Working Group II: Impacts, Adaptation and Vulnerability

Other reports in this collection High Level of Intensive Water Management

The water resources of North America have been heavily modified and intensively managed to serve a variety of human purposes. Investments in water control and delivery infrastructure range from small, privately constructed impoundments, diversion works, and levees to major multi-purpose projects constructed by federal, state, or provincial governments. The usable human-made reservoir capacity in North America is equal to approximately 22% of average annual runoff, compared to a worldwide average of 10% (Dynesius and Nilsson, 1994). Development has been most intensive in the United States, where there are approximately 75,000 structures classified as dams, with a combined storage capacity approximating 70% of mean annual runoff, or about 1,300 km3 (1 billion acre-feet) (Graf, 1999). Current water-management infrastructure has allowed the citizens of North America to make productive use of water and to reduce the adverse impacts of extreme high and low flows—but often at the cost of radically altering the natural functioning of aquatic ecosystems. The design of reservoirs and control structures and current operational protocols are based on the past hydrological record. Stationarity in the statistical characteristics of streamflow typically is assumed to apply for the future operational life of the facility. A change in mean flow or in variability could cause the physical infrastructure to be inadequate for the intended purposes or increase the risk of failure of the water resource system under extremes of drought or flood. In large water systems, such risks are buffered by robustness and resilience in the design of the system (Matalas, 1998); smaller systems may be more vulnerable under climate scenarios beyond those considered in their design.

In addition, North Americans have created laws and institutions that govern allocation of water among competing uses and define the rights and obligations of individuals, government entities, and other organizations with respect to particular water resources. These institutional aspects vary by region and have changed over time, reflecting differences in climatic and historical circumstances and changing societal values. In the western United States and western Canadian provinces, the economic importance of out-of-stream water uses drove the historical development of the prior appropriation system of water law, whereas U.S. states and Canadian provinces east of the 100th meridian generally adhere to riparian or riparian-based permit systems of water law (Chandler, 1913; Hutchins, 1971; Bates et al., 1993; Scott and Coustalin, 1995). Recently, concerns about endangered species, water quality, and other public trust values have led to changes in permitted uses of some water rights in the United States, and environmental legislation is now a powerful force in determining the location, design, and feasibility of new water projects (California Supreme Court, 1983; Wilkinson, 1989; Butler, 1990; Miller et al., 1996). A new development in the United States is that some dams are being removed or considered for removal to alleviate impairment of the aquatic ecosystem and to restore fisheries (WWPRAC, 1998).

Because North America's water management institutions and infrastructure evolved partly as adaptations to current climate variability, we expect these investments to be useful in fostering adaptability to some of the effects of long-term climate change. However, to the extent that water management facilities have impaired the health and diversity of aquatic ecosystems, they may exacerbate the adverse environmental consequences of global climate change by reducing the resilience of natural systems to further climatic stress.

Table 15-1: Human development in North America.a
Attribute Canada USA Mexico Rest of World
1995 land area (ha per capita) 31.4 3.4 2.2 2.1
1995 protected areas (ha per capita) 3 0.6 0.1 0.2
1998 internal renewable water (m3 per capita yr-1) 94,373 8,983 4,508 6,332
1987/95 annual freshwater water withdrawal (m3 per capita) (Note b) (Note b) 601
1995 electric consumption (kWhr per capita) 17,047 12,660 1,813 1,689
1994 commercial energy use (kg oil equivalent per capita) 7,854 7,819 1,079
1995 CO2 emission (t per capita) 14.8 20.5 3.5 3.2
1995 population over 65 (% of total) 12.0 12.6 4.5 6.2
1995 life expectancy at birth (yr) 79.1 76.4 73.0 62.9
1995 urban population (% of total) 77 76 61 43
1995 population in cities of 750,000 or more (% of total) 41 42 18
1990 labor force in agriculture (% of total) 3 3 22 52
1990 labor force in industry (% of total) 25 26 35 20
1990 labor force in services (% of total) 71 71 42 29
1995 GDP (US$ PPP per capita) 21,916 26,977 3,600 4,851
a Data from UNDP(1999), Organisation for Economic Cooperation and Development (; and Instituto Nacional de Estadistica Geografia e Informatica, Mexico (
b The United Nations has data for Canada and the United States, but they were not included in the report (UNDP, 1999). The report shows use of 1,069 m3 per capita for industrial countries. — = data not available.

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