15.1.2.1. 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
|
| |
|