Energy and Water: A Matter of Interdependence
The long-term development and production of energy resources will inescapably affect or interact with other natural resources. Biofuels may compete with cropland and put upward pressure on food costs. Siting requirements for different energy systems could foreclose other demands for open space or land.
With energy and water, there is a particularly close linkage, insofar as water resources represent essential inputs into energy production while, at the same time, energy availability is a key factor in effective water resource use.
In what follows, the first three cases illustrate how water constraints bear on the production of energy. The last two cases illustrate water-related demand for energy.
Hydroelectric Generation
It supplies approximately a fifth of global electricity production, the major countries (in rank order) being China, Canada, Brazil, and the U.S. It is estimated that a large magnitude of economically feasible hydro potential remains to be developed with China, Latin America, India, and Central Africa among the leading candidates. Notwithstanding hydro’s attractiveness as a clean and renewable energy source, its long-term viability may be clouded. There is uncertainty concerning snowpack melt, runoff, and precipitation — essentials in a reliable baseload facility; the risk of inundation of land, the need for large-scale population resettlement, as in the case of the Yangtze Three Gorges dam, silting of rivers, and competition with alternative uses, such as commercial fishing, navigation, and recreation. Constraints on the availability of hydro can therefore mean enhanced demands on other energy sources.
Cooling Systems at Thermal Power Stations
Whether fossil fuels, nuclear or solar thermal-powered, the associated cooling and condensing requirements represent a major need for water. In the U.S., about half of annual water withdrawals are for power-plant cooling; for the world as a whole, the share is around 40%.
To be sure, as a “non-consumptive” use of water, the predominant process—once-through cooling—need not preclude other uses of the discharged water, though heightened temperature of water released in rivers (e.g., at a series of French nuclear reactors along the Rhone) can affect water quality and other uses. It is also the case that while coastal siting of power plants would allow the use of seawater as the condensing medium, such siting opportunities are both limited and, when situated in bays or estuaries, controversial due to feared ecological damage. The dry (i.e., closed-loop) cooling tower alternative mutes such environmental concerns and consumes little water but, being substantially more costly tends not to be a generating company’s preferred option.
Unconventional Liquids Production
There is an understandable appeal in the exploitation of oil shale, coal, and oil sands because of their undisputed abundance. But even if breakthroughs in carbon capture and sequestration can successfully deal with their disproportionately high carbon intensity, their significant claim on water availability could prove a distinct impediment, either because of the quantity of water needed in their conversion process, their location in water-short areas, or both.
Irrigation and Water Transfers
Agriculture represents the single most important sector of consumptive water use — nearly 90% worldwide. Application of more efficient irrigation practices—presently deterred by widespread subsidization and underpricing of water—can reduce such demand appreciably. But with aquifer depletion requiring steadily more pumping and a greater need to ship water from well-endowed to poorly endowed areas as, in the U.S., from Northern to Southern California, electricity requirements rise accordingly. The irrigation and water-transfer challenge also arises in areas whose water shortage is aggravated by competing multi-territorial claims (e.g., among Israel, Palestine, and Jordan) and where institutions for joint management of scarce resources are embryonic. Finally, the problem of securing adequate energy for irrigation and pumping can be aggravated in places (e.g., Pakistan) where a shortage of both electric generating and transmission capacity compels farmers to face the still higher costs of diesel generators.
Desalination
With freshwater comprising a mere 2.5% and saltwater an estimated 97.5% of global water supply, the potential for making productive use of the latter has been a matter of intense preoccupation for decades. And, in fact, the technology for converting seawater (or other brackish or saline water) into freshwater has been known for an equally long time but, principally due to its high (and therefore costly) energy intensity, its use has been limited to two kinds of situations. In intermittently, but not (or not yet) chronically water-short areas (e.g. Santa Barbara, Calif.), its high cost confines its use to meeting periodic peak-demand needs. A different situation prevails in pervasively arid conditions, as in several Arabian-peninsula and nearby states, where some desalination capacity is indispensable. On the upbeat side, the desalting conversion cost, while more or less stagnant for years, seems finally on something of a downward path. Given global economic growth, coupled to more widespread aridity, such a cost breakthrough could be good news.
The Bottom Line
It is debatable whether the stress associated with the energy sector’s water needs or that arising from water-intensive consumers of energy are already symptomatic of changing weather patterns attributable to global warming. But shifts in the timing and pattern of runoff from spring snowmelt and winter rainfall in the U.S. are characterized in a recent U.S. Geological Survey (USGS) report as at least consistent with what, in the future, may more directly be recognized as a consequence of temperature, precipitation, and other phenomena driven by climate change.
Yet, irrespective of the added burden that may result from climate change, adequate and affordable energy and water are clearly indispensable for human development; and as illustrated here, they will continue to be interlinked in countless ways. Such cross-cutting and symbiotic relationships, among these and other natural resources will have to be part of a development planner’s kit of tools for years to come.
—Joel Darmstadter is a senior fellow at Resources for the Future. This article originally appeared at www.weathervane.rff.org and is reprinted with permission.