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differences in streamflow, vegetation, evapotranspiration, variability of precipitation, and other factors important to water management. Some of the most noticeable changes in catchment hydrologic fluxes (rainfall amount, evaporation rate and amount, and streamflow rates) and states (soil moisture depth and distribution in time and space) are found in threshold climates—that is, climates where relatively small changes in vegetative state or meteorological inputs have amplified effects.

One important topic, the hydroclimatology and ecosystems of urban areas, many of which are located in hydrologic threshold regions, has not been included explicitly in the colloquium. The relevant issues for urban areas are those associated with massive importation of water and subsequent changes in the natural hydrologic balance. It is not uncommon for imported water to be the equivalent of about twice the annual rainfall volume. Transfers of this magnitude influence the hydrologic cycle locally at the mesoscale (horizontal distances of 20 to 30 km) and influence the hydroclimatological balance at the export locations.

In an editorial written to mark the beginning of the second quarter century of the journal Water Resources Research, Charles Howe emphasized the role of technology, institutions, and politics in water resource management. He concluded:

. . . [I]t remains true, as it was [25 years ago], that socially responsible decisions require broad public participation, channeled through appropriate institutions. Institutions must change in response to changing public values, and institutional change is costly, but vital. Democracy, unfortunately for some, is messy and costly, but we will be better off pursuing the right goals somewhat inefficiently than pursuing the wrong goal efficiently (Howe, 1990).

It was in the spirit of these observations that the colloquium proceeded. All present—participants from academia, industry, and government—were eager to discuss the implications of possible climate change and to find ways to increase the resilience of our water systems in the face of increased uncertainty.

SHARING WATER RESOURCES

Edith Brown Weiss began the colloquium with a keynote address entitled "Sharing Water Resources with Future Gener-



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