Pulwarty, R. S., 2003: Climate and water in the West: Science, information, and decision-making. Water Resources Update, 124, 4-12.


The U.S. West is a place of varying and changing physical and ecological conditions that control regional climate, hydrology, and geomorphology. It is also a place of evolving social demographics, settlement, resource use and values. The factors conditioning present and future water resources management in the Western U.S. have been summarized as: increasing population and consumption, uncertain reserved water rights (in particular quantification of Native American rights), increasing transfer of water rights to cities, deteriorating water quality, environmental water allocation, ground water overdraft, outmoded institutions, aging urban water infrastructures, and the changing nature of federal, state and local interaction.

Climate change is expected to have major effects on precipitation, temperature, and land-surface feedbacks including evapotranspiration. In particular the Southwest could face higher temperatures with reduced water flow in the Colorado. Snowpack could also likely melt earlier in the season leading to earlier season flooding and less water to meet summer demands. In the semiarid Southwest even relatively small changes in precipitation can have large impacts on water supplies. Water managers have available tools for dealing with risk and uncertainty mostly derived from relatively short climatic records (<100 years). As is clear from numerous paleoclimatic records and sources climate has never been "stable" for long periods even if we have created statistical artifacts such as climate averages and event recurrence estimations based on short records. For example in most parts of Colorado reliable flow measurements for major streams have been recorded only over the last 50 to 100 years and precipitation measurements over the last 20 to 60 years.

Water banking and inter-basin transfers have been used to mitigate the effects of short-term drought. The lessons and impacts of these adjustment strategies are still be gathered. However the maintenance of reliable supply during periods of severe long-term droughts of 10 years to 100 years (the timescales of project implementation and ecosystem management efforts) know to have occurred in the West over the past 1000 years is as yet untested. The spatial extent and persistence of drought may produce shortages not only in the locale considered but also in neighboring regions that otherwise are supposed to make surplus water available for inter-basin transfers. On the other hand, the transformation of the Red River in North Dakota in the spring of 1997 provides a recent reminder of what can happen when too much water arrives in too short a time (Downtown and Pielke, 2001). Increases in flood and drought variability would thus require a re-examination of emergency design assumptions, operating rules, system optimization, and contingency measures for existing and planned water management systems (Stakhiv, 1998).

Measures undertaken by Federal and State agencies to inform management include improvements in streamflow and demand forecasting, use of advance decision support systems, development of drought indicators, conjunctive ground water/surface water use models, monitoring of water supply and distribution, water-use efficiency technologies and public information communication and coordination. The sectors and stakeholders (including instream and withdrawal uses) affected in each region are (1) water rights holders, (2) agriculture (including business and farmers in area of origin), (3) hydropower, (4) the environment (including instream flows and water quality), (5) urban interest, (6) Indian tribes, and (7) non-agricultural rural areas. These sectors and the adaptive mechanisms developed over time are all sensitive to climatic variations and changes.

For the most part, studies of the potential impacts of future climate change fall between two poles: (1) no adaptation is too great for societies or ecosystems to make; or (2) impose possible future climates on today's ecological, demographics, industrial, urban distributions and tally the resulting disruptions, itself resulting in extremely uncertain estimates (Clark, 1985). The primary reason offered for responding to climate change now is that immediate benefits can be gained by removing maladaptive policies and practices. In addition it is argued that climate change may be more rapid and more pronounced than current estimates suggest. Estimating the nature, timing and even direction of the physical changes at regional and local scales is of primary interest to water planners and managers and involves many uncertainties (Frederick and Gleick, 1999). Even if the physical risk can be specified, assessing vulnerability (in terms of risk, impacts and capacity to act) remains problematic.

Unexpected events are possible. However, devising effective societal responses to potential climate change impacts face several practical constraints based on the way the climate change problem is defined (see Brooks, 1977 among others):

  • By definition, the effects lie just far enough into the future. Their assessment and control involves trade-off between the interests of current and future generations.

  • Predicted effects are highly uncertain and difficult to prove to the satisfaction of all experts.

  • When effects are long-term and cumulative, the costs of delaying action often appear small compared with the immediate economic costs.

  • Long-term environmental problems can seldom be dealt with by single discrete actions or policies but respond only to a continuing, sustained effort, supported by steady public attention and visibility.

Non-technical considerations are thus always present. In this paper the focus will be on some of these considerations and will include recommendations for potentially overcoming barriers to using climate information more effectively. Most policy measures being proposed are unconstrained by the contingencies of the dynamic social, political and economic contexts in which implementation is supposed to occur. Multiple studies (e.g., Changnon, 2000) indicate that water managers do not believe there is enough certainty associated with climate-related predictions to justify a change in management approach. Some of that belief may be based on an incomplete understanding of the basis and meaning of those predictions. In these instances, new tools to evaluate alternatives in the context of uncertainty and risk could help water managers "know enough to act." Indeed, as is well-documented, "uncertainty" may be used as an excuse to escape what are in fact difficult political decisions (Pulwarty and Redmond, 1997; Rayner et al., 2001). As noted by George Brown, the late Chair of the U.S. House of Representatives Science Committee, "Uncertainty is not the hallmark of bad science, it is the hallmark of honest science. This perennial question, 'Do we know enough to act?' is inherently a policy question not a scientific one."

While there have been increasing calls for research to be "stakeholder driven," the risk is run of rushing preliminary untested research results and products into practical settings. Scientists may appear to be advocates of particular groups over others. Primarily, it is argued here that there is limited appreciation and understanding of how knowledge is incorporated in practice, especially in situations with high decision stakes and system uncertainty. The discussion of the physical aspects of climate change, and its associated uncertainties will be left to others.