Global Change Consulting Consortium, Inc.
Water “wedges” – can they be defined and can they help to generate action on water issues? An introduction to issues of water supply at scales up to global
The discussion here is not intended to be comprehensive, as this would require a book or set of books. These essays are more about providing discussion points and less in the way of scholarly documentation. The emphasis is on Web-accessible references.
We highlight a number of current issues. The GCCC is, of course, willing to address topics beyond those covered here.
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Outline of this document.
Each highlighted (underlined) item is a hyperlink to a section of this document.
Issues and corresponding actions
(Actions not readily resolved)
(Actions not enumerated in detail)
(Actions not enumerated in detail)
What are wedges?
In 2004, Pacala and Socolow addressed the challenge of reducing greenhouse gas emissions by introducing the concept of sustainability wedges. Each wedge is an action that can be taken to reduce carbon emissions cumulatively by 25 gigatons (Gt) over the next 50 years. Lacking these controls, global emissions are projected, under a common scenario, to double from the 2004 rate of 6.5 Gt per year. Consequences for climate and thus for human and other biospheric activities are projected to be severe. Seven such wedges, implemented concurrently, could stabilize total emissions at 6.5 Gt per year. Below is a figure from that article [If the image below does not load, you may have VML (Vector Markup Language) disabled in Internet Explorer (IE). It is re-enabled if you install a security patch from MicroSoft or the latest update for IE, or if you follow instructions on this link. You can also see the image directly from this link]>:
The authors proposed 15 specific wedges, each estimated at saving the emission of the aforementioned 25 Gt C. In their wording, one such wedge is efficient vehicles: increase fuel economy for 2 billion cars from 30 to 60 mpg, while attending to issues of car size and power. Another is capturing CO2 at baseload power plants: introduce CCS at 800 GW coal or 1600 GW natural gas plants (compared with 1060 GW coal in 1999); the authors comment that the technology already in use for hydrogen production.
It should be noted that emissions of 6.5 GtC per year still entail significant climate changes. Wallace Broecker argues compellingly that emissions need to be brought to 0 to 20% of this level within 50 years.
Water use is facing problems that are (only) partly analogous to carbon emissions. There is a nonsustainable pattern of use, with many leverage points to return to sustainability. In this presentation, we discuss the many origins of water problems (waste, inefficiency, mismanagement, natural hazards, etc.) only implicitly, in considering options to improve water use.
We limit the topic here to disparities between supply and demand. Floods as an unmanageable oversupply are not considered here, other than their potential to disrupt water supplies.
We might resolve these issues in several ways. Here is one way to partition the issues:
1) Oversubscription of current supplies. This is evident locally and regionally. The river compacts in the Western US that allocate river flow to various states have long had problems, one of which is that allocations were inadvertently based on historic high flows, such as 1929-1950 on the Colorado River. International examples are abundant and rising in number. Examples include: Israel, Jordan, Lebanon, and the Occupied Territories (Hasbani, Litani, Jordan Rivers); Turkey, Syria, and Iraq(Tigris and Euphrates); US and Mexico (Rio Grande and Colorado River); China, Burma, Vietnam, Cambodia, Thailand, and Laos (Mekong); and Ethiopia and Sudan. As a national newspaper phrased it, water may be “the next oil” in resource competition and resource wars.
Adding to the problems of joint claims are natural
variations in river flow. In seasons of
low flow, and especially in droughts, the margin between flow and claims narrows
or becomes negative. Current droughts
(date of writing: 2008) in both the Southwestern and Southeastern US have
caused economic consequences and recriminations. Temperate
On the converse side, floods exceed the safe operating
capacity of water systems, often causing great damage to them. Hurricanes (cyclones, typhoons) and monsoons
comprise one set of originators. Poor
siting decisions and operational mismangement greatly multiply the damage, as
evident in the damage to
Options to address the problems of oversubscription include:
A) Mediation for equity,
foremost. However, litigation (e.g.,
B) Reducing demand, and growth of demand, in end-use
i) Efficiency in water use: there are technologies and incentives. Some technologies address efficiency in the primary use of managed supplies, which is irrigation. Irrigation accounts for 70% of water withdrawals globally and 40% of food harvest. These include changes in irrigation systems, such as drip vs. furrow vs. flood vs. sprinkler, offering reductions in soil evaporation and direct evaporation into the air. Other technologies address municipal and industrial (M & I) use. These may be low-tech changes or simple enabling regulations, including legalization of graywater use from residences for gardening. Others require a greater investment in relatively mature technologies, such as recycling (see also 2nd article), or development of improved technologies, as in many industrial processes.
