Integrated regional assessment: the South Platte Basin

The first case study in the "Western Water Assessment" directs the attention of a team of physical and social scientists to the South Platte Basin: assessing regional sensitivities, identifying climate information users, and generating research questions and hypotheses. We seek to understand physical and social conditions and trends that make water resource management more or less vulnerable to climate and more or less sensitive to climate information. Poster presentations elaborate on the issues raised in this overview paper.

The basin is semi-arid, relying on mountain snowpack and surface runoff for 70% of its water supplies. The climate features significant seasonal and multi-year variations and a marked ENSO signal. A key recent trend is toward warmer, wetter conditions, with a run of wet years during the last decade. The climate may be fooling resource planners by offering a wet spell during a regional development boom while simultaneously maintaining its inherent, occasional extended dry spells.

The social systems in the basin are changing fast, with a booming post-industrial economy. The basin is urbanizing rapidly (the Front Range corridor is among the top five fastest growing metropolitan areas in the U.S.), but still encompasses significant agriculture (the nation's third-largest irrigation system). Thus we address both urban and agricultural climate sensitivities, and the effect of urban water transfers on system vulnerability. We think transfers quicken during drier periods, feeding on municipal water managers' well-known risk aversion. Transfers ease urban water vulnerability while presumably heightening agricultural sensitivities, though agricultural effects vary with alternative development options. Urban growth means more waste-water which must be diluted by streamflow. The regulatory process for waste discharge is based on limited hydrological records (10-15 years) and appears inadequate to protect water quality over the long-run given typical climate variability.

Water managers in the basin run the gamut from individuals, like homeowners maintaining lawns and farmers irrigating crops, to managers of complex water systems. A small subset are also consumers of climate information. Users often work within rigid policies, which pay little attention to potential climate fluctuation, except to define who loses in dry years. For many, the most salient annual hydro-climatic event is the spring runoff pulse. They have a keen interest in the seasonal evolution of snowpack, and, thus, a potential interest in climate forecasts, especially monthly forecasts with up to 6-month lead time.

Reconnaissance suggests that only very few of the most sophisticated users currently employ climate forecasts, perhaps due to professional practices, rules and regulations, and an aversion to relying on uncertain information. The literature suggests users are especially averse to certain outcomes, like limiting water deliveries because of a forecast but subsequently delivering normal, or even greater than normal, supplies. Limited forecast use must be reconciled with our assessment of decision-settings, which suggests good potential for use of forecasts of even modest skill, especially as operations are modified to meet new needs (e.g., endangered species). This potential is enhanced by system complexity that offers managers several options for modifying management during unusual demand or supply conditions.