Distribution Supply and Demand

Perhaps the most important variables that affect water availability on regional and global scales are distribution, supply, and demand. Global and regional climate patterns result in differential distribution of water resources over the globe and regionally. Within this climate framework exists a regional dynamic of distribution that is attributable to infrastructure. When services are not equitably distributed amongst users, access is inhibited for those outside the service area. This issue is most prominent in rural areas of developing countries, as most water infrastructure is concentrated near urban centers and agricultural regions, but it also affects the urban poor in cases where service to wealthier neighborhoods is given priority. Another major effect on urban supply is development; as the surface area of paved land increases, runoff also increases, while the infiltration of rainfall into the water table decreases. This is especially important in arid urban areas where groundwater is the principle water source.

As mentioned above, supply is as much a function of demand as it is a function of distribution. For this reason, demand management is important in the consideration of solutions to the problem of access. Water demand management entails reducing the demands on freshwater through conservation and pollution abatement. Pollution is important to demand management because polluted water places a demand on freshwater as a carrier of pollutants [4]. Conservation can be utilized in both the household and agricultural sectors to reduce demand. The logic of demand management theory is that by decreasing supply inhibitors (pollution and over consumption/overuse), we can effectively decrease demands on freshwater. Use of this terminology is risky though, as it could be interpreted to mean that by increasing supply we effectively decrease demand. This is not the case, however, as increasing supply in this model requires a reduction in demand before an increase in supply can be achieved. We must also be aware that using language that connotes an increase in supply may lead to inefficient use of water by giving the impression that a supply surplus exists. Full-cost water pricing may be the best method for reducing household use, but we should note that this method should only be employed in conjunction with subsidization for those who cannot afford to pay the full cost.

Demand is not limited to local populations, either. Many watersheds cross state and national boundaries, complicating the political aspects of demand. Collaborative management techniques may help to solve transboundary disputes that not only create more demand for resources, but that also affect regional and local distribution and supply. The collaborative watershed management model seeks to increase the efficiency of and coordination among the many interests for a given watershed. By increasing stakeholder participation, decentralizing the decision making process, and adopting the watershed as the water management unit, the collaborative effort should, in theory, result in more successful and more sustainable management of the watershed. Mostafa Dolatyar and Tim Gray demonstrate that collaborative management techniques are especially applicable in the Middle East, where most of the major water sources cross jurisdictional boundaries and many stakeholders are involved [5].

With a nearly exponential increase in global demand over the past 40 years, freshwater supplies are being pushed to their limits more than ever. This is especially critical in arid regions, such as the southwestern U.S., most of Africa, parts of Europe and Asia, and the Middle East. Figure 7.1 shows the increase in global population from 1950 to 2000. Figure 7.2 shows the increase in global water usage from 1950 to 2000. Notice that the rate of increase, or slope, of the two curves is nearly identical. This suggests a strong correlation between population and water consumption; however, this correlation is not as straightforward as it may seem at first. The majority of water use takes place in the industrial sector, followed by the agricultural and domestic sectors, respectively. Nevertheless, as population increases, industrial and agricultural production also increase, so there is an indirect correlation at the very least. We should note, of course, that as industrial and agricultural production increase, so do both surface and groundwater pollution.

World population1950-2000

1950 1960 1970 1980 1990 Year

2000

Figure 7.1 World population by year from 1950 to 2000 (Data from United Nations Department of Economic and Social Affairs Population Division, World Population Prospects: The 2004 Revision, available from http://www.un.org/ esa/population/unpop.htm, 2004. With permission.)

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