Water-use efficiency by crop plants themselves is addressed in a separate essay. Some leverage points exist here, in cultural practices and, less so, in crop breeding.
Amenity plants in parks, gardens, and lawns consume a moderate amount of water. This amount may loom large in arid zones. Regulations on planting and watering are often invoked. Golf courses are large water users and are increasing in number in countries both developed and less-developed. Some are placed on highly permeable sandy soils and lose much water by deep drainage. Regulations on golf courses appear to be rudimentary, at best.
Some efficiencies need to be
evaluated in a larger sense. Human diets
that are low in meat and dairy products can be nutritionally equivalent to
diets high in meat and dairy products.
At the same time, they require markedly less crop growth for supporting
the intermediate food converters, the domestic animals. Thus, they require far less water use in
irrigation. The current trend in the new
economies, particularly of
Incentives begin with metering and pricing of water supplies, which are not without hazards of reduced availability to marginal populations. Pricing of products that involve heavy water use is an incentive at the other end of the production line.
Cutting the growth of demand. The two greatest pressures for increased water
demand are population growth and rising affluence in the new economies of
C) Increasing the total supply of managed water. Water rarely presents itself in a readily managed form, such as springs. We commonly need to capture, store, and transmit water, as well as preserve it from contamination or recover it from contaminated sources. Most populations around the globe derive water from natural precipitation onto watersheds, which have widely varying degrees of management. Options for increasing supplies include:
i) Increasing the capture of runoff and subsurface flows on watersheds. Enormous efforts are made in various locations to condition watersheds, particularly attending to vegetative cover. Adequate cover retards surface flows, reducing floods that not only damage structures and affect land productivity (albeit sometimes positively – witness the Nile flood of the past) but also deliver water at rates that exceed immediate use and storage capacity. Surface cover also increases infiltration into soil. This can generate subsurface flows for aquifer recharge. Of course, plant cover also generates plant transpiration of soil water back into the air as a loss to managed supplies. A balance needs to be struck.
ii) New renewable water
sources within the reach of population centers with common technology
are relatively few and modest in capacity.
New water sources for local populations are still being found,
with benefits of peaceful resolution of conflicts, but these are on moderate
scales. (Distant rivers of large
capacity are covered later in this essay.) Few rivers remain unexploited near
such centers, and there is a considerable, if variable, sensitivity to adverse
ecological consequences of further exploitation. Of course, a great fraction of people (39%
currently) live within
100 km of a coastline. Consequently,
desalination of seawater is of interest, and is practiced on scales that are large by engineering standards
if modest in the total hydrologic cycle.
It is energy-intensive, so it is unlikely to be expandable massively in
scope. Renewable energy from wind does power one large facility in Perth, Western
Australia. Desalination of inland brackish water is more practical, though
still somewhat energy-intensive. One
recent installation at
iii) Fossil water sources – aquifers – for potable water and water
suitable for all irrigation are in various stage of exploitation around the
world. These vary in the degree or rate
to which each is recharged by current precipitation, thus, in the effective age
of the water and the prospects of renewal at usable rates. Some aquifers or bolsons are heavily depleted
and near the end of their lifetime, such as the Ogalalla aquifer in
the central US. Others are being rapidly
exploited, such as the Nubian
Sandstone aquifer. Yet others are
under consideration, such as the Jornada and Mesilla bolsons in southern
Brackish aquifers are probably more abundant than freshwater aquifers. They are discussed in section (ii) above.
