached its height and began to decline (Fig. 1.2). The concept of a bell-shaped oil production curve has been proven for a well, an oil field, a region, and is thought to hold true worldwide. The theory of peak oil also envisions that once half of oil reserves have been produced, oil would become increasingly more difficult and expensive to extract because the most accessible sources of petroleum had already been tapped.
In recent years, the concept of peak oil has received renewed attention because of growing concern that the world as a whole is approaching the point of declining petroleum production. No one knows when global oil production will actually peak, and forecasts of the date range from early in the 21st century to after 2025. One of many recent estimates suggests that oil production may peak as early as 2012 at 100 million barrels of oil per day (Gold and Davis 2007). The actual peak of production depends on the demand and cost of oil, the economics of technologies for extracting oil, the rate of discovery of new reserves compared to the rate of extraction, the cost of alternative energy sources, and political factors. Figure 1.3 shows total U.S. and global oil production from 1970 to 2007.
There are many reasons for growing concern over reaching the point of maximum production of oil. In particular, the population of the planet continues to grow rapidly, driving rising demand for energy in the form of liquid fuels. This growing demand, together with the fact that alternatives or substitutes for oil remain economically expensive and technologically immature, raises the specter of energy shortages, constraints on industrial activity, and economic disruptions. And in summer 2008, when the price of oil shot to $140 per barrel, the concept of peak oil began to feel all too tangible.
Comparison of Water and Oil
Does production or use of water follow a similar bell-shaped curve? In the growing concern about global and local water shortages and scarcity, is the concept of "peak water" valid and useful to water planners, managers, and users?
In the following sections, we consider the differences and similarities between oil and water to evaluate whether a peak in the production of water is possible, and in what contexts it may be relevant. We assess existing limits to the amount of water and oil available on earth. Oil and water are also compared in terms of the renewability of the resource, whether the substance is consumed or not during use, and whether its use is global or local in scale. We also look at whether substitutes for the resources are possible. Our major findings are summarized in Table 1.1. Based on this analysis, in the next section we evaluate the utility of the term "peak water."
First, we look at the question of limits on total water availability. While it is clear that we will at some point in the future run out of oil (or, to be more precise, economically and environmentally accessible oil), will we run out of water? Considering this question on a planet covered with water may seem odd, but as the following section illustrates, there are distinct differences in the amount of water that exists in stocks versus that which is available in flows of the hydrologic cycle.
Are We Running Out of Water?
The total quantity of both water and oil on Earth are literally limited, though the more important question is whether they are practically limited. The origins of petroleum rest with biological and chemical processes that turned decaying plant carbon into stocks of liquid and solid "fossil fuels" over the geologic time of millions of years. The origins of water on Earth are less certain, but most geologists agree that the water on the planet is of cosmic origins from around the time when the planet itself was formed (Box 1.1).
How much water is there on Earth and where is it? Table 1.2 shows the distribution of the main components of the world's water. The Earth has a stock of approximately 1.4 billion cubic kilometers of water, spread over a wide variety of forms and locations. Of this water, the vast majority (nearly 97%) is salt water in the oceans. The world's total freshwater reserves are estimated at around 35 million cubic kilometers. Most of this, however, is locked up in glaciers and permanent snow cover, or in deep groundwater, inaccessible to humans.
Considering the total volume of water on Earth, the concept of running out of water at the global scale is of little practical utility. There are huge volumes of water—many thousands of times the volumes that humans appropriate for all purposes. In the early 2000s, total global withdrawals of water were approximately 3,700 km3 per year, a tiny fraction of the estimated stock of 35 million km3 of water (Gleick 2006).
A more accurate, and sobering, way to evaluate human uses of water, however, would look at the total impact of human appropriations through the use of rainfall, surface and groundwater stocks, soil moisture, and so on. An early effort to evaluate these uses estimated that humans already appropriate over 50% of all renewable and "accessible" freshwater flows (Postel et al. 1996), including a fairly large fraction of water that is used instream for dilution of human wastes. It is important to note, however, that these uses are of the "renewable" flows of water, which we explain later. In theory, this use can continue indefinitely without any effect on future availability because of the renewability of the resource. Still, while water itself is renewable, many uses of water will degrade its quality to such an extent that this theoretically "available" water is practically useless. Improving the quality of this water for reuse will require the input of energy, technology, biological treatment, or dilution with more water.
