Water is a resource of fundamental importance for basic human survival, for ecosystems, and for many key economic activities, including agriculture, power generation, and various industries. The quantity and quality of water must be considered in assessing present-day and future resources. In many parts of the world, water already is a scarce resource, and this situation seems certain to worsen as demand increases and water quality deteriorates, even in the absence of climate change. Abundance of the resource at a given location can be quantified by water availability, which is a function of local supply, inflow, consumption, and population. The quality of water resources can be described by a range of indicators, including organic/fecal pollution, nutrients, heavy metals, pesticides, suspended sediments, total dissolved salts, dissolved oxygen, and pH.
Several recent global analyses of water resources have been published (Raskin et al., 1997; Gleick, 1998; Shiklomanov, 1998; Alcamo et al., 2000). Some estimates are shown in Table 3-3. For regional and local impact studies, reference conditions can be more difficult to specify because of large temporal variability in the levels of lakes, rivers, and groundwater and human interventions (e.g., flow regulation and impoundment, land-use changes, water abstraction, effluent return, and river diversions; Arnell et al., 1996).
Industrial wastes, urban sewage discharge, application of chemicals in agriculture,
atmospheric deposition of pollutants, and salinization negatively affect the
quality of surface and groundwaters. Problems are especially acute in newly
industrialized countries (UNEP/GEMS, 1995). Fecal pollution of freshwater basins
as a result of untreated sewage seriously threatens human health in some regions.
Overall, 26% of the population (more than 1 billion people) in developing countries
still do not have access to safe drinking water, and 66% do not have adequate
environmental sanitation facilitiescontributing to almost 15,000 deaths
each day from water-related diseases, nearly two-thirds of which are diarrheal
(WHO, 1995; Gleick, 1998; see Chapter 9).
Table 3-4: The role of various types of climate
scenarios and an evaluation of their advantages and disadvantages according to the five criteria described in the text. Note that in some applications, a combination of methods may be usedfor example, regional modeling and a weather generator (WGI TAR Chapter 13, Table 13.1). |
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Scenario Type or Tool |
Description/Use
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Advantagesa
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Disadvantagesa
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Incremental |
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Analog | ||||
Palaeoclimatic |
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Instrumental |
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Spatial |
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Climate Model-Based |
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Direct AOGCM outputs |
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High- resolution/ stretched grid (AGCM) |
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Regional models |
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Climate Model-Based (cont.) |
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Statistical downscaling |
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Climate scenario generators |
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Weather Generators |
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Expert Judgment |
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a Numbers in parentheses within the Advantages and Disadvantages columns indicate that they are relevant to the criteria described. The five criteria follow: 1) Consistency at regional level with global projections; 2) physical plausibility and realism, such that changes in different climatic variables are mutually consistent and credible and spatial and temporal patterns of change are realistic; 3) appropriateness of information for impact assessments (i.e., resolution, time horizon, variables); 4) representativeness of potential range of future regional climate change; and 5) accessibility for use in impact assessments. |
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