Increasing the efficiency of storage and delivery. The cheapest storage of surface flows is in
reservoirs. These increase the surface
area as well as the volume, so that they suffer losses to evaporation. The Elephant Butte reservoir in southern
storage, such as envisioned by the
River flows or hydrographs, even
with reservoirs in place, are not timed to human needs for irrigation and
M&I use. Consider the major rivers (
In all, the storage and diversion of such river flows is subject to optimization of reservoir operation. The problem is of surprisingly high dimensionality and requires powerful approximation methods; these have been developed, but not universally applied.
Controlling the use of water by
riparian plants, both native and exotic, may be considered as an aspect of
efficiency. Clearly, native vegetation
is usually regarded as having intrinsic value for recreation, flood control,
habitat for species of economic value (e.g., direct use for grazing, timber,
and indirect value as habitat for birds and insects that exert control over
insect pests). Exotic species have
invaded many riparian zones, with tamarisk (Tamarix spp.) as the prime
example. Their presence is regarded
variously as very negative, for their water use, to having mixed impact
(tamarisk on the
Water delivery for irrigation is the greatest concern for delivery efficiency, given that M&I usage is significantly smaller. Lining of canals abets efficiency, while reducing support for native riparian vegetation that has acclimated to using leakage water. There is some concern for loss of basic biodiversity, but also for loss of plants for insects and birds that offer a degree of insect control as an unmanaged ecosystem service.
Water delivery for municipal and
industrial use is less by volume, but more costly for infrastructure. Antiquated systems cause water loss and
contamination. In the
v) Enabling the use of
supplies previously contaminated (other than by simple salts – already
discussed in Sec. (ii) above).
Contamination occurs either naturally, as in arsenic-bearing groundwater
Arsenic contamination that causes
cancers and organ damage is under considerable active research. The challenge is to develop inexpensive
technologies for poor nations such as
Removal of other chemical contaminants comprises a broad array of research areas, because there are many unique chemistries, such as for metallic ions, organic solvents, and pesticides. Processing is typically costly. Relatively cheap technologies such as reverse osmosis used in simple desalination fail to remove many organic compounds and uncharged inorganics such as boric acid. Extreme loads of contamination occur in acid mine drainage. The only practical solution is preventing the sulfide oxidation and/or drainage in the first place.
Biological oxygen demand arises from organic matter introduced into waters, both naturally and through human activities, particularly disposal of raw sewage, which is unfortunately common. For communities with central water plants, the technologies are mature, if somewhat burdensome economically for poor communities. Sewage treatment in less-developed countries (LDCs) is an enormous challenge that easily merits a much longer discussion than can be afforded here.
Biotic contaminants can be classified as infectious or non-infectious. Non-infectious agents include compounds produced biologically with chemical toxicity or noxious taste or odor. Common infectious agents in industrial nations include the protist species Cryptosporidium and bacteria of the species Campylobacter. In other nations, the range of pathogens is wider, including Vibrio (cholera) bacteria as an example. Natural river flows in tropical countries present non-microbial pathogens, notably the liver-fluke agent of schistosomiasis, persisting in circulation because inhabitants urinate in rivers. Even in temperate, industrial nations, there are bodies of still water (ponds, small lakes) with devastatingly pathogenic amoebae. Prevention of pathogen introduction is always more effective than removal but is absent in many water supplies in LDCs. Global efforts to address this problem are numerous and cannot be adequately reviewed here. Floods often exacerbate pathogen problems, adding another dimension to pathogen control. Pathogen detection is incomplete, even in industrial nations. Indicator species, such as relatively innocuous Escherechia coli, are used as surrogates. Unknown threats exist.