Renewable vs. Nonrenewable Resources
In any comparison between oil and water, it is vital to distinguish between renewable and nonrenewable resources. The key difference between these is that renewable resources are flow (or rate) limited; nonrenewable resources are stock limited (Ehrlich et al. 1977). Stock-limited resources, especially fossil fuels, can be depleted without being replenished on a time-scale of practical interest. Stocks of oil, for example, accumulated over millions of years. How long oil lasts depends on our ability to find it, the rate we use it, and the cost of removing and using it; the volume of oil stocks is effectively independent of any natural rates of replenishment because such rates are so slow.
Flow-limited resources can be virtually inexhaustible over time, because their use does not diminish the production of the next unit. Such resources, such as solar energy, are, however, limited in the flow rate, i.e., the amount available per unit time. Our use of solar energy has no effect on the next amount produced by the sun, but our ability to capture solar energy is a function of the rate at which it is delivered.
Water is a unique renewable natural resource that demonstrates characteristics of both flow-limited and stock-limited resources, because of the wide range of forms and locations for freshwater. This dual characteristic of water has implications for the applicability of the term peak water. Overall, water is a renewable resource with rapid flows from one stock and form to another, and the production of water typically has no effect on natural recharge rates. But there are also fixed or isolated stocks of local water resources that can be consumed at rates far faster than natural rates of renewal, or for which the rate of recharge is extremely slow. Most of these are groundwater aquifers—often called "fossil" aquifers because of their slow recharge rates—but some surface water storage in the form of lakes or glaciers can also be used at rates exceeding natural renewal, a problem that may be worsened by climate change, as noted later and in Chapter 3.
Consumptive vs. Non-Consumptive Uses
Another key factor in evaluating the utility of the concept of a resource peak is whether water and oil are used in consumptive or non-consumptive ways. Practically every use of petroleum is consumptive; once the energy is extracted and used, it is degraded in quality. Almost every year, the amount of oil consumed matches the amount of oil produced, and sometimes we consume more than is produced that year. Thus a production curve for oil is solely dependent on access to new oil.
Not all uses of water are consumptive and even water that has been "consumed" is not lost to the hydrologic cycle or to future use—it is simply recycled by natural systems. Consumptive uses of water only refer to uses of water that make that water unavailable for immediate or short-term reuse within the same watershed. Such consumptive uses include water that has evaporated, transpired, been incorporated into products or crops, heavily contaminated, or consumed by humans or animals. As discussed in the section on the renewability of water resources, some stocks of water can be effectively consumed locally. When withdrawals are not replaced on a timescale of interest to society, eventually that stock becomes depleted. The water itself remains in the hydrologic cycle, in another stock or flow, but it is no longer available for use in the region originally found. There are also many non-consumptive uses of water, including water used for cooling in industrial and energy production, and water used for washing, flushing, or other residential uses if that water can be collected, treated, and reused.
Transportability of Water
Because the Earth will never "run out" of freshwater, growing concerns about water scarcity must, therefore, be the result of something other than a concern about literally consuming a limited resource. And, of course, they are; water challenges are the result of the tremendously uneven distribution (due to both natural and human factors) of water on earth, the economic and physical constraints on tapping some of the largest volumes (such as deep groundwater and ice in Antarctica and Greenland) of freshwater, human contamination of some readily available stocks, and the high costs of moving water from one place to another.
This last point—the "transportability" of water—is highly relevant to the concept of peaking. Oil is transported around the world because it has a high economic value compared to the cost of transportation. As a result, there is, effectively a single global stock of oil that can be depleted, and regional constraints can be overcome by moving oil from the point of production to any point of use. In contrast, water is expensive to move any large distance, compared to its value. As a result, there is no single, fungible global stock of water, and regional constraints become a legitimate and serious concern.
(Continues...)
Excerpted from The World's Water 2008-2009 by Peter H. Gleick. Copyright © 2009 Pacific Institute for Studies in Development, Environment, and Security. Excerpted by permission of ISLAND PRESS.
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