The idea of forecasting by the use of historical climate analogies has been used by Glantz (1988; 1989), who poses four caveats in their use. First, the use of the climate analogy should be made clear so that it is not misleading when viewed in a different context. Second, the climate analogy should not be overextended to support unjustified conclusions. Third, one should recognize that the analogy may be inappropriate for cultural or historical reasons. Fourth, one should note that analogies can lead to the development of possible but inconsistent scenarios.

The use of historical climate analogies provides a different look into the future than that provided by large-scale computer models. Furthermore, climate analogies provide an insight into how the responsible agencies actually dealt with the climate variability as it occurred

The topic of the operation of water resource systems under climatic stress addressed here is, of course, not new. One of the best discussions of this can be found in the National Research Council's Climate, Climate Change, and Water Supply (1977) study. This study emphasizes that ''unless the exact sequence of future flows can be predicted with certainty there may be little benefit to hydrologic system design.'' The study proposes designing water resource systems with robustness (the ability to perform reasonably well under a variety of possible climates) and resilience (the ability of a system designed for one climate and set of conditions to be modified in response to persistent new climates or conditions) (Matalas and Fiering, 1977). The question to be considered here, then, is whether climate analogies can be used to determine whether or not an existing water resource system exhibits the properties of robustness and resilience.

Forecasting by analogy using the Colorado River as an example also has been studied by Brown (1988). However, she focused on the Colorado River Compact rather than on floods and droughts along the river.

If the streamflow in the Colorado River somehow could be equated with the number of words written about it, the river would constantly flow as a torrent (Dracup, 1977; Dracup et al., 1985; Hundley, 1975; Rhodes et al., 1984).

The Colorado River dominates water resource development in the seven states of the southwestern United States (see Figure 10.1).