Redistributing resources, or
water transfers. Large-scale
rerouting of rivers from wet to dry regions is already practiced around the
world to support both irrigation and M&I use of cities. Some diversions are used for drainage, as
well. Support of
As with famines, a large part of
the problem is typically distribution not total production. Amartya Sen made this case for food
transfers, but water, as a high-volume commodity, is even more difficult to
transfer in quantities needed. A social
complication is that people have chosen to live in water-limited areas, for
personal and political reasons (e.g., Manifest
Destiny in the
Massive water transfers are technologically feasible, as evidenced by current projects. Their ecological, social, and climatic consequences are still being weighed. It is almost inconceivable that current diversions will be abandoned. Rational and inclusive deliberation of envisioned diversions is not assured.
E) Planning for natural extremes: floods and droughts.
Several major river systems that support hundreds of
millions of people frequently flood and frequently go dry. Human intervention greatly exacerbates these
extremes. The Huang He (Yellow River) in
If one searches for the term “flood management,” one commonly finds references to insurance plans, not for physical infrastructure and design to ameliorate floods. This is an unhealthy situation. More useful management includes mapping of floodplains and water routing under various scenarios, development of appropriate dams and reservoirs, and regulations for siting homes and commercial operations. Increasingly, attention must be paid to climate change. Shifts in precipitation extremes are already evident at many locations around the world. The assumption of stationarity, that natural systems stay within certain bounds, is now untenable. The timing of extremes cannot be predicted, nor even the run of normal weather for times greater than a few weeks. Planning must be done on the basis of statistics of obsevations, which are problematic in many areas of the globe with little technological infrastructure; satellite estimates of precipitation are indirect and have large error bands. Climate models, too, have trouble predicting rainfall regimes. Combined with the intricacies of hydrology, the intellectual demands in planning for extremes are considerable, while feasible.
Along with planning for droughts and floods comes planning for attendant losses of crops and potential famines. Remote sensing has wide coverage and immediacy, making it a particularly effective tool for predicting famines originating in extremes in the water regime.
2) Reduction in manageable supplies from changes in the hydrologic cycle. The western US shows a trend – with
considerable variability - to reduced
snowpack, which is the dominant source of flow in major rivers (e.g., 75% for the Rio Grande). Glaciers
are diminishing essentially worldwide. Consequently, flow in the major
rivers of India Bangladesh, and Southeast Asia - the Ganges, Indus,
Brahmaputra, Mekong, Thanlwin, Yangtze and
These hydrologic changes appear linked to global climate
change. No local or regional actions
have much potential to effect solutions. Neither can we expect that global
action will be timely. Adaptation,
limited as it may be in effectiveness, appears to be the major recourse. This involves many of the actions noted in
Sec. 1 above, applied with greater
vigor and perhaps desperation, particularly for
food security in Asia and
Large changes in the hydrologic cycle are predicted from tropical deforestation. In various modelling studies, loss of Amazonian forests is predicted to decrease precipitation markedly, by reducing moisture recycling by plant transpiration. Models disagree on the increase surface temperatures. The changes are predicted to be irreversible: new forests could not be started under these adverse conditions. Fortunately, this irreversibility is not predicted to be universal; it may not apply in some major geographic regions.
One need, in making the best adaptation, is precise quantification of the hydrologic cycle. Snowpack monitoring by a combination of ground stations and satellite remote sensing is advancing, at least for use in industrial nations. Monitoring of ice caps and soil moisture reserves is also advancing. The GRACE program (Gravity Recovery and Climate Experiment), as an example, can detect soil moisture changes at the level of mm depth equivalents, resolving areas as small as several hundred km in linear dimension. Streamflow gauges have become easier to deploy and to monitor remotely.
3) Loss of utility from pollution. Human waste and industrial and mining effluents added to water markedly reduce its utility to humans, as does saline water incursion induced by excessive water withdrawals from some aquifers. This issue is complementary to (i.e., the obverse side of) the issue of reclaiming such contaminated water, discussed in Sec. 1.C.v above. The same processes and considerations apply.
One may inquire if there are trends, resulting in net gains
or losses of water utility related to contamination. Industrial nations have become rather
vigilant and have succeeded in cleaning up a number of major bodies of water,
such as the
Oil and gas extraction is a growing threat to water quantity
and quality in regions that include the
4) Collateral impacts of
water management. A wide range of
issues may be considered here. Some are
social and economic, including loss of livelihood of local populations when
rivers are diverted, aquifers are depleted, or reservoirs displace
residents. Others are biotic. After the Aswan High Dam was completed
Defining wedges and generating action on water issues
1) Can the concept of wedges be useful? Many people and many groups are addressing the issues above, from individual citizens to international agencies. Does it help to define wedges or other groupings of water issues? Water wedges, just like carbon wedges, are an aggregation of individual actions, and a disaggregation of the overwhelming whole. Aggregation may aid in coordinating actions, adding value to individual actions when they are performed in concert. Simply identifying necessary connections can be of value. Disaggregation may aid in making issues look soluble, when the entangled whole looks beyond the scope of any group to perform.
We may ask if carbon wedges have achieved such utility. This is not yet clear. Groups with large resources in funding and technical skills are tackling large and interconnected problems. For example, the Electric Power Research Institute (EPRI) has coordinated efforts on carbon sequestration at power plants, efficiency gains in electricity transmission, advanced nuclear reactors, and more. Whether they were directly inspired by the Pacala and Socolow concept is not to be discerned in the EPRI Website; a search for “wedges” gave no hits, while a search for “Pacala” returned only one hit, a technical paper on C sequestration in chestnut trees. The Fall 2007 meeting of the American Geophysical Union, attended by more than 14,000 scientists, engineers, policymakers, and journalists, is arguably the largest forum for discussing climate change. There were more than 80 sessions involving perhaps 20 to 500 people each about climate change and the role of carbon emissions therein. Carbon wedges were mentioned in detail several times, but not commonly. Retreating from action to scholarly discussion, one sees that the 2004 journal article by Pacala and Socolow has been cited 142 times up to August, 2008. Many of the citations are in policy journals, others in journals of ecology or climate change or other fields. The article is thus popular among scientists, though not overwhelmingly so.
2) Perhaps rankings by cost and cost-effectiveness are more compelling, or make wedges more compelling. Perhaps a more compelling presentation is that of cost of various actions to reduce carbon emissions, from the McKinsey Quarterly:
(Useful figure can only be viewed in full report at link above, by policies ofMcKinsey & Co; it’s the 1st figure, on p. 4.
Building insulation is most cost-effective; net cost is negative à pure benefit; nuclear power is near break-even; biodiesel is among most costly. Carbon sequestration has a net cost, but one must consider avoided external cost of climate change to all other parties, in this and all the actions.)
A similar ranking of costs for actions on water issues might be done. One difference from the case of carbon abatement is that the single objective function (amount of C abated) is less apparent in the case of water. Simply using the total water available to humans does little to ameliorate problems of regional shortfalls, or equity among populations. One might instead set a goal of a stated fraction of the human population achieving sufficiency. Costs of each action would vary according to the chosen fraction. Going beyond simple costing, one can optimize the mix of actions subject to the constraint of a specified total cost. A number of non-economic constraints might have to be applied, including ecological and social consequences. At least one optimization method has been proposed, if only for design of a single water network.
3) More about cost: who pays for the actions? The incentives to pursue any or all of the above actions may be classified as economic, legal/regulatory, political, or moral. Economic incentives may be the most pervasive, in the sense that supply, demand, and price are among the primary considerations of both users and suppliers. From an economic perspective, we may ask then, Do we have shortages, from oversubscription and other origins? In the water market as a whole, shortages are a matter of price, in classical economics. The standard curve of demand rises at low prices, while the curve of supply declines. A low price sets demand higher than supply, generating a shortage as the difference of the two. On the other hand, for the right (higher) price, almost any total demand can be satisfied. This may require implementing more costly technologies such as desalination, with attendant shifts of monetary resources from other activities. Yet, at any price, there are people who are rationed out. Demand is a composite from many users, with varying abilities or willingness to pay. Some get bargain prices, others pay more or can’t pay enough to meet their demands. One variation is implementing price discrimination, or market segmentation, whether done by suppliers or distributors. Price discrimination may enable greater efficiency in the market, with the optimum defined by water transfers bestowing equality of marginal net benefit among all uses, such as agriculture, manufacturing, and residential use or some other set of disaggregated uses.
Another common restructuring of the market is by regulation. A society may consider water as a public good and may consequently aim for equity among members of the population, whose differences in ability to pay does not parallel their needs. A society may also consider equity between generations, via preserving utility for future generations. Regulations may be then be imposed by legal bodies. There are a number of analyses that indicate regulations or public ownership of water supplies as working against efficiency in the market. Consequently, privatization of some large water markets has been proceeding, even in low-income nations – and not without considerable controversy. One hopes that the creative tension between equity and efficiency has pragmatic solutions.
Of course, in all economic analysis, we must be aware of the assumptions. These include that fully rational decision are made by users and suppliers, as well as having full and symmetrical use of information by all users and suppliers, both of which have serious limitations.
Equity and efficiency
both have additional dimensions. Costs may
be considered in the large, including what are termed external costs, such as
use of a public good (e.g., the atmosphere as a sink for pollutants) without
direct cost to the supplier or the user.
Clean Air and Clean Water Acts in the
Finally, many markets,
including that of water, have been structured by political actions of power
blocs that may act contrary to economic efficiency and/or equity. Federally-funded water projects in the
Water issues in general entail all these incentives and tensions. Untangling all the considerations is difficult, as evidenced in the paucity of reform in US water law. Overlapping of legal and regulatory authorities among different institutions is problematic, likely requiring institutional restructuring to achieve efficiency and equity. In the US, surface water is regulated in various aspects jointly by many agencies, including the US Geological Survey, The Bureau of Reclamation, the Environmental Protection Agency, the Army Corps of Engineers, the National Oceanic and Atmospheric Administration, river commissions, and regional and local water districts.
Is the situation so constrained that little room is left for improving efficiency and equity? We believe it is not, that improvement is possible, and that it is enabled by exposition of full information about the issues, that is, developing a complete context. We see this as the foremost opportunity in the process. We in the Consortium are ready to be engaged in any contracts to advance this work.
References not generally available online:
Brown, M., Funk, C. C., Galu, G., Choularton, R. 2007. Earlier famine warning possible using remote sensing and models. Eos 88: 381-382.
Deacon, J. E., Williams, A.
E., Williams, C. D., Williams, J. E. 2007. Fueling population growth in
and J. Coonrod. 2007. Climate Change and Its Implications for
Lamb, D; Erskine, PD; Parrotta, JA. 2005. Restoration of degraded tropical forest landscapes. Science 310:1628-1632.
Myneni, R. B., C. J. Tucker, G. Asrar, and C. D. Keeling (1998), Interannual variations in satellite-sensed vegetation index data from 1981 to 1991, J. Geophys. Res., 103(D6), 6145–6160. There are numerous subsequent references.
Reisner, M. 1986.
Schneider, JM; Garbrecht,
JD. 2006. Dependability and
effectiveness of seasonal forecasts for agricultural applications.
Transactions of the ASAE 49:
Teegavarapu, RSV; Simonovic, SP. 2002. Optimal operation of reservoir systems using simulated annealing. Water Resources Management 16, no.5, p.401-428.
Troch, P., Durcik, M., Seneviratne, S., Hirschi, M., Teuling, A., Hurkmans, R., and Hasan, S. 2007. New data sets to estimate terrestrial water storage change. Eos 88: 469-470.
Ward, F. 2007. Decision support for water policy: a review of economic concepts and tools. Water Policy 9: 1-31.
Yermiyahu, U., Tal, A., Ben-Gal, A., Bar-Tal, A., Tarchitzky, J., Lahav, O. 2007. Rethinking desalinated water quality and agriculture. Science 318: 920